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Downclimbing and the evolution of ape forelimb morphologies.
Luke D Fannin1,2, Mary S Joy1, Nathaniel J Dominy1,3
1Department of Anthropology, Dartmouth College, Hanover, NH 03755, USA.
Royal Society Open Science
|September 8, 2023
Summary
Ape forelimbs exhibit greater flexibility, particularly during vertical descent (downclimbing). This study reveals larger shoulder and elbow joint angles in chimpanzees and sooty mangabeys during downclimbing, highlighting its evolutionary significance.
Area of Science:
- Primate locomotion
- Comparative biomechanics
- Evolutionary anthropology
Background:
- Hominoid primates (apes) possess more flexible forelimbs than monkeys, especially at shoulder, elbow, and wrist joints.
- Previous kinematic studies found minimal differences in forelimb joint angles between apes and monkeys during vertical ascent (upclimbing).
Purpose of the Study:
- To investigate the influence of climbing directionality on forelimb kinematics in wild chimpanzees (Pan troglodytes) and sooty mangabeys (Cercocebus atys).
- To test the hypothesis that vertical descent (downclimbing) is a key activity driving forelimb adaptations in apes.
Main Methods:
- Field-based kinematic analysis of wild chimpanzees and sooty mangabeys during vertical climbing.
- Quantification of forelimb joint excursion angles (shoulder, elbow) during both upclimbing and downclimbing.
Main Results:
- Both chimpanzees and sooty mangabeys exhibited larger shoulder and elbow joint angles during downclimbing compared to upclimbing.
- The magnitude of increased joint angles during downclimbing was most pronounced in chimpanzees.
Conclusions:
- Downclimbing plays a significant functional role in primate locomotion, influencing forelimb joint mobility.
- These findings support hypotheses linking vertical climbing, particularly descent, to the evolution of ape forelimb anatomy, including the human lineage.
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