1Anthropology, City University of New York, Graduate Center, 2New York Consortium in Evolutionary Primatology, NYCEP, 3Evolutionary Anthropology, Duke University, 4Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, 5Department of Anthropology, Washington University in St. Louis, 6Congo Program, Wildlife Conservation Society, 7Global Health Institute, Duke University
April 16, 2020 , Platinum Ballroom
Arboreal behavior is thought to be constrained in humans and earlier hominins compared to living apes. Humans have proportionally shorter arms and less arm muscle mass than chimpanzees and gorillas, which could reduce strength and endurance and limit climbing. Here we set out to investigate the determinants of grip strength and endurance in a controlled sample of n=28 U.S. rock climbers, and test whether strength limits tree climbing in a sample of n=15 Mbendjele foragers from the Republic of Congo. Compared to non-climbers, rock climbers had greater maximum grip strength and better endurance, measured as time to failure at 70% maximum voluntary grip force. Pre-climb maximum grip strength was positively correlated with body mass (p<0.05). After 27 meters of ascent and 27 meters of descent on a vertical wall, mean strength and endurance decreased by 15±2 % and 43±7 % respectively. Both measures recovered to pre-climb values after 15 minutes of rest. In Mbendjele foragers, we found that men ascended an average of 52±4 meters per day when collecting arboreal resources, significantly more than Western lowland gorillas (29 meters/day) inhabiting the same forests, but significantly less than chimpanzees (102 meters/day). Mbendjele men’s grip strength exceeded that of U.S. rock climbers and was not significantly lower after tree climbing (p=0.39). Together, these results show human foragers can accrue daily climbing rates comparable to other African apes without approaching the limits of arm strength or endurance. We discuss implications for understanding the ecology and evolution of living hominoids and fossil hominins.
This project was partially funded by the Leakey Foundation (general grant) and the National Science Foundation (grants 1732194 and 1646736).