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Home , Aquatic ape hypothesis, Australopithecus, Homo, Lucy (Australopithecus)

The Reflection of an An Aquatic Approach to Evolution

A thesis submitted to the Miami University Honors Program in partial fulfillment of the requirements for University Honors with Distinction

by

Erica Kempf

December 2006 Oxord, Ohio

Acknowledgements There are a number of people I would like to thank for their help in the production of this story. Linda Marchant was my advisor and provided invaluable data, advice, support, and motivation during this venture. Lynn and Greg Kempf offered helpful feedback throughout, but especially during the early stages of writing. Mary Cayton and Scott Suarez kindly agreed to read the last draft of my project, and gave me final grammatical suggestions to further polish my final copy. I am also grateful to the people whose enthusiasm and moral support throughout the long process of writing this story kept me going: Amanda Zorn, Kait Jones, Ali Wolkin, Ashley Piening, Lindsay Good, Rachel Mount and Jamie Eckert. Special thanks also go to Randy Fiedler for the initial idea to begin this work and for his help in getting started.

Table of Contents

Introduction viii

Map x

Kinship Chart xi

1 Meer 1

2 Natte 13

3 Bain 18

4 Welle 22

5 Etang 28

6 Praia 34

7 Lago 39

8 Samman 43

9 Rio 47

10 Alga 51

11 Gens 56

Works Consulted 59

Introduction

The study of how have come to be what we are has fascinated us for as long as we have written such things down, and for countless generations before that through oral . Every human culture has some of creation myth, a tale of how people came to be on Earth, ranging from molded mud to thrown rocks to drops of deity’s blood and nearly everything in between. When human fossils were first discovered, science offered its own explanations, which have been corrected and fine-tuned with each new discovery. Charles Darwin provided a mechanism for change over time, natural selection. Gregor Mendel showed how parents passed on genetic information to their offspring via alleles. James Watson and Francis Crick discovered the structure of DNA. The Leakey family discovered and analyzed early human ancestor fossils in . spent decades studying the behavior of for clues about what makes us similar to and different from our closest living relatives. All of these people, and many others, have allowed for huge leaps forward in our scientific understanding of how humans have become what we are today, and their contributions are indispensable. However, as they are probably the first to admit, there are still many unanswered questions about the evolution of humankind. DNA analysis provides valuable information about relationships between but has a limited ability to predict behavior. has provided a wealth of knowledge about our ancestral anatomy, behavior, and environment, but only a limited number of bones fossilize and are discovered. Advances in these fields will continue to uncover new knowledge and lead to a greater understanding of ourselves, but we are not there yet. One of the areas of most uncertainty is the time directly following the split of humans from the last common ancestor between chimpanzees and humans. What was it that made one group of African so different from all the others? A variety of explanations have been proposed, but none are accepted as the definitive cause. These theories range from changes in environment to changes in social structure to meat eating, and all have their advantages and drawbacks. In this story, I have chosen one theory, nicknamed the aquatic ape theory, for explaining what may have caused this divergence of humans from the other apes. This aquatic theory is certainly not the only theory of why and how this change could have taken place, and perhaps is not even the most plausible explanation, but it does offer an explanation for several traits unique to humans. The story presented here follows one band of creatures as they progress from the last common ancestor between humans and chimpanzees until they are firmly established as a hominin that walked the plains of Africa, striding on two feet. The time span, nearly five million , is almost incomprehensible for humans who live such a short time comparatively. To ensure that readers (and the writer) are not overwhelmed by the sheer amount of time in question, the characters of this story will remain the same throughout this vast expanse. The storyline will seem to pass only through one generation in the life of this band, although obviously the same individual band members would not have survived for five million years. Similarly, the snapshots of life presented in each chapter are not meant to represent literal days or weeks, but rather a progression of what could have happened in the several hundred thousand years between each chapter. Sometimes new behaviors are

adopted with incredible rapidity, and then long periods of time pass with little change. Sometimes, though, it takes generations for a new behavior to become established and perfected. New ways to do things are often discovered by chance, and the scenarios described in the following pages are only educated guesses about how certain behaviors might have first been established based on modern behavior. Ultimately this is a “what if” story. What if the were true? What would have driven our ancestors to spend a significant amount of time in the water? How would they have acted while they were there? What made them return exclusively to dry land again? The introduction to each chapter presents scientific data relevant to aspects of each chapter, and the bibliography at the end provides the scientific sources the author used in predicting the band’s behaviors and physical characteristics. These scientific sections are meant to offer support to this hypothesis and resources for curious readers, rather than to offer undisputed proof that any of the following events occurred.

Contemporary Map of the in

Kinship Chart

Meer Alga

Etang Welle

Natte Rio Etang

Samman Teich Furt

Gens

The Reflection of an Ape An Aquatic Approach to

A thesis submitted to the Miami University Honors Program in partial fulfillment of the requirements for University Honors with Distinction

by

Erica Kempf

December 2006 Oxord, Ohio Acknowledgements There are a number of people I would like to thank for their help in the production of this story. Linda Marchant was my advisor and provided invaluable data, advice, support, and motivation during this venture. Lynn and Greg Kempf offered helpful feedback throughout, but especially during the early stages of writing. Mary Cayton and Scott Suarez kindly agreed to read the last draft of my project, and gave me final grammatical suggestions to further polish my final copy. I am also grateful to the people whose enthusiasm and moral support throughout the long process of writing this story kept me going: Amanda Zorn, Kait Jones, Ali Wolkin, Ashley Piening, Lindsay Good, Rachel Mount and Jamie Eckert. Special thanks go to Randy Fiedler for the initial idea to begin this work and for his help in getting started.

Table of Contents

Introduction ii

Map iv

Kinship Chart v

1 Meer 1

2 Natte 11

3 Bain 19

4 Welle 26

5 Etang 35

6 Praia 44

7 Lago 52

8 Samman 59

9 Rio 66

10 Alga 72

11 Gens 80

Works Consulted 85

1

Danakil Alps (Afar, Ethiopia) 9 Million Years Ago Meer (Sea; German)

The Afar region is located in , along the coast of the Red Sea. Today huge salt plains cover this area. The local people collect and carry out this salt for sale; salt is the only cash crop in this otherwise inhospitable region. The modern day salt plains of Afar are all that is left of a vast inland sea that once covered the region. Around 9 million years ago the three geological rifts that converge in the shifted and the Red Sea flowed into Afar. Later, another shift occurred, blocking the sea’s retreat and turning Afar into a huge saltwater lake. The lake slowly evaporated over millions of years and left thick crusts of salt as its only remnants. A similar process is occurring in the Dead Sea today, which is steadily increasing in salinity as it evaporates. Around the same time in Africa, an ape lineage split. This ape lineage is sometimes referred to as the last common ancestor, or LCA. The modern genera of (chimpanzees) and (humans) are the living descendants of this split. The time estimation for this split is based on our understanding of the molecular clock and the accumulation of mutations in the DNA of the two since the divergence. An analysis of and human DNA suggests that this event occurred between 7 and 9 million years ago. It is difficult to determine from the array of fossil evidence exactly which fossils belong to the LCA. These fossils may not have yet been discovered or preserved so that they may be discovered at all. However, modern day animals may offer clues as to the of these ancestral apes. Deciding which animals make the best model for the LCA is based on a variety of fossil and behavioral data. It is assumed that the LCA more closely resembled Pan than Homo because it is more likely that uniquely human traits such as naked skin, standing upright and large brains evolved after the split between 2

humans and chimpanzees rather than before the split. The alternative explanation would be that the LCA evolved these human traits and then the chimpanzee line evolved back to the ancestral condition, which involves more steps and is refuted by the fossil evidence. The prevalent theory, then, is that the major morphological and behavioral differences that humans exhibit evolved after the split, and chimpanzees provide a model for what the LCA may have been like. However, it is important to remember that chimpanzees also have been evolving for 7-9 million years since the LCA; therefore, they are not exact models either. Using the above assumptions, the LCA would have walked on four legs, spent considerable time in the trees, and sometimes knuckle-walked on the ground. They would have had an omnivorous diet, eating a great deal of fruit but also leaves, insects, nuts, and small animals. They probably also had a polygamous mating system and a brain approximately one-third the size of humans today. An environmental or climatic change occurred that caused a group of these apes to change dramatically over millions of years and become human, while the rest changed much less noticeably to become the chimpanzee and of today. The question of what that change was remains unanswered, but perhaps the split of the LCA and the flood of Afar are not unrelated.

Meer sits up, sniffing. The sun glints off the thick chestnut brown fur that covers her body, but her deep set black eyes squint with alarm. Something unusual is happening, the ground under her feet is moving. In her thirteen years of life she has never experienced the earth shaking, and she does not know what to make of it. When she looks across the valley, she sees the ground rippling as water does when she bumps it with her muzzle to drink. Suddenly the earthquake intensifies. Large rocks break off the cliff and roll down the hillside. Meer gives a waa-bark of alarm - - a warning reserved only for moments of great fear. Welle, another young mother, echoes her call, and others soon join in. Meer’s daughter Natte had been exploring the thick underbrush not far from her mother and 3

quickly rushes to her when she hears her mother’s frightened call. At one old she has only recently taken more than a few steps from her mother’s comforting presence. Natte climbs onto Meer’s chest and clings to her mother’s . She presses herself tightly against her mother’s chest as Meer hurries up the hill, away from the rocks crashing at the bottom. Welle’s three-year-old son, Teich, had been up in a tree when the shaking started. At the sound of Welle’s terrified call, he swings himself down fast, snapping twigs in his haste. His mother is already moving up the hill when he reaches the ground. He calls in panic as he hurries through the thickly growing trees to find her. Welle, hearing her son’s cries, pauses to let him catch up to her. He rounds a tree, spots his mother, and runs to her, trying to cling to her stomach. Welle detaches her clinging son and pushes the larger infant onto her back instead. Teich grasps chunks of hair to keep his balance as Welle quickens her pace. The rest of the band is ahead of the pair, and their calls of alarm drift back to Welle and her son with each new crash of rock on rock. The long uphill trip takes most of the morning. Each bout of violent shaking causes some of the band to race forward while others cower on the ground. By the end of the uphill trek the band is spread throughout the trees. As Meer and Natte near the crest of the hill, an even more violent tremor strikes. Several of the trees wobble alarmingly, but the band does not seem to notice in its panic. A tree over Meer’s head tilts at a forty-five degree angle, bringing up a huge rootball and spraying dirt that blinds Meer and knocks her to the ground. The tree’s branches are tangled with neighboring trees, so it does not fall further, but limbs creak and groan under the sudden weight. As if the earth tired itself after its final violent display, the shaking subsides and the ground remains level and unmoving. After blinking the dirt from her eyes, Meer stands up on wobbling legs. Her daughter was knocked from her stomach in the fall, and Meer calls out to her desperately, searching the ground nearby. She hears several calls she recognizes from the direction of the hilltop, but not her daughter’s. The rest of the band is milling around uncertainly in a clearing on the top of the hill, and Meer scrambles toward them. Just as she reaches the 4

clearing, she sees a huddled mass of light brown hair on the ground at the base of a tree that she recognizes as her daughter. She sprints to her and carefully lifts her daughter to her breast. Natte had hit her head after being thrown from her mother’s chest. She had been disoriented and had run in the direction of her band instead of searching for her mother. Realizing after a few hundred feet that her mother was not close behind, she had given in to the terror of the day and laid down where she was. Meer begins grooming Natte, a response in times of stress or uncertainty. She notices a thin cut over Natte’s eye and a slight bump. She prods the injury and picks the small twigs and grass out of the wound. There is not much blood, so she adjusts her daughter on her stomach and moves toward the rest of the band. The band is on a high hilltop, clear of vegetation, which offers a clear view of the land all around. They can see over the tree-covered hillside and out onto the flat forest beyond. There are other rises scattered across the forest, which stretches as far as they can see. Behind their hill rises a series of higher and higher peaks they have never visited. As the band stares at them now, the few trees managing to grow on these mountains stand out against the light colored rocks and earth. Streaks of darker brown are visible against the light background where boulders ripped gouges as they tumbled down the mountainside. Otherwise there is little to see on these low mountains. None of the fruit trees or dense undergrowth the band feeds on grow at those high elevations. They turn back toward the lush forest where they had lived. Far in the distance they can see an opening where a river runs, and smaller open sections where the streams that feed it snake across the land. This water usually does not concern them; they wade through shallow streams as they travel their home range with little difficulty. Occasionally they even nibble the plants growing on the water’s edge. However, they cannot swim and have a healthy fear of deep or fast-moving water. Last year a youngster had been exploring along the bank of the far off river during the peak of the wet season when it was wide and deep. He was stalking a large insect, trying to get close enough to the brightly colored bug to pounce, and was too focused on 5

his game to notice where he was. The bug took flight, and the youngster jumped into the air in a last effort to satisfy his curiosity. When he landed, the ground under him gave way, and he slid down the eroded bank into the rushing water. He managed to grab a clump of grass on the water’s edge and clung to it for a moment, screaming. His frightened calls brought his mother and three others to the bank, but the grass roots were not strong enough to hold him. He was washed into the middle of the river. His mother watched helplessly as her son’s head disappeared beneath the water, not surfacing again. Yesterday they had splashed through a small stream at the base of this hill without pause. It was hardly more than a trickle at this time of year. Now they can hear the rushing water, even from the top of the hill. It sounds angry and swift moving, like the river that carried off the juvenile so many months ago. Hyd stands up and rushes to the edge of the forest, shaking branches and threat calling at the stream. He is the largest male in the group, and his threat display is impressive. His thick black hair stands on end, making his massive form look even larger than usual. One ear is shredded from his fights with his superiors as a youth, but his fighting has paid off. He is now the alpha male of the group, and all the others get out of his way or rush to reassure him when he shows his anger. Hyd is not used to being afraid or uncertain. In his three years as the dominant male he has never felt as unsure as he does today. His display at the rushing water accomplishes nothing, and his temper flares. He returns to the group and chases a juvenile from a large rock. As the youngster retreats in fear, Hyd, feeling better, settles himself on the top, where he has a good view of the surrounding area. The band continues to be uneasy, and all the surviving members huddle near the base of the rock, grooming each other for reassurance. Their band had been medium-sized, with fifty members sharing the same range before the earth began to shake. Now only forty individuals gather in the high clearing. Suddenly the tense air is broken by a loud greeting, a series of pant hoots from Hyd. His breathy calls get louder and faster as he rushes down from atop his rock. Etang, a large adult male who often grooms Hyd, appears out of the trees in front of Hyd. Hyd wraps his arms around Etang, and the two embrace before returning to the group. Many of the 6

others greet Etang with excitement, and the tension is lessened a moment with this small celebration of reunion. It returns gradually as the day wears on though. There are no other reunions. Nine of their members are lost. The ground still seemed unsteady, shuddering periodically, but after the first few aftershocks produce no ill effects. The band stops giving alarm calls. The noise from the water is also increasing, but slowly. Every so often one of the adults will stare toward it and hesitantly take a few steps. None venture nearer. Teich, Welle’s three-year-old son, is too young to stay apprehensive for long. As the adults begin to calm down he wanders to the edge of the trees and discovers a termite mound that has been disturbed by the earthquake. The worker termites are busy repairing the damage falling sticks and shaking earth have done to their mound. The sides of the mound crawl with so many moving bodies. Teich picks up one of the fallen sticks and jabs it into the mound. He watches intently as more termites rush out to defend their home from this new attack. He has watched his mother poke twig tools into termite mounds and eat the bugs that run onto them, so he knows that poking mounds sometimes results in food. However, he had not yet perfected the termite fishing technique of the adults. He squeals as the first termite makes its way up the stick and bites down on Teich’s sensitive finger. Teich removes the offending termite and eats it just as he feels another bite farther up his arm. This is too much for him, and he retreats a few paces from the mound. He calls to his mother, hoping for her help in his painful new game. Welle looks up from her grooming for a moment at the sound of her son’s cries. She walks to him and picks the few remaining termites from his hair. Then, not one to miss an opportunity to feed, Welle picks up a thin stem, quickly strips off the leaves, and begins fishing herself. Teich watches his mother a safe distance from the mound for a few minutes. Then he clambers onto her back and dangles from one arm in front of her face, wanting her to play with him. She bats him away impatiently and returns to her fishing, inserting her stem into a small hole in the termite mound, then removing it quickly and eating the clinging insects. 7

Meer rests for a minute in the shade and then goes in search of Welle, who had been grooming her. Catching sight of Welle on the edge of the trees, she wanders over. Once she sees the termite mound, she quickly finds a twig of her own and approaches Welle. Meer nudges her hard, hair bristling slightly, until Welle gives up her spot and retreats to the far side of the mound. Meer takes up fishing with enthusiasm, and her movements wake her daughter, who still clings to Meer’s chest. Natte reaches out a small and pulls her mother’s stick away from her. She brings it to her face and studies it, biting on one end for a moment before she tires of this new toy and drops it on the ground. Her mother patiently retrieves her daughter’s discarded plaything and resumes fishing. Three more times her daughter steals Meer’s tool, and finally Meer tires of the game and moves away from the mound to rest in the shade. Only then does Welle return to the more productive side of the mound and continue her feeding. It is now late in the afternoon, and most of the band members have full stomachs. It is hot and the band is exhausted from the panic of the morning. They retreat upward again to lie in the shade of the rock at the top of the hill. Hyd returns to his spot on top of the rock and turns to look out over the forest below. He barks in alarm. Where the small stream used to run, now a broad expanse of water can be seen through the trees. It is moving fast and has pulled several trees from the ground. He calls again, his hair standing on end, and several adults run to him looking for the cause of his alarm. They turn to look and catch sight of the water just as another large tree is pulled down and crashes into those already in the water. The resulting noise is loud enough to be heard clearly from their hilltop vantage point. The rest of the band turns and watches the water, which is now creeping visibly up the side of their hill. In the distance they see the much larger river flood its banks and begin to creep steadily toward them. They spend the rest of the day watching the water, making only short foraging trips to the edge of the woods. As dusk falls, Welle climbs into a treetop to build a sleep nest as she has done every day since she left her own mother’s side twelve years ago. It takes only a few minutes for her to pull down small springy branches and weave them 8

together with leaves to create a comfortable platform for sleeping. Teich climbs tentatively up beside her. For the last few weeks Welle had begun weaning her son, pushing Teich away from her nipple when he has tried to nurse and keeping him out of the sleeping nest they used to share. Teich perfected his own nest building skills many months before, sometimes making nests to play in during the middle of the day. He and the other youngsters would ambush each other while they lay in the nests, or cuddle up together for a afternoon nap. Although Teich is a proficient nest builder, he much prefers sleeping with his mother at night for comfort and security, and because he can sometimes sneak a suckle while they drift off to sleep. Tonight Teich can feel the unease of the other band members. That, along with the unfamiliar sounds of rushing water and the lack of suitable nest trees close to his mother, makes him hopeful that he can join her in her nest once again. Welle puts the finishing touches on her bed, and Teich inches up the tree toward her. As dusk fades to night, Teich gives up his pretense of sneaking up on his mother and takes a more direct approach. Catapulting himself onto his mother’s back, he is relieved when Welle moves over and allows Teich to snuggle next to her. He roots for a nipple, but his mother seems not to notice and turns her back on her son. Teich cries softly for a moment, but quickly drifts off to sleep, tired from the day’s excitement and comforted by the warmth of her mother’s back. The band is slow to rise the next morning. Usually all the members exit their nests soon after dawn to begin their morning grooming and foraging, but this morning the sounds of the day are muted by the rush of water, disorienting the band. The stream at the foot of their hill is no longer just a stream, but now a broad, slow-moving river. The band was awakened several times during the night as trees were uprooted in the floodwater and crashed into one another. The stream at the base of their hill has swollen alarmingly during the night and is now surprisingly close to the much larger river, which is usually a full day’s travel from the base of the hill. Now the two are close enough together that the band can easily make the trip between them in an hour. 9

Natte sits up quickly, startling Meer in her haste. The water is too close and too unfamiliar; she lets out a loud wraa of alarm, waking the remaining band members from their sleep. As they make their way down from their nests, the flood waters visibly advance, now a quarter of the way up the hill on which they slept. The band is frightened of the crashes from the fallen trees and the sound of water moving fast. They make their way across the clearing at the top of the hill and look out at the other side. This side is not as steep, and the water is a good deal farther away, but they can still see it, sparkling through the trees as the sunlight strikes it. They cannot retreat higher into the mountains and survive in any case, because no fruit grow there, but they are now entirely cut off from farther travel. They are on an island. Over the next several weeks they settle into a routine much like they have had for countless years before. They spend most of their time foraging through the trees on their new island, searching for ripe fruit, nuts, and young tender shoots to eat. In the heat of the day they rest in the shade of a dense patch of trees to stay cool. They stay away from the shores of their island, having no need to venture near them. There are several small brooks on this island to drink from, and enough vegetation and insect mounds to feed the band. Every day before dusk they return to Hyd’s rock, and he looks out over what used to be the flat forest where they lived. The flood waters continue to rise. Occasionally the earth shakes again, but never as much as that first morning. One day Meer looks out and sees not a flooded forest but a scattering of islands separated by wide expanses of water, with the occasional tree top breaking the surface. The islands closest to her are small, sometimes only a few trees grow on them, but she can see larger ones in the distance, poking out of the water like termite mounds poking out of the earth. It reminds her of something, a scene she had seen as a juvenile several years before her daughter was born. The band had been pushed out of their home range by rivals, and they had gone into the outskirts of the forest where the trees grew farther apart and had less fruit. They had traveled longer distances every day to find enough to eat and one day had come to the edge of the forest. She had looked out over a sandy beach with 10

a few scattered stands of grass and seen the largest river she could remember. Being young and curious, she and several other youngsters had scampered out onto the beach, marveling at the way the sand moved under their four feet. As they stood cautiously on the edge of the water, they stared across and could not see the other side of this river. She remembered feeling uneasy looking at all that water, and she feels the same way now.

She had actually been staring at the ancient Red Sea, which separates Africa from the Middle East. When she sensed a similarity, she was more correct than she knew. The earthquake that had sent the band for higher ground had been caused by a shift in the rift under part of Ethiopia, and had opened a channel for the sea to come inland. It flowed through this ever-narrowing channel before the slow movement of the rift closed it again, preventing the waters from returning to the Red Sea and flooding a portion of Afar hundreds of miles wide. The band was now on what was previously one of the higher foothills of the Danakil Alps, and what is now one of the Danakil Islands.

11

Danakil Island 8.7 Million Years Ago Natte (Wet; Dutch)

There are four major forces of evolution: mutation, gene flow, genetic drift, and natural selection. Mutation and natural selection are the most often thought of mechanisms for evolutionary change. Mutation is what provides the diversity on which natural selection acts. Mutations arise in the genetic makeup of individuals randomly, and individuals with disadvantageous mutations for their current environment die out or produce fewer offspring than those individuals with beneficial mutations. This process of natural selection allows the advantageous mutations to become more common in a population, while the harmful ones become less common. The two lesser-known forces of evolution are gene flow and genetic drift. Gene flow is the movement of genes from one population to another. This process introduces new mutations into a population and also serves to make populations more genetically similar over time. Genetic drift is the shift in genetic frequencies from one generation to another within a population that is caused by random chance. For example, two brunette parents may have one brunette child and one blond child, which changes the frequency of brunettes in the second generation due to random fluctuations. Evolution, which is driven by these four forces, occurs in two ways. Microevolution is the small scale accumulation of different allele frequencies that does not result in the creation of a new species. An example of this trend in humans would be the higher frequency of blond hair in Europe than in Africa. The alleles for blond hair are more common among Europeans than among Africans, although both are members of the species Homo sapiens. These two populations, which are geographically separated, have undergone microevolutionary changes which have resulted in slightly different allele frequencies within the species. 12

Macroevolution, on the other hand, is the process that results in separate species. It can be thought of as an accumulation of the allele frequency shifts seen in microevolution, but over geological time. There is some debate among scientists as to which of these two processes is more prevalent and where exactly microevolution ends and macroevolution begins. Speciation occurs when a new biological species arises through evolutionary processes. One way this happens is through allopatric speciation, where distinct populations of a species are divided by some geographic barrier, such as an ocean or a mountain range. As time passes, the now-isolated populations are under different selective pressures, and allele changes continue to accumulate. After enough time has passed, these differences in genes become so numerous that even if the geographic barrier were removed, the two populations would no longer be able to successfully share genetic information: they are now two distinctive species. A small band of last common ancestors that suddenly found themselves isolated on an island in the middle of a large inland sea would have experienced the effects of geographic isolation. If their isolation continued, genetic mutation and natural selection would have changed their DNA significantly and in different ways from that of the mainland group of last common ancestors. These changes eventually could have resulted in two new species, one that led to the chimpanzees of today and one that led to modern humans. In this scenario water is the major difference in the environment of these two populations. As the band became more acclimated to their island home, they may have begun foraging more aquatically and using the water as protection from the midday heat.

Natte is hungry. She has been weaned from her mother for nearly a year, but at four she is not big enough to always protect the food she finds. This morning she is lucky and has found a small cluster of figs hidden between leaves that the others have missed. She settles down in the crook of a tree with her figs, making quiet food-grunts of pleasure. Hyd approaches her tree from the ground and peers up at her. She is easy to recognize against the dark green leaves because her hair is a light brown, while the rest of 13

the band ranges in color from dark brown to black. Her face, too, is light, although many youngsters have lighter faces than fur. Her eyes are not the black that is most common in the band, but instead are a lighter gray, almost blue. Hyd grunts in surprise when he sees she has found fruit. The whole band is struggling to find enough to eat on this island, and Hyd is not used to going hungry. He swings himself up into Natte’s tree using a low branch, and Natte backs up anxiously, trying to get her prize out of his sight. Hyd gives a soft bark and shakes the vegetation over his head in annoyance. Natte, fearful of the large male, abandons her fruit. She climbs higher into the tree, onto the thin branches where the much heavier Hyd can not reach her. She huddles miserably near the top of the tree and looks out at the water as the rest of the band forages around her. She stares unseeing at the water until the glare off the waves makes her turn her eyes away. She directs her attention to the beach, just visible from her high branch. No one spends much time there because it has none of the fruit they eat. They also still remember their fear the day it burst its banks and cut them off from the forest where they lived. The band members knows they cannot cross this river as they have done with others in the past. They cannot see the other side of this water, and it is much too deep for them to wade across, so they avoid it. The waters have receded only a little since the flood, leaving an area of a hundred yards next to the shore covered in a jumble of fallen trees, mangled vegetation, and animal bones bleaching in the sun. This clutter is not what draws Natte’s gaze from her treetop, but rather the short grasses rippling on the edge of the water. This primitive variety of cordgrass has floated to the shore of their island and taken root since the flood. To Natte’s hungry eyes, the mass of softly undulating green sprouts looks like the perfect place to have an unmolested meal. She makes her way slowly down from her high branch, careful to avoid Hyd, who is still feeding on her figs. Content with his fruit, he lets her pass with only a glance in her direction. Meer is feeding at the base of a nearby tree. Natte begins grooming her and after several minutes prods her in the direction of the shore. At first Meer is unmoved by her daughter’s attempts to steer her 14

away from her own food, but eventually Meer finishes her fruit and allows herself to be led away. Welle, who was feeding near Meer, moves with the group, her son Teich following along behind. The group walks steadily downhill, occasionally stopping to investigate fruit that has not been discovered. After an hour they reach the edge of the beach. Meer and Welle are nervous about this change from forest to waterfront and begin grooming each other in the shade of the trees. Natte and Teich have been playing roughly during the last part of the trip, chasing each other through the trees. They pause at the edge of the beach, uneasy at their mother’s reluctance. Natte sits on a low branch, sniffing the salty tang of the air that wafts up from the water. Teich climbs higher into the tree for a better look at the new scene. He decides after a moment, with the boldness of a young male, that he is more interested in play than he is nervous. He studies Natte, directly below him, for a moment and then pounces on his unsuspecting playmate. They both tumble down onto the beach, chase each other, and launch mock attacks. Tiring of this play, they take stock of their surroundings. Natte sees the grass she spotted from the tree earlier. At the same time she looks back at her mother, who is still grooming Welle in the shade of the trees. Had someone been watching her, she would have appeared almost comical standing between her potential meal and her mother, unable to decide which way to go. She gives a hoo of distress to her mother, who looks up for a moment. Seeing her daughter not in need of immediate help, Meer goes back to her grooming. Teich has less trouble deciding. He runs whimpering back to his mother when his calls bring no response. Natte is hungrier, though. She makes up her and creeps cautiously toward the new growth of grass, tall enough to blow in the wind but still pale green and tender. It is growing right on the edge of the lapping water, its roots submerged but the blades well out of the water. She tears out a handful and begins to munch on it, happy to have something to fill her stomach. The taste is pleasant, not as good as ripe fruit but better than the mature tree leaves she had been reduced to eating lately. She reaches for another handful and continues feeding for several minutes until 15

the edge is gone from her hunger. She then retreats to where her group is sitting and presents her skinny back to her mother for a reassuring groom. After several minutes Natte begins pulling at her mother’s arm, trying to entice her to come to the water’s edge with her. Meer refuses to budge, not wanting to give up the shade of the forest in the heat of the day and still leery of the beach. Natte returns to the beach alone. Teich, meanwhile, has become more adventurous. Having watched Natte feed with apparent enjoyment, his stomach feels particularly empty. He picks his way along the edge of the forest until he is directly across from where Natte sits among the grasses. He takes a few tentative steps out into the open then looks back to where Natte stands, watching him. He cries in alarm as he trips over a partially buried tree branch and goes sprawling. Natte looks up from her feeding, and seeing her playmate sprawled on the ground, proceeds out to Teich. She inspects him for injuries for a moment, like her mother does to her when she falls. She picks through the long brown hair on his legs, peering at the light skin underneath. Seeing nothing, she moves her grooming to his head. Too young to keep her attention on one thing long, Natte becomes fascinated with Teich’s ears. Teich is patient with his young playmate’s explorations for a few moments, but shakes her off when she begins pulling his long earlobes and poking her fingers inside. Teich stands up and pushes the smaller Natte away, then walks slowly toward the shore, this time watching the ground. They both settle down near the edge of the water within arm’s reach of the cordgrass. They feed, reaching out periodically for another handful of their newfound food. Eventually the adults approach and watch their children eating for a few minutes, then they too pull up handfuls of grass. Natte is no longer hungry, and now she is ready to play. She ventures closer to the water and gazes down at the murky bottom. Teich reaches out just then to grab the patch of grass right under Natte’s nose. She jerks up in surprise, losing her footing in the slippery mud on the beach, and steps heavily into the 16

water. The resulting splash sends Meer and Welle farther from the water’s edge and brings a threatening gesture from Teich. As the afternoon fades to evening, the two adult females get impatient to return to higher ground and build sleeping nests in a more familiar area. They start off, and soon their children follow, stomachs full for the first time in several days. The group makes its way up the hill slowly and reaches the top of the hill as darkness falls. For several days they return to the beach, eating their fill of the grasses and the occasional fruit along the forest edge. One afternoon they hear the excited calls of some of the other band members just up the hill and out of sight. Meer starts back toward the commotion, ready to join in whatever is exciting their band mates. Natte grabs one last handful of grass as she turns to follow her mother, accidentally uprooting the whole plant instead of just pulling off the succulent tops. Used to moving along the ground on all fours, she holds the plants clinched in one fist so they do not interfere with her walking. She hurries after the retreating form of her mother and catches up quickly. Teich begins to follow his playmate, curious about the cause of the commotion. As he reaches the edge of the trees, he looks back toward his mother, Welle, and sees that she has not moved. He calls to her, wanting to follow Natte but not ready to be so far from his mother. She moves farther from her son, traveling down the beach away from the noisy band. She always avoids large gatherings, nervous around so many individuals. Teich looks once more at his playmate before giving up and returning to his mother. When Meer and Natte arrive, they spot a tree laden with ripe fruits. Several of the group have just come together and are greeting each other enthusiastically. Hyd, always on the lookout for insubordination from other males, uses this opportunity to show his authority. He begins an impressive dominance display, hurling rocks and shaking branches in the direction of two other males. Bain and Etang, the unlucky victims of Hyd’s attack, are brothers who had been off by themselves for several days. They had finished eating and were peacefully grooming each other before Hyd and ten others had come upon them. Both brothers are more interested in food and grooming than in conflict and are quick to try and placate the excitable Hyd. Bain, the older and smaller of 17

the two, crouches low to the ground and makes submissive pant-grunts, while Etang quickly moves away and up a nearby tree. Hyd, confident that his dominance is not being challenged, settles down into a mutual grooming session with Bain. Meer moves into the group as everyone settles down, and Natte stays on the outskirts, munching the few remaining blades of grass that stayed in her fist as she clamored through the undergrowth. The roots, which she has not tasted before, are crunchy and slightly tangy, different from the blades she is used to. Her crunching attracts the attention of several of the other band members, who examine the grass that had fallen to the ground near her. After Meer tires of grooming and has eaten her fill of fruit, she follows her daughter back toward the shore. Five of the others move with the pair away from the larger group. As this smaller group reaches the end of the trees, two fall back. These two are young females who joined the band not long before the flood and have never explored this far down the slope before. The established females in the band dislike strangers, and in the beginning would attack the new females if they found them unprotected. The males, however, were eager to mate with the new and sexually receptive females and offer their willing protection as long as the females do not stray far. The resident females are beginning to accept the newcomers, but attacks still happen, and these two are not eager to travel so far from male protection. Natte and Meer leave the cover of the forest and move to the edge of the water near where Teich and Welle are still feeding. They sit down near the grass and begin feeding again, and soon the others join them. Praia and Lago, both adolescents, are the first to venture out, but soon the others follow. Natte again tries to pull up the roots of the grass as she did earlier. This stand of grass is farther from the water, though, and its roots are not as waterlogged. Natte tugs on the blades, but they break off in her hand, roots still firmly in the ground. With plenty of tender blades to eat and new playmates, she gives up on the roots. Several months pass in much the same way. Eventually all members of the band make their way down to the water’s edge to investigate the grass growing there, but many 18

are still nervous around the water and bring their handfuls of grass and roots into the shade of the trees to eat. It is now the height of the summer, and the scorching sun beats down on the small group at the edge of the water. Praia and Lago have already retired to the shade and watch Natte, Teich, and Bain sitting in the shallow water. Twenty others are scattered through several of the trees nearby, eating fruit. The six-year-old Teich is pestering Bain, jumping up and down in the water near him. The small tidal waves created by his bouncing rock Bain as he tries to feed. Bain has been patient, swatting halfheartedly at Teich but not making a real effort and missing him entirely. Teich has gotten braver and with one particularly violent stomp manages to send water over Bain’s head. Bain’s hair begins to rise, a response that usually makes him look bigger and more intimidating. This defense is less effective than usual because his hair is matted to his body with water. This further irritates him and he launches into a full threat display, moving out of the water onto the beach and throwing sticks and rocks in Teich’s direction. These make impressive splashes, and Bain is quite pleased with the results. Teich retreats farther into the water and Natte follows him, unfortunately caught in the middle of this conflict. Bain, satisfied, goes back to feeding in peace. Teich and Natte are now farther from shore than they have ever been before, the water lapping at their hips and shoulders. They have gotten used to the water in the years they have spent near the shore, and even enjoy the cool feeling of the water on their and feet in the heat of the day. This is an altogether different feeling, although not completely unpleasant. Nevertheless, they attempt to walk out of the water again, thinking perhaps of joining the others in the shade for their traditional noontime rest. Bain bristles again and lets out a bark of warning, flinging another clump of mud into the water in warning. Natte and Teich stay put, shoulder deep in the water. It is not as relaxing as lounging under a shady tree, but it is, at least, cooler.

19

Danakil Shore 8.3 million years ago

Bain (Bath; French)

When one considers what makes humans different from the other apes, it is tempting to look at some of our more impressive features: our , our large brains, our communication skills, our morals. So strong is the desire to pick out these types of differences that the first fossil hunters, looking for the missing link between humans and other apes, expected to find creatures resembling large-brained chimpanzees. The infamous Piltdown was exactly what they were looking for - - a large brained creature with very ape-like and teeth. However, as dating techniques advanced and other fossils were found, the Piltdown man was revealed as a hoax, a planted human with a modified jaw. The search for a missing link continued. Eventually multiple specimens of early human ancestors ( and the ) were discovered, and one thing became clear—these animals did not have human sized brains. In fact, afarensis () had an interior skull volume (cranial capacity) of 400 cc, about one third the size of modern humans (1,400 cc) and very close to the 350 cc of modern chimpanzees. Although cranial capacity does not completely determine intelligence level (human geniuses can range from 1,000cc to 2,000cc), it does give a rough idea of mental capabilities between animals. These early human ancestors had chimpanzee-sized brains, and thus probably were not debating politics or composing love poems. If it was not large brains and the cognitive ability that comes with them that set the first humans apart from other apes, what was it? The somewhat surprising answer is bipedality, or walking upright on two feet. The earliest fossils that have been attributed to human ancestors show varying degrees of bipedality, which can be seen in the 20

placement of the skull and the structure of the . The first evolutionary step that led to modern humans was quite literally a step, and an upright one at that. The question that has since plagued scientists is why bipedality was ever adopted by humans. Very few other animals and no other have ever habitually moved about in this way, and for good reason. Walking upright is difficult. It takes longer to learn, creates knee and back problems, varicose veins, hemorrhoids, more difficult births, and dangerous changes in blood pressure. It is not faster than running on four legs, as the cheetah can attest, nor is it more energy efficient. It also exposes the animal’s vulnerable stomach to attack. Another obstacle this form of locomotion presents is that it would have been awkward in its early stages before the pelvis and other skeletal features evolved to better suit it. So what could have caused humans to choose this costly and initially clumsy form of locomotion? The pressure to keep one’s head above water is a powerful incentive and offers a potential explanation for this otherwise difficult-to- explain choice of walking style. Water not only would have provided the incentive for walking on two feet, it also would have made the transition easier. With its weightless quality, water makes balancing on just two legs less demanding than on dry land. The buoyancy provided by salt water also removed some of the stress on the lower limbs and back, perhaps allowing these creatures to stay upright for longer and forage farther from land, gathering more resources. When they returned to land, they surely walked again on all fours, still being unable to get far without the aid of water to hold them up and help them balance, but the first steps had been taken.

Bain opens his eyes and peers over the edge of his sleeping nest, squinting against the sun’s glare off the water. He hears the rustling of other nearby band members as they awake for the morning in their own nests. Suddenly the peace of the morning is broken as Hyd launches himself from his own nest in the tree above Bain, screaming and shaking branches almost in Bain’s face. Hyd has been alpha male for five years and is used to 21

getting his way. He mates with the most receptive females, takes the best feeding spots, and is groomed often by his subordinates to show their loyalty. But Bain has grown up into a fully adult male. Although not as tall as Hyd and some of the other big males, he is solidly built with thick, powerful arms. Though he is still young, the hair on his back and head shows a hint of glossy silver in the sun. As he has matured, he has begun reacting less to Hyd’s dominance displays, sometimes ignoring Hyd’s attempts to displace Bain from his preferred feeding spots. This insubordination has resulted in violence, a few swats and on one occasion, a tumble down the slope and nearly into the water. These contests are becoming more frequent, especially when Bain is near his brother Etang. Together the two brothers are a real threat to Hyd’s leadership. This morning Hyd wakes up feeling irritable. Yesterday evening Hyd threatened Bain as he was making his nest for the night. Bain had chosen a spot Hyd wanted, and Hyd rushed at him in the hopes that Bain would surrender the spot. Instead the noise of the scuffle drew Etang’s attention, and he rushed to his brother’s defense. The two brothers advanced on Hyd menacingly, and Hyd gave up his claim on the nest site he wanted and moved higher into the tree. This morning, though, Etang is nowhere to be seen. Hyd takes the opportunity to reaffirm his dominance over Bain. As he shakes the branches of the tree and shrieks wildly, Bain quickly retreats down the tree and moves toward the water. The sounds of the scuffle awakens the rest of the band. Soon everyone is out of their sleeping trees, grooming each other and beginning to feed. Bain is not long alone near the shore after his retreat. Welle and Meer make their way toward the bank, with Teich and Natte trailing along behind them. The youngsters waste little time before settling themselves at the water’s edge. They have perfected their root extraction technique, selecting plants whose roots are fully submerged in water and grasping the stalks close to the ground. Meer and Welle watch their children pull up the roots as the two mothers munch on the tips of the plants. Occasionally they too pull up a bunch of 22

roots, but mostly they simply sort through the ones their offspring harvest and drop on the sand. Many of the band members do not venture near the water’s edge, preferring to stay on familiar, solid ground. But a few individuals regularly feed there and are becoming more comfortable with the new watery feeding grounds. Praia and Lago, two adolescents, appear on the shore. They are old enough to leave their mothers regularly and often join Natte and Teich near the water to pull up roots for themselves. Bain also does not shy from the water. He likes the food he finds on the shore and takes advantage of his splashing display to get what he wants. As the sun begins to burn hotly, Teich tires of pulling up roots. He takes several steps into the water, letting the water flow over his four limbs in the hopes that it will cool him off. His left hands slips on a smooth rock just out of sight under the mud. He barely stumbles, but curious, grasps the stone and brings it up to investigate. Balancing on three limbs, he stares at the offending rock. It has a peculiar shape, not round or jagged like the ones he is used to, but a long oval thicker on one edge and tapered to a thin ridge on the other. He turns it over and sees a crack all the way along the thin edge, which exposes a hint of pale white inside. He is not holding a rock after all, but a clam that had been badly battered in a recent storm. He puts his small fingers inside the crack and feels something wet and slightly slimy, not all that different from the inside of a fruit. He tries to force his fingers in farther and feels the shell open slightly. Crouching in the water to free both hands, he manages to get both sets of fingers inside and pull the damaged shell apart. Dropping the empty half of the shell into the water, he pokes the strange rubbery creature inside and is surprised when it moves slightly. He sniffs it and notices the strong fishy smell, then holds tightly to the bottom shell while he pries the clam out. His first tentative bite of this strange new creature is pleasant, although unfamiliar. It reminds him of the meat from some of the small animals the band occasionally catches, but different too. When the males of the band catch an animal, the meat is especially prized. Teich is too young 23

to hunt himself and has only ever been able to taste tiny scraps. He quickly swallows the rest of the clam before any of the others have a chance to come steal it from him. Lago notices him chewing and walks into the water toward him. Lago sniffs at the clam shell still floating on the water’s surface. Lago’s face takes on a quizzical expression. His large brow wrinkles, and his long lips, usually hanging slack, are pressed tightly together as he watches Teich. Teich drops low into the water and scoots along on his belly, moving his hands in front of him until he encounters another hard object the same shape as the last clam shell. The violent storm that passed their island a few days ago dislodged and damaged many clams around their island, and this one is also cracked. A corner of its shell is broken off, making it even easier for Teich to get at the meat inside. Lago watches in apparent fascination as Teich swallows his second clam. Praia and Natte make their way over and watch as Teich continues to find and eat clams. Lago is the first to try Teich’s technique. He scoots along the sandy bottom with his arms outstretched, watching Teich’s every move. He is so intent on Teich that he doesn’t notice the log lying in the water and falls over it, sputtering as he swallows water and sand. He retreats to the dry beach and watches for a while before regaining enough dignity to join the group again. Gradually they get the hang of clam catching, and all four of them manage to find at least one clam. Praia’s, Lago’s, and Teich’s clams all have cracks or broken pieces and are easy to open, but Natte’s clam is undamaged by the storm. Only a very thin crack runs along the thin edge of her clam, and she has to work her fingernails slowly into the crack and pry much harder than the others before her clam opens and she can eat the meat inside. Over the next several weeks most of the band members make their way down to the shore and see what the youngsters are doing. Soon most of them take advantage of Teich’s discovery and gorge themselves on clams. One afternoon Bain and Etang find a section of shore particularly thick with clams and happily feed while many of the other band members rest on the shore. Bain feels a clam under his foot and reaches down excitedly to bring it to the surface, expecting a meal. This is a particularly stubborn clam, one he cannot get his 24

fingers into no matter how much he struggles. Frustrated, he throws the clam at the shore, where it bounces a few times, then lands, then begins burrowing itself under the mud. Hyd, just emerging from the trees a few yards away, takes Bain’s gesture as a threat. He quickly grabs a nearby rock and throws it toward Bain. Rearing up on two legs and bristling, Hyd loudly calls his challenge and rushes toward Bain, stopping at the water’s edge. Bain is at a disadvantage in the water with nothing impressive-looking nearby to throw. He stands up as well, then brings his arms violently down, showering Hyd with a huge splash. Hyd backs up, coughing and shaking the stinging salt water from his eyes. Bain repeats his performance, adjusting his angle to get an even bigger splash. Etang, noticing the commotion, rushes over and joins his brother in spraying Hyd with water. Hyd has not spent as much time in the water as the others, preferring to stay on dry land and eat the last remaining fruits. He is nervous and unsure about charging in after the two brothers. He makes several mock charges but is greeted with fresh splashing assaults each time, and he eventually gives up and retreats from the shore, dripping wet and dejected. This encounter marks the beginning of the end for Hyd as the most powerful male. He is never again able to challenge the two brothers when they are together and usually does not dominate Bain even when he is alone. The splash display is more intimidating than rock throwing or branch shaking, and oftentimes Bain follows him away from shore and attacks him on dry ground as well. One day Bain attacks Hyd in a feeding tree, knocks him onto the ground, and stomps on him before he can get up. Then Bain chases him up a small tree and guards the bottom for several hours afterward, not allowing Hyd to come down. After this humiliating defeat, Bain is established as the dominant male of the band, never again to be displaced by Hyd. While the dominance battle rages between the two males, life goes on much as usual for the band. They delight in the new food, and many band members search for 25

clams nearly every day. After several months of this intensive searching, the clams become harder to find along the shore. Those near the beach have all been found or have moved out into deeper waters. Teich wants more clams. He has looked for the last three days and has given up every time to go back to pulling roots because he had not found any clams. On this fourth day he tries a little farther from the shore, straining to hold his neck high and his head out of water, pushing himself up on all four limbs. His efforts pay off because he feels the familiar shape under his hand. He tries to pull it up out of the water but does not have enough balance on his tiptoes to stand on three legs. He lurches forward and is totally submerged in the water. He comes up sputtering, very unhappy but still pressing his clam against the sea floor with one hand. He rears up instead, balancing better on two feet with his clam now above the water, clutched in his hand. He pulls the shell off his prize and eats with pleasure. Looking out over the water, which is now only just above his waist, he takes a few tentative steps farther out and is rewarded by feeling another clam under one foot. He reaches down and retrieves it, wetting himself up to his nose in the process but enjoying the tasty results. Standing up again, he takes another few steps forward, then another, searching for the elusive clams. As the water began to lap at his shoulders, he turned back toward land and sees Natte and Lago standing in the shallows. He is now farther out to sea than anyone else of his species has ever been.

26

Danakil Sea 8 million years ago

Welle (Waves; German)

On average humans are the fattest of the , with body fat percentages for healthy individuals around 15% for men and 27% for women. Most other primates, chimpanzees included, rarely exceed five percent body fat in the wild. Humans can and do achieve very low body fat percentages occasionally, athletes for example, but doing so compromises their reproduction, lowering sperm count in males and stopping ovulation in females. Humans, then, are biologically required to be fat, more than twice as fat as our nearest relatives. Fat, for the most part, is rare in non-human animals, especially in prey species, because it is expensive. Carrying around extra bulk slows one down, making it more likely that an individual will end up as a meal for a hungry predator than will live to pass on her genes. It also requires more or higher-calorie food to maintain a high level of fat, making it difficult to retain during times of drought or famine. So why would one of the primates become dependent on a high level of fat to reproduce when it is so expensive to maintain? One undeniable advantage fat gives its bearer is the ability to float. If a human body drops much below 15% body fat, it will cease to float, and that person will be forced to expend more energy during simply to stay on the surface of the water, decreasing their forward speed. At around three percent body fat, it is nearly impossible for a human to make forward progress in the water, because all of their energy is needed to keep their head above water. Interestingly, this approximates the body fat percentage that is required to sustain life in humans. Dropping much below that will put the person in danger of death by starvation.

27

It should not be surprising, then, that wild chimpanzees cannot swim. It is not that they choose not to, it is that their body fat level is too low for them to stay above water. However, when chimpanzees are held in captivity with unlimited access to food and inadequate exercise, they may reach a body fat as high as 15-20%. Our group of chimpanzee-like primates, with the discovery of protein and fat rich seafood requiring relatively little energy to extract, may have put on fat similarly to modern day captive chimpanzees. Because of the lack of large predators on smaller islands, increased fat would not have been a hindrance to survival, and the potential ability to swim could have been a powerful asset.

Bain, Etang, and Lago awake early and begin grooming before many of the other band members rise from their own nests. Wandering through the thick underbrush of the hillside, they discover a particularly heavily laden fruit tree, and all three climb into it. Etang, larger than either of his two companions, settles himself in the middle fork of the tree, while the other two sit on less comfortable branches. They occasionally brush against each other as they reach for fruits, although they do not seem to mind the closeness. As Bain chews a bite of fruit, he absently grooms his brother, first on Etang’s chest, then moving his hand up to ruffle the hair on his cheeks. Lago, still young enough to be more interested in play than anything else, jumps up and down on a branch above the pair’s head until the leaves brush their foreheads. The brothers ignore the youngster as they continue to eat, but after several minutes, Etang loses his patience and chases the frisky Lago high into the tree. Bain calls out reassuringly to Lago as he grooms Etang, easing the tension his brother often creates. An unlucky troop of monkeys is crossing the forest at the same time, also looking for something to eat. Etang is the first to spot them, and his pant-hoots of anticipation begin quietly and accelerate in pitch and frequency to an ear-splitting climax. Bain responds by jumping into a nearby tree, where several of the juvenile monkeys are feeding. Etang’s call attracts four other nearby males, and all seven of the males join with pant-hoots of their own as they move toward the monkeys. Lago quickly swings his 28

way through the canopy into a tree on one side of Bain’s, while the other males position themselves in trees and on the ground nearby. Bain charges the monkeys, forcing one higher into his own tree while three others flee into neighboring trees. One of the monkeys leaps into Lago’s tree, and Lago rushes toward him. Lago is larger than the and gains on him as he scampers across the tree branches. Just as Lago reaches out his arms to strike, the monkey throws himself into a neighboring tree. He just manages to grasp the end of a thin branch before falling toward the ground thirty feet below. The branch bends under the sudden weight but holds, and after dangling by one arm for a moment, the monkey pulls himself onto a thicker branch and escapes into the forest. Lago pulls up short, staring out over the vast empty space between the two trees. He has never taken part in a hunt before, although he has watched them from the time he was still young enough to cling to his mother’s stomach. He looks around, chewing his lips in agitation, to see if any of the others notice his hesitation, then he follows the retreating monkey with his eyes as it disappears into the trees. The other males have been luckier. Bain and two of the others have managed to grab monkeys before they could escape. Now they bite into the heads of their catches, ending the young monkeys’ struggle to escape. The rest of the band arrives, drawn by the excited noises of the hunters. Several adult females climb up the tree and sit near the feeding hunters, trying to get part of the kills. One female holds out her hand and calls softly to a male and is rewarded with a scrap of meat. Another begs the same way to the other male, but this male ignores her. She inches her hand closer to the monkey carcass. The male glares at her and then goes back to feeding. She gets bolder and attempts to take a bit of meat, but the male snatches it back and cuffs the female, who retreats down the tree in fear. Meer is among these females, and she approaches Etang in his tree. She is sexually receptive, a bright pink patch of swollen sexual skin visible on her rear end as she climbs. She presents this to Etang, and he sniffs appreciatively. He allows her to carry away a section of the back leg with some meat still attached. She settles close to 29

him, hoping his presence will discourage the other males from taking away her newly won prize. Natte watches this exchange closely and hurries up the tree to her mother to begs for scraps. Several of the adolescents and lower ranking females gather under the trees where the dismemberment is taking place. When a bit of blood or entrails fall through the leaves, they investigate and sometimes are rewarded with small morsels. Etang rests after gorging himself on the meat of his monkey. As he shifts his weight to get more comfortable, the carcass falls from the crook of the tree onto the forest floor. Two juveniles who had been waiting for fallen meat scraps at the base of the tree are suddenly rewarded with an only partially eaten monkey. Most of the meat from the limbs is gone, but some meat and viscera still cling to the trunk. The larger of the juveniles grabs an exposed arm bone and runs off into the underbrush. His companion chases after him, hoping to share in the feast. Several other stragglers follow, searching the ground for bits of flesh that may have fallen in the rush. By the time Etang makes his way down the tree, his monkey has disappeared in the trees. Since he is no longer hungry after eating most of his kill, he does not pursue it. Instead he makes his way down to the shore and into the water. He has been to the shore many times and has even managed to find a few clams, but he can never quite figure out how to open them. He has discovered that this is no great hardship for him, though. He usually just takes clams away from the younger members of the band after they have opened them. When he reaches the shore, he sees Praia standing chest deep in the water, her black hair making ripples around her. She has recently reached maturity, and although she is large for a female her age, she is smaller than Etang, and he makes her uneasy. She has watched males pound anyone close to them when they became upset or irritated, especially if they are smaller. She knows it is best to be on guard and leave quickly when male tempers flare. Before Etang arrived, she had found a clam but was unable pry it opened. She is about to drop it and search for another as Etang enters the water. Many times band members can get their fingers, or at least their nails, into the crack separating the two 30

shells of the clam and pry it open. Sometimes, though, the clam is sealed tight, and no matter how diligently they work, they cannot open it. Etang walks closer to her, waiting until she opens the clam so that he can take it away from her. He is able to stay on all fours because he is bigger than she is, and his head is still out of the water. This is too much for Praia. Usually standing upright is a threat, used to intimidate rivals, and she does not want Etang to think she is challenging him. She drops her sealed clam into the water and attempts to go down on all fours again. The water is too deep for her to keep her head out of water with all four feet on the ground, so her head disappears under the water. Still nervous about seeming to challenge Etang and now frightened by the deep water, she pushes herself upward with all four limbs. When her head breaks the surface of the water, she attempts to run forward. Surprisingly, it seems to work even though her feet are not touching the sea floor. She moves forward a body length by the force of her treading hands and feet until her head sinks under the surface of the water again. This time she is ready for the dunking. She pushes off with more power from the ground and keeps her hands closer to her mouth, hoping to keep the water away. This works even better. She can now tread with her legs and push her face out of the water with her arms without touching the bottom. Fascinated by her new game, she forgets about Etang for a moment and practices her new skill, moving back toward shore until she touches solid ground. Etang takes little interest in this innovation and instead feels for the clam she dropped. He finds it with a foot and brings it out of the water to open. He has no more luck opening it than Praia did and quickly became frustrated. He is used to small animals, such as monkeys, which are easy to eat once they have been caught. He reaches the end of his patience and throws the offending clam hard in the direction of the shore. It makes a satisfying crunch as it hits a large rock on the beach, startling Welle, who had been resting there. Welle is crouched near the edge of the shore, sitting on the large rock as she nurses her new baby, Furt. She gave birth less than a month ago and looks fatigued. Her 31

usually thick and glossy dark brown coat hangs limply from her body, and she watches her older son Teich eat clams through sunken eyes. The clam startles her, and she barks in alarm. Her irritation is short lived and is replaced by interest when she sees what it is that has startled her. The clam is a very welcome addition to her diet. She has not been able to go out deep enough into the water to find her own clams since her son has been born, and she is suffering the ill effects of prolonged malnutrition. Furt, like all the infants of the band, was small and helpless at birth, and at a month old can still only cling to his mother’s belly as she walks or climbs for food. The first day after Welle gave birth, she walked into the water as usual, only to have Furt cry out in alarm when the water reached him. She looked down questioning at the complaining infant, and then took another few tentative steps forward. Furt’s crying increased and she finally stood upright, balancing on two legs as had become customary when the band looked for clams. The newborn Furt was not expecting the quick change in position and was not clinging tightly enough to his mother. He attempted to hold on, but gravity pulled him down farther and farther until his legs dangled in the water. Welle, made uneasy by her child’s cries and the dangers of the water, grabbed the distressed infant and retreated. When she returned to dry land, she lay back in the sun and thoroughly groomed her wet baby until he quieted, then stared gloomily at the water. Since that day she has not ventured into the water. Her body has been relying on the fat deposits she developed before giving birth, when she was still eating many clams each day. Now she is not plump like the rest of the band. Instead her and hips are visible under her hair. Their island has been changing. There are fewer fruiting trees than when they arrived, which makes getting enough to eat only on land more and more difficult. This is not an inconvenience to most of the band, who enjoy clams and water grasses, but for new mothers like Welle it has been almost fatal. Some barely manage to find enough to eat until their infants are old enough to cling on to their mothers without getting wet. After her initial surprise at the sudden entrance of the clam, Welle recognizes the welcome treat and gets up immediately to investigate. The clam has bounced off the rock 32

and landed in the dirt not far away. Welle inspects it and sees it is one of the sealed clams she cannot open. She tries again and again to insert her fingers into the paper-thin crack along one side but simply cannot do it. She throws it down in disgust, accidentally hitting the rock with it. This time the clam shell, weakened from the first hit, cracks. Welle wastes no time scraping out and eating the meat inside. Welle keeps a lookout for these sealed clams in the days that follow. She often sits on the edge of the shore eating cattails and cordgrass, some of the only food she can find, and nurses Furt while she watches Teich hunting clams. In the afternoon of her first day of watching, he finds one he cannot open and begins to drop it, but Welle hurries toward him. She makes the begging noises she makes after monkey hunts when she wants some of the meat, but Teich does not understand what his mother wants with a clam she cannot open. She calls again, this time in exasperation, but settles down on the edge of the water to nibble on the cattails again. She repeats her performance with the next sealed clam Teich finds, this time taking a few steps toward him into the water. He walks uncertainly toward his mother and holds out the clam to her. She takes it and returns to her rock. Teich watches her, perplexed, as she throws the clam at the rock, this time missing it completely. On her second attempt she hits the rock, and a small crack appears in the clamshell, but it is not enough to allow her to pry it apart. Teich, curious, comes over to investigate his mother’s strange behavior. He watches as she continues and is finally rewarded as the shell cracks apart and she eats the clam inside. Losing interest in his mother’s new activity, he returns to the water. The rest of the afternoon passes, and the others of the band make their way down into the water, sometimes in small groups, sometimes all alone. Their beach menu has expanded to include many varieties of clams and mussels, as well as some seaweed and cattails, so most of the band spend at least some of their day in the water feeding. Meer makes her way away from the shore and begins her own foraging with Natte not far behind. Welle continues to wait for Teich to find more sealed clams. He finally seems to understand that she wants the ones he cannot open and obliges her by throwing 33

them toward shore. Meer watches this activity intently, paying particular attention when Welle manages to crack one apart. As the band settles down for the night, Meer returns to the spot where Welle worked that day and sniffs the empty shells. The next day Meer finds one of the sealed clams and brings it out of the water to where Welle is sitting. She, too, tries to open it with the rock, but only manages to scratch the clam along the side, not using enough force to open the shell. She loses interest and drops it in the sand. Welle retrieves it, and after several tries manages to break it open like the others. Meer gives a huu of puzzlement and returns to the rock, looking at it intently to see if she can discover the secret to the clam cracking. Not seeing anything to explain Welle’s success where she failed, she retreats to the water to continue her foraging. The next time she find a sealed clam, she looks quizzically at Welle, who starts toward her, begging. Again Meer attempts to crack the clam herself and fails, only to watch Welle eat it a moment later. Meer and Welle develop a habit after the first few days of begging and uncertainty. If Meer happens upon a clam she cannot open during her daily foraging, she brings it to the rock where Welle waits. Welle opens the clam and sometimes Meer begs part of it from her, while sometimes Welle eats it. A month later Meer is sexually receptive again, and many of the males stay near her, waiting for a chance to copulate. Etang is especially persistent and drives off many of the competitors with the help of his brother Bain. With his sudden nearness he notices Meer’s unusual relationship with Welle. He watches at first with disinterest as Meer brings her sealed clams to Welle. But once he sees Welle eating the clams, he becomes more interested in the process. Here is a female who can open clams he cannot. He searches until he finds a clam of his own and brings it to the rock for Welle to open. He watches her throw it against the rock, then he takes the now-opened clam from Welle and inspects the meat inside before gulping it down. In the days that follow Meer’s sexual swellings become even more pronounced, indicating she is nearing the peak of her receptiveness. One morning she manages to escape the group of males who constantly surround her, intent on reproduction. She is 34

feeding with Natte on a hillside far from the shore. Etang approaches through the underbrush and begins shaking branches at Meer, wanting her to follow him farther from the band. She ignores him, continuing to feed. He tries several more times, getting closer and more violent with each branch shaking session. Finally, losing patience, he jumps on her, hitting her several times, then pulling her arm in the direction he wants her to go. She reluctantly follows as he sets off toward the top of the hill, Natte trailing along uncertainly behind them. Meer stops again as they pass a tree with several piece of fruit still attached. He waits patiently as she feeds on the fruit and then begins his courtship displays again, to be ignored once more. The whole process is repeated, and this time she follows him less reluctantly. He doesn’t stop his trek until they are far from the shore in an area the band does not frequent. The vegetation is different here, greener with less fruit. The tall trees of the forest near the shore are replaced by more stunted and twisted brush, shaped by the prevailing winds that blow over the highly elevated hilltop. The band has long since stopped making the long trek up the hill in large groups, because they never find enough fruit to satisfy everyone. Only smaller groups make their way this high, and then only for short times. Etang and Meer stay here, mating frequently, for several days. Natte is confused by the constant presence of Etang, and her mother grooms her frequently to calm and reassure her. As Meer’s swelling subsides, she is no longer sexually exciting to Etang, so he drifts away. The two females leave as well and make their way down the hill, closer to shore.

Such consortships are observed in chimpanzees, who otherwise practice promiscuous mating habits. Females are sometimes sequestered from the rest of the males in the group by an opportunistic male during the time they are the most receptive, making it more likely that he will be the father of her offspring.

35

Afar Depression 7.7 million years ago

Etang (; French)

Natural selection is one of the most often cited forces of evolution. Natural selection occurs when an individual has a trait that makes its owner more likely to survive in a given environment. This individual would be more likely to survive and produce healthy offspring (who then produce healthy offspring) than an individual who lacks the beneficial trait. Over time, these beneficial heritable traits become more common in the gene pool, while maladaptive ones become less common because their owners die before producing as many healthy offspring. The peppered moth, Biston betularia, is a modern example of natural selection in action. Prior to the industrial revolution most of these moths were light-colored; dark colored moths occurred only rarely and were considered collector’s items. As soot and pollutants turned the trunks of trees a darker color, light colored moths were more likely to be seen and eaten by birds, thus dying early. Over time the dark moths became more common because they survived longer and had more offspring. Today, with the successful efforts to clean up pollution, the peppered moths are again becoming predominantly light colored. A band of last common ancestors separated on an island would have been subject to a variety of selection pressures in their new environment that the LCA on the mainland were not. One of these pressures could have been for bipedality. Those individuals who could stand upright longer and walk farther distances through the water would have been able to find more food, in turn making them healthier and stronger. These individuals would have left behind more children than their weaker, less healthy peers, and their offspring would have stood upright more efficiently like their parents. This cycle would have been repeated as the band became more and more adapted to an upright stance. 36

Two major skeletal changes are important to maintain an upright posture for extended periods: the shape and orientation of the pelvis and the position of the head on the neck. The of all non-human apes are tall (top to bottom) and thin (front to back). Humans, on the other hand, have much shorter and thicker pelvises that are shaped like bowls. Our highly modified pelvises give us the support to walk upright by creating a basin for our internal organs and producing hip joints that give us our unique striding ability. Our foramen magnum, the hole in our where the vertebral column attaches to the brain, is also modified for our upright posture. In quadrupedal animals this hole is located near the back of the skull so that the head is held level when the animal is on all fours. The foramen magnum is shifted forward to some degree in primates, especially the great apes, because these primates spend a significant amount of time with their trunks erect. In humans this trend is carried even further. The foramen magnum is located directly underneath the skull, so that the head balances on the neck and is level when an individual is fully upright. Natural selection could have begun shaping these two skeletal changes over the last million years that our band of last common ancestors was isolated on their island. These microevolutionary changes may have accumulated to the point that the band would be on the brink of their first speciation event, which would change them into the first species along the road that would lead to Homo sapiens. A more aquatic environment may have necessitated other changes in our ancestors, in addition to a trend toward bipedality. Mothers with small infants would have had difficulty feeding themselves and their babies with aquatic foraging because of the dangers water presents to small children. However, greater paternal involvement in childrearing, such as bringing food to the mother or watching her offspring while she foraged, would have allowed aquatic motherhood to continue. A male expending some of his energy to obtain food for a child, however, would only have benefit to his genes if that male could be certain he was the father of that offspring. Therefore a more monogamous 37

mating system may have been another development related to a more aquatic environment, because it would have ensured greater paternal certainty.

Meer and Natte return to the shore after Meer’s consortship with Etang. Bain is the first to see them, and he makes his way out of the water toward Meer. She stands still as he circles around her, sniffing for signs that she is still receptive. Finding none, he moves away, allowing Meer and her daughter to enter the water unmolested. That afternoon several other males approach Meer, but none show interest past a sniff or two. Natte is unsure about this sudden male attention toward her mother. This is the first time her mother has come into estrus since her birth. At first she stays close to her mother, needing reassurance. After the first few males move away from her mother without much interest, she relaxes. Eventually she moves out onto the beach to play with another youngster. A month passes and life continues as usual for Meer and Natte, until Meer once again shows the pink swellings of sexual receptiveness. After an exhausting two days of being harassed by the band’s males, Meer is persuaded to follow Etang up the hill away from the band. Four more months pass without another sign of receptivity from Meer, and her stomach is getting perceptibly bigger. Natte often grooms her mother and goes over Meer’s newly enlarged belly gently with particular interest. For the last month their grooming sessions have been getting longer and more frequent. Now when Natte tries to get her mother to play, Meer turns away or only plays half-heartedly. When she does play with her daughter, Meer often stops early to build a day nest and rest through the afternoon heat. Natte is changing as well. She is approaching adolescence and begins to put on fat. With her new, plumper form, she more closely resembles the adult females of the group. She ventures out into the water, farther all the time, and looks for food the others have missed. 38

Natte sits on the beach while her mother rests and sees Praia paddling around, rather awkwardly, but farther away from the shore than Natte has ever been. Natte cocks her head, watching. Still a curious youngster, she splashes into the water to investigate, rising up on two legs as soon as the water reaches her stomach. She wades out as far as she can, leaving only her face out of the water. Since the first day Praia realized she could run in the water without her feet touching the ground, she has gained confidence in her swimming ability. Natte’s obvious interest makes her even surer of herself, and she swims back and forth in front of Natte, seeming to encourage her to try. Natte lets her upper body drop until she is nearly horizontal in the water with her legs running underneath her. She inches forward, farther away from the shore. She kicks harder, adjusting her feet to get more forward power. She makes it to Praia and then turns to look for her mother on the beach. She whimpers in fear when she sees how far she has come. Quickly she tries to put her feet back on the bottom, only to have her head sink below the surface. Her feet find the bottom, and she kicks off and comes up sputtering. Praia is right beside her, and because she is taller, she can just reach the sea floor and keep her nose above the water. Natte grabs Praia and clings to the hair on her neck as she catches her breath. Praia begins to groom Natte, parting her wet hair and removing a bit of seaweed. As Natte calms down, she begins to kick her feet gently in the water, creating small waves that rock the pair. This motion reminds Natte of a strong wind moving her sleeping nest. Still holding onto Praia, she stretches her legs out so she is lounging flat in the water. Her legs do not sink in this position, but float up so she sees her toes peeking out of the water. She lets go of Praia and still does not sink. She gives a low pant of laughter as she floats on her back, paddling her hands. Praia follows, swimming beside her for a moment. Praia’s splashes send water into Natte’s mouth, and Natte pushes harder with her arms to get her head out of the water. Natte coughs for a moment, then relaxes and tries swimming forward again. As she gets more comfortable, she looks back at the receding shoreline and does not feel the 39

same panic as before. Eventually she and Praia both get tired from their swimming and start back toward shore. Natte panics again when she realizes just how far she is from dry land, and attempts to stand. Both she and Praia are surprised when Natte’s feet find purchase and she stands, only chest deep in water. Praia quickly drops her own feet, and they both stand on a shallow sandbar. They wade along this new discovery and find that it gets even shallower if they take a few paces farther from the shore. They drop down on all fours again, as they usually do when on land or in shallow enough water. After they take a few steps with all four limbs, they cross over the crest of the sandbar, and the water quickly deepens, forcing them to stand upright once more. They wade along the sandbar, and suddenly Praia trips over what she thinks is a submerged tree trunk. She barks in pain as it cuts into her leg. She knows sunken wood should not cut her this way, so she retreats to the shallow top of the sandbar and pulls her leg from the water to inspect it. Two half moon shaped wounds are visible through the black hair on her shin, and a drop of blood makes a momentary red spot in the water where it falls. She dips her leg in the water and winces as the salt-water stings the cuts. Natte follows Praia as she retreats, fearful of an unknown danger from under the water. As Natte watches Praia, though, she becomes less concerned. Praia is not acting as though she fears an attack. In fact, Praia, who is through inspecting her leg, moves near the spot she was injured and peers into the water. Natte follows her, but their earlier tramping through the sandy bottom makes the usually clear water murky, so neither can see the bottom. Slowly the sediment settles, and they can see the submerged tree, with curious lumps all along its edges. Praia is confused and apprehensive about the sharp tree and she takes a tentative step forward, then pauses to scan the surrounding area for movement. Natte can tell from her body that, although Praia is unsure, she does not fear an attack. This is all the assurance Natte needs. Even as an infant Natte was allowed to explore unusual objects. Natte investigated small , termite nests, and unknown fruit trees while her mother watched. The only times her mother stopped Natte from exploring something unfamiliar 40

was when Meer or others close by showed the telltale signs of fear. Raised hair and the open mouth grin of fear warn Natte away from strange situations, but Praia is not afraid now. Praia is merely tentative, and Natte has learned that this means to approach cautiously, not necessarily to run away. Natte sees nothing moving under the water aside from the darting of small minnows she knows from the shallows near the beach. She takes another step forward, and Praia follows her, until both females can reach down and inspect the tree trunk. The bumps feel strangely familiar. They are shaped like the clams and mussels they pull up near the beach, but smaller and sharper on the edges. The pointed edges are what cut Praia as she tripped over they tree. They have discovered oysters, attached to the decaying wood of a fallen tree. Praia wraps her fingers carefully around the blunt edges of the oyster and tries to pull it up as she has pulled clams from the sea floor many times before. This oyster is more strongly attached, and it does not come loose on her first attempt. She gets a better grip and tugs harder. The oyster suddenly breaks free and sends her sprawling backward into the water. She wades to the shallowest part of the sand bank, squats in the water, and tries to pry open her oyster as she does so often with clams. This oyster is too small to grip well and is sealed tightly against invasion. Praia knows from watching the adults that rock tools can open clams, so she searches the sandy bottom for a rock. Usually the adults throw the clams at the rock until the clam cracks, a technique Welle learned accidentally, and many of the others have picked it up. Running her hands along the bottom, Praia feels one. She grasps it and then faces a new problem. She cannot put her rock on dry ground and throw the oyster at it, because she cannot swim to the shore and hold her oyster at the same time. She tries instead to put the rock on the shallowest part of the sandbar, which is still a foot underwater. When she tries to throw the oyster at it, though, all she gets is a splash as the oyster sinks out of sight. She retrieves her fallen oyster and modifies her technique. She starts with the oyster underwater and tries to push it hard enough against 41

the rock to crack the shell, but the water slows down her movements too much and the oyster does not break. Trying to make a platform, she squats in the water so that her knees break the surface, then places the rock on her knees. She loses her balance before she can even raise her arm to throw the oyster. Natte watches her friend’s antics with a puzzled expression, not understanding what Praia is trying to accomplish. She walks back to the oyster tree and tries to detach her own food. As she reaches down, she is not as careful as Praia, and the edge of her oyster cuts into the palm of her hand. Natte lets go, then she selects a different oyster, this time feeling the edges carefully for blunt spots before she tugs it free. She returns to Praia and sits down on the sandbar, which is deep enough that only her head is visible above the water. She holds the oyster out of the water and tries to open it, but has the same difficulty Praia did; it is tightly sealed. Praia is frustrated with her ineffective rock technique and is getting hungry. Natte is smaller than Praia and close by, making her an ideal target for relieving stress. Praia stands up, towering over the seated Natte, and barks roughly. Natte drops her oyster and retreats farther down the sand bar. This does not satisfy Praia, who chases after her, splashing. Her splash display lacks strength though, because she has an oyster in one hand and a rock in the other. She does not want to throw either, still hoping to be able to open the oyster. She bangs them together instead, hoping that this will make a satisfyingly loud noise. It does make a satisfying sound, though not the one she is expecting. The oyster shell crunches under the pressure of the rock, and Praia momentarily forgets Natte. The thin oyster shell is demolished, and Praia picks the larger shell pieces out of the meat inside. She pulls the oyster out of the remaining shell and eats it, her irritation disappearing. Natte sees that Praia has abandoned her earlier attack and is chewing happily on the oyster. She returns to where she dropped her oyster and watches Praia as she pulls up several more, cracks and eats them. Natte tries to copy Praia but does not notice the rock and tries to hit the oyster with her hand. She succeeds only in bruising her knuckles; the 42

oyster remains undamaged. Cradling her cut and bruised hand, she decides that these oysters are too much work and starts back toward the shore. Praia has eaten enough oysters for the time being. She dislikes the idea of being alone so far from shore, so she follows Natte. They make their way back, swimming until they tire, then floating on their backs to rest before they swim again. It is late afternoon before they return to the shore, and they settle down to eat shore grasses before night falls. Natte finds her mother close by and is glad to be reunited after the day’s separation. As the band begins to prepare for night, Natte makes herself a nest near her mother and drifts off to sleep quickly. Over the next few week many of the band members begin to take an interest in Praia’s swimming abilities. Most learn that they can bring their feet off the bottom and lounge on their backs while they eat the seaweed that grows offshore. Some of the more adventurous even begin to follow Praia when she swims toward the sandbar, although they lose interest before they make it all the way there. Praia returns to shore with them instead of braving the open water on her own. One day Lago floats near the sandbar while he feeds. Praia swims after him, finds her oyster tree, and detaches a few. She wades onto the sand bar, and Lago follows, baffled at the shallowness of the water this far from land. He watches Praia crack and eat her oysters, then go back to find more. He follows her, and after a few cut fingers, has a handful of his own. After a few false attempts he manages to crack an oyster, and his loud food grunts announce that he is enjoying the new food. As the days pass, more and more of the band are tempted by the prospect of food to make their way out to the sandbar. Meanwhile, Meer’s stomach continues to grow until one day she wanders off by herself and is gone for several days. When she reappears, she has a new baby girl, Rio, clinging to her stomach. As she makes her way toward shore, the band members nearby pant-hoot excitedly in greeting. Natte, apprehensive with her mother’s absence, is the first to approach Meer and begin grooming her. When Natte tries to groom the infant, Meer moves away from her daughter and takes baby Rio with her. For several weeks 43

after the birth of her second child, Meer is an object of interest to the band. Babies, although not uncommon in the band, are also not everyday occurrences. Everyone wants to inspect this new arrival. Meer gradually allows Natte and many of the other females and adolescents to inspect the baby and groom her occasionally, but moves away if any of the adult males approach too closely. The one exception is Etang. After their two consortships, Etang stays close to Meer and Welle. He continues to bring Welle the occasional hard-to-open clam because he never has mastered the art of cracking them himself. Now Meer is faced with the same problem as Welle, she cannot take her new baby into the water. Now that Furt is a year old, Welle can again go into the water to find her own clams, so now she brings sealed clams to Meer. Etang continues to bring his share as well, so Meer is well provisioned. One day Meer grooms Etang after he brings her a clam. Rio, who is accustomed to Etang, reaches out and grasps his hair, pulling herself toward him playfully. Meer pauses in her grooming to look from her daughter to Etang, but does not seem concerned as she continues to pick at a scab on Etang’s side. Rio manages to pull herself all the way over onto Etang’s stomach and clings to him the same way she does her mother. Meer finishes with Etang’s grooming and makes her way toward the water’s edge. She stops momentarily to nibble a plant growing there, then, free to enter the water for the first time in months, she plunges in to search for something more substantial to eat. For half an hour Meer feeds in the water, turning to watch Etang occasionally as he sits in the shade with baby Rio in his lap. Finally satisfied, Meer makes her way out of the water and over to her child, pulling her from Etang’s lap into her own as the baby roots for a nipple and begins to nurse.

44

Afar Depression 7.3 million years ago

Praia (Beach; Portuguese)

Humans were once thought to be unique in their capacity to wage war on their neighbors. However, intergroup aggression has now been identified in chimpanzees. At the Gombe, study site a community of chimpanzees split into two smaller ones, and the stronger of these groups proceeded to systematically hunt down and kill all the adult males of the weaker group. Jane Goodall, who had been observing these chimpanzees in the wild since 1965, watched as one previous friend held down another while others tore out his throat and detached his testicles, leaving him mortally wounded. This “civil war” is not the only example of warfare among chimpanzees. Groups of males have also been observed going on patrols along the edge of their range, quietly searching for isolated individuals that they sometimes beat to death if they find them alone. This violence is not restricted to males. Females, especially those at the peak of their sexual receptiveness, occasionally accompany a group of males and take part in the violence as well. Females and infants are not immune from being attacked themselves, and strange females or their infant offspring will also be attacked and killed if they are separated from the rest of their group and encounter a patrolling group of males from outside their community. It seems that civil war, brutality, and lethal aggression are among the legacies we share with our chimpanzee cousins. Environmental changes could have thrown our band into contact with other bands of the same species. The hot African sun would have caused the gradual evaporation of the inland sea until land bridges connected many of the islands. The new foraging ground available to the band on their expanded island might have come at steep price; their island might now contain another band. Throughout the sea’s water levels had fluctuated, making some bands closer together, then farther apart through two 45

million years. Strangers occasionally met, encounters which could have resulted in violence, or in something of a different nature. When a male chimpanzee encounters a lone receptive females, he often “makes love not war,” preferring reproduction to violence. Some of these neighboring females eventually leave the community they were born in and join the bands of their male consorts.

Lago sniffs the air and calls softly. This morning he has been tempted farther inland than usual by a few clusters of ripe figs and notices the intriguing scent of a female in estrus. He sniffs again, then looks up into a nearby tree and spots the receptive female. It is not one of the females of his band, which makes her all the more appealing. She shifts in the tree, and he catches sight of her swollen sexual skin, a shell pink advertisement of her receptiveness. He calls again, this time louder, and shakes nearby branches carefully. Although he is a fully adult twelve-year-old male, he is still young and not ready to take on a fight with a dominant male of a strange band. The last time he attempted to seduce a strange female, he had encountered difficulties. Things began well, but as he consummated his new union, the unknown female suddenly became upset by his attention and began screaming her outrage. She was a young female, not used to strange males so near her. Biologically she was driven to seek a mating partner, but the act itself was more than she was ready for. Her screams brought males running from her own band, and Lago had retreated into the water with angry males on his heels. He had swum far out to sea before the strange males ceased their threatening attacks and he was able to make his way back to his own band. This time, though, he is in luck. This female appears to be alone, at least for the moment. He shakes his branch again, this time more violently, to get her attention. She looks down from her perch in the tree and appraises him and his courtship display. After a moment she climbs down from her feeding tree and makes her way over to him. He turns and leads her back the way he has come, preferring to get his new consort as far from enemy territory as possible. 46

Lago is used to concealing his amorous activities. Being a young adult, and small for his age, he does not often approach receptive females of his own band in the open because bigger males chase him away from their favorite females. Instead, he waits until the other males lose interest for a moment and then sneaks in for a quick round of mating before they notice him. Now his female stops, after traveling only a hundred yards, and he begins his display again, shaking branches and calling more loudly as he attempts to lead her away. She follows again until both of them arrive in an area Lago knows, although most of his band does not frequent this spot. Now free to consummate his union without fear of an assault, he mates with her. After the initial copulation the pair settles down to groom each other then wander off in search of edible leaves. Terrestrial food sources are becoming more difficult to find. During the dry season fruit is scarce, and even edible leaves are beginning to disappear. The pair spends most of the day foraging, taking frequent breaks to copulate. As evening approaches, the female climbs a tree and begins pulling branches in to make a nest. Lago climbs up near her and watches, then settles down with her in the nest and grooms her until it is nearly dark before leaving to make his own nest nearby. The next two days are much the same. On the third day the female’s swellings begin to go down, and she wanders off in search of her own band. Lago watches her go, then retreats to the more abundant food of the shore. As Lago steps out onto the beach, he is greeted by Bain and Etang, whose loud pant-hoots work the other close members of the band into an excited gathering. Lago, quick to assure the big males of their dominance, hunches down and tries to appear as small as possible. He approaches them in a crouching walk and begins grooming them. Many of the others join in the grooming session, happy for the companionship. Lago and Etang both groom Bain, ruffling his hair and removing bits of vegetation and dead skin while they make lip-smacking noises of pleasure. After a quarter of an hour Bain hears the distant sounds of feeding pleasure from a group of his band members and leaves the grooming group to walk to the water’s edge. 47

After staring out over the water at a small distant island for several minutes, he wades into the water with several other males and begins swimming leisurely in that direction. A few of the youngsters discovered the small island several years ago. They had been playing and drifted farther and farther from the adults. Praia and Lago were the unofficial leaders of the group and had led the excursions toward the small island when it became visible in the distance. Several others had followed them, knowing that Praia and Lago often found interesting and tasty things on their expeditions. Three of the youngsters trailing after them stopped before they got to the island, more interested in play than exploration. Praia and Lago made it to the island with only a few loyal followers. As they made their way up the sloping sandy beach, they encountered a welcome trickle of a stream winding its way along the edge of the beach. The explorers drank deeply and continued cautiously along the edge of the shore until they discovered several trees, heavily laden with fruit. Their grunts of enjoyment attracted the attention of a few of the stragglers who hadn’t quite made it to the island before. For several days the small group stayed on the island, stuffing themselves on the abundant fruit. Since that first discovery most of the band had made it to the fruit island, which, although too small to supply the whole band with fruit, did offer an alternative to seafood. As the rival band on the main island continued to grow, fruit became scarcer and the band made more frequent trips to the fruit island. Welle approaches the grooming males and begins grooming Etang’s back, careful to keep him between herself and the other males. As she shifts to get a better view, the reason becomes obvious. A four-month-old female infant clings to her belly, suckling while she watches the big males with fascination. This is Welle’s third child, and she has grown accustomed to Etang providing support to her and her offspring. It had started with a few clams and crabs to tempt her into joining him on a consortship. Etang’s continued interest proved he was capable and willing to watch after young Furt as she foraged in the water until Furt was old enough to go in with her, and Welle knew she had little to fear from the other males if Etang was close by. 48

Welle was only too aware of the need for this type of protection. As an adolescent, foraging away from the band with her mother and baby brother, she had heard the cries of strange males in the distance. Her mother had become tense and started to move back toward the center of the band’s home range. The calls stopped, though, and the trio settled down to eat once more at the base of a nearby fig tree. Suddenly two strange males bounded out of the underbrush straight toward Welle’s mother. She screamed in terror as she attempted to run away from the males, but she was not fast enough. Welle watched in horror as her mother was bowled over again and again by the males, each time curling herself over her clinging infant. The males quickly overpowered the smaller female - one pummeled her while the other pried the infant from her belly. Giving Welle’s mother one last bite, both males climbed a nearby tree, dragging the screaming infant by one arm. Welle’s mother attempted to follow them. The male holding her infant used the baby as a club to beat Welle’s mother back down the tree. Finally she gave up her efforts and retreated to the nearby tree where Welle cowered, and watched as the males bit into the skull of her infant and then began tearing chunks of meat and limbs away from his body to feed. Welle and her battered mother continued to watch the grizzly scene until one of the males noticed their presence and started down the tree, brandishing a leg bone in their direction. Both females retreated through the forest back toward their band, fearful of another attack if they remained. Aware of the grim consequences of allowing strange males close to her baby, Welle is especially cautious. Usually the males from one’s own band do not attack their females’ infants, but it is not impossible. Welle, assuring herself that the males are showing no undue interest in her new baby, carefully pries him off her lap and places him on the thick hair of Etang’s stomach. Etang is unconcerned, having gotten used to similar behavior with Welle’s last son, Furt. He peers down at his tiny new passenger, grooming her for a moment, then turns and retreats to the forest’s edge to for termites. Welle is now free to go into the water for food without fear of her baby drowning and proceeds quickly to her favorite spot. A quick swim puts her far enough from shore 49

that she cannot touch the bottom, so she instead floats lazily on her back. Great stands of seaweed grow here, far enough from shore not to be dislodged by waves. The seaweed tickles Welle’s back as she floats above it, kicking her feet slightly as she reaches one arm down to pull off a few leaves. As she lays relaxed, in the salty water she hears a warning cry from Etang. She quickly drops her food and turns herself upright in the water, looking around. She has learned that Etang is not only useful for watching her infant while she feeds in the water, but he also often watches her while she is there and warns her if dangerous predators approach. Most of the predators large enough to threaten the members of the band do not come this close to shore, but crocodiles and water snakes can pose real threats. Seeing no immediate danger, Welle looks toward Etang, and realizes that he has not been watching her after all, but is calling about a threat of a different sort. Strangers are coming. Almost every male and many of the females of the other band on the island are rushing from the forest toward the band. They are throwing rocks and dragging branches as they break onto the open beach, catching the band by surprise. The band retreats, vastly outnumbered. Many of the band are on the fruit island now because several fruit trees have ripe fruit. The remaining few had all been on the beach, fearing this larger band too much to venture far into the interior. Only three adult males remain on the main island, along with several juveniles and females with infants. Praia is the closest to the forest when the rival band attacks, and a big male pushes her down and pummels her head and shoulders. She is still young but large for her age and sex, and she fights back for a moment. His greater size and strength eventually prevail, and she gives up the fight and lies huddled as small as she can on the beach. The rest of the band has retreated almost to the water, and two of the males look back as she cries out in fear and pain. They turn around and begin to charge back up the beach toward the struggling Praia. The big male backs off and barks loudly, seeming to call for support from his comrades. Praia unfolds herself from her crumpled position and drags herself away from the violent male, limping heavily. She makes it to the water’s edge before the other males organize to join in the attack. The males of her own band follow 50

her into the water and use huge splash displays to keep the rival males from catching Praia in the water. Meanwhile, Welle is torn between retreating from the violent rival band and rushing to Etang to retrieve her infant. Her concern for her child takes priority, and she swims toward Etang, reaching him just as he begins to swim. Her baby has climbed up onto his neck and is struggling to hold onto Etang’s now slippery wet hair as he moves through the water. Welle attempts to retrieve her baby while treading water near Etang, but only succeedes in dislodging him from Etang’s neck and dropping him into the water. The band members all move near each other in the water, attempting to take comfort in each other’s presence. Praia has managed to swim out to the rest of the band but is now floating listlessly on the edge of her group. With all the bodies churning the water, Welle cannot find her child immediately and searches frantically. Etang takes up the search as well, and they soon locate the missing infant, bobbing up and down in the rough water, wailing. Welle again attempts to rescue her baby, and this time she succeeds. She manages to get him to perch on the back of her neck and starts slowly swimming toward the distant island. The rival band’s males follow them into the water and stand chest deep, splashing wildly at the retreating band. They do not swim after them, and their splashes and calls fade away as the band members retreat out of earshot. Praia, however, is not able to swim very far, and has to stop and float often. She manages to make it to the oyster sandbar before collapsing onto the submerged ground. Her pitiful cries are too weak to reach the ears of most of the remaining band, and the few straggling females that do hear her are too concerned with getting their infants to safety to take on an additional burden. Teich, a young male who recently reached full adulthood, hears her cries. At his age he travels often with the adult males, spending little time with his mother, Welle. With her new baby, Welle has little time for him anyway. Teich, though adult, is still easily upset by new situations, and this threat is too much for him. He has fallen back to rejoin Welle, hoping for comfort. Welle is too focused on keeping her infant out of water to give her full-grown son any attention. Teich, distraught by the events of the day, stops 51

swimming and floats on his back, calling softly to himself. After several minutes he has regained enough composure to hear Praia’s cries of pain that the other’s have missed. Distracted from his own distress he approaches Praia and begins grooming her, trying to clean the wounds on her head and face. As late afternoon approaches, the water level rises, making it impossible for Praia to continue to lie on the sandbar and keep her head out of water. Teich prods her into a crouching position, and she manages to nibble some passing strands of seaweed. The food, along with the long rest and comfort by her sympathetic companion, seem to have revived Praia somewhat, and the two start off toward the island, swimming slowly.

52

Afar Depression 7.0 million years ago

Lago (Lake; Spanish)

Tool use was once thought to be what distinguished human beings from other animals - what made us unique. But, like so many other “uniquely” human traits, it has been found that other animals use tools as well. A progression of sorts can be seen in the tool use of other animals. Non-great ape examples of tool use are usually limited to only one type of tool that is used only in one very specific situation. Otters use rocks balanced on their chests to crack the hard shells of a variety of seafood. Some species of birds have been observed to fashion twigs into hooks to retrieve food in laboratories, and some crows place walnuts on the road during red lights, wait until cars crush the hard shells, then retrieve the nut meat when the light again turns red. One species of burrowing owl even uses bait to catch prey, gathering large quantities of dung to attract dung beetles, their primary prey. This sharply contrasts with human behavior, where tools are used in novel ways and for multiple tasks. When one looks at the chimpanzee, these lines begin to blur. In the 1960’s, primatologist Jane Goodall observed a startling behavior in wild chimpanzees. The chimpanzees ate termites from large mounds constructed on the forest floor, which in itself was not surprising. Many primates consume insects. The fascinating part was the way they extracted the termites. The apes inserted grass or twig tools into the mounds and removed them with termites attached. Even more surprising, the chimpanzees manufactured these tools, breaking twigs to the correct size or stripping off projecting shoots for more effective use. Since these first observations chimpanzees have been seen using many other tools. They shake branches and hurl rocks during threatening displays to make themselves look more intimidating, use rocks and wooden hammers to crack 53

open hard-shelled fruits and nuts, and use leaves to wipe themselves clean or as sponges to drink hard-to-reach water. Chimpanzees, with their range of tool use and manufacture, provide a transition between human and non-human tool use. Today a wide gap exists between chimpanzees and humans in the use of tools, with humans using significantly more complex tools at significantly higher frequencies than chimpanzee. Our band, although still very chimpanzee-like in most physical and mental aspects, may have begun to move toward a more human-like method of tool use, gradually shifting from a chimpanzee toolkit toward a more modern human one. This transition toward a more sophisticated use of tools would have been made more likely by the shift in diet proposed for our band. Our band had been relying on seafood as a major component of their diet for several million years. Omega-3 fatty acids are present in higher quantities in seafood than in any terrestrial source and are crucial in brain development. It is possible, therefore, that although the absolute size of the band’s brains have not increased from that of a chimpanzee, that new neural connections have developed that allow the band to use even more complex tools than contemporary apes.

Praia lounges by the stream, looking out onto the shallow water dotted with members of her band. Farther away, small islands break the line of the horizon. She recognizes the dark smudge farthest out to sea as her childhood playmate, Lago. She sees his head disappear under the water and bubbles rise from the spot. The bubbles make a lazy line toward shore, and Lago reemerges, holding a large clump of kelp in his mouth. He stands up and pulls the food from his mouth with his hands, carefully detaching the few long strands that have twisted themselves around his head. Lago settles down on his haunches in the shallows to munch on his kelp, and Praia loses interest, preferring to get something to eat for herself. She stands up, stretches her legs carefully, and takes a few steps on all four limbs before pushing herself fully 54

upright. Her right leg still bears scars from the attack on her, and the raised pink flesh is visible through her dark hair. The day her band was chased from their large home island, she had barely been able to retreat with the rest of the band to the distant fruit island. If she had been another female, she might not have made it away at all, but she was large for her sex and strong. She had fought the strange males as best she could until the males of her own band had arrived, something the other females might have been too timid to try. The last part of her journey was a hazy memory - exhaustion and blood loss had made her delirious. Teich had dragged her onto the shore of their new home. Normally males would have only done such a thing for another male. The bonds between the males and females of the band were not as strong as those of the males to each other. But Praia was a special case. She had joined the males many times when they patrolled the borders of their range, and she was the only female in their band who had successfully caught a monkey in a hunt. She slept for several days after her arrival on the small island, waking only to drag herself to the small stream on their new home island. Since then she had spent most of her days resting on the bank of the stream and eating the small bitter leaves that grew on the nearby bushes. The first day she tried to stand up, her leg had collapsed under her, the torn muscle not strong enough to support her weight. As she gained strength, she attempted a modified four-legged walk, keeping most of her weight on her three good legs until the injured leg had healed. Now she only limps slightly as she walks down the slope to the edge of the water. Lago finishes his food as she approaches, and she follows him as he wades into the water again. He goes back to the kelp bed he discovered some way away from shore. The band regularly eats seaweed, which grows in large patches all around their island out past the breaking waves. Lago prefers to dive down and pull up the long strands of kelp near its base so that he can take his food to shallower water to eat in comfort. Praia floats on her back and watches as he dives to retrieve another handful, feeling the tips of the tall kelp brush her legs occasionally. 55

She submerges enough to pull a few leaves from a nearby plant, then floats again to eat. Lago surfaces and holds the kelp strands in his mouth as he grooms Praia for a moment. He begins to swim toward one of the smaller islands nearby. Their island is the largest of a series scattered around this area of the sea, and the band members often rest on one of the others before returning to the main island. For Lago, the other island is a closer swim. Praia knows she is not as strong as Lago, and swimming tires her out quickly. She prefers to stay in the water, eating only the tender new growth at the tip of the seaweed. As she floats on her back, alternately watching the water and chewing the salty kelp leaves, her breasts occasionally break the water. At eleven years old she is nearly an adult female, but not quite. Her breasts and hips are not as full as those of the older females but clearly distinguish her from the males and juveniles of the band. They also make her suited to this floating feeding style, helping her keep afloat with less effort than Lago. Meer floats nearby, also feeding. Her youngest daughter, the three-year-old Rio, is clinging to her mother’s arm. This is the first times Meer has taken Rio into the water for more than a few minutes at a time. Before, Meer has left Rio playing on the shore with either Welle or Etang while she ventured into the water for something to eat. Rio has been in the water many times before, but always in the shallows where she could feel the bottom under her feet. Rio knows that she and Meer are farther from the shore than usual, and it makes her uneasy. Meer offers Rio a section of kelp, and Rio sniffs it and begins to nibble at the edges. Rio, forgetting her initial insecurity, spots Praia eating not far away and decides to go investigate. She pushes herself away from her mother’s chest and begins paddling toward Praia, her mother trailing behind her. Rio grabs onto the wet hair on Praia’s side and tries to pull herself on top of Praia’s stomach, something she has done several times before on the beach when she joined the other youngsters in pestering the older band members. Praia, unaccustomed to supporting another’s weight in the water, even the small Rio, is dunked under the water. 56

She comes up sputtering and splashing, and Meer takes two quick strokes toward the floundering pair and grabs her daughter. Rio, frightened, clings to her mother’s shoulder as Meer swats at Praia, then swims, one-handed, back toward the shore. Praia wipes her eyes clear of the stinging salt water and goes back to feeding, glad to be rid of the high- ranking female’s offspring. Although Praia is naturally drawn to babies and has been glad to play with Rio in the past, Rio is growing up. When the baby used to cling to her mother and stare at Praia with wide eyes, Praia would watch her and inch her way closer to the baby. These days, though, Rio has taken to pouncing on Praia or swatting at her in imitation of her mother. Praia, normally not one to be intimidated, is at a loss when Rio does this, not wanting to offend Meer by returning the blows or refusing to play with the demanding baby. Rio’s swimming lessons continue through the hot months of summer. One morning Meer and Rio make their way to the stream to drink before they head into the water to forage. Over the last few months the swiftly moving stream had changed into a sluggish trickle. It is now more difficult for the band members to get enough water to drink. No rain has fallen for nearly two weeks, and the even the trickle is no longer there. Meer hunkers down on the ground, nearly lying on her stomach, and purses her lips to extract what moisture she can from a puddle-sized depression in the mud. Rio copies her, but puts her lips too close to the mud and coughs as the thin mud coats her lips and nostrils. Some of the other band members approach and also try to drink. Lago tears leaves off a nearby trees and chews them a few times. Pulling the spongy leaf ball out of his mouth, he places it into a miniscule puddle and holds it to his mouth, sucking to extract what moisture he can. He removes it again and continues to use his leaf sponge to get a few more mouthfuls of water before it disintegrates. The gathered group, now nearly half the band and numbering twenty individuals, remains at the remnants of the stream, trying to get a few drops of before moving on. Nearly all the group has been to one of the nearby small islands and knows 57

there is water on several of the others. They wander down toward shore, several of the adult males picking up rocks that fit easily into their hands as they go. Although the band travels between the islands with some regularity already, they know the dangers of crossing the stretches of deep water that lie between the islands. Rarely does an individual cross on his or her own, and often a group will go together. The males frequently bring rocks and sticks to throw that will frighten off potential predators if they get too close. This group, containing several females with small babies, is even more in need of protection. The six adult males that have gathered on the shore with projectiles make their way into the water, and many of the others follow. Lago and two other males who were already on the beach rush to find rocks of their own. These three bring up the rear as the band begins wading toward the closest of the small islands. As the water gets deeper, the males are faced with the problem of what to do with their weapons. Some, with smaller rocks or sticks, hold them in their mouths as they swim. Lago’s rock is too large to put in his mouth, and he grasps it tightly in one hand and swims lopsided while he holds it. Halfway to the destination, Bain, who is in the front, gives a high pitched call of alarm, building into a frantic series of waa-barks. The fifteen members of the band trailing behind him look around, searching for the cause of his alarm. A green log ten feet long breaks the surface, two gleaming eyes just barely visible above the water. The movement of so many bodies roused the interest of a saltwater crocodile who had been sunning itself on the bank of the far island. He has approached underwater until he has neared the band, breaking the water now so that he can clearly see what is causing the commotion. He approaches the band from the side, and five of the males throw the rocks they have gathered. Four splash near his head, not doing damage but raising big splashes. The fifth lands on his head, behind his armored eyes. The big crocodile submerges again, seemingly frightened off by the inexplicable splashing and painful hit. The band continues on, watchful of the water around them. The males spread out in the group, and Etang moves close to Meer and Welle. Rio, who has become a 58

proficient swimmer in the months following her first lesson, is so far able to keep up with her mother. Welle, however, is beginning to fall behind, burdened with the awkward weight of her infant, who is trying to cling to his mother’s neck to stay out of the water. Etang gently removes the clinging infant and relocates him to his own neck, allowing Welle to catch up with the group once again. Suddenly another alarm is called, this one fraught with terror and desperation. The crocodile has not been scared off by the band’s display, but has instead stalked them from beneath the water. Lago, at the end of the band and made clumsy by his weapon, has failed to see the croc’s eyes as they have broken the surface behind him. The ripple caused when the croc opened its large alertes Lago to its presence, but not in time. His frightened scream abruptly ends in a burbling noise as the croc clamps down on Lago’s back and rolls him over into the water. Bubbles rise from the spot, but Lago does not reappear.

59

Hadar, Ethiopia 6.7 million years ago

Samman (Pool; Swedish)

Mammalian females usually show some outward sign of ovulation. Female dogs and cats come into heat, a period where they actively seek out males with which to mate. The female chimpanzee has periods of estrus that occur every 35 days when the sexual skin around her vagina and anus swells to several times the normal size and turns bright pink. Female chimpanzees also emit pheromones detectable by the male, and their breasts swell slightly. Human females differ from this pattern of announcing their sexual receptiveness. They do not show outward signs of being receptive at certain times, either by releasing detectable pheromones, dramatically changing their behavior, or exhibiting obvious physical changes. Human females conceal their ovulation, or perhaps more accurately, appear to be constantly receptive, so that males (and they themselves) are unaware of when they are able to conceive. In many species of animals intercourse is virtually non-existent during periods when the female is not sexually receptive. This makes sense from an evolutionary perspective; mating during these times will not result in offspring and will take time and energy that could be used for other vital functions, like foraging or socializing with other group members. The human system, however, is set up much differently. Intercourse occurs throughout a woman’s cycle, with only a slight peak during ovulation. Women have permanently enlarged breasts throughout their post-puberty years and engage in sex regardless of whether they are ovulating or not. Nature seems to have reversed her ploy. Instead of making a female sexually desirable only when sex will likely result in a pregnancy, human females are sexually desirable constantly, even when conception is impossible. 60

The question then becomes, why have such a system? Concealed ovulation has been suggested as a system especially suited for a monogamous social system. The logic goes that if a female appears constantly receptive, then a male has to remain near her constantly to ensure that the children she bears are his. This is drastically different from the system of announced ovulation, where the male only has to monopolize a female for a small portion of the time when she is receptive. This greater male involvement allows females to raise healthier children, supported by both parents instead of by a lone mother.

Samman, an eight-year-old male, sniffs the air and whimpers softly. He can find no trace of his mother’s scent, or any other’s of his band. He sits down, resting his bleeding feet. He has walked non-stop for almost a full day. Three days ago he and his mother were off by themselves, feeding on figs high in a tree above the swiftly moving stream. His mother had just spotted a group of ripe figs far out on a branch. She began walking toward it, balancing on two feet as she went, using small twigs to steady herself. Suddenly the branch she was walking along, weakened by insects, gave way. Samman’s mother dangled for an instant before plummeting toward the ground. With a sickening thud, her head made contact with a branch and she began to rotate, tumbling toward the stream. She was dead before her body hit the ground, and she splashed heavily into the stream. After a long dry season the rains had finally come, and this usually calm stream was now deep and fast moving. As Samman made his way down the tree in search of his mother, her body was carried downstream. By the time he made it to the ground, she was nowhere to be seen. His frantic calls brought no answering reply from his mother, and he found himself alone in the forest. For twenty-four hours he had stayed by the tree he and his mother had last occupied, sometimes rushing from one side of the stream to the other, sending up great splashes as he crossed, sometimes sitting listlessly on the ground, staring into space. 61

Eventually he gave up his vigil and set off in search of the rest of his band, thinking they were somewhere on the island. He was mistaken. A neighboring island’s fruit trees were just ripening, and his band had left to take advantage of this short-lived food supply. He wandered the entire perimeter of the island, calling, but was never answered. He was truly alone. Now, collapsing from stress, hunger, and fatigue, he lies on his side, one arm trailing in the rushing water of the stream that had carried his mother away. His eyes close, his tensed muscles relax, and he sleeps. Natte and Meer tread water, catching their breaths after their long dives. Meer has an oyster in both hands, turns over onto her back, and kicks toward shore. Natte, not as good at finding oysters on the rocky bottom as her mother, has only found one. She follows her mother, swimming one-handed to keep up. As the two females wade out of the water, five pairs of male eyes watch them. Etang, one of the watchers, climbs down from his tree perch where he has been watching the females swim. He walks toward the pair, the three-year-old Rio clinging to his back. The group makes their way up the steep bank, Meer and Natte on two legs holding their oysters and Etang on all fours with Rio astride his back. As they reach the crest of the hill, the beach flattens, and Meer drops her oysters and sits down near a pile of stones. Natte flops onto the ground heavily beside her mother, tired from the diving of the morning. Meer selects a flat stone and smoothes a place in the sand to set it. She places the rock on the base she has prepared and taps it. Her platform rocks slightly on the sand because the underside is uneven. She picks it up again and inspects the underside of her rock, noting a nodule on one side. She scoops out a little sand and places the rock down again. This time the rock doesn’t wobble. She places her oyster onto this anvil and selects another rock from the pile. She hits her oyster on the narrow edge with this new rock until a piece of the shell comes loose. Lifting the oyster toward her face, she prods the opening with a finger, testing it. Finding that she cannot get at the meat inside, she returns her oyster to the rock. Another hit with the rock near the hole she has already 62

made breaks off a larger piece. Upon inspection she finds she can scrape out the oyster meat inside. Etang has seen this process many times and quickly loses interest. He watches the toddling Rio try to climb a slender sapling, and suddenly finds himself left out of the meal. Meer drops the empty oyster shell, and Etang hurries to retrieve it. He pries the rest of the shell apart and is rewarded with a few bites of meat left clinging to the inside of the shell that Meer had not been able to retrieve. Meer has gone back to cracking her remaining oyster and is scratching out another oyster for herself. Natte now places her oyster on the anvil and picks up a stone. Her first attempt misses the oyster completely, but she gradually improves and has soon cracked her own oyster. However, she is distracted. She sees her little sister Rio jumping high into the air using the bent-over sapling as a spring. She wants to join in the play and abandons her oyster in favor of acrobatics. She grabs the branch on Rio’s next trip toward the ground and tries to jump up, but the tree is too small to hoist her weight as it had done Rio’s. After a few unsuccessful jumps Natte lets go of her new toy and watches her sister play instead. Meer has finished her second oyster and returns to the rock where Natte’s abandoned oyster lies. Although she was able to crack the shell, Natte lacked the expertise of her mother and crushed much of the meat as well. Etang, spotting the exposed meat in Meer’s hands, cannot restrain himself any longer. He lunges at Meer and she backs away, taking the oyster with her. Etang tries again, this time calling threateningly and shaking a nearby branch before rushing at Meer. Meer, still unwilling to concede her meal, hurries away. Etang chases after her and bowls her over, pulling the oyster from her hand. He backs away and eats the half-squashed oyster, picking the bits of crunchy shell out of his mouth. Meer slinks toward him as he finishes his meal, hoping for reassurance after their squabble. She bobs her head submissively a few times and presents her rump to him in the well-known signal for copulation. Etang obliges, and after a brief burst of mating, the two settle down to groom each other as they watch the children play in the trees. 63

This is the first time in several months that the band has been to this island. After the drought forced them to leave the larger island, they had been traveling between smaller islands regularly. Many of the small islands had some sort of fresh water, and all had at least a few fruiting trees. None of them were large enough for the band to live on permanently - they always ran out of fruit after a day or two. The females now eat much less fruit than they once did because the larger males usually chase them away from this valuable resource. This has forced the females to spend more time looking for food in the sea. Meer becomes tired of watching her children play and heads off in search of water. Rio trails behind her mother, and Natte quickly follows, trying to pick Rio up and carry her on her back as she has seen her mother and Etang do so many times. Rio perches on her sister for a moment, but she is nearly half her sister’s size and the effect is comical. Natte staggers along under her sister’s weight until she is forced to give up, sinking to the ground to rest while Rio scampers off after her mother. Rio breaks through the trees to find her mother bent over a shape on the bank of the river. Hurrying up to her mother, she climbs onto her broad back, pokes her head over Meer’s shoulder, and peers at the still body. It is one of their kind, but not anyone she has ever seen before. The body of the little male lies motionless except for the slight rise and fall of his chest. Meer takes a few steps backward and stumbles over a rock, almost falling into the stream in her haste. Natte finds herself alone in the forest without her mother or sister for comfort, hurries after them, and rejoins her mother just as Meer rights herself. The band is mistrustful of strangers, especially males. Many of the females in this band have emigrated from other neighboring bands, but males stay in the group in which they are born throughout their lives. Encountering a strange male is usually cause for retreat, because they are oftentimes violent. This little male does not pose that kind of threat, however. He is too young to be on his own. It would be several years before he normally would have started going significant distances from his mother with the older males, and even longer before he made his way through the forest alone. In fact, he is 64

barely older than Natte, just entering adolescence. Meer does not sense any other strangers nearby, and in fact does not think there are any other groups on this island. The trees and underbrush are too thick to be able to see from one side of the island to the other, but they had only traveled ten minutes from the beach, and she could already see the glint of water through the trees on the other side of the island. When they first arrived on this new island, Bain started a frenzy of pant hoots and was joined by the rest of the males, one after another, until the air virtually shook with the force of their calls. This elicited no response from anywhere on the island, so it was very unlikely that any other bands were there. Meer approaches Samman tentatively, and nudges him with her foot. He shudders slightly but does not revive. Rio, intrigued by this new stranger and lacking much of the fear of her wary mother, dismounts from her mother’s back and pokes curious fingers into his nose and ears. Under the increasingly vigorous pokes of Rio, Samman finally opens his eyes and stares up into the curious faces of all three females. He grunts in a mixture of surprise and alarm, but is too weak from his lack of food or water to do more than sit up and scoot backward a few feet. Meer and Rio back up a few paces, unsure what to do about this frightened stranger, but Natte cannot pass up the opportunity for a playmate so close to her own age. She takes a few small steps forward, holding her body low to the ground, and makes little playful hoos. Samman cocks his head as he looks at her, as if to decide whether she is sincere in her friendship. Natte stops just short of him and extends her hand slowly. He reaches out his own hand until their fingers find each other and intertwine. After a few minutes of gentle hand holding, Natte takes another step toward Samman and begins grooming him, picking bits of leaves out of his hair. After a few minutes of this, Natte walks to the water to get a drink, and Samman trails behind her. After watching her drink for a minute, he lowers his mouth to the water and drinks deeply. Keeping his eyes on Natte, he sees her walk a few steps to a tree with several very ripe figs on it and begin to eat. Listening to her lips smacking in pleasure at her rare 65

treat, his appetite suddenly returns, and he hurries to the tree to select his own fruit. Meer and Rio approach the tree, and all four sit quietly as they finish the remaining figs. After the meal Meer stands up and begins to walk away. Rio scrambles after her and pulls herself up onto her mother’s back, happy for a chance to lazily ride along after filling her stomach. Natte takes a hesitant step toward the retreating forms of Meer and Rio, then looks back at Samman who is still sitting in the tree. She calls softly to Samman, then follows her mother through the underbrush. Samman climbs down from the tree and hurries after the group, and the two youngsters catch up to Meer and Rio just as they reach the beach.

Chimpanzees need their mothers long after they have been weaned. When a chimpanzee mother is killed before her child is fully mature, the child will often become lethargic and stop eating until they too die. In some cases orphans are adopted by older siblings or other band members, making it much more likely they will survive the death of their mothers. Humans are the only animals known to take this adoption to the next step, adopting children who are not related or well known to them. This behavior is extensive, being found with some frequency in a variety of societies ranging from to the North American arctic to West Africa. The widespread nature of this practice suggests that it has been present for some time in the human line, probably extending back to our early ancestors.

66

Northwestern Afar Depression 6.5 million years ago

Rio (River; Spanish)

In some Japanese and Korean villages a special group of people harvest food from the sea floor off the coast. They spend up to five hours a day in the water diving for a variety of seafood including clams, eels, abalones, octopi, and sea urchins. They dive as deep as 17 meters, may stay submerged for 82 seconds and average 60 dives an hour in water as cold as 42 degrees Fahrenheit. These are the ama, or diving women. They have supported themselves and their families with the profits from these dives for countless generations. It may seem surprising that such divers would be women. Usually physically strenuous jobs or athletic competitions are dominated by men. However, in all extreme water sports women outperform men on a regular basis. Not only can they stay in cold water longer than men without shivering due to their higher body fat, they can also dive deeper without an air tank and swim longer faster. The longest distance ever swum without flippers is 122 miles (from Mexico to Cuba) and was accomplished by a woman. The record for the fastest crossing of the English Channel is also held by a woman. In the world of long distance swimming females have an edge over men. Not only does their body fat give them extra buoyancy and insulation, but it also provides more energy as it is broken down. And it goes beyond body fat. Women can usually swim faster and longer than men with the same body fat percentage. The reasons for this are thought to be two-fold. First, a woman can be quite healthy at a body fat of 30 %, while a man at the same body fat is obese and thus not able to perform at peak athletic ability. Second, men have more muscle mass than women of comparable build, and muscle mass requires a lot of oxygen. In the water, where buoyancy reduces weight to almost nothing, resistance, not strength, becomes a limiting factor. Bulky muscles typical of males 67

require more energy to supply with oxygen than the leaner muscles typical of females. These larger male muscles do not add enough speed in the water to make up for the energy they require and the loss of hydrodynamics they cause. Thus the bulky muscles that make men faster and stronger than women on the dry land reduce men’s diving ability and slow swimming times over long distances. These differences in body type between men and women are marked in modern humans and likely have been present in our ancestors for millennia. These differences may have created (or been created by) a division of labor between males and females of a band living in and around the water. Females would have been biologically more able to swim farther from shore and dive deeper to retrieve submerged food. Males, with their greater strength, would have been better suited to monopolize the few terrestrial resources and offer protection from aquatic predators.

Rio is lying outstretched in the water, her arms over her head and toes pointed, trying to make herself as long as possible. She enjoys the water and likes the feeling of her hair drifting this way and that against her body as she floats. Today she has discovered a new game. If she lays flat and takes a deep breath in, she will come out of the water like a cork and can look around at her mother and the others close by. When she breathes out, she sinks all the way down so that just the tip of her nose and the ends of her toes break the surface. With her ears submerged now, she can hear the underwater sounds. She recognizes the rhythmic pulsing sound of her mother’s legs working to keep her afloat nearby. Suddenly she hears a louder splash, followed by the blub blub sound of bubbles rising to the surface. Her older sister Natte, diving for clams. She takes a large breath in through her nose and bobs upward again. The sounds change, and she hears the call of a bird overhead, the gentle lapping of water around her own body, and in the distance, the crashing sound of waves breaking on the shore. Natte breaks the surface again after her dive, in hand. She comes up right next to Rio, sending a wave over her nose and mouth and ruining the delicate 68

balancing game Rio has been playing. Rio snorts in annoyance, clearing the water from her nose and mouth. She paddles away from Natte and closer to her mother just as Meer prepares for a dive. Meer takes three shallow breaths, then a deeper one, and throws her body forward, kicking her legs to propel herself head-first toward the bottom. Rio wants to follow her mother and takes a series of breaths herself. She too tries to dive head-first into the water, but instead pushes herself sideways and takes a few awkward strokes three feet under the water before popping up again. She tries again and is a little more successful, managing to make a diagonal descent to almost ten feet before the unpleasant pressure in her ears makes her return to the surface. Meer is already there, catching her breath after an unsuccessful dive. She floats for a minute, gathering energy, before she is ready to begin again. As her head goes underwater, she opens her eyes, searching for movement in the crevices of rock below her. She sees a silvery flash for an instant before it disappears again between two dark gray rocks. She kicks her feet harder and grabs hold of one of the rocks for support, letting her body relax as she searches again. Suddenly her hand darts out and grabs the shiny tip of an eel’s tail that had been resting between the two rocks. Her nails sink into its flesh before the eel can swim away. Meer’s other hand grasps the eel closer to its head as her feet find purchase on the rocky bottom. She pushes herself toward the surface of the water and brings her two hands together quickly, folding the eel in half and breaking its back. By the time she breaks the surface and takes a gasping breath, the eel has ceased its wriggling. Meer lies on her back in the water as she bites into the fleshy back of her catch. Natte and Rio both see the long silver fish in their mother’s hands and come over to investigate. Natte nudges Meer, upsetting her balancing act as Rio tries to climb onto her lap and poke at the eel. Rio, now five years old, accompanies her mother nearly every time she goes into the water for food. Often, however, she gets tired or cold and pesters Etang or one of the other females until they swim back with her to the shore. She usually floats calmly, 69

munching seaweed as her mother dives or splashes with other youngsters. She has yet to master the art of diving, although she is getting better as she tries to follow her mother. Meer gives up her hopes for a peaceful meal and tears off pieces of eel flesh for Rio, who jumps off her mother’s quickly sinking stomach to eat. Natte is hoping for a handout, so she continues to nudge at her mother and maneuvers her mouth close to the fish, but Meer moves away. Natte gives up and, taking a deep breath, dives down again in search of her own food. As the shadows on the shore begin to lengthen, the group of diving females returns to the beach. Bain is the first male out of the tree to greet the returning females. He and many of the other males have been perched in the tree for much of the day, eating figs and watching the females. When he reaches the ground, one of the mature females rushes toward him, then crouches in front of him. Bain allows her to take the infant clinging to his stomach. The infant immediately finds his mother’s nipple and begins nursing happily. Bain grooms the female while her baby nurses, and she hands him a large clam she found on her last dive. Other males come down from the tree as well and go off with one or a few of the females, exchanging infants they may have watched during the day for sex or bits of seafood brought in from the shore. The band settles down for the night early, making nests in low trees. Samman makes his nest close to Meer and her daughters. In the last few years he has grown up quickly, and after some initial threats from the other males, has found his niche in the social life of the band. He usually is close to Meer or Natte, but has started to perch in trees with the older males when the females go into the water. As the sun rises the next morning, the males are excitable, rushing at each other and calling more than usual. After an hour of grooming and mock threats, ten of the males make their way into the water and wade out until they are chest deep. Several of the females, seeming to understand what they are planning, join them. Fifteen band members now have formed a rough half circle ending at the shore, with several others waiting expectantly on the beach, watching the proceedings. 70

All the band members in the water sit or stand quietly. The older males peer intently down into the water, glancing at the rest of the group occasionally. After a half hour of quiet Etang spots a silver flash just under the surface. Bain sees another, and soon half the members in the water can see flashes of scales as a school of fish move into the shallows to . Still the fishers stay motionless until Bain gives a quiet call and takes a step forward toward shore. Quickly and quietly all the others take a step toward shore, and the horseshoe tightens slightly. After another pause Bain calls again, and another step forward brings all the fishers close enough together to reach out and touch one another. Everyone’s eyes are focused under the water, and several more steps bring them shoulder-to-shoulder, five feet from the bank. Those of the band not in the water move even closer to the shore and lean forward, arms outstretched in front of them. After another moment the tense quite of the morning is shattered as Bain lunges forward, trying to grab the closest fish. The whole band launches into action, those in the water grasping with their arms at the nearest fish, those on land using their body weight to try and pin a fish to the ground. Of the twenty-five member team that began this hunt, six have emerged with fish. Rio has never seen a fish hunt before. Last year the band was traveling during fish spawning season and not organized enough for any structured hunts, and she was too young before that to know what was happening. This year, however, she watches transfixed from the shore. When she tries to follow her mother into the water, Teich chases her away angrily, so she does not try again, only watches intently. As the splashing subsides, she ventures out again, keeping a close eye on Teich for signs of displeasure. Teich is not one of the lucky ones who has captured a fish, so he positions himself close to one of the successful males, hoping to get a handout when the big male is done. Rio also enters the water, but less out of hunger and more to be a part of the excitement. She splashes into the shallows toward her mother, who is crouching in front of Etang. Etang sits on the ground, water lapping at his stomach and grasping a heavy 71

fish between his knees as he leans down to bite into its underbelly. Meer takes a tentative step closer and raises her hand toward Etang, making small grooming movements on his free arm. She inches even closer until her mouth is only a few inches from his and whimpers softly. Etang lifts his head as he chews a mouthful, and Meer takes a small bite of the exposed flesh. Etang tears more vigorously at the belly of the fish, and suddenly eggs gush out, staining the water a rosy color. Meer grabs at a handful of the floating eggs and eats them with relish, reaching for another. The excited calls of the band announce that two of the other fish are also spawning females, and the band’s contented food grunts show their pleasure at this unexpected treat. Although only six fish were caught, all were large, and nearly everyone gets a bite of flesh and a handful of eggs. After the excitement in the water the band retires to the shade of the scattered trees along the shore to rest. In a few days they will follow the large fish to another island, never to return to this one again.

The composition of the sea is changing. Several million years of evaporation have increased the salinity to the point where the seafood and water plants the band has come to rely on are dying. They follow fish and vegetation away from the middle of the sea and closer to the fresh water tributaries that feed into it. Their days in the water are numbered. They have taken those first irreversible steps out of the water.

72

Ethiopia 6.3 million years ago

Alga (Algae; Italian)

Motherhood varies greatly among animals. For some, like the sea turtle, motherhood ends with the laying of eggs, and a mother will never see her babies. Primates lie on the opposite end of the spectrum, providing extensive and long-lasting maternal care. The great apes take this trend to an extreme. A chimpanzee infant often does not break contact with her mother for the first six months of her life and does not become physically independent until she is seven or eight years old. In humans this is even more extreme, and many human children do not become truly independent of their parents until they have entered their twenties. This long period of infant and childhood dependency creates a strong mother- infant bond that often survives long past the age when a mother is physically necessary to sustain life. Indeed, this bond can be so strong that an eight-and-a-half year old juvenile chimpanzee at Gombe died one month after his mother. Even though he was years past the age when he relied on his mother for milk, he appeared to have died of grief, refusing to eat or move away from the place where she died until he too wasted away. In some chimpanzees, as well as in some humans, this mother-infant bond is less robust than in others. Most chimpanzee mothers are very patient with the offspring, carefully carrying them, playing with them, and reassuring them until they are several years old. Some mothers, however, do not show the same level of maternal care. They do not spend much time playing with their offspring and show less concern for them when they are distressed. The “good” mothers often are high ranking and have high ranking offspring that are well adjusted to society. The offspring of less competent, often lower ranking, mothers frequently do not interact normally with the rest of their group and are less interested in their own offspring. 73

Thus rank, which is also influenced by other factors, has a great impact on the lives of chimpanzees. High ranking males often have more mating opportunities and can command more highly prized foods. High ranking females have larger ranges and can protect their favorite food sources from others. Rank also plays a part in determining migration patters. In chimpanzee society females often leave their home group when they reach adulthood to join a neighboring group. This system prevents females from conceiving offspring by close male relatives. However, the daughters of some high ranking mothers do not emigrate, but stay in their natal community throughout life, enjoying their mother’s rank and the large territory that comes with it. These females, however, often do travel to other bands when they are in estrus, which protects against inbreeding.

Alga sits slumped on the beach, staring out over the water. The landscape has changed. No longer is she staring at a sea with islands dotting the water. Now land dominates her view. She is staring down the mouth of a river, watching the silver water snake through low hills and disappear into the thick vegetation of the forest. She cannot see the edges of this land, and she senses that it is different from the islands she is used to. Out of the corner of her eye she sees a spray of water and hears an accompanying splash. A split second later she launches herself into the water toward the spot. Opening her eyes underwater, she notes that the sting of salt is gone and the water is getting fresher. She comes up for air and then submerges again quietly, watching. What looks like a lumpy rock darts by her, zigzagging near the muddy bottom. Kicking off from the bottom with both feet, Alga brushes the fast-moving rock with her fingertips. She cannot get a grip on the slippery sides, and it dashes away again. Her head breaks the surface, and she gulps air before returning underwater to wait for her prey. After three more breaths she gives up, disappointed. It is rare that she gets a chance for fresh turtle meat, and she is unhappy that this one escaped. Still hungry, she settles for vegetation instead 74

and floats in the shallows to pull up handfuls of the feathery grasses that grow there. From this position she watches her full-grown daughter, Welle, emerge from the forest. Welle has not seen her mother for several days and hurries to great the aging Alga. Alga too splashes back toward shore to see her daughter. The two meet on the wet sand at the edge of the water and embrace, touching lips for a moment before beginning to groom each other. They grasp hands and extend them above their heads, then pick through the hard-to-reach hair on the undersides of their arms and sides. Furt, Welle’s seven-years-old son, has been following closely behind his mother. Now he splashes happily in the water watching the two females. He is hot after his trek through the forest and opens his mouth in a grin of pleasure as he throws the cool water over his head. Welle and Alga settle themselves comfortably on the water’s edge for a long grooming session. Furt, cooler now, leaves the water to explore a fallen log nearby. As he approaches, he notices a turtle sunning itself on the log and slows his approach, hoping the turtle will not notice him. A branch snaps under Furt’s foot, and the turtle’s head swivels around in his direction. The turtle watches this small primate for a moment but does not retreat. Were he a more experienced hunter, Furt might have taken this as a warning. Animals that show no fear usually had a good reason. But Furt is too excited by the prospect of turtle meat to be discouraged, especially since this turtle is bigger than any other he has seen, nearly as long as his own arm. He does not stop his attack even when he notices the long trailing tail, different from the other turtles he has seen. He is only two paces from his quarry and takes another tentative step forward. The turtle’s head swivels around again and this time the turtle stands up, hissing loudly. Furt stumbles forward in surprise. He has never heard a turtle make noise before. Furt lets out a piercing alarm call just as the turtle propels itself forward on thick legs, mouth open. The turtle’s jaws snap shut for an instant on Furt’s leg, just below the knee. The two-inch long, jagged gash that appears caused another call from Furt, this time of fear and pain. When Welle and Alga make their way to him, all they can see of the danger is the retreating tail of the turtle before it disappears over the bank. Welle rushes to her son 75

and tries to groom his injury, but he pulls away from her painful investigation and limps into the forest. He sits in the shade for several minutes, looking somewhat dazed by his run-in with the snapping turtle. Blood trickles down his leg and mats in his hair. He scratches at this itchy coating and inspects his sticky fingers. Looking around, he selects several large leaves from a nearby bush and uses them to dab at his wound, cleaning it. He prods the gash a few times until no new blood spills out onto his leaves, then he wanders off in the direction of his mother and Alga. He finds the two females, along with ten others of his band, in the mouth of the river Alga watched earlier. They munch on a new type of grass, this one sweeter and more tender than what they are used to in the open waters. He walks into the water to join them, only to gasp in pain when the still slightly salty water reaches the wound on his leg. He retreats from the edge of the water and inspects his wound again. This time, when Welle approaches, he does not pull away. He lets her pick the dirt and dried blood from the edges of the cut. Welle, reassured that his injury is not serious, walks farther into the forest away from the band, searching for fruit. Furt trails after her, unwilling to venture into the water again so soon. As the pair walks through the unfamiliar underbrush farther inland, they stop occasionally to eat bunches of leaves. With the approach of night the pair pauses to look back toward the shore where they left their band, as if considering a return to them. Welle glances once more at the forest ahead and spots a tree heavily laden with ripe fruit. She lets out a soft hoot of excitement and rushes to the spot. Furt follows quickly on her heels, and the two gorge themselves. Fruit is often hard to find, so usually when they do find it, the larger males force them out of the best feeding spots. Only when Etang is in the group of males are Welle and her children able to keep their fruit and eat in peace. After the feast Welle and Furt become nervous with their new surroundings and walk back in the direction of the shore. Before leaving the tree, though, they each gather a handful of the fruit to eat as they walk back. Just as the sun sets, they reach the trees where the rest of their band has made nests for the night and quickly make beds for 76

themselves. Furt is too full to finish the last of his fruit and carefully places it in one corner of his bed, hoping that none of the others will spot it and take it from him before he can eat it the next morning. The sun reemerges through the trees the next morning, and Furt awakes hungry. He scrambles around in his bed until he finds his fruit, then tries to eat it quickly before the others see. He would have been successful, too, if his elder brother Teich had not been an even earlier riser. At fifteen Teich is fully adult and large. When he was much younger, he developed a friendship with Etang because Etang spent so much time with his mother, Welle. After his younger brother Furt was born, he spent even more time with Etang. When his mother went into the water, she would leave baby Furt with Etang. Teich preferred the company of the males to being in the water all day, so he stayed and watched his little brother. One day, after a successful hunt, Etang and Teich were sitting in a tree together sharing the meat. Another male approached and tried to take a piece of meat from Teich. Teich was anxious to protect his prize and began a loud and energetic threat display at the larger male. Etang watched a moment as he chewed a bite of monkey. The larger male, taken aback for a moment at this brazen youngster, had recovered himself and was cuffing Teich. Etang stood up on two legs and puffed out his hair. His brother Bain was nearby and also stood. The other male stopped his hand in midair and retreated quickly from the angry brothers and their charge. Since that day Etang has often backed up Teich when he gets himself into trouble. Teich has gotten more sure of himself and has started threatening other males. This morning Teich has awakened early and is looking for Etang, hoping for support if he ambushes one of the males as he sleeps. Instead he spies Furt munching on the last of his fruit. Teich changes his target and rushes at Furt instead. He needs none of Etang’s help to control his little brother. He reaches Furt just as he stuffs the last bit of fruit in his mouth along with a few leaves. His mouth stuffed to overflowing with his early morning meal, Furt cowers in front of the irritated Teich. Teich wants the fruit 77

from his brother, and his threatening noises increase in pitch and tempo until the morning air is split with his cries as he shakes branches and glowers at his young brother. Furt is now terrified by his noisy tormentor and quickly swallows the offending mouthful. He pushes himself over the edge of his bed, catches a branch with one hand, and swings himself away from Teich. The other band members have been aroused by the commotion and poke their heads out of their own beds to investigate. With the angry Teich still on his heels, Furt spots the familiar face of Etang and hurries up the tree toward him. Teich does not want to rush screaming at his useful ally first thing in the morning, so he ignores Furt’s upward move. He continues straight along the ground, shaking branches and calling his frustration into the forest until he encounters an unsuspecting female at the base of her sleeping tree. He bowls her over and swats at her a few times as she crouches low on the ground. When she offers no resistance, he ceases his attack and takes a step back. The flustered female stretches out a hand for reassurance, and Teich brings her hand to his lips, kissing it to comfort her. Feeling better after venting his frustration, he returns to the middle of the group and joins the party of grooming males he has awakened. Welle starts into the forest toward the fruiting tree she found the day before, and Alga and Furt followe behind her, hoping for more fruit. Teich and Etang watch as they go and a few minutes later disengage themselves from the grooming party and follow after them along with several of the other females. Welle and Alga reach the tree first because a strangely scented flowering bush along the way has distracted Furt. The tree comes into view as they break through the thick underbrush, and Alga, who is the hungriest, rushes forward. A split second later she notices a small deer carcass wedged in the crook of the tree next to the fruit, and at the same moment sees a flash of tawny brown to one side. She lets out a petrified scream of alarm which ends almost before it leaves her mouth. She does not call again. The leopard’s teeth have clamped tight around her neck, and she collapses to the ground, pulled down by the weight of the predator. 78

Welle sees the attack and backs away quickly, not taking her eyes from the unknown yet terrifying predator. Furt and the others rush toward the sound of Alga’s last agonizing cry. They stop when they see Welle, trembling with fear. Furt follows his mother’s gaze to Alga’s limp body wedged between the forelegs of the leopard. The leopard is staring right back at them, body tense, ready to fight to keep its deer if necessary. The group continues to back up until vegetation screens them from the leopard’s sight. They then turn and run into the water, calling warnings to the band left on the beach. All the band within earshot respond to the warning and rush into the water to join the ten frightened band members already there. The water becomes a seething mass of bodies, all jostling to be close to one another for comfort. Welle has not taken her eyes from the spot where her mother’s limp body lies hidden in the trees and is the first to see the leopard approaching. He weaves his way through the trees, pulling the body of the deer under him as he walks. She screams in alarm, and the rest of the band take up the call until their screams echo through the forest. The leopard disappears into the undergrowth once again, and the band finally falls silent. The band moves farther from the shore into the middle of the river and calms as time passes. The leopard does not reappear. However, they do not dare to return to shore with the leopard so close by, and one by one they make their way across the river to the bank on the other side. The occasional burst of food calls can be heard echoing out over the river as the band finds fruiting trees on the new island. At last only Etang and Welle are left in the water, until Etang too moves toward the opposite bank. He turns back to look at Welle, still unmoving in the water. He goes back to her and pats her shoulder, then pulls her arm to lead her away. Welle shakes him off violently. He gives up and makes his way to the far shore alone. Welle stays rooted in place until night falls, only then making her way across the moonlit water to the shore where her band has made nests in the overhanging trees. She makes no nest in a tree this night, but curls up in the sand, facing the last place she saw her mother, whimpering softly as she falls asleep. 79

The return to the mainland opens up new food possibilities to the band unavailable in the salty sea to which they had become adapted. However, it offers new dangers as well. Large land predators would have been unable to survive on small islands, which lacked enough prey to support them. These predators, however, would have flourished on the mainland of Africa, and now pose a real threat to band members. As the band takes advantage of the new freshwater foods and fruiting trees along the river’s edge, they move upstream and branch out along various waterways of Ethiopia. With each generation they could have shifted their home range a few miles, and by the time we see them again, they will have moved out of Afar and into the center of Africa.

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Chad 6.0 million years ago

Gens (People; French)

Sahelanthropus tchadensis is thought to be the oldest fossil of a hominin yet discovered. The fragments of six individuals of this species have been found in the central African country of Chad and have been dated to between 6 and 7 million years old. One of these fossils is a nearly complete skull (minus lower jaw) that has been nicknamed Toumai (meaning hope of life in the local language). Although this skull offers valuable insight into the morphology of this species, being buried for millions of years under shifting rock and earth has distorted the skull. Multiple independent experts have worked on reconstructing this fossil, but details of how the pieces fit together are still disputed. Several traits appear to set these creatures apart from other apes. The nose and mouth region of this species does not protrude forward as much as in apes; these individuals have a reduced muzzle and a more human-looking flat face. Also, the canine teeth of this species are thought by some to be reduced in males so that they are of similar size in both sexes. In living ape species larger canines in males usually indicate that males fight or threaten each other for access to sexually receptive females. This reduction in male canine size in suggests male- male competition was reduced, possibly hinting at a more monogamous mating system. Perhaps most important, is the evidence for bipedality in these creatures. A fossil can be named a dental hominin if it shows certain teeth characteristics, but the true test of a hominin remains upright walking. No postcrania (bones beneath the skull) have been found for Sahelanthropus as yet, so undisputed proof that they walked upright is not yet available, but the suggestion is there. In the reconstructed skull the foramen magnum of Toumai appears to be positioned farther forward than in modern quadrupedal apes. 81

This forward position is mandatory for habitual bipedal walking. The shape of the hole is also more similar to upright walking humans than quadrupedal apes, lending further support to the theory that Toumai walked erect. The Sahelanthropus fossils were found in a location that also included the fossils of many species of , turtles, lizards, snakes, crocodiles, hippopotami and otters, as well as hyenas, monkeys, aardvarks, elephants, and giraffes. This suggests that these creatures lived on the shore of a large lake that was surrounded by forests and grasslands.

Samman sits balanced in the crook of a tree, staring out over the water in front of him. If he squints his eyes against the glare of the sun off the water, he can just make out the shape of land across the water. The lake is a large one, but not as large as the inland sea his ancestors once inhabited. In front of him several of the females crouch in the water, waiting for the bubbles that indicate a clam or lobster in the shallows of the lake. He pays particular attention to Natte. Her awkward, lumbering movements set her apart from the lithe movements of the other females. She straightens up onto two legs, putting one hand on her back for support while the other clasps a lobster. Fully upright, Natte’s distended stomach is unmistakable; she is nearly full term with her first pregnancy. Still knee deep in water, Natte inspects her catch. The lobster is doing what lobsters do best, trying to clamp his claws down on whatever it is that has disturbed him. Although Natte is young, she is not a novice at catching lobsters. She has watched others get their fingers pinched by lobsters, and more than once has seen hard won food scuttle back into the water while the hunter has cradled an injured body part. Grasping the lobster tightly behind its pincers, her fingers on each side of its body, she carefully detaches each large claw in turn. Holding the still wriggling body of the lobster in one hand and the meaty pincers in the other, she wades back onto dry land. Samman makes his way down from his tree with a purple hard-shelled fruit in one hand. He meets Natte and sits beside her in the shade. Natte runs her fingers along the 82

tail of the lobster until she finds a crack she can get a fingernail beneath. She pries back the hard covering of her lobster and takes big bites out of the tender meat of the tail. She finishes the meat in the body and moves on to one of the pincers, using a rock to make a crack in the harder shell. Samman pries open his fruit and begins to eat, pausing often to watch Natte. As she finishes the first claw, Samman scoots closer to her and holds out a hand with a bit of fruit in it. Natte pauses in her feeding and sniffs at the offered fruit, then takes a small bite. Deciding she likes it, she grabs the piece Samman offers and stuffs it into her mouth, one cheek bulging as she gives a lopsided grin. Samman extends his hand again, this time taking the other claw. Natte does not pause in her chewing, and Samman settles closer to her and uses the same rock to crack his own claw. After all the food is eaten, both reach out drowsily to groom each other as the sun burns brightly overhead. A few minutes later Meer, Natte’s mother, exits the water after an unsuccessful morning. She approaches the grooming pair and picks at the discarded bits of lobster and fruit rind on the ground. Natte starts toward her mother, not ready to concede the few remaining scrapes. Meer lowers her head submissively and begins to groom her daughter’s distended belly. Suddenly Natte’s stomach contracts sharply under her mother’s grooming hands, and a soft groan escapes Natte’s mouth. Natte gets to her feet, using her mother for support. The two females move away from the group and into the forest. Samman watches the retreating back of Natte as she makes her way through the underbrush until she disappears into the foliage. He keeps his eyes riveted to the spot where she disappeared long after she is gone, and he doesn’t return to the trees again. Natte sinks down on a soft patch of earth when she is out of sight of the rest of her group. Meer watches her daughter for a moment, then moves away to a nearby fruiting tree. She pulls herself up into the tree and settles down to eat, glancing every so often at her daughter on the ground. 83

Natte is busy building herself a ground nest, pulling branches from low trees and nearby bushes into a platform much larger than she would usually make. Her nest complete, she munches on young leaves for a moment before lying down. In another moment she is up again, gathering more leaves and slender branches to add to her nest. She tucks the last leaf into place just as Meer comes down from the tree, fruit in hand. Meer approaches her daughter’s nest slowly and places the fruit within reach of her daughter’s arms. Natte reaches out, takes the fruit, and eats it. Meer takes another step forward and begins to make grooming motions on her daughter’s hair, stroking her gently as her contractions get closer together. Every few minutes Natte stands up to shift her weight or to add more leaves to her nest. Natte begins to strain, concentration twisting her features as she holds a sturdy branch in her nest for support. The hours pass as Natte has cycles of contractions. The contractions intensify, she strains even harder, and a few minutes later the baby Gens emerges between Natte’s legs. She reaches down and pulls her new infant to her. Natte reaches for a bunch of leaves and uses them to wipe her baby’s face and body clean. She cradles her infant in her arms and peers intently into the little face, memorizing her daughter’s features. Gens’s muzzle is smaller than other band infants, giving her a curious flat-faced appearance, but otherwise the baby girl is healthy. Gens reaches for her mother, tiny hands grasping for her hair. Natte holds the baby up to her breast, and Gens roots for a nipple and latches on. As the baby nurses Natte continues to strain until the afterbirth is delivered as well. When the baby has gotten her fill, she curls her fingers even more tightly into the hair on her mother’s stomach and drifts off to sleep. Natte gathers the baby and placenta together in her arms, gets up slowly, and makes her way over to the nearby fruit tree. She grasps a low branch carefully with one hand, using the other to support Gens as she pulls herself up into the tree to feed. Her mother sits in the tree next to Natte and grooms her daughter and her new infant. After a few hours Natte is tired, and she returns to her ground nest to rest. As 84

soon as she has settled herself comfortably, Samman finds her. He first inspects Natte, grooming her and calling softly until he is assured that she is safe. Satisfied, he reaches out a hand to touch Gens. Natte watches without fear as her mate strokes their first child. Comforted by his presence and tired from the day’s activities, she drifts off to sleep. Samman continues to groom their baby until both mother and child are sleeping. He can hear the unmistakable calls of the band echoing through the trees as he climbs a nearby tree to watch over his family.

A new species has just been born. Gens is the first known hominin, a Sahelanthropus tchadensis. In the fossil record the exact individual who represents a speciation event cannot be identified as clearly as Gens is. This is because of the gradual buildup of change and the incompleteness of the fossil record. It is difficult to pinpoint exactly when one species stops and another begins. However, that point does exist. There had to have been one mother, one mutation away from being a new species, who gave birth to a child who was the new species. This band, and the others of their kind, will continue down the path toward becoming human. Over time, descendants of this ancestor will adapt to different environments, resulting in different hominin species. All but one will lead to an evolutionary dead end. Gens is the first of the recognizable human ancestors. Her descendants will grow up to discover the wheel, build civilizations, and ultimately, to ponder their own origins.

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