Understanding Climate's Influence on Human Evolution (2010) / Chapter Skim
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2 Existing Understanding of the Environmental Context for Hominin Evolution
2 Existing Understanding of the Environmental Context for Hominin Evolution
Pages 16-43
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From page 16... ...
Although there is ongoing scientific research in each of these disciplinary areas to address the myriad scientific uncertainties and inconsistencies that will always exist in predominantly data-limited fields, the overview summaries presented here will not attempt to analyze or present the details of these uncertainties and inconsistencies. MAJOR EVENTS IN HUMAN EVOLUTION The pattern and process of human evolution can be described on the basis of a combination of comparative anatomy, the fossil record, and primate and human genetics (Kimbel and Martin, 1993)
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From page 17... ...
17 EXistiNg UNdERstANdiNg FIGURE 2.1 Highly simplified summary of hominin evolution over the past 8 Ma -- the numerous terminating "twigs" schematically illustrate evolutionary "dead-ends." panzees, humans -- is firmly established, the dates of these branching splits are less certain (Kumar et al., 2005)
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From page 18... ...
. East Africa Rift System shown in purple.
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From page 19... ...
A related hominin -- A. africanus -- is well known but poorly dated from South African cave sites.
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From page 20... ...
By about 2.0 Ma, fossils of early Homo and sites with animal bones and stone tools are relatively common. However, it is important to emphasize that although these hominins have been assigned to the genus Homo, this does not imply that they were very much like modern humans in anatomy and behavior.
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From page 21... ...
. The remains of Homo habilis are known from East Africa (Tobias, 1991; Wood, 1991)
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From page 22... ...
8. The development of the Acheulean stone tool culture at about 1.6 Ma.
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From page 23... ...
Together, these produced the interaction of atmospheric air masses with topographic and oceanic effects that controlled the specific regional climates that impinged on evolving hominins. The history of East African tectonics and orography is dominated by the development of the East African Rift System (Tiercelin and Lezzar, 2002)
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From page 24... ...
. Rainfall throughout most of the East African rift valley is derived from moisture off the Indian Ocean, and is strongly influenced by regional differences in sea surface temperatures (Hastenrath et al., 1993)
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From page 25... ...
The sparse existing records broadly support the view that East African climate changed from warmer, wetter conditions in the late Miocene and early Pliocene to a more seasonallycontrasted, cooler, and drier (and perhaps more variable) climate during the late Pliocene (after ~3 Ma)
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From page 26... ...
The Lake Malawi basin, at the southern end of the East African Rift Valley, was relatively
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From page 27... ...
; (C) East African soil carbonate δ 13C data (Cerling, 1992; Cerling et al., 1994; Wynn, 2004)
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From page 28... ...
The Mediterranean sapropel record provides some of the most compelling evidence that North African climate has responded to orbital precession regula tion of monsoonal climate since at least the late Miocene (Hilgen, 1991; Hilgen et al., 1995; Lourens et al., 1996; Kroon et al., 1998)
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From page 29... ...
. The right panel shows, on an outcrop scale, ap proximately 50 sapropel layers of late Miocene age (~9 Ma)
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From page 30... ...
The adaptations that are evident in the faunal assemblages recovered with hominins provide a valuable line of evidence that can be used to reconstruct paleoenvironments and track environmental change. One of the best ways to reconstruct the habitat and ecosystems in which hominins lived is to analyze the fossil flora associated with hominin sites -- the pollen, leaf fossils, and other plant parts.
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From page 31... ...
Two rhino species are found at almost all African hominin localities, and Eurasian rhino species have been recovered with Neanderthals and modern humans in Europe and with modern humans in North Africa. Both African rhino species can be found in the same types of savanna habitats, although the Black Rhino generally prefers more bush and tree cover.
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From page 32... ...
There were long-term changes in the seasonal distribution of rain in the later Miocene, with leaf analysis showing that the length of dry seasons increased by many months in the middle to late Miocene, and then shortened again near the Mio-Pliocene boundary (Jacobs and Deino, 1996; Jacobs et al., 1999)
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From page 33... ...
indicate that some of the fauna, which were adapted to more open habitats, were consuming grasses that grow in a much cooler environment than is present in Africa today. Consequently, there appear to have been heterogeneous landscapes during the late Miocene of East Africa, including forests, woodlands, and grasslands.
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From page 34... ...
The adaptations evident in the fossil faunas show a great deal of variability with respect to habitat type, but there are more arboreal, and thus forest-associated, animals found in the late Miocene than the middle Pliocene. Through the early to middle Pliocene there is also evidence for environmental events that apparently caused species isolation not only in distant parts of the continent, but also between some of the East African sites.
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From page 35... ...
robustus fossils tended to occur only during relatively arid intervals, when sediments and bones more easily entered subterranean caves, and it has been proposed that southern Africa, in general, represented a more stable landscape than those associated with East African hominins (de Ruiter et al., 2009)
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From page 36... ...
Second, the fauna recovered at the Neanderthal localities in the Middle East are the same as the fauna recovered with Homo sapiens from the same area, although there are indications that Neanderthals focused on exploiting fewer species, whereas H sapiens used a broader range of animals as food (Reed and Fish, 2005)
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From page 37... ...
New technologies variously involving the use of stone, the intensified hunting of animals and reaping of wild plants, and the potential to build shelters, to clear landscapes using fire, and to play a role in extinctions of other organisms, together with the developing ability to communicate and plan coordinated activity -- all set the stage for a fundamental change in human ecology involving the transition from mobile hunting-gathering to food production and the emergence of human-dominated ecosystems. Framed in the context of late Pliocene and Pleistocene climate change, the capacity to make tools, exploit new foods, control fire, build durable shelters, and organize complex social activity reflect evolutionary responses that enabled human ancestors to survive and adapt to environmental risks and uncertainties (Potts, 1996b, 1998)
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From page 38... ...
Innovations in stone technology began to occur at a slightly faster rate after 300 ka, as smaller, more diverse, and easily transported tool kits began to replace handaxes and other large cutting tools that had dominated stone technology for the previous 1.3 million years. Early populations of Homo sapiens had developed the capacity to invent specialized tools (e.g., projectile points by at least 105 ka, and bone harpoon points by ~80 ka)
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From page 39... ...
These types of objects indicate an ability to code information symbolically -- the essence of language. These artifacts first occur in the African archeological record between 285 ka and 70 ka, associated with the early evolution of Homo sapiens (Barham, 2002; Henshilwood et al., 2002; d'Errico et al., 2005)
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From page 40... ...
months in the middle to Mediterranean. shoulders, • First late Miocene, and then drop in global atmospheric CO2 concentrations.
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From page 41... ...
species disappeared • After 2.8 Ma: Expanded ampli- from East African tudes of North African wet-dry record. cycles.
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From page 42... ...
• 1.8-1.6 Ma: Greatest expansion cycles and Homo with smaller • 790 ka: of C4 vegetation in East Africa. shift to 100-ky cheek teeth, larger Oldest definite cyclicity.
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From page 43... ...
sapiens in refugia during MIS-6. • ~60 ka: Dispersal EXistiNg UNdERstANdiNg of modern H
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