Reference Work Entry

Handbook of Paleoanthropology

pp 1441-1481


4 Role of Environmental Stimuli in Hominid Origins

  • Elisabeth S. Vrba


Environmental stimuli have influenced the evolution of hominids and other mammals at the levels of ontogeny, organismal adaptation, and speciation. I review some agreement which has emerged— as well as persistent debates— on the issue of environmental linkages to hominid adaptation. I discuss some current hypotheses which link physical change, adaptation, and speciation in general and in hominids in particular (including hypotheses on the role of ecological specialization and generalization, the coordinated stasis and variability selection hypotheses, habitat theory and the turnover pulse hypothesis); and revisit some persistent debates (such as on whether or not there was mammalian species’ turnover in the Turkana Basin during the Plio-Pleistocene). The relation of hominid evolution to the recent finding of several turnover pulses coincident with global cooling trends in the 10-Ma Recent record of all African larger mammals is considered. One example of hypotheses which address issues of environmental stimuli of ontogenetic evolution is the heterochrony pulse hypothesis: the generative properties shared among lineages can result not only in coherence of morphological changes but also in a strongly nonrandom timing of heterochrony events, as diverse lineages respond in parallel by similar kinds of heterochrony to the same environmental changes. I give some mammalian and hominid examples involving body enlargement by prolongation of growth, and attendant “shuffling” of body proportions including relative increase in brain volume, namely encephalization.