Bruce Bagemihl - Biological Exuberance

Transgendered or intersexual Common Chimpanzees occasionally occur as well. One individual who was physically and anatomically a male was chromosomally a mosaic, combining both the male (XY) and the female (XX) chromosome types.

Frequency: The prevalence of same-sex activities between male Common Chimpanzees is highly variable. Mounting between males constitutes anywhere from 1–2 percent to one-third or one-half of the behaviors involved in reassurance, enlistment of support, and other activities during or following conflicts. Kissing and embracing between males constitute from 12–30 percent of such interactions (depending on the population). Overall, 29–33 percent of all mounting activity occurs between males. Less detailed information is available for females, but a similar range of frequencies is probably involved. Other homosexual activities such as bumprump and oral or manual stimulation of genitals have so far been observed largely in captivity, where they may be fairly common.

Orientation: Most adult male Chimpanzees that participate in same-sex mounting, genital handling, or other activities also mate with females. Younger (adolescent or juvenile) males, who occasionally engage in such activities as fellatio or mutual genital rubbing, may be less heterosexually involved. In some populations, virtually all adult males participate in same-sex mounting, although such behavior may constitute anywhere from one-fifth to three-quarters of an individual’s mounting activity. Females that participate in same-sex activities are also usually functionally bisexual, copulating with males as well. However, a few individuals appear to be more exclusively homosexual: one female, for example, refused to mate with males and was only involved sexually with other females for many years. She even developed a close relationship with another female and her offspring. Socially, she occupied an intermediate position between the male and female subgroups: she often associated with males and “ganged up” with them against other individuals, but she also maintained primary bonds with females and sometimes even defended them against the sexual advances of males. Later, however, she also mated with males.

Common Chimpanzees engage in a variety of nonprocreative heterosexual practices that parallel their same-sex behaviors. Heterosexual oral sex involves both cunnilingus (males licking the vagina or mouthing the labia) and fellatio (females sucking or nuzzling the penis). Manual stimulation of the genitals also occurs: males sometimes insert a finger into the vagina (the female may then move his hand in order to stimulate herself), while females occasionally fondle their partner’s penis. In addition, bumprump takes place between males and females (sometimes including thrusting and scrotum handling), and both sexes masturbate—stimulating their own genitals manually or with various implements. Some males even perform AUTO-FELLATIO, i.e., they suck their own penis. Male Chimpanzees occasionally mount females without achieving penetration or ejaculate after withdrawing; they may also mate with females who are not in heat. Another form of nonprocreative sex is copulation during pregnancy: some females participate in heterosexual activity for 75–80 percent of the time that they are pregnant. In addition, male Chimps have been observed copulating with female Savanna Baboons in the wild.

When females are in heat, they typically mate numerous times and with multiple partners—as often as six or more times a day (sometimes with two to seven males in quick succession), for a total of several hundred times for each baby conceived. In some cases, though, heterosexual relations are less than amicable: males occasionally try to force females to consort and mate with them by threatening and even violently attacking them, and females often display “blunt refusal” or “abhorrence” reactions toward the advances of older males. Copulations are often interrupted or harassed by other Chimps trying to disrupt the sexual activities. In addition, infanticide and even cannibalism occasionally occur. For example, infants conceived outside the community may be killed by the resident males, and most females mate with males belonging to their own social group. However, in some populations a considerable number of females seek partners outside their group, engaging in “furtive” matings with them. In one community, for example, more than half of all offspring were sired by males living in other groups.

Although incestuous matings between adults are not common, mothers engage in sexual activity with their infant sons fairly often. Young females typically experience a one-to-three-year period of ADOLESCENT STERILITY after their first menstruation, during which time they mate heterosexually without conceiving. Some adult females practice a unique form of birth control: they simulate the contraceptive effect of nursing by stimulating their own nipples, in some cases preventing pregnancy for up to ten years. Females may also experience a postreproductive or “menopausal” period later in their lives, lasting up to two years (about 4–5 percent of the maximum life span). During this time they often continue to mate, accounting for up to 20 percent of all female sexual activity in a group.

* asterisked references discuss homosexuality/transgender

*Adang, O. M. J., J. A. B. Wensing, and J. A. R. A. M. van Hooff (1987) “The Arnhem Zoo Colony of Chimpanzees Pan troglodytes: Development and Management Techniques.” International Zoo Yearbook 26:236–48.

*Bingham, H. C. (1928) “Sex Development in Apes.” Comparative Psychology Monographs 5:1–165.

Bygott, J. D. (1979) “Agonistic Behavior, Dominance, and Social Structure in Wild Chimpanzees of the Gombe National Park.” In D. A. Hamburg and E. R. McCown, eds., The Great Apes, pp. 405-28. Menlo Park, Calif.: Benjamin Cummings.

*———(1974) “Agonistic Behavior and Dominance in Wild Chimpanzees.” Ph.D. thesis, Cambridge University.

Dahl, J. F., K. J. Lauterbach, and C. A. Duffey (1996) “Birth Control in Female Chimpanzees: Self-Directed Behaviors and Infant-Mother Interactions.” American Journal of Physical Anthropology supp. 22:93.

*Egozcue, J. (1972) “Chromosomal Abnormalities in Primates.” In E. 1. Goldsmith and J. Moor-Jankowski, eds., Medical Primatology 1972, part I, pp. 336–41. Basel: S. Karger.

Gagneux, P. , D. S. Woodruff, and C. Boesch (1997) “Furtive Mating in Female Chimpanzees.” Nature 387:358–59.

*Goodall, J. (1986) The Chimpanzees of Gombe: Patterns of Behavior. Cambridge, Mass.: Belknap Press.

(1977) “Infant Killing and Cannibalism in Free Living Chimpanzees.” Folia Primatologica 28:259–82.

*———(1965) “Chimpanzees of the Gombe Stream Reserve.” In 1. deVore, ed., Primate Behavior: Field Studies of Monkeys and Apes, pp. 425–73. New York: Holt, Rinehart & Winston.

*Köhler, W. (1925) The Mentality of Apes. London: Routledge & Kegan Paul.

*Kollar, E. J., W. C. Beckwith, and R. B. Edgerton (1968) “Sexual Behavior of the ARL Colony Chimpanzees.” Journal of Nervous and Mental Disease 147:444–59.

*Kollar, E. J., R. B. Edgerton, and W. C. Beckwith (1968) “An Evaluation of the Behavior of the ARL Colony Chimpanzees.” Archives of General Psychiatry 19:580-94.

*Kortlandt, A. (1962) “Chimpanzees in the Wild.” Scientific American 206(5):128-38.

*Lawick-Goodall, J. van (1968) “The Behavior of Free-Living Chimpanzees in the Gombe Stream Reserve.” Animal Behavior Monographs 1:161–311.