Biological Exuberance: Animal Homosexuality and Natural Diversity

Even within a given category of bisexuality—say, simultaneous bisexuality involving interspersed homosexual and heterosexual activity—each individual within a population generally exhibits a unique sexual orientation profile, consisting of his or her own particular combination of same- and opposite-sex activity. The concept of a scale or continuum as developed by Alfred Kinsey for describing human sexual orientation is useful here: within each species, individuals generally fall along a range from those exhibiting predominantly or exclusively heterosexual behavior, to those exhibiting a balance of both, to those exhibiting predominantly or exclusively homosexual behavior, and every variation in between.²⁰ Species as a whole also differ as to where the majority of individuals fall along this continuum, and how many engage in more exclusive homosexuality or heterosexuality as opposed to more equal bisexuality. Thus, among Bonobos every female participates in both homosexual and heterosexual activity, but the proportion of same-sex behavior exhibited by each of the females in one particular troop varied between 33 percent and 88 percent (averaging 64 percent); in female Red Deer, from 0–100 percent (averaging 49 percent); among Bonnet Macaque males, between 12 percent and 59 percent (averaging 28 percent); in male Pig-tailed Macaques, from 6–22 percent (averaging 18 percent); and among Kob females, from 1–58 percent (averaging 11 percent).²¹ In other words, within an overall pattern of bisexuality, individual animals exhibit varying “degrees” of bisexuality—different “preferences,” as it were, for homosexual as opposed to heterosexual activity.

These findings are particularly relevant since the concept of a scale or continuum of (homo)sexual behavior and orientation is yet another example of something still thought to be “uniquely human.” The Bonobo data (as well as that for the other species) directly refute one primatologist’s recent claim that “all wild primates we have seen within a particular species are equally homosexual … . If you lined up ten female bonobos, it’s not like one would be a 6 on the Kinsey scale and another a 2. They would all be the same number. It’s only humans who adopt identities.” ²² Of course, the Kinsey scale is specifically a measure of behaviors and not identities (it was designed expressly to bypass the often problematic issue of people’s “self-identification”), and certainly no animal studies purport to assess anything as subjective as sexual “identity.” In its intended usage, though, the Kinsey scale (or a comparable measure of sexual gradations) in fact appears to be particularly apt for Bonobos. The figures cited above are based on the work of Dr. Gen’ichi Idani in Congo (Zaire), who studied a troop consisting of (coincidentally) exactly ten female Bonobos and tabulated all their homosexual genital rubbings versus heterosexual copulations over a three-month period. The percentages of homosexual activity in these individuals were 33, 36, 47, 68, 68, 70, 75, 75, 82, and 88 percent. Idani also tabulated the number of different male and female partners of each female (another possible measure of degree of bisexuality or behavioral “preference”). Again, the percentage of partners that were same-sex exhibits a range across all females: 36, 50, 50, 54, 67, 67, 67, 69, 71, and 80 percent. Clearly these individuals fall into a spectrum in terms of their sexual behavior and thus exhibit different degrees of bisexuality in terms of their sexual orientation (although none are in fact exclusively heterosexual or homosexual).²³