Gestation generally requires 5-6 months, and a single infant is usually produced. Infants sometimes are dramatically different in coat color from adults and often have unpigmented hands and faces. That condition does not vary according to any systematic taxonomic scheme, and the period before full adult coloration varies. The functional significance of natal coats remains speculative.
Weaning is not an abrupt event but a process lasting over several months. Although many infants continue to nurse until the next sibling is born, most can feed themselves at 6 months but remain socially dependent on their mothers and return to their mothers when disturbed and to sleep. Young infants are carried ventrally, and only in some species (e.g., baboons and geladas) do they predictably transfer to dorsal carriage after the first 2 or 3 months (Altmann 1980; De Vore 1963).
After the first year, juvenile animals can become more and more involved in peer groups, especially males. Several years might pass before puberty occurs. Puberty is also not an event but a process, and the gradual change to full adult status can take several years, a period sometimes recognized as the period of adolescence and subadult states (Bernstein and others 1991). First menstruation can precede fertility by a year or more and often occurs when a female is only half her full adult weight and before she sheds all her milk dentition (deciduous teeth). Males can achieve fertility long before they normally participate as adult males in breeding. It is during this time that males often transfer out of their natal group.
Cercopithecine monkeys are relatively easy to breed in captivity, and infants can be produced under almost any condition that allows a fertile male access to an ovulating female. Early rearing conditions, as discussed in Chapter 3, will have a substantial impact on the social development of infants and later reproductive competence. In general, infants reared in social contexts that approximate those of natural troops have the best prognosis as future breeders.
Studies of cognition using Old World monkeys have generally focused on macaque subjects. Rhesus monkeys have been the subject of numerous perceptual studies, and information on visual capacities is summarized in De Valois and Jacobs (1971). (See also Bayne and Davis 1983 and Leary and others 1985.)
Whereas Old World monkeys are not generally recognized as tool-users, they are highly skilled in manipulating objects. They are adept at numerous puzzle problems (e.g., bent wire) and readily learn to use joysticks to perform video tasks (Washburn and Rumbaugh 1992). Once skilled in a task, they will work at it with persistence, not needing to be rewarded with food to sustain their performance (Harlow and others 1950; Washburn and Rumbaugh 1992), but they prefer to work on tasks of their own selection. Many activities originally reinforced with food seem to become reinforcing in themselves, and monkeys will often work a familiar task, ignoring the food rewards offered.