Did Lucy Walk, Climb, or Both?
Much has been made of our ancestors “coming down out of the trees,” and many researchers view terrestrial bipedalism as the hallmark of “humanness.” After all, most of our living primate relatives—the great apes, specifically—still spend their time in the trees. Humans are the only member of the family devoted to the ground, living terrestrial rather than arboreal lives, but that wasn’t always the case. The fossil record shows that our predecessors were arboreal habitués, that is, until Lucy arrived on the scene.
About 3.5 million years ago in Africa, this new creature, Australopithecus afarensis, appeared; Lucy was the first specimen discovered. Anthropologists agree that A. afarensis was bipedal, but had Lucy and her legions totally forsaken the trees? The question is at the root of a controversy that still rages. “Australopithecus afarensis possessed a rigid ankle and an arched, nongrasping foot,” write Nathaniel Dominy and his co-authors in Proceedings of the National Academy of Sciences. “These traits are widely interpreted as being functionally incompatible with climbing and thus definitive markers of terrestriality.”