Biological Exuberance: Animal Homosexuality and Natural Diversity

When a male Giraffe sniffs a female’s rear end—without any mounting, erection, penetration, or ejaculation—he is described as being sexually interested in her and his behavior is classified as primarily, if not exclusively, sexual. Yet when a male Giraffe sniffs another male’s genitals, mounts him with an erect penis, and ejaculates—then he is engaging in “aggressive” or “dominance” behavior, and his actions are considered to be, at most, only secondarily or superficially sexual. In one study of Bank Swallows, all chases between males and females were assumed to be sexual even though they were rarely seen to result in copulation. Indeed, the majority of bird studies label dyads composed of a male and female as “[heterosexual] pairs” in spite of the fact that overt sexual (mounting) activity is rarely verified for all such couples. In contrast, most investigators will not even consider classifying same-sex interactions in birds to be courtship, sexual, or pair-bonding activity—even when they involve the same behavior patterns used in heterosexual contexts—unless mounting is observed. Certain associations between male and female Savanna Baboons and Rhesus Macaques are described as “sexual” relationships or “pair-bonds” even though they often do not include sexual activity. In contrast, bonds between same-sex individuals in these species are characterized as nonsexual “coalitions” or “alliances” even though they may involve sexual activities (as well as the same intensity and longevity found in heterosexual bonds). Finally, the “piping display” of the Oystercatcher described earlier was initially assumed to be a courtship behavior, largely because it is a common activity between males and females. Subsequent studies have shown that this is in fact a primarily nonsexual (territorial or dominance) interaction.¹⁰⁶

Another strategy adopted by scientists when confronted with an apparently sexual behavior occurring between two males or two females is to deny its sexual content in both same-sex and opposite-sex contexts. For example, because female Crested Black Macaques show behavioral signs of orgasm during homosexual as well as heterosexual mounts, one scientist concluded that this behavior is not reliable evidence of female orgasm in either situation. The fact that intercourse and other sexual interactions occur between like-sexed individuals in Bottlenose and Spinner Dolphins is often taken to be “proof” that such behaviors have become largely divorced from their sexual content and are now forms of “greeting” or “social communication,” even in heterosexual contexts. Similarly, copulation in Common Murres has many nonreproductive features: in addition to occurring between males, in heterosexual pairs it frequently takes place before the female becomes fertile. Drawing an explicit analogy with “nonsexual” mounting in primates, one ornithologist suggested that in this bird heterosexual mounting must therefore serve an “appeasement” function rather than being principally a sexual behavior, i.e., females invite their male partners to mate in order to deflect aggression from them. Likewise, nonprocreative copulations in both heterosexual and homosexual contexts in Blue-bellied Rollers are categorized as a form of ritualized aggression or appeasement.¹⁰⁷

A difference in form between homosexual and heterosexual behaviors is often interpreted as a difference in their sexual content. The reasoning is that if same-sex activity does not resemble opposite-sex activity, and only opposite-sex activity is by definition sexual, then same-sex activity cannot be sexual. For example, in Rhesus Macaques most heterosexual copulations involve a series of mounts by the male, only the last of which typically involves ejaculation. Because mounts between males are often single rather than series mounts, they are frequently classified as nonsexual, even when they include clear signs of sexual arousal such as erection, pelvic thrusting, penetration, and even ejaculation. A similar interpretation has also been suggested for mounting between male Japanese Macaques. In contrast, significant differences in form also exist between heterosexual copulation in Macaques (with series mounting) and male masturbatory patterns, yet both activities are clearly sexual and are typically classified as such.¹⁰⁸