The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Changes in long bone strength correspond to shifts in locomotor behavior during development in chimpanzees (Pan troglodytes)


Anthropology, University of Michigan

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Changes in locomotion are likely to be reflected in bone strength and shape since stress placed on bone through habitual behaviors during early development can cause significant responses. Previous research has shown that when humans go through the abrupt shift in locomotion from crawling to walking at about one year of age, there is a corresponding increase in femoral to humeral strength. Chimpanzees likewise go through a locomotor shift during development, transitioning (albeit gradually) from primarily suspensory behavior to predominantly quadrupedal knuckle-walking. It is therefore predicted that in chimpanzees, initial forelimb usage will increase humeral diaphyseal strength over that of the femur, and that later, hindlimb loading during quadrupedalism will lead to greater femoral strength.

This hypothesis was tested using skeletons of wild-caught individuals from museum collections. Long bone geometric properties were derived from micro CT scans of the midshaft of the humerus and femur. Principal Moments of Area (i.e. Imax /Imin) and Second Moments of Area (J, Z) were calculated from the images using BoneJ (version 1.3.2).

As predicted based on locomotor data, this study found that very young chimpanzees have stronger humeri than femora with a trend of increasingly stronger femoral to humeral second moments of area over time. Changes in femoral to humeral strength were more subtle compared to the trend found in humans, but this corresponds to a more gradual shift in locomotion, and nonetheless illustrates a comparable relationship between behavioral and morphological development.

This study was funded by the NSF and the Leakey Foundation.

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