Human origins Tim White

INSTANT EXPERT 5

101106_IE_Human origins.indd 25 21/10/10 14:13:28 evolving search FOR OUR ORIGINS, FROM DARWIN TO TODAY technology NOT FROM CHIMPS

Technology has transformed our search for human Nineteenth-century sceptics origins. The majority of methods used to date the illustrated what many people saw rocks that hold fossilised bones and artefacts are as the implausibility of human based on radioactive decay. For example, radioisotopic evolution with a cartoon depicting dating of the layers of volcanic ash sandwiching the Darwin’s head atop the body of a remains of “Ardi”, the partial skeleton of Ardipithecus knuckle-walking chimpanzee. ramidus (see below right), show that the sediments Even though Darwin was clear in which the skeleton was found were laid down from the start that we had not 4.4 million years ago. evolved from living chimpanzees, Using micro–computed tomography (micro-CT), similar ideas, and the “missing we can peer inside fossils without damaging them. link” concept, have stuck with us. In the case of Ardi, 5000 micro-CT “slices” through the Darwin’s champion, Thomas fragments of her squashed and scattered skull allowed Huxley, concluded from his own a team at the University of Tokyo in Japan to assemble anatomical studies of African apes that they were our closest living a virtual model and then “print” the skull on a 3D printer. relatives, a conclusion vindicated when molecular studies Other technologies that have had a huge impact showed – and continue to show – how genetically close these include differential GPS to map our finds with sub-metre animals are to us. Ironically, Darwin was almost alone accuracy and to pinpoint the location of ancient stone in calling for restraint in the use of modern tool quarries, satellite imagery to identify surface primates as “stand-in”, proxy ancestors. outcrops of ancient sediments and image-stabilised The recent discovery of human ancestors binoculars to examine those outcrops from afar. that were quite unlike chimps, dating from We use mass spectrometers to examine the soil soon after the two lines split, has shown around any animals we find and also measure the that his caution was well founded, and isotopic composition of their tooth enamel. This how living chimps have evolved a great helps us determine their environment and diet. We deal in relation to the common ancestor use digitisers to capture and analyse the shape of that we once shared with them. fossils. We can even match the chemical fingerprints of rocks thousands of kilometres apart. For example, we have matched volcanic ash from the Middle Awash, our study area in Ethiopia’s Afar Depression, to ash outcrops in other sites in Africa and to volcanic layers in deep-sea cores from the Gulf of Aden. The archaeopalaeontology tool kit has come a long way from little hammers and brushes.

WHAT’S IN A NAME? l de u

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and restored “Ardi” at the / A the members of the human clade (on our of Ardipithecus ramidus University of Tokyo side of the last common ancestor we white

tim shared with chimps) as “hominid”. ii | NewScientist

101106_IE_Human origins.indd 18 22/10/10 15:29:03 search FOR OUR ORIGINS, FROM DARWIN TO TODAY

Charles Darwin’s only remark about in his seminal work On The Origin of Species was that “light will be thrown on the origin of man and his history”. In his autobiography, Darwin justifies his brevity: “It would have been useless and injurious… to have paraded, without giving any evidence, my conviction with respect to his origin.” His boldest statement was in The Descent of Man, where he concluded: “It is somewhat more probable that our early progenitors lived on the African continent than elsewhere.” Today, thanks to a range of discoveries and technologies, we can tell in amazing detail the story that Darwin only guessed at.

the big picture

Twelve million years ago, Earth was chimpanzees. By 6 million years a planet of the apes. Fossil evidence ago, a daughter genus had evolved shows there were many ape species primitive bipedality and smaller spread across the Old World, from canines. Some 2 million years later, Namibia to Germany to China. About its descendants had extended their 7 million years ago, a long-gone range across Africa. After another African species whose fossils have million years, one of the species in yet to be found was the last common the genus Australopithecus sparked ancestor shared by humans and our a technological revolution based on closest living relatives, the stone tool manufacture that helped to push later hominids beyond Africa and across Europe and Asia. The genus is the group of species that includes modern people as well as the first hominids to have left Africa. The first species ARDIPITHECUS: of the genus to do this, Homo erectus, THE HOMINID rapidly spread from Africa into Eurasia by 1.8 million years ago, reaching We still lack enough fossils to say much about the very deposits dated at 4.4 million years Indonesia and Spain, though this earliest hominids. The key features of the fossils that upset all of those expectations was still long before the ice ages have been found suggest that they walked on two because it is so different from even began. Many cycles of cold and legs. We know their social system was different to that the most primitive Australopithecus. nearly a million years later, another of any other living or fossil ape because the canines of The partial skeleton, nicknamed African descendent of Homo males were much smaller and blunter than those of “Ardi”, suggests that our last erectus – one that would eventually non-human apes, and so did not function as weapons. common ancestor with chimpanzees vaingloriously name itself Homo African fossils of these earliest hominids from was not a halfway-house between a sapiens – again ventured beyond about 6 million years ago have been given different chimpanzee and a human, but rather the continent. It has now reached names: tchadensis, found in Chad; a creature that lacked many of the the moon, and perhaps soon, will tugenensis from Kenya; and Ardipithecus specialisations seen in our closest stand on a neighbouring planet. kadabba from Ethiopia. None resembles modern cousins, such as knuckle-walking, Not bad for a two-legged primate. apes, and all share anatomical features only with a fruit-based diet, male-male combat later Australopithecus. and climbing. A. ramidus was a mosaic Before these fossils were found, many organism: partly bipedal, omnivorous researchers had predicted that we would keep finding with small canines, relatively little Australopithecus-like hominids all the way back to difference between the sexes and the fork between hominids and the evolutionary line a preference for woodland habitats. leading to modern chimpanzees. The recent discovery Ardi represents the first phase of of a skeleton of Ardipithecus ramidus from Ethiopian hominid evolution.

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CACTUS OR BUSH?

The late American palaeontologist Steven Jay Homo Homo Homo Gould wrote a classic essay in 1977 in which floresiensis sapiens neanderthalensis he predicted that the hominid family tree Homo heidelbergensis would prove to be “bushy”. Today, it is common Homo rhodesiensis to see lists of more than 25 different hominid species, and Gould’s prediction is often declared to be fulfilled. 1 Homo erectus Not so fast. Many of these species are “Sinanthropus” “chronospecies”, which evolve from one to the other, such as the earliest two Australopithecus boisei Australopithecus species, A. afarensis and A. anamensis. These names are merely Homo ergaster arbitrary divisions of a single evolving lineage. Australopithecus robustus A modern biologist addressing the question 2 Australopithecus crassidens of species diversity counts the number of Homo habilis Australopithecus sediba related species existing at any one time. When we do the same thing across the hominid fossil record, what we get is not a bush but Australopithecus Stone tool from Gona, Australopithecus aethiopicus Ethiopia, made about something like a saguaro cactus, with only a garhi 2.6 million years ago few branches or species lineages. Indeed, the greatest diversity among hominid species 3 Australopithecus africanus appears to be at around 2 million years ago, when as many as four different lineages

“briefly” co-existed in Africa. Australopithecus afarensis TECHNOLOGICAL The key question turns out to be not how AGO YEARS OF MILLIONS many species there were per se, but rather primate why species diversity has been so limited on our branch of the evolutionary tree compared 4 Hominids are frustratingly rare in with other mammals like fruit bats or South Australopithecus anamensis the fossil record, but at some time American monkeys? The reason is probably around 2.6 million years ago they that our ancestors’ niche kept broadening, Ardipithecus ramidus began to leave calling cards, in the as a woodland omnivore 6 million years ago form of stone artefacts. expanded ecologically into more open At the adjacent archaeological environments, and then again as technology sites of the Gona and Middle further extended its capability and horizons. 5 Awash in Ethiopia, there is now abundant and unambiguous Four Australopithecus species are considered "robust” evidence of the earliest stone tools Alternative names made by hominids. The fossilised bones of large mammals bear definite traces of marks made by sharp instruments. 6 Ardipithecus kadabba The production of sharp-edged Orrorin tugenensis Sahelanthropus tchadensis stone flakes enabled hominids to eat large amounts of meat and marrow previously unavailable to l p primates. At the same time, the s ROBUST f/ selective pressures associated with s /m such activities – particularly for a AUSTRALOPITHECUS trueba bipedal primate operating ier v a

cooperatively under the noses of j Look at the skull on the right. Would and it appears in the fossil record ull

abundant predators, from hyenas k you say it looked robust? That’s what more than 2.5 million years ago, in s

to sabre-toothed cats – would lead palaeontologist Robert Broom eastern Africa, with its last members inset to dramatic anatomical change as y- thought when it was found in South some 1.2 million years ago. By that gett the braincase enlarged in Homo. / Africa in the late 1930s, naming this late date, our genus, Homo, had been ing Stone technology greatly d hominid Paranthropus robustus. It has on the scene for more than a million har widened our ancestors’ ecological oversized molars, tiny canines and years. There are many mysteries niche, as well as their geographic incisors, a massive lower jaw, dished about robust Australopithecus still to robert / range, enabling H. erectus to reach face, small brain and, usually, a bony be solved, but one thing is clear: this hager

hite Europe and Indonesia more than crest atop its skull. It came to be side of 2.5 million years ago, our es m m w m a ti 1.5 million years ago. j known as “robust” Australopithecus, lineage was not alone.

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101106_IE_Human origins.indd 20 22/10/10 15:25:14

AFRICAN ORIGINS

Homo Homo Homo A mountain of evidence has accumulated showing that our ancestors floresiensis sapiens neanderthalensis emerged in Africa. What is less clear-cut is what spurred their Homo Homo rhodesiensis heidelbergensis evolution. The answer lies in the environments in which our predecessors lived, and the influence of technology, which hugely expanded their ecological niche. 1 Homo erectus “Sinanthropus”

Australopithecus boisei

Homo ergaster Australopithecus robustus

2 Australopithecus crassidens Homo habilis Australopithecus sediba THE SAVANNAH Australopithecus Australopithecus aethiopicus garhi HYPOTHESIS Many modern palaeoanthropologists invoke climate 3 Australopithecus africanus change as the motor for our evolution. But they are hardly the first to recognise the impact of the environment. Long before relevant fossils were found,

Australopithecus afarensis an early proponent of evolution, Jean-Baptiste Lamarck,

MILLIONS OF YEARS AGO YEARS OF MILLIONS saw as pivotal in the evolution of our ancestors from tree dwellers to bipeds. He was followed by in the 1920s, who argued correctly 4 that the fossil child he named Australopithecus was Australopithecus anamensis adapted to open environments. But the popularity of the “savannah hypothesis” began to wane in the 1990s, when Ardipithecus fossils Ardipithecus ramidus ”This side of 2.5 million were found in contexts suggesting a woodland habitat. years ago, our lineage Today independent lines of evidence suggest that the earliest hominids were indeed woodland creatures: 5 was not alone” climbing adaptations; diet as deduced from the shape, wear and isotopic composition of teeth; and the Four Australopithecus species thousands of plants, insects, snails, birds and mammals are considered "robust” Alternative names that also prefer such habitats and are abundant in the same localities. Australopithecus came next, though, and does appear to have been associated with more open landscapes. 6 Ardipithecus kadabba It has been known since the 1940s that the hip, knee Orrorin tugenensis and foot of Australopithecus were adapted to Sahelanthropus tchadensis bipedality. However, it was the discovery of the “Lucy” fossils (see right) in Ethiopia and fossilised footprints in Tanzania during the 1970s that established this genus as representative of the evolutionary phase from which later hominids evolved. By 3 million years ago, Australopithecus species had spread from north to south across much of Africa. To 20th-century anthropologists, Australopithecus seemed like an unstable transition between ape and human. Now, however, in the light of the Ardipithecus discoveries, this genus is seen as a long-lasting phase of our evolution. As well as gaining the means for habitual two-footed walking, robust forms became adapted to heavy chewing and developed relatively “Lucy”, the fossil of large back teeth with thicker enamel (see “Robust Australopithecus

Skull of Australopithecus Australopithecus”, left). Some contemporary but ill afarensis, is

robustus, from less robust species is likely to have given rise to the d L. br 3.2 million years old avi

Swartkrans, South Africa Homo genus. d

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101106_IE_Human origins.indd 21 21/10/10 14:12:10 advance OF CIVILISATION It has long been dogma that it was only when people domesticated NEANDERTHAL FATES plants and animals – otherwise known as agriculture – that they were able to Ever since their settle down and begin to build cities discovery in the and create monumental architecture. mid-19th century, the This plausible version of technological place of Neanderthals in evolution is now being strongly human evolution has challenged by discoveries in the been a mystery. Early olic Middle East. s evolutionists adopted

At the site of Göbekli Tepe in kola them as evidence of /ni s south-east Turkey, an 11,000-year- human evolution, but as

old site has recently been uncovered. reuter more and more fossils It boasts T-shaped limestone pillars of were recovered from around the Mediterranean, it various heights, up to 6 metres, became clear that these forms were peculiar hominids. carved with images of animals. They With the excavation of further sites in Europe, the were erected here in a monumental archaeological record showed a rapid technological circular arrangement, 20 metres in change just as they disappeared. diameter. This structure pre-dates the Debate about whether Neanderthals were domestication of plants and animals. ancestors or cousins persisted for decades, but fossil The people who built it still lived by discoveries and genetics have finally solved this hunting and gathering. problem. Early anatomically near-modern and modern This and other sites discovered in people lived in Africa long before the Neanderthals the region challenge the notion that perished about 35,000 years ago. Genomic studies agriculture was the catalyst for what suggest that there was possibly slight interbreeding we loosely call “civilisation”. Could it between them, with leakage – of at most a few per be that symbolism, ritual and religion cent – of genes from Neanderthals into human came first and that these were the populations.They were our evolutionary close cousins, cause, rather than the consequence, but the equivalent of a separately evolving species. of domestication and agriculture?

HOW TO SPOT A ‘HOBBIT’ Göbekli Tepe in Turkey, with its The discovery of the remains of diminutive humans on limestone pillars and the Indonesian island of Flores, east of Java, captured carved images the world’s imagination in 2003. The remains were named Homo floresiensis and, almost inevitably, nicknamed “hobbits”. Three hypotheses have been put forward to explain these Flores Island fossil hominids, which date from between 90,000 and 18,000 years ago. One is that their heads were abnormally small as a result of a congenital condition. However, no good match has been found between this microcephaly and a modern developmental disturbance of this kind. The second hypothesis sees a very early occupation of Flores by hominids who were small, language, symbolism, with small brains. In other words, far-flung AGRICULTURE… AND BEYOND Australopithecus or very early Homo. This also seems unlikely, given the times, distances, geographies When did humans acquire language? It is a question the planned sowing and harvesting and anatomies. that anthropologists and linguists still puzzle over. of plants. The third, most Some suggest it was very late, only after we had Those of us old enough to likely, scenario is that become H. sapiens and begun to spread beyond Africa remember the Apollo spacecraft or nearby H. erectus or

sometime after the emergence of anatomically the dial telephone have witnessed so ss H. sapiens became modern humans around 60,000 years ago. The much technological innovation established there, rapidly founding of basic languages may have accelerated within a couple of generations that evolving into hobbits

trade and, as Matt Ridley argues in The Rational we find it difficult to appreciate preaif/camera via the well-known er/l Optimist, trade is to culture as sex is to biology. that this speed of change is ta b phenomenon of island

The first evidence of symbolic behaviour comes as exceptional. For thousands of years, ihar dwarfing. All researchers w ea

100,000-year-old South African shell beads and ochre Babylonian farmers did the same b agree that more evidence / s incised with designs. Around 10,000 years ago, in the things, with the same tools, that is needed to solve the reuter Fertile Crescent of Mesopotamia and the Levant, came their great-grandfathers had done. Steinhil Berthold mystery of H. floresiensis.

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101106_IE_Human origins.indd 22 22/10/10 15:31:02 RISE OF THE MODERN MIND

The initial hominid expansion from Africa occurred about 2 million years ago, long before the Neanderthals had evolved in Europe. The direct ancestors of our species spread out from Africa much later, after they had already become anatomically and behaviourally much more human. In Asia and Europe they would encounter populations of hominid species from earlier migrations that had evolved their own differences. These species became extinct, while the new hominids from Africa went on to evolve relatively superficial features that today characterise the geographically diverse populations of our species.

OUT OF AFRICA, twice

~45,000 Years before present ~30,000 ~13,500 YBP YBP ~130,000– The first hominid expansion from 170,000 Africa came about 2 million years ago, YBP as revealed by stone tools and an ~65,000 ~70,000 outstanding collection of hominid YBP YBP fossils at the site of Dmanisi in

Georgia. This expansion has sometimes been called “Out of Africa, Part 1”, but the implication that hominids ever deserted Africa is manifestly incorrect. This continent continued to be the crucible of our evolution. Even the emigrant Homo erectus and its hand-axe technology By 160,000 years ago, African child’s cranium show that it was Human migration routes are ubiquitous in Africa, with evidence hominids were nearly anatomically defleshed when fresh, and then based on analysis of of the species’ occupation from the modern, with faces a little taller than repeatedly handled. mitochondrial DNA Cape to near Cairo. ours, and skulls a little more robust. Examination of the DNA of people Darwin predicted that Africa would Their brain sizes were fully modern. today shows we all carry inside us a one day yield fossils to illuminate In Ethiopia, at a locality called Herto by kind of “living fossil” that opens a human evolution. Today, he would be the local Afar people, the crania of two window on our past. Whether delighted to learn we have found adults and a child represent some of modern human DNA samples are fossils not only from the first two the best evidence of the anatomy of taken in the Arctic or the Congo, our phases of human evolution, but also these early people, who lived by a lake. DNA is remarkably similar to each within our own genus, Homo. The Among their activities was the other’s, especially when compared earliest is H. habilis, makers of stone butchery of hippopotamus carcasses with the variation seen in most flakes and cores that dominated with their sophisticated stone tool kits. other mammals. And the variation technology for almost a million years. Herto humans were also doing observed is greatest among Next came H. erectus. What is clear is things that we would recognise as African populations. that our ancestors continued to evolve distinctively human: they were What this means is that we are a in Africa as more northerly latitudes practicing mortuary rituals. Fine recent species, and that the ancestors were repeatedly buried in thick ice. cut marks and polishing on a of all modern people were Africans.

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101106_IE_Human origins.indd 23 21/10/10 14:13:01 Tim D. White Professor of integrative Next biology and director of the Human Evolution Research INSTANT Center at the University of EXPERT California, Berkeley Tecumseh Fitch Language white 4 December tim

LESSONS FROM AN AFRICAN VALLEY

Set in Africa’s north-east corner, H. rhodesiensis and then into Recommended reading the Afar rift holds a unique record the nearly anatomically modern The Complete World of Human Evolution by Chris Stringer and Peter of hominid history. Seasonal floods H. sapiens idaltu. In some of the Andrews (Thames & Hudson) have carried sediments into this basin, youngest strata, we find fossils so The First Human: The race to discover where they have been accumulating anatomically modern that they could our earliest ancestors by Ann Gibbons (Anchor) for millennia. It was there last be lost among the 7 billion of us on Science, Evolution and Creationism February that our Middle Awash field Earth today. In these layered rocks by National Academy of Sciences camp was inundated. When the we also find an unparalleled record (National Academies Press) Evolution vs. Creationism: An floodwaters evaporated, the of stone-tool technology. introduction by Eugenie C. Scott millimetre of silt left behind became As Darwin would surely appreciate, (University of California Press) the youngest stratum in a succession this evidence is overwhelming – the Why Evolution is True by Jerry A. Coyne (Penguin) of sediment layers that mammalian species we call H. sapiens Evolution Since Darwin: The first is today about 1.5 kilometres thick. has deep evolutionary roots in Africa. 150 years by Michael Bell, Douglas These layers have been Why does it matter? Human Futuyma, Walter Eanes and Jeffrey Levinton (Sinauer Associates) accumulating for 6 million years as evolutionary history has important rivers and lakes came and went. Near lessons for our species. We now know Websites the bottom of this succession of rocks that all of our closest relatives have Middle Awash Project: bit.ly/aqWntN Discovering Ardi: bit.ly/PZuDb is Ardipithecus – not a chimpanzee, gone extinct, leaving only more National Geographic on the Middle and not a human – but from the distant African apes. The perspective Awash: bit.ly/9IHlvD earliest portion of our branch of the that this knowledge provides is both Science on Ardipithecus ramidus: bit.ly/1iyXm9 hominid family tree. timely and essential to the bipedal, In 4.2 million-year-old strata we large-brained, innovative, technological Cover image: Tim White found the earliest Australopithecus, primate whose grasping hands now followed by remains of the “Lucy” hold the power to determine our species in sandstones that are future on planet Earth. 3.4 million years old. Above this, Given the facts, it would not be in sediments 2.5 million years old, wise to gamble on the widely held are traces of the butchery of large but risky notion that our future will mammals accompanied by some of be guided to good ends by divine the earliest stone tools. intervention. Having evolved the One million years ago, this valley capacity to influence the global future, was populated by hand-axe-making it is high time the species begins to Homo erectus, which evolved into act sapiently.

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