Punch force in bipeds

“The structure of the human fist provides buttressing that increases the stiffness of the second MCP joint by fourfold and, as a result of force transfer through the thenar eminence, more than doubles the ability of the proximal phalanges to transmit ‘punching’ force. [Quadrupeds like] Chimpanzees are poorly suited to human-like buttressing by the thenar eminence and thumb. Additionally, both the thenar eminence and thumb are relatively small in chimpanzees, further limiting the capacity of the first digit to provide buttressing of the fist. [...] The evolution of human-like manual proportions were largely coincident with the evolution of habitual bipedalism. 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”

From *Protective buttressing of the human fist and the evolution of hominin hands*, David R. Carrier, Professor of Comparative Biomechanics at University of Utah & Michael H. Morgan, MD. doi: 10.1242/jeb.075713