DeSilva videotaped wild chimpanzees — our closest living animal relatives — in Uganda to study their bodies while climbing. He measured the angle of dorsiflexion, or how far the ankle could rotate so that the toes point upward, and found that chimps can make much more extreme ankle rotations than modern humans.
To investigate whether early hominins were more like modern humans or chimpanzees, DeSilva analyzed the ankle bones in fossils of human ancestors at various times from 1.5 million to 4 million years ago. He discovered that early humans during this span have dorsiflexion ranges similar to those of modern humans, and couldn't have climbed trees in quite the same way as chimps do, if they climbed at all.
Randy Susman will have something to say about this, I am sure.