Development of posture and locomotion in free-ranging primates.

Postural and locomotor development is described for free-ranging groups of three monkey species: Macaca mulatta (rhesus macaque), M. radiata (bonnet macaque) and Presbytis entellus (hanuman langur). Behaviors are discussed in terms of infant-1, infant-2, juvenile, adult and elderly age groups. Analysis is based on high-speed motion pictures and videos. Infant-1 monkeys continually cling to their mother's ventral surface with strong hand and foot grasps. Independent motor coordination develops during the infant-2 period. The greatest postural and locomotor activity, both qualitatively and quantitatively, is achieved during the juvenile period. The adult and elderly periods are characterized by a progressive reduction in the variety and, eventually, quality of these motor abilities. Macaques and langurs differ, however, in the course of their behavioral development. These findings have implications for concepts of underlying neural mechanisms, indicate possible species differences in the development of these mechanisms, and demonstrate that the spectrum of volitional behaviors practiced by different age groups of free-ranging animals is broader than that observed in the laboratory setting.