Sexual behavior of the arl colony chimpanzees.

Abstract

This is a report of studies of the sexual behavior of the ARL Colony chimpanzees from July, 1966, through August, 1967. The ARL Colony has an innovation designated the DPS Chimpanzee Consortium which permits the containment of social groups of chimpanzees on 30 acres of New Mexico desert. The solicitation, mounting and copulatory behavior of the consortium animals was similar in form to that reported in field studies. However, the incidence of both copulatory and masturbatory behavior was much higher than in the wild. In spite of this overall high incidence of copulatory behavior, three of the five adult males, who were cage-reared and presumably sex-segregated until maturity, were not observed to copulate when they had the opportunity to do so. However, they seemed to show no reduction in sexual drive. Two masturbated frequently and all three practiced perverse sexual acts. Both adolescent and juvenile males were interested in estrous females and actively solicited, mounted and copulated with them frequently. Three of the four adult consortium females tended to avoid copulation. However, this reluctance of adult females to copulate could be overcome by a large aggressive male and all of the adult consortium females became pregnant. It is hypothesized that feral-born but cage-reared, sex-segregated chimpanzees are capable of normal mating behavior if they are given an opportunity to experiment and learn before a critical period occurring during late adolescence and early adulthood. An adult who has passed this critical period is either unable to learn to copulate or to orient adequately toward an estrous female, although the sexual drive is manifested in masturbation and other ways. There was also a higher incidence of nonsexual mounting and presenting by consortium animals of both sexes than has been reported in the wild. The older females frequently “mothered” small juveniles, but most noteworthy was the fact that many male chimpanzees also interacted with small juveniles in a maternal-like manner. Unlike wild females, the consortium females frequently displayed aggressive dominance behavior toward males as well as other females. The consortium females were also the frequent victims of male aggression, which has been rarely noted in the field. Hypotheses to explain these apparent gender role shifts are offered.