Tectonics and Human Evolution
King, Geoffrey, Bailey, Geoff, Antiquity
The dominant conception of human origins during the past five decades has been one of a transition from vegetarian apes living mainly in trees to ground-dwelling humans exploiting the large game herds of the African savannah in response to increased global aridity and reduction of tree cover. The modern consensus is that this process first occurred in Africa, beginning at least as early as 4.5 million years ago with Ardipithecus ramidus, or perhaps earlier in the light of the recent finds in the Chad basin (Brunet etal. 2002) and Kenya (Senut et al. 2001), evolving through the Australopithecines, and leading to the evolution of the genus Homo after 2.5 Ma. The emergence of Homo erectus (or H. ergaster as some prefer) at ~1.8 million years ago, saw a capacity to range widely over open terrain, the widespread use of stone tools, a greater dependency on animal protein whether by scavenging or hunting, and dispersal more widely within and beyond Africa (Cachel & Harris 1998; Delson et al. 2000; Klein 1999).
There are, however, some longstanding difficulties with the ecology of this process. As Carl Sauer presciently observed over 40 years ago:
'The various kinds of primates can be described as to their proper habitats: for early man [sic] there is no such agreement and the most familiar assignment of him to living in savanna plains is perhaps the least likely. He was not specialised for predation; he was inept at flight or concealment; he was neither very strong nor fast.' (Sauer 1962: 42)
The modern control of large plains is in fact a very recent development in human prehistory, dependent on the domestication of riding animals. The alliance between the horse and modern humans took place on the plains of Asia as late as 6000 years ago, and rapidly spread throughout Eurasia in subsequent millennia, followed in historical times by the conquest of the plains of the Americas and Australia (Clutton-Brock 1999; Keegan 1993). In more arid regions the camel played a comparable role over a similar time range. Even the hunting of large herbivore herds on the steppe-tundra of Pleistocene Europe and the grasslands of the Great Plains in North America seems to have appeared relatively late in the prehistoric sequence and perhaps in some regions only as a marginal and specialised adaptation (Dixon 2001). In historical times and in many places, indigenous populations were driven to the hills where the man-horse combination of their enemies could not penetrate. In modern conflict, motorised war machines have replaced the horse so that only in mountainous retreats, rough terrain or urban streets, can individuals or small bands hope for tactical advantage. An animal with our body form is disadvantaged in many ways in flat terrain but well adapted to morphologically complex environments, including evermore elaborate artificial structures. Leaving the trees to live on the savannah plains seems a paradoxical if not improbable strategy for the survival of early human populations, exposing them to greater risks and fiercer competition with better-adapted animals.
For Sauer, the resolution of this paradox lay in shorelines and coasts as environments most likely to select for early human characteristics such as bipedalism and tool-making, a proposal difficult to reconcile with the pattern of the currently available evidence (but see Erlandson 2001). For others, the persistence of trees, even as patchy resources, is cited as a potential refuge from danger. The development of bipedalism early on in the process of human evolutionary divergence, faunal and palaeovegetational associations suggesting well-wooded conditions in the period from about 4 to 2.5 million years ago and anatomical features in Australopithecines indicating continued adaptation to tree living lend some support to such a notion (Reed 1997; Rogers et al. 1994).
Here, we develop an alternative hypothesis, which focuses on complex topography and the role of active tectonics. …