Monkey performance: the development of bipedalism in trained Japanese monkeys.

A series of studies collaborated by the Suo-sarumawashi (Japanese Monkey Performance) revealed the potential for bipedalism in Japanese monkey. The long-term training which aimed at stable upright posture introduced marked lumbar lordosis in monkeys. This feature is comparable to the humans' condition not only morphologically, but also functionally. The developed lordosis was retained even in normal pronograde posture of the monkeys. Bone remodeling in the postcranial skeleton also evidenced functional adaptations for stresses induced by sustained bipedalism. Postcrania of a trained monkey showed highly increased structural strength of bones and relatively large articular dimensions. Despite such adaptations, modifications of hindlimb bones were rather distinctive from humans' condition. This indicates a compromise between functional necessity and genetically determined anatomy. The hindlimb of Japanese monkey seemed to be more specialized for quadrupedal locomotion in many aspects compared to the vertebral column.