Although both the thumbs and big toes of humans are longer and stronger than those of African apes, the different abilities they confer have led scientists to believe that the digits evolved independently. However, it seems that human hands and feet may have evolved together after all.
Campbell Rolian of the University of Calgary in Canada and his colleagues compared hand and foot traits from 202 adult humans and 89 chimpanzees. They found that the traits vary together in each species; for example, long thumbs correlate with long big toes. The researchers then simulated how selection pressure on one extremity affects the other's shape. Feet and hands still varied together, which suggests that they coevolved.
The authors propose that the evolution of long, strong big toes for bipedalism caused similar changes in the thumb, which may have improved dexterity and led to the use of stone tools.
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Evolution: All thumbs and toes. Nature 463, 712 (2010). https://doi.org/10.1038/463712d
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DOI: https://doi.org/10.1038/463712d
