Postcranial skeleton of a macaque trained for bipedal standing and walking and implications for functional adaptation.

The postcranial skeleton of a Japanese macaque that had been trained for bipedalism over an 11-year period was studied. Considerable modifications in the hindlimb bones caused by bipedal postural and locomotor behaviour were observed. Changes occurred in joint morphology, articular dimensions and shape-dependent strength of long bones, reflecting the causal relationship between function and morphology. However, the conditions under which the modifications are developed are somewhat different from those in humans, as the monkey's bipedalism is distinct from that of humans. The modifications seem to result from a compromise between functional requirements and the genetically determined anatomy of the essentially quadrupedal monkey.