Sperm-Swapping and Other Flights of Fancy

Attempts to determine the evolutionary “function” of homosexuality have sometimes led to even more obscure and implausible “explanations,” all revolving (predictably) around heterosexual breeding. For example, some scientists have suggested that homosexuality is a form of reproductive “competition”: females have sex (or form pair-bonds) with other females to monopolize their partner’s time and thereby prevent her from mating heterosexually, while males mount each other to reduce or redirect their rival’s sexual drive.⁷² However, in many species homosexual interactions are actively initiated by the animals who are mounted rather than by the mounters, and the participants often have a friendly rather than a competitive relationship with each other.⁷³ Moreover, there is no evidence that participation in homosexual mounting reduces heterosexual activity—indeed, in some species the opposite is true, for the greatest amount of heterosexual mating is accomplished by precisely those individuals who are also the most active homosexually (as discussed previously). And, as already mentioned, in many animals homosexual activity does not even take place during the breeding season or is only exhibited by a small proportion of individuals.

Another version of this competition hypothesis is that homosexuality is a way of directly interfering with the heterosexual activity of a rival. In a number of birds—Pukeko, Guianan Cock-of-the-Rock, Ocher-bellied Flycatchers, and Buff-breasted Sandpipers—homosexual activity is claimed to be a form of “disruption” whereby one male prevents another from mating with a female, while possibly also “usurping” his partner and mating heterosexually himself. The specifics of same-sex courtship and mating in each case, however, do not support this interpretation. In Pukeko, for example, males do sometimes interrupt heterosexual mating attempts by inviting the other male to mount them, but they do not generally take advantage of the situation to mate with the female partner. Moreover, this occurs only infrequently, and males are more likely to ignore heterosexual matings by other males or watch them without interfering than they are to try to prevent them from occurring. In addition, even if a male were trying to use homosexuality as a way to disrupt a heterosexual mating, this strategy would not “work” unless the other male found the prospect of mounting him more appealing than completing his heterosexual copulation. Ironically, then, a “disruption” interpretation of same-sex mounting in this species—typically presented as an example of the primacy of heterosexual relations—actually entails the assumption that male Pukeko would prefer homosexual activity. In Ocher-bellied Flycatchers, the suggestion that males are trying to disrupt heterosexual matings, or to gain access to females, is entirely speculative. Males have never been seen mating with a female as a result of a homosexual interaction in this species, and in fact females are not even present during the majority of courtship pursuits between males. Homosexual activity is also classified as a form of courtship “disruption” in the Guianan Cock-of-the-Rock, yet there is little evidence in favor of this explanation. As much, if not more, homosexual activity takes place when females are not present on the male’s display territories, and males who initiate such “disruptions” almost never gain access to members of the opposite sex as a result and have rarely even been observed mating with females. Furthermore, visits by yearling males involving homosexual activity are distinct from true courtship disruptions, which are performed by rival adult males. Yearling visits are directed toward a wide variety of males, all of whom cooperate in the interaction. In contrast, rival males target only the most successful heterosexual breeders and are violently attacked by the males they try to disrupt. In addition, same-sex interactions are sometimes directed toward adult nonbreeders, who do not participate in heterosexual mating at all, so it is difficult to see how this could be a form of “disruption.”⁷⁴

One species in which at least some homosexual activity appears to be genuinely associated with disruption of heterosexual mating is the Buff-breasted Sandpiper, in which rival males often interrupt each other’s courtship attempts by mounting and pecking them. However, even in this case, the benefits of such activity are not clear-cut, since “disruption” does not always result in more favorable mating opportunities for the “disrupter” or reduced mating for the “disruptee.” Although a “disruptive” male is often able to lure females away from his rival, in other cases he may keep returning to mount the rival without trying to mate with any females. In addition, detailed studies have shown that a male’s success at copulating with females is not in fact related to his ability to repel disrupting males. Moreover, not all homosexual mounting is directly involved with disruption of heterosexual courtship, while many disruptions occur without any homosexual activity.⁷⁵ This brings up a point that is also relevant for other species. Many animals—including ones that exhibit homosexuality in other contexts—use direct tactics to interrupt or harass heterosexual matings. These include threatening or physically attacking couples during copulation, and trying to pull or dislodge the partners from each other. Even if homosexual behavior were in some instances being used as a form of heterosexual disruption, it would still remain to be explained why some species—or only some individuals in a species—resort to this fairly unusual and indirect strategy, when more effective and efficient measures are available.

Other zoologists have proposed, in all seriousness, that homosexual copulation is a way of transferring or “swapping” sperm between same-sex partners for heterosexual (breeding) purposes. For example, one ornithologist has suggested that a male bird might deposit his sperm in another male’s genital tract during a homosexual mating so that the latter would then pass it on to a female during heterosexual copulation, indirectly fertilizing the female with the first male’s sperm.⁷⁶ Not only is this explanation highly implausible, it is factually incorrect for many species. Homosexual matings often take place outside of the breeding season or when females are nonfertilizable. In addition, male birds often solicit homosexual mounts from other males or actively facilitate homosexual interactions, which should not occur if they are a form of “insemination rivalry.” Finally, male birds frequently defecate when they are stressed (birds use the same orifice for all excretory and sexual functions)—thus, if same-sex activity were not consensual, males could easily empty their genital tract of any sperm that might have been put there by a rival male.⁷⁷

Even more absurdly, this “explanation” has been proposed for lesbian copulations in Pukeko, where no sperm is directly involved. The claim is that female birds mate with each other to transfer ejaculate between them from previous heterosexual matings. And why exactly would they do this? Zoologists have suggested that this is not so they can “fertilize” each other, but so that they can obscure paternity, i.e., confuse several males as to who is the actual father and thereby “trick” more males into caring for their young. This is implausible, however, since a number of other mechanisms already insure that paternity is obscured and parental care is shared in this species. These include multiple copulations by females with all males in the group, variability in timing of ovulation, absence of mate guarding or copulation disruptions, and an independent tendency of males to be “generous” or “indiscriminate” in their parental efforts (i.e., caring for all chicks regardless of whether they fathered them or even mated with any females at all). Another dubious speculation is that female Pukeko copulate with each other so as to “synchronize” their sexual cycles, thereby allowing them to lay their eggs at the same time (which is thought to be a more efficient reproductive strategy). Once again, there is no evidence that lesbian copulations have this effect.⁷⁸

It’s hard to imagine more convoluted and conjectural accounts of homosexuality than these. While many of these ideas are highly unlikely and scientifically unsubstantiated, they can actually be traced to misconceptions about human homosexuality that are deeply entrenched in our culture. For example, the belief that lesbian sexual activity serves to transfer semen from heterosexual intercourse can be found in some of the earliest written records concerning same-sex activity in people. A twelfth-century Irish story about Niall Frassach, a king who died in 778 A.D., makes use of this theme:

A woman came to the king carrying a boy child … “find out for me who the carnal father of this boy is, for … I have not known guilt with a man for many years now.” The king was silent then. “Have you had playful mating with another woman?” said he. “And do not conceal it if you have.” “I will not conceal it,” said she. “I have.” “It is true,” said the king. “That woman had mated with a man just before, and the semen which he left with her, she put it into your womb in the tumbling, so that it was begotten in your womb.”⁷⁹

In discussing this curious tale, historian John Boswell remarks that it reveals a “preoccupation with women as bearers and conduits of bloodlines rather than as beings with their own erotic lives and needs.”⁸⁰ It is an alarming comment on the “progress” of history that, nearly 900 years later, almost identical ideas about female animals should reappear under the guise of scientific theories, with scarcely any improvement in the perceptions of same-sex activity (or females, for that matter).

What Is Valuable?

Homosexuality is popularly considered to be nonreproductive or even counter(re)productive. In this section we have considered a wide range of proposals about the possible evolutionary value (and genetics) of homosexuality that challenge this “commonsense” view. These proposals concern ways that homosexuality might somehow contribute to the perpetuation of the species, either directly (for example, by improving an animal’s reproductive prowess or increasing its heterosexual mating opportunities) or indirectly (for example, by providing breeding animals with “helpers” or acting as a population regulation mechanism). Implausible as some of these ideas may sound, many aspects of animal homosexuality run counter to preconceived ideas, not the least of which is the widespread participation of breeding animals in homosexual activity. A number of other unexpected phenomena in several species led us to consider further whether some of these proposals might actually have some explanatory value. Examination of deeper patterns within a broader range of animals, however, as well as more rigorous investigation of specific cases, showed that they do not. Thus, in the end we have arrived back at our starting point: homosexuality, whether in breeding or nonbreeding individuals, does not generally contribute to the reproduction of the species. This is an obvious point, perhaps, but one whose very obviousness has usually precluded a serious investigation of its validity. And so once again we are confronted with the evolutionary “paradox” of homosexuality: Why does same-sex activity persist—reappearing in species after species, generation after generation, individual after individual—when it is not “useful”?

Part of the problem is that “usefulness” or “value” in most biological theorizing is narrowly defined to refer only to reproduction. A common thread running through each of the proposals considered in this section is that they view homosexuality only in terms of how it could contribute to breeding or facilitate mating relations between males and females, rather than in terms of any intrinsic value it might have. This brings us to the final, and overarching, problem with all such “evolutionarily valuable” explanations. Scientists have often been led to absurd conclusions about the putative “function” of homosexuality precisely because evolutionary theory cannot readily countenance behaviors that are apparently “useless”—and for a behavior to be “useful” it must contribute in some way to mating and reproduction. Perhaps it is the very notion of “utility” or “value” that needs to be reexamined. In the realm of human culture and biology, the idea that life revolves around heterosexuality and that everything in life can be related, ultimately, to reproduction—a view sometimes known as heterocentrism or heterosexism—is currently being challenged on a number of fronts.⁸¹ Yet this view would appear to be a self-evident truth where animals are concerned, since the passing on of genetic material through reproduction is considered to be the very foundation of biology and evolution. In the next section we will see that, on the contrary, this belief is as incomplete a description of animal biology as it is of human society.