Bruce Bagemihl - Biological Exuberance

Even if males of some species are genuinely aroused by sexual activity between females, the evidence clearly shows that females are unconcerned with the effect of their behavior on males and do not structure their participation in homosexuality to maximize its impact on heterosexuality. Yet in spite of all this counterevidence, biologists still claim that a primary “function” of homosexual activity in females is to arouse males: “The sight of one female mounting another is said to excite males sexually in Squirrel monkeys and it may do so to males of other species too, for example men watching pornographic films of lesbian activity.” 63By drawing an explicit parallel to human sexuality, the author of this statement hopes to argue for the evolutionary “usefulness” of homosexuality—but the analogy actually highlights the fundamental absurdity of this “explanation,” as well as its dependence on cultural rather than biological factors. True, many heterosexual men are aroused by the sight of two women having sex together, and lesbian sexuality is often packaged and trivialized as pornography to be consumed by straight men. But it would be ridiculous to conclude, on the basis of this, that lesbians have sex “in order” to arouse heterosexual men—yet this is exactly the type of reductionist thinking that is routinely applied to homosexual behavior in animals. It is also highly revealing that homosexual behavior among male animals is virtually never described as being stimulating for females. 64

Perhaps the most widespread version of the idea that homosexuality is really just a form of reproductive behavior concerns same-sex pairing in birds. It is frequently asserted that the “function” of such associations is to allow females to successfully raise young when they are unable to obtain a male mate. Not only is the initial premise of this explanation—that homosexual pairs result from the unavailability of members of the opposite sex—incorrect, but first and foremost, birds do not usually form same-sex pairs specifically to undertake parenting. 65Species in which homosexual pairs never attempt to raise young are nearly as common as those in which same-sex parenting does occur. Even in those species where female pairs lay eggs, the proportion of their eggs that are actually fertile is usually low, indicating that the females do not mate with males or “try” to raise a family—fertil—ity rates as low as 0 percent for Kittiwakes, 0–15 percent for Western Gulls, 4–30 percent in Herring Gulls, 33 percent for Silver Gulls, and 8 percent in some populations of Ring-billed Gulls have been documented. 66In addition, female pairs whose clutches are entirely infertile have been reported for Mute Swans, Black-winged Stilts, Roseate Terns, Blue Tits, Red-backed Shrikes, King and Gentoo Penguins, and Lovebirds (among others). Female Jackdaws who have lost their male partners sometimes pair up with nonbreeding females. However, these associations develop regardless of whether the widow has young, demonstrating that females do not form same-sex associations solely for the purpose of obtaining help in raising offspring. Moreover, only 10 percent of widowed females are involved in homosexual pairs, so even if such partnerships were “reproductively” motivated, it remains to be explained why only some females take advantage of such alternative parenting arrangements.

Furthermore, there are several different forms of same-sex parenting among birds (and other animals). In some cases, individuals develop full pair-bonds with their coparent, including courtship and sexual activity, and the partnership typically exists prior to and extends beyond the duration of parenting (e.g., Western Gulls, Black-winged Stilts). In other species, partners who already have offspring simply enter into a joint-parenting arrangement with no associated courtship or sexual activity between them, often lasting only until the young have been raised (e.g., Lesser Scaup Ducks). In still other cases, animals develop an intermediate arrangement, with “platonic” coparenting between individuals who may nevertheless continue to associate together even when not breeding (e.g., Acorn Woodpeckers, Squirrel Monkeys). And finally, in many species (e.g., Greylag Geese, Oystercatchers), individuals form bisexual trios that parent their offspring together (often contrasting with heterosexual trios and/or homosexual pairs within the same species). 67All four types of arrangement could be interpreted as “strategies” to raise young, yet the differences between them remain unaddressed if homosexual associations are seen strictly as coparenting arrangements.

The putative benefits of same-sex breeding associations are also generally belied by the fact that not many individuals take advantage of them. The proportion of birds who participate in homosexual pairings or joint parenting arrangements is often relatively small—much smaller, in fact, than would be expected if this were simply an efficient or beneficial reproductive strategy. For example, most male Greater Rheas and Emus raise their young as single parents, but occasionally two males join forces, incubating their eggs in tandem and raising their chicks together. Single parenting can be taxing in these species—partnerless males, for instance, may fast during the entire incubation period, and single Greater Rhea fathers often lose eggs because they can’t keep large clutches warm—so it has been suggested that two males may be better equipped to handle the difficulties of parenting by helping each other. However, only a small fraction of nests are tended by two males (less than 3 percent in Greater Rheas): if this were truly a useful parenting strategy, why wouldn’t all males—or at least a larger proportion—be using it? Clearly something more—or something else—is involved in associations between males than simply the parenting benefits they may accrue. To further confound the picture, in Greater Rheas both same-sex coparenting and same-sex nest helpers occur. While some males jointly parent the same brood of young, a much higher percentage (about a quarter, still a minority of the population) are assisted by an adolescent male who separately parents one of their nests. Once again, this raises the question of why some males opt for joint parenting, others “choose” to have male helpers, while most do neither. And in many species the supposed advantages of coparenting as opposed to single parenting are in fact illusory. Most female Lesser Scaups raise their young with no help from males, but occasionally two or three females coparent. It is usually assumed that this strategy gives such females an advantage in parenting, but detailed studies of parental investment have shown that same-sex coparents are no more and no less successful than single parents. Moreover, each female in such an arrangement generally spends the same amount of time in parenting duties as do single females, i.e., she is not “relieved” of some of her responsibilities by her companion. In other words, there is essentially no reproductive advantage to joining forces with a parenting partner in this species. 68

Nor is the occurrence of homosexual pairing in other species correlated with the supposed advantages of having an opposite-sex partner to help with parenting. Even in birds where male-female coparenting is typical, there are often significant differences between species in how essential that biparental care is to successful chick-raising. In some birds, females can raise young without the assistance of a male partner, while in other species the male’s contribution is indispensable. If homosexual pairing were somehow related to the (in)ability of single birds to raise young on their own, one would expect same-sex associations to occur in species where biparental care is more important, i.e., where single birds cannot raise young on their own—yet the facts do not support this. Consider two parallel examples: Snow Geese and Black-billed Magpies. Homosexual pairing in female Snow Geese is claimed to allow otherwise single birds to raise young. However, biparental care is not essential for successful reproduction in this species: when females in heterosexual pairs have their male partners taken away from them, they are quite capable of raising their young as single parents. On the other hand, biparental care is essential in Black-billed Magpies, since females are unable to raise offspring on their own when they lose (or are deprived of) their male mates. Yet homosexual pairs of Magpies do not raise young together, nor do widowed females form same-sex pairs in this species (unlike the closely related Jackdaws). This is exactly the opposite of what would be expected if mateless birds were forming homosexual associations to enable them to parent. 69