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Chapter 4: Whai Can the Fossil Record Tell Lis About Human Origins? anthropq what does it mean to be human? FOURTH EDITION Robert H. Lavenda St. Cloud State University Emily A. Schultz St. Cloud State University NewYork Oxford ^ot8OXFORD UNIVERSITY PRESS What can the fossil record tell us about human origi ns? Anthropology has made major contributions to our understanling of human biological and cultural evolution. This chapter tells the story of what we have learned from fossils, stone tools, and other cultural remains, from the appearance of our earliest known ancestors about 6 millioil years ago through the appearance of modern Homo sapiens about 200,000 years ago. CHAPTER OUTLINE What ls Macroevolution? The Culture of H. erectus What Do We Know about the What ls Hominin Evolution? H. erectusthe Hunter? Upper Paleolithic/Late Stone Who Were the First Hominins What Happened to H. erectus? Age (40,000?-1 2,000 Years Ago)? (6-3 mya)? How Did Homo sopiens Evolve? The Origin of Bipedalism What ls the Fossil Evidence for What Happened to the Changes in Hominin Dentition the Transition to Modern H. Neandertals? Who Were the Later sapiens? How Many Kinds of Upper Australopiths (3-1.5 mya)? Where Did Modern H. sapiens Paleolithic/Late Stone Age How Many Species of Come from? Cultures Were There? Australopith Were There? Who Were the Neandertals Where Did Modern H. sapiens How Can Anthropologists (1 30,000-35,000 Years Ago)? Migrate in Late Pleistocene Explain the Human Transition? What Do We Know about Times? What Do We Know about Early Middle Paleolithic/Middle Eastern Asia and Siberia Homo (2.4-1.5 mya)? Stone Age Culture? The Americas Expansion of the Australopith Did Neandertals Hunt? Australasia Brain What Do We Know about Two Million Years of Human How Many Species of Early Anatomically Modern Evolution HomoWere There? Humans (200,000 Years Ago Chapter Summary Earliest Evidence of Culture: to Present)? For Review Stone Tools What Can Genetics Tell Us Key Terms about Modern Human Who Was Homo erectus Suggested Readings (1.8-1.7 mya to 0.5-0.4 mya)? Origins? Morphological Traits of H, erectus The discovery of o new hominin species, Homo naledi, is revealed to the public in Johannesburg, South Africa, in 2015. 95 96 CHAPTER 4: WHAI CAN THE FOSSIL RECORD TELL LIS ABOUT HUMAN ORIGINS? TABLE 4.1 Models of Macroevolution PHYLETIC GRADUALISM PUNCTUATED EQUITlBRIA Macroevolution A uniform process, the eventual outcome of Differentfrom microevolution, not a uniform l microevolution, given enough time process l Motor of The result of anagenesis, the gradual transfor- The result of cladogenesis, the rapid produc- new species alongside parent I speciation mation of one species into another species tion of multiple i species I I i Species boundary Species boundaries are arbitrary Species boundaries are real i Consequences No sharp breaks in fossil record between old Speciation achieves the shifting of"genetic I and new species and morphological centers of gravity of parent I and daughter species" such that "each species I I is now free to accumulate more variation and hence more potential species differences" I (Tattersall 1998,163) f hapter 2 presented some of the central concepts of time and is concerned with tracing (and explaining) the \-r mode- evolutionary theory and Chapter 3 used extinction of old species and the origin of new species. some of these concepts to locate human beings within the Evidence for these processes comes from close study of primate order. In this chapter we tum to a consideration fossils and oJ the comparative anatomy of living organ- of the fossil evidence that provides evidence for the evo- isms. As we shall see, the way we understand macroevo- lutionary history of our species, highlighting the ways in lution shapes our understanding of human evolution. which that history differed from that of our closest primate Until the 1970s, most evolutionary biologists were relatives. As such, this chapter will be adopting the per- more or less convinced thatthe problems of macroevolu- spective of macroevolution, which focuses on long-term tion had been solved in a satisfactory manner by Darwin evolutionary changes, especially the origins of new species himself. Darwin claimed, and neo-Darwinians agreed, and their diversification across space and time over mil- that macroevolution-the origin of new species-is lions of years. Spanning many generations and the growth simply what happens when microevolution continues and decay of many difrferent ecological settings, macroevo- over a long enough period of time (Table 4.1). Such a lution is measured in geological time. Microevolution, view seemed plausible because, as we have seen, all these by contrast, devotes attention to short-term evolutionary evolutionary thinkers assumed that, over time, genetic changes that occur within a given species over relatively and environmental changes are inevitable. Mutation few generations. It is measured in what is sometimes (if unchecked by natural selection) inevitably changes called "ecological time," or the pace of time as experienced a species' physical attributes over time in the same way by organisms living and adapting to their ecological set- that the natural environment, perpetually subject to tings. The study of microevolutionary processes affecting uniformitarian processes of erosion and uplift, never re- the human species will be the topic of Chapter 5. mains constant. Evolution was thought to occur when independent processes of genetic change and environ- mental change intersect in the phenotypes of organisms What ls Macroevolution? living in a particular habitat. In his final formulation of the theory of natural se- Macroevolution studies evolution at or above the spe- lection, Darwin argued that there is no such thing as cies level over extremely long stretches of geological a fixed species, precisely because evolution is gradual. And evolution is gradual because environments change slowly. Lamarck's concept of long-term evolutionary itx- microevolution A subfield of evolutionary studies that devotes attention change was also gradualistic, except that he pictured to shoft-term evolutionary changes that occur within a given species over dividual members of a long-lived natural kind (and their relatively few generations of ecological time, offspring) tracking the changing environment over a macroevolution A subfield of evolutionary studies that focuses on long- long period of time. For Darwin, however, a species grad' term evolutionary changes, especially the origins of new species and their a diversification across space and over millions of years of geological time, ually transforms itself over time into a new species, anagenesis The slow gradual transformation of a single species over time. process called anagenesis, although the actual boundary What ls Macroevolution? 97 Species B Species C Species B Species A Species C FIGURE 4.1 Research and theories about punctuated Natural equilibria have challenged the <-Years of ---> selection common neo-Darwinian under- accumulated "fine-tunes" standing of speciation by means change by of phyletic gradualism. natu ra I selectlon Punctuation of ------> <- Macromutation(s) in equilibrium su bpopu lations/ new envlronmental niches----> birth of Equilibrium multiple (species A does new not change) Population splits species $. into two new # environments Species A ffi Species A ffi Phyletic gradualism Punctuated equilibrium between species can never be detected but only drawn other living primates (see Chapter 3). Gould and El- arbitrarily. Darwin's theory of the origin of new species dredge (1977) contended that evolutionary change is is called phyletic gradualism (Figure 4.1). not a uniform process but rather that most of evolution- Arguing for phyletic gradualism made a lot of sense ary history has been characterized by relatively stable + in Darwin's day, given the kind of opposition he faced, species coexisting in equilibrium (plural, eqttilibria). Oc- and it has many defenders today. But some biologists casionally, however, that equilibrium is punctuated by have argued that phyletic gradualism does not explain sudden bursts of speciation, when extinctions are wide- a number of things that evolutionary theory must ex- spread and many new species appear. This view is called plain. In particular, it cannot explain the fact that a the theory of punctuated equilibrium (see Figure 4. I ). single fossil species often seems to have given birth to Gould and Eldredge claimed "that speciation is orders of a number of descendant species, a process called clado- magnitude more important than phyletic evolution as a genesis. What about those breaks in the fossil record mode of evolutionarychange" (116). that led Cuvier to argue that old species disappeared But if phyletic gradualism is not the rule, where do and new species appeared with what, from the point new species come from? Gould and Eldredge (1,977) of view of geological time, was extreme rapidity? Is argue that drastic changes in the natural environment this just the result of poor preservation of intermediate trigger extinction and speciation by destroying habitats forms, or do new species arise suddenly without having and breaking reproductive communities apart. When to go through any drawn-out intermediate stages? Or this happens, the populations that remain have both do the fossils that we thought represented intermedi- a radically modified gene pool and the opportunity to ate stages in the anagenesis of a single species actually construct a new niche in a radically modified environ- belong to several different species that resulted from the ment. When adaptive equilibria are punctuated this way, process of cladogenesis? speciation is still thought to require thousands or hun- In the early 1970s, these problems led evolutionists dreds of thousands of years to be completed. From the Stephen Jay Gould and Niles Eldredge to propose that perspective of ecological time, the process still appears the rate and manner of evolutionary change may differ "gradual," but from the perspective of geological time, at the level of genes, of organisms, and of species.
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