"It was shocking," said DeSilva, an assistant professor of anthropology at Boston University. "I mean, 80 years of research has argued that humans don't do this."

Or at least 80 years in DeSilva's field. Last month, when he published his study in the American Journal of Physical Anthropology, two podiatrists said they'd seen a similar variation in patients' feet. But they weren't familiar with the term "midtarsal break"—suggesting, DeSilva said, the need for "collaboration with as many different disciplines as possible."

DeSilva connected his unexpected discovery—he was originally researching variations in the foot's arch—to a two-million-year-old fossil human called Australopithecus sediba. DeSilva's research suggests it moved like today's apes, which have bendy feet unbound by bones. Chimps, for instance, tumble