Human Ancestors Were Not Knuckle-Walkers

This ScienceDaily piece reports on a recent paper by Tracy Kivell and Daniel Schmitt, in PNAS. Despite decades-worth of argument, they say, we have not yet resolved whether or not human bipedalism evolved from a terrestrial knuckle-walking ancestor, or a more generalized arboreal ape ancestor. For the first time, they have minutely compared wrist morphology among a number of primate species and conclude that two different forms of knuckle-walking have independently evolved - an extended wrist posture with bony stops to prevent the wrist from over-bending, in chimps, and a locked 'columnar' stance in gorillas where the arms and wrists extend straight down. The duo point out that there are a number of subtle differences in wrist morphology between humans and chimps which suggest to them that we did not evolve from a chimp-mode knuckle-walker but a more generalized arboreal primate ancestor.