The Coevolution of Human Hands and Feet

Abstract

Human hands and feet have longer, more robust first digits, and shorter lateral digits compared to African apes. 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 digital proportions coevolved in human hands and feet because of underlying developmental linkages that increase phenotypic covariation between them. Here we show that phenotypic covariation between serially homologous fingers and toes in Homo and Pan is not only higher than expected, it also causes these digits to evolve along highly parallel trajectories under episodes of simulated directional selection, even when selection pressures push their means in divergent directions. Further, our estimates of the selection pressures required to produce human-like fingers and toes from an African ape-like ancestor indicate that selection on the toes was substantially stronger, and likely led to parallel phenotypic changes in the hands. Our data support the hypothesis that human hands and feet coevolved, and 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.

Protective buttressing of the human fist and the evolution of hominin hands

“…The protective buttressing hypothesis is entirely compatible with the hypotheses that the derived proportions of human hands evolved: (1) in response to selection for increased precision and strength of grasping associated with manual manipulation (Napier, 1965;Marzke, 1983;Marzke, 1997;Susman, 1979;Susman, 1998) and (2) in response to selection on the foot for terrestrial locomotion, which resulted in coevolution of the hand (Alba et al, 2003;Rolian et al, 2010). It seems reasonable that selection for improved terrestrial locomotion, manual dexterity and fighting performance may all have played a role in the evolution of the proportions of the hands of hominins.…”

“…This is likely the result of selection for increased manual dexterity being released from the constraining influence of selection for performance in an arboreal environment (Alba et al, 2003). Alternatively, it has been suggested that the hand proportions of hominins may partially, or largely, be a pleiotrophic result of selection on the foot for terrestrial locomotion (Alba et al, 2003;Rolian et al, 2010). A third reason that human-like manual proportions appear in the fossil record coincident with evidence of habitual bipedalism is that sexual selection for improved fighting performance may have contributed to the evolution of both (Carrier, 2011;present study).…”

“…Recently, many of the derived proportions of the human hand have also been suggested to be a pleiotropic result of selection on the foot for terrestrial locomotion (Alba et al, 2003;Rolian et al, 2010). Hands and feet are serially homologous structures that share similar developmental pathways.…”

In vitrostrain in human metacarpal bones during striking: testing the pugilism hypothesis of hominin hand evolution

“…There are compelling reasons to suspect that the proportions of the hominin hand were influenced by selection on the foot for terrestrial locomotion (Alba et al, 2003;Rolian et al, 2010). Hand proportions may also have been influenced by other unidentified developmental constraints, as well as other aspects of selection and/ or by genetic drift.…”

“…These hand proportions are generally thought to be crucial to the great manipulative skills of humans and are usually associated with tool manufacture and use (Napier, 1962;Marzke, 1997;Susman, 1998;Young, 2003;Almécija et al, 2010Almécija et al, , 2015. Recently, many of the derived proportions of the hominin hand have also been suggested to be a pleiotropic result of selection on the foot for terrestrial locomotion (Alba et al, 2003;Rolian et al, 2010). There are clear arguments suggesting that both of these factors played a role in the evolution of hominin hand proportions.…”