Biological Exuberance: Animal Homosexuality and Natural Diversity

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.

*Kohler, 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.

*Nishida, T. (1997) “Sexual Behavior of Adult Male Chimpanzees of the Mahale Mountains National Park, Tanzania.” Primates 38:379–98.

———(1990) The Chimpanzees of the Mahale Mountains: Sexual and Life History Strategies. Tokyo: University of Tokyo Press.

———(1979) “The Social Structure of Chimpanzees of the Mahale Mountains.” In D. A. Hamburg and E. R. McCown, eds., The Great Apes, pp. 73–121. Menlo Park, Calif.: Benjamin Cummings.

*———(1970) “Social Behavior and Relationship Among Wild Chimpanzees of the Mahali Mountains.” Primates 11:47–87.

*Nishida, T., and K. Hosaka (1996) “Coalition Strategies Among Adult Male Chimpanzees of the Mahale Mountains, Tanzania.” In W. C. McGrew, L. F. Marchant, and T. Nishida, eds., Great Ape Societies, pp. 114–34. Cambridge: Cambridge University Press.

*Reynolds, V., and F. Reynolds (1965) “Chimpanzees of the Budongo Forest.” In 1. deVore, ed., Primate Behavior: Field Studies of Monkeys and Apes, pp. 368–424. New York: Holt, Rinehart & Winston.

Takahata, Y., N. Koyama, and S. Suzuki (1995) “Do the Old Aged Females Experience a Long Postreproductive Life Span?: The Cases of Japanese Macaques and Chimpanzees.” Primates 36:169–80.

Tutin, C. E. G., and P. R. McGinnis (1981) “Chimpanzee Reproduction in the Wild.” In C.E. Graham, ed., Reproductive Biology of the Great Apes, pp. 239–64. New York: Academic Press.

*Tutin, C. E. G., and W. C. McGrew (1973a) “Chimpanzee Copulatory Behavior.” Folia Primatologica 19:237–56.

———(1973b) “Sexual Behavior of Group-Living Adolescent Chimpanzees.” American Journal of Physical Anthropology 38:195–200.

*de Waal, F. B. M. (1982) Chimpanzee Politics: Power and Sex Among Apes. New York: Harper & Row.

*de Waal, F. B. M., and J. A. R. A. M. van Hooff (1981) “Side-directed Communication and Agonistic Interactions in Chimpanzees.” Behavior 77:164–98.

Wrangham, R. W. (1997) “Subtle, Secret Female Chimpanzees.” Science 277:774–75.

*Yerkes, R. M. (1939) “Social Dominance and Sexual Status in the Chimpanzee.” Quarterly Review of Biology 14:115-36.

IDENTIFICATION: A massive ape (adult males generally weigh over 300 pounds) with black fur; old males are called silverbacks because of the silvery-gray fur on their backs. DISTRIBUTION: Central Africa including Congo (Zaire), Uganda, Rwanda; southeastern Nigeria to southern Congo; endangered. HABITAT: Bamboo forests, rain forests. STUDY AREAS: Virunga Mountains, Rwanda and Congo (Zaire), subspecies G.g. beringei, the Mountain Gorilla; Basel, Metro Toronto, and St. Louis Zoos, subspecies G.g. gorilla, the Lowland Gorilla.

Social Organization

Gorillas live in small groups of eight to fifteen individuals, usually consisting of three to six adult females, one mature male, one to two juvenile males, and five to seven immature offspring. All-male groups also regularly occur. The mating system is polygynous, i.e., the mature male mates with all of the females in the group. The females are usually not related to each other, since they generally leave their family group once reaching adulthood—in many other group-living primates, males leave a core group of (usually related) females.

Description

Behavioral Expression: Within her group, a female Gorilla sometimes forms an intense pairlike friendship with another female, spending as much time with her as with the breeding male of the group. Her interactions with this “favorite” female consist of constant touching while they spend time together, sitting with each other or lying one against the other, and frequent mutual grooming. Female Gorillas also frequently have sex with other females in their group. In a typical lesbian interaction, one female approaches another directly, often making copulatory vocalizations, after which they may sit quietly together for a while. Often they will begin to fondle each other’s genitals or bring their face into intimate contact with the other’s vulva, smelling or touching with their mouths. This is usually followed by embracing in a face-to-face position (usually lying down) with rubbing of the genitals against each other, sometimes accompanied by growling, grunting, screaming, or pulsing whimpers. The animals may also pause during periods of pelvic thrusting to caress each other, shift their positions, or masturbate themselves.

Lesbian sexual activity is notable for its differences from heterosexual copulation, probably related to an emphasis on achieving mutual pleasure. First of all, the more intimate face-to-face position is rarely used between males and females, who instead mate with the male mounting from behind (and often with the male thrusting and vocalizing significantly less than his partner). Sexual interactions between females are also generally more affectionate, involving much more embracing and grooming, and they usually last longer. One study revealed that sexual interactions between females last on average five times longer than heterosexual ones, and that lesbian activity involves considerably more thrusting and genital stimulation.

Female Gorillas also exhibit clear preferences for particular female sexual partners within their group. Although lesbian activity generally occurs among all members of a group, each female usually has a favorite partner with whom she interacts more often. Homosexuality is also integrated into the general reproductive cycle of the group: breeding females (including mothers) have sex with other females as much as do nonbreeding females, and lesbian sex is common even during pregnancy, sometimes as late as a week or two before birth.

Although male Gorillas (especially younger animals) sometimes mount each other in cosexual groups, homosexuality occurs most commonly in all-male groups, where probably more than 90 percent of all same-sex activity between males takes place. Such groups result when females leave their home group to join another, or when males occasionally leave their own group upon reaching maturity and band together. All-male groups persist for many years and have a complex network of homosexual pairings. Each male has preferred partners whom he courts and has sex with; some interact with only one other male in the group, while others have multiple partners (up to five have been recorded for one individual). Durations of individual pairings can be anywhere from a few months to a year or more. Participants are sometimes related to each other: in one all-male group, about 40 percent of all homosexual activity occurred between half brothers. There is often intense competition among the males for “preferred” partners—often the younger males—and older, higher-ranking males frequently “guard” their favorite males and fight to protect them from the advances of other males. Nevertheless, rates of aggression are significantly lower in all-male groups than in cosexual groups, and some male groups exhibit a high degree of cohesiveness attributable to the sexual bonding and mediating activities of their members.

When one male Gorilla is courting another, he approaches while making intense panting sounds; sometimes