Research from Dartmouth postdoc and Guarini alum Luke Fannin resolves a long-running debate over ape and monkey foot evolution.
Chimpanzees bend their ankles more than 45 degrees to climb trees safely. Mangabey monkeys barely bend their ankles at all — but new research shows they bend their midfoot by almost exactly the same amount.
The finding, recently published in the Proceedings of the National Academy of Sciences (PNAS), comes from Luke Fannin, Guarini ’25, who filmed wild sooty mangabeys climbing in Côte d’Ivoire’s Taï National Park with co-authors Carmen Pape and W. Scott McGraw of Ohio State University.
Fannin, a postdoctoral researcher with Dartmouth’s Dominy Lab and with the Wild Minds Lab at the University of St Andrews, measured mangabey midfoot dorsiflexion at 46 degrees on average during vertical climbs — nearly identical to chimpanzee ankle dorsiflexion, and slightly higher than the ankle dorsiflexion that was previously recorded in human hunter-gatherers who regularly climb.
“It’s a cool example of convergent evolution,” Fannin said. “Natural selection using a different anatomical means — ankle versus foot — to achieve the same fitness goal: a safe vertical climb.”
The result offers a new angle on a long-standing debate over whether early human ancestors had “ape-like” or “monkey-like” feet. Fannin’s data suggest the distinction may matter less than assumed: either foot type could support serious climbing.
Fannin, the Guarini School’s 2025 Hannah T. Croasdale Award winner and a Schmidt Science Fellow, will join Ohio State University’s department of anthropology as an assistant professor in the fall. Read more about the study on PNAS.org.
