Craniofacial Variation and Developmental Divergence in Primate and Human Evolution

Many questions about developmental divergence in human (and non-human primate) evolution can be fruitfully explored through investigation of the extant primate phenotype. Here I discuss two approaches that use patterns of variation in extant primates to consider hypotheses of 'tinkering' both in their own lineages, and also as applied to the fossil record of human evolution. In the first, I show how comparisons of ontogenetic morphological integration in extant humans and apes can be used to consider the developmental underpinnings of the morphological change seen in the transition from the prognathic australopith face to the relatively smaller, orthognathic Homo face. In the second approach, I demonstrate how studies of craniofacial variation in hybrid baboons can be used as models for considering developmental divergence in Plio-Pleistocene primates, including fossil hominins. Of particular interest is the fact that unusual non-metric dental and sutural variation in these hybrids appears to be a sensitive indicator of evolutionary developmental divergence. Future studies would profit from focusing on the breadth and especially the overlap of morphological variation among extant primate taxa in order to determine the degree to which underlying genetic similarity in functional regions, and difference in regulatory regions, explains the variable primate phenotype.