3 - The biology of human migration: the ape that won’t commit?

Summary

Introduction

Humans occupied almost all global regions prior to the emergence of agriculture and subsequent technological evolution, emphasizing the extraordinary biological and behavioral versatility of our species. Understanding this versatility may shed light on the past colonizing activities of our species, and on the selective pressures that favored the emergence of such adaptablity. The same plasticity is increasingly appreciated by biomedical research, investigating our present vulnerability to chronic degenerative disease in the expanding obesogenic niche.

The prevailing view in evolutionary anthropology has long been that the primary cause of between-population human phenotypic variability was genetic response to natural selection. As we enter the post-genomic era, it is increasingly common to search for genetic signatures of natural selection using genome-wide scans (Harris and Meyer, 2006; Laland et al., 2010). Comparisons with other apes indicate, however, that contemporary humans are characterized by a relatively high degree of genetic unity, given our unprecedented geographical distribution (Bakewell et al., 2007; Gagneux et al., 1999). Further studies suggest that human genetic adaptation appears to occur less through strong selection on novel alleles, and more through subtle alterations in the frequency of existing alleles (Hancock et al., 2010a, 2010b). There is also mounting evidence that a proportion of the genetic component of human phenotypic diversity can be attributed to random or neutral evolutionary mechanisms rather than natural selection (Harvati and Weaver, 2006; Roseman, 2004).