Downclimbing and the evolution of ape forelimb morphologies

Hominoids (non-human apes and hominins) are distinct from cercopithecoid monkeys in possessing more flexible forelimb joints, including high excursion angles at the shoulder and elbow. Both vertical climbing and forelimb suspension have been hypothesized to explain these skeletal differences, but field kinematic studies have found few differences in forelimb excursion during vertical climbs between chimpanzees and monkeys. Previous studies have focused largely on ascent (upclimbing) mechanics, while kinematic strategies employed during descents (downclimbs) are usually ignored. Here, we test the role that vertical climbing directionality plays in patterns of forelimb joint kinematics in wild populations of chimpanzees (Pan troglodytes) and sooty mangabeys (Cercocebus atys). We found that vertical descent produces greater degrees of elbow extension and shoulder flexion in chimpanzees compared to their vertical ascents, a pattern not shared with mangabeys. Chimpanzees used their forelimbs..., ,