By Meilan Solly
The earliest hominins split their days between the trees and the ground, alternately adopting ape-like tree-swinging behaviors and human-like bipedalism, or walking upright on two feet—albeit in a crouched position. By the time Lucy and her Australopithecus afarensis relatives arrived on the scene some four million years ago, bipedalism had largely overtaken tree-dwelling, but according to a study published in the Proceedings of the National Academy of Sciences, these human ancestors likely lacked a key evolutionary adaptation: the rigid big toe.
BBC News’ Angus Davison reports that the new findings suggest the big toe, which enables humans to push off of the ground while walking and running, was one of the last parts of the foot to evolve.
“It might have been last because it was the hardest to change,” lead author Peter Fernandez, a biomedicist at Milwaukee’s Marquette University, tells Davison. “We also think there was a compromise. The big toe could still be used for grasping, as our ancestors spent a fair amount of their time in the trees before becoming fully committed to walking on the ground.”