Monkey Foot Flexibility Challenges Assumptions About Early Human-Chimp Ancestor’s Climbing

A team from Ohio State University captured high-resolution footage of wild sooty mangabey monkeys in the Taï Forest of Ivory Coast, documenting their ability to climb straight tree trunks by flexing the middle part of their feet. Measurements showed as much as 46 degrees of mid-foot bending, a range comparable to the 45-degree ankle lift of chimpanzees and far beyond the 20-degree limit of human ankles. Study co-author W. Scott McGraw noted that this demonstrates functional equivalence in climbing despite different foot anatomies.

Luke Fannin emphasized that fossil-based assumptions linking foot shape to climbing ability need revision, as monkeys without chimp-like ankles can still climb vertically. The research, appearing in PNAS, suggests that the last common ancestor of humans and chimpanzees may have possessed a more monkey-like foot yet still been an adept arboreal climber. Funding came from institutions including Dartmouth College, the Explorer's Club, the U.S. National Science Foundation, and others, with former undergraduate Carmen Pape also contributing.