Biological Exuberance: Animal Homosexuality and Natural Diversity

contact is initiated with one (or both) males reaching out to touch the other, or one may make a more subtle soliciting approach. Sexual activity involves one male mounting another and thrusting, in either the face-to-face or front-to-back position; both males often emit grumbling, growling, or panting sounds. Orgasm is signaled when the animal emits a deep sigh on dismounting, and often there is direct evidence of ejaculation (e.g., semen spilled on his partner). Most males both mount and are mounted, except for the oldest silverback males, who only mount. Like lesbian interactions, male homosexual encounters tend to last, on average, longer than heterosexual ones and to use the face-to-face position more often than in male-female interactions (though less often than between females). Male Gorillas also touch and fondle each other’s genitals in addition to mounting one another.

Male Gorillas having sex with each other in the mountain rain forests of Rwanda, showing two mounting positions: front-to-back (left) and face-to-face

Frequency: In cosexual groups, 9 percent of all sexual activity is lesbian and 58 percent of all social/affectionate interactions of females are with other females (mostly with their “favorite” partner); about 2 percent of mounting episodes occur between adult males in such groups. Among younger animals (e.g., adolescents and juveniles) in cosexual groups, 7–36 percent of mounts are between males and 9–14 percent between females. Male homosexual courtship and copulation occur daily in some all-male groups and are thought to exceed the amount of heterosexual activity that takes place in cosexual groups. Some males may engage in homosexual copulation more than 75 times a year in such groups, and homosexual courtship, at its peak, can take place as often as 7 times an hour. Up to 10 percent of groups in some populations are all-male, and Gorillas spend an average of six years in such groups, with some males staying ten or more years (and even occasionally remaining until their death).

Orientation: Many female Gorillas are bisexual, having sexual and affectionate relationships with both males and females, but there are clear differences in the extent to which various individuals participate in homosexual versus heterosexual activity. In general, it appears that a continuum exists from those females who prefer lesbian activity (they account for a large proportion of the same-sex interactions), to those who have a fairly equal amount of interaction with both males and females, to those who interact primarily with males. Many male Gorillas are probably sequentially bisexual, spending portions of their lives having only homosexual encounters (in all-male groups), followed by periods of only heterosexual interactions, and so on. Other males, especially younger ones, may be simultaneously bisexual. Depending on the circumstances (such as the particular group composition), some males may also have primarily or exclusively homosexual interactions throughout their lives, while others may have only heterosexual ones, but it appears that all males at least have the capacity for bisexuality.

Nonreproductive and Alternative Heterosexualities

As noted above, sex (both heterosexual and homosexual) during pregnancy is common among Gorillas. Both males and females also engage in masturbation, and younger animals frequently participate in nonpenetrative sexual activity. Mountings of the latter type are usually incestuous, involving siblings, half siblings, or (more rarely) parents and their offspring (or their siblings’ offspring). In captivity, oral sex and manual stimulation of genitals have also been observed in heterosexual interactions. Male Gorillas generally appear to have less interest in sex than females and are sometimes rather reluctant or perfunctory participants in mating. Heterosexual interactions are nearly always initiated by females (whose advances are often initially ignored by the males), males often thrust and vocalize much less than females during copulation (often for no more than 20 seconds), and females generally determine when a particular sexual interaction is finished. However, females may be sexually inactive for up to three or four years while nursing their young. Infanticide is quite common among wild Gorillas: more than 40 percent of all infant deaths in one population were due to infanticide, usually by an adult male trying to gain breeding access to a female (although females have been known to kill infants as well). Probably all adult males commit infanticide at least once during their lifetime, while most females are likely to lose at least one infant during their lifetime to killing by another of their own species.

Sources

*asterisked references discuss homosexuality/transgender

*Coffin, R. (1978) “Sexual Behavior in a Group of Captive Young Gorillas.” Boletin de Estudios Medicos y Bi-ologicos 30:65-69.

*Fischer, R. B. and R.D. Nadler (1978) “Affiliative, Playful, and Homosexual Interactions of Adult Female Lowland Gorillas.” Primates 19:657-64.

*Fossey, D. (1990) “New Observations of Gorillas in the Wild.” In Grzimek’s Encyclopedia of Mammals, vol. 2, pp. 449-62. New York: McGraw-Hill.

(1984) “Infanticide in Mountain Gorillas (Gorilla gorilla beringei) with Comparative Notes on Chimpanzees.” In G. Hausfater and S. B. Hrdy, eds., Infanticide: Comparative and Evolutionary Perspectives, pp. 217–35. New York: Aldine.

*———(1983) Gorillas in the Mist. Boston: Houghton Mifflin.

*Harcourt, A. H. (1988) “Bachelor Groups of Gorillas in Captivity: The Situation in the Wild.” Dodo 25:54-61.

*———(1979a) “Social Relations Among Adult Female Mountain Gorillas.” Animal Behavior 27:251-64.

————(1979b) “Social Relationships Between Adult Male and Female Mountain Gorillas in the Wild.” Animal Behavior 27:325-42.

*Harcourt, A. H., D. Fossey, K. J. Stewart, and D. P. Watts (1980) “Reproduction in Wild Gorillas and Some Comparisons with Chimpanzees.” Journal of Reproduction and Fertility suppl. 28:59– 70.

Harcourt, A. H., and K. J. Stewart (1978) “Sexual Behavior of Wild Mountain Gorillas.” In D. J. Chivers and J. Herbert, eds., Recent Advances in Primatology, vol. 1, pp. 611-12. New York: Academic Press.

*Harcourt, A. H., K. J. Stewart, and D. Fossey (1981) “Gorilla Reproduction in the Wild.” In C. E. Graham, ed., Reproductive Biology of the Great Apes, pp. 265-79. New York: Academic Press.

*Hess, J. P. (1973) “Some Observations on the Sexual Behavior of Captive Lowland Gorillas, Gorilla g. gorilla (Savage and Wyman).” In R. P. Michael and J. H. Crook, eds., Comparative Ecology and Behavior of Primates, pp. 507-81. London: Academic Press.

*Nadler, R. D. (1986) “Sex-Related Behavior of Immature Wild Mountain Gorillas.” Developmental Psychobiology 19:125-37.

*Porton, I., and M. White (1996) “Managing an All-Male Group of Gorillas: Eight Years of Experience at the St. Louis Zoological Park.” In AAZPA Regional Conference Proceedings, pp. 720-28. Wheeling, W.V.: American Association of Zoological Parks and Aquariums.

*Robbins, M. M. (1996) “Male-Male Interactions in Heterosexual and All-Male Wild Mountain Gorilla Groups.” Ethology 102:942-65.

*———(1995) “A Demographic Analysis of Male Life History and Social Structure of Mountain Gorillas.” Behavior 132:21-47.

*Schaller, G. (1963) The Mountain Gorilla. Chicago: University of Chicago Press.

*Stewart, K. J. (1977) “Birth of a Wild Mountain Gorilla (Gorilla gorilla beringei).” Primates 18:965-76.

Watts, D. P. (1990) “Mountain Gorilla Life Histories, Reproductive Competition, and Sociosexual Behavior and Some Implications for Captive Husbandry.” Zoo Biology 9:185-200.

———(1989) “Infanticide in Mountain Gorillas: New Cases and a Reconsideration of the Evidence.” Ethology 81:1-18.

*Yamagiwa, J. (1987a) “Intra- and Inter-Group Interactions of an All-Male Group of Virunga Mountain Gorillas