Meeting Abstract

P2.110  Tuesday, Jan. 5  Did human fingers and toes coevolve? ROLIAN, Campbell*; LIEBERMAN, Daniel; HALLGRIMSSON, Benedikt; University of Calgary; Harvard University; University of Calgary campbellrolian@gmail.com

Human hands and feet have similarly derived digital proportions compared to African apes, including longer, more robust first rays, and shorter lateral rays. These similarities are often assumed to be independently-evolved adaptations for manipulative activities and bipedalism, respectively. However, hands and feet are serially homologous structures that share virtually identical developmental blueprints, raising the possibility that some aspects of digital morphology coevolved in human hands and feet because of underlying genetic/developmental linkages that increase phenotypic covariation between them. Here we show that magnitudes of covariation between homologous traits in the feet and hands of Homo, and especially Pan not only exceed the average level of covariation across all traits, but also exceed covariation magnitudes within these structures. Further, when subjected to episodes of simulated directional selection, this increased covariation causes the fingers and toes to evolve along highly parallel trajectories, even when selection pressures push their means in divergent directions. Our estimates of the selection pressures required to produce human-like fingers and toes from a chimpanzee-like ancestor indicate that selection on the toes was substantially stronger, and likely led to parallel phenotypic changes in the hands. Our data not only support the hypothesis that human hands and feet coevolved, but also suggest that the evolution of long robust big toes and short lateral toes for bipedalism led to changes in hominin fingers that may have facilitated the emergence of stone tool technology.