For the Good of the Family and the Species?

Homosexual or transgendered individuals in many human societies perform a special role, acting as shamans, teachers, or caretakers for the benefit of the tribe as a whole, or for particular families. A number of biologists have suggested that homosexuality in animals may work in a similar fashion. One proposal is that homosexual animals, while not reproducing themselves, act as “helpers” in raising the offspring of their relatives, thereby contributing indirectly to the passing on of their own genes. Another idea is that homosexuality, because it is nonreproductive, acts as a self-regulating mechanism to control a species’ population growth.⁴ Both of these theories have generated considerable controversy, yet little concrete evidence to either support or refute them has been brought forward. Moreover, neither of these proposals has been evaluated with respect to animals—even though they are directly testable with data from animal species—probably because a comprehensive and detailed survey of nonhuman homosexuality has not been previously available. Once the relevant facets of behavior and social organization are considered, however, it becomes quite clear that neither of these hypotheses can be correct.

Underlying each of these proposals is the assumption that animals who engage in homosexuality do not reproduce (and must therefore “contribute” in some other way)—yet this is patently false. As we saw in earlier chapters, bisexuality is widespread in the animal kingdom: in more than half of the mammal and bird species in which homosexuality occurs, at least some individuals engage in both same-sex and opposite-sex interactions. Moreover, actual breeding by animals who participate in homosexuality has been verified in more than 65 species. This includes animals who are heterosexually paired and raise offspring but have outside homosexual interactions (Greenshanks, Little Egrets, Tree Swallows, Gray-capped Social Weavers); animals who engage in homosexuality as single parents (Japanese Macaques, Hanuman Langurs, Northern Fur Seals); animals who raise offspring in bisexual trios or quartets (Black Swans, Greylag Geese, Oystercatchers, Jackdaws) or in same-sex pairs as a result of outside heterosexual matings (Ring-billed Gulls, Western Gulls); females who participate in homosexual activity while pregnant (Gorillas, Takhi, Vicunas) or even while their infants are clinging to them (Bonobos); animals who breed at some point in their lives prior to or following a period of homosexuality (Orang-utans, Rufous Rat Kangaroos, Emus, Silver Gulls, Bicolored Antbirds); homosexuality among those individuals in a population who monopolize most of the breeding opportunities (Nilgiri Langurs, Mountain Zebras, Bighorn Sheep, Ruffs, Pukeko); and animals that have incestuous homosexual relations with their own offspring (White-handed Gibbons, Red Foxes, Livingstone’s Fruit Bats, Ocellated Antbirds). Thus, animals use multiple strategies to combine homosexuality with breeding, and even animals who may “prefer” homosexuality or have more same-sex than opposite-sex interactions can successfully raise offspring.⁵ It is simply not true that animals who participate in homosexuality are unable to reproduce and pass on their genes to future generations. Of course, some animals are exclusively homosexual and never reproduce (as discussed in chapter 2) or else are unsuccessful breeders in either a heterosexual or a homosexual context, but reproduction is most definitely not limited to animals that only have heterosexual contacts.

Setting aside the fact that the initial premise of these two hypotheses is incorrect, is there nevertheless any validity to the substance and implications of each of these proposals? As it turns out, the animal world offers us a ready-made natural “laboratory,” as it were, to test the first hypothesis, that homosexual animals act as “helpers” for other members of their own species or families. Numerous animals have developed a variety of “helping systems” in which individuals contribute to the care and upbringing of youngsters that are not their own offspring (although they may be relatives). These arrangements take several different forms: communal or cooperative breeding systems (group-living arrangements in which only some animals breed while the others assist them); “day-care” systems such as crèches or nursery groups, in which youngsters from more than one family are pooled together and watched over by one or two caretakers; alloparenting, in which individuals assist parents in duties such as feeding, protecting, carrying, or even “baby-sitting” their offspring; and adoption, involving foster-parenting of orphaned, lost, or abandoned youngsters.⁶ Yet virtually none of these helper systems is preferentially “staffed” by homosexual animals or associated in any particular way with homosexuality. True, some individuals that engage in homosexuality certainly do act as helpers in some of these systems, but there is not a privileged association between homosexuality and helping as has been hypothesized. In fact, in some instances the connection between homosexuality and helping is the exact opposite of what is predicted by this hypothesis.

A pregnant female Takhi (Przewalski’s Horse) mounting another female from the side. Breeding animals in many species participate in homosexual activity.

Consider the example of communal breeding systems: this form of social organization is especially prevalent among birds, where it is found in at least 222 species—yet homosexuality occurs in only 8 (4 percent) of these.⁷ Although caution must always be exercised when drawing conclusions based on the absence of homosexuality in a species, nevertheless this proportion is far less than would be expected if helpers were somehow predisposed to homosexuality, or if individuals that participated in homosexuality were somehow predisposed to helping.⁸ Moreover, in each of these 8 cases the specifics of which birds participate in homosexuality and/or helping do not follow the predicted patterns. In Pukeko and Gray-capped Social Weavers, for example, only breeding birds, not their helpers, engage in homosexuality—directly counter to what is predicted by this hypothesis. In other cases, homosexuality is not limited to helpers, but is also found in breeders: all Acorn Woodpecker communal group members—breeder and helper alike—participate in same-sex mounting, while in Tasmanian Native Hens, Dusky Moorhens, and Mexican and San Blas Jays, homosexuality occurs in both breeders and helpers, but only in a small proportion of each (i.e., many or most helpers do not engage in same-sex relations at all). Finally, homosexuality in Pied Kingfishers is characteristic of neither breeders nor helpers: rather, a subset of the nonbreeding population that does not participate in the helper system is involved in same-sex activity.⁹

Likewise, the other forms of parental help found in animals do not support any connection between helping behavior and homosexuality. Creches, alloparenting, and adoption occur in numerous species without homosexuality. Of those mammals and birds in which at least some individuals do engage in homosexual activity, these types of helping systems are found in less than a third of the species, and they also occur in less than half of the species in which at least some individuals are exclusively homosexual. Moreover, in none of these cases is there a specific association between homosexuality and helping. For example, in many animals helping is performed only by members of the sex in which homosexuality is absent (e.g., Nilgiri Langurs, in which females may help take care of each other’s offspring, but only males participate in homosexuality) or else it is characteristic of (heterosexual) breeding animals who assist other heterosexual breeders (for example, parents who take turns watching over a crèche, or who help feed and protect other parents’ youngsters).¹⁰ In no instance is helping restricted to animals that engage exclusively, primarily, or even sporadically in homosexuality, nor is it even more prevalent in such individuals.¹¹ In some species we find even more confounding situations: among Hanuman Langurs, for instance, “helpers” actually enable breeding animals to participate in homosexual activity. Mothers in this species often engage in same-sex mounting, but only when they have been temporarily “freed” from their parental duties by other individuals who “baby-sit” their young.¹²

What about the idea that homosexuality acts as a mechanism to regulate population growth? Again, little concrete evidence supports this hypothesis, and there are also serious problems with its underlying premises.¹³ Aside from the fact that many animals engaging in homosexual activity continue to reproduce (as already mentioned), it is unlikely that population growth would be seriously affected even if a large proportion of animals were exclusively homosexual. Most animal populations can and do support large numbers of nonbreeding individuals without suffering a decrease in numbers: indeed, in many species a majority of individuals do not reproduce without any adverse effects on the population as a whole. In Damaraland mole-rats, for example, 90–98 percent of all individuals never breed during their lifetime, yet the population sustains itself and even continues to grow. Scientists have also calculated that a stable Killer Whale population can include up to 30 percent nonreproducing females without experiencing any decline. A significant pool of nonbreeding individuals exists in many other species, and up to 90 percent or more of one sex may fail to mate and/or breed.¹⁴ Thus, exclusive homosexuality on a much more massive scale than that seen in any species would have to occur before homosexuality could even begin to impact on population growth and size.

A number of animals experience periodic and often dramatic fluctuations in their numbers, sometimes undergoing regular five- or ten-year cycles of population increase and decrease—for example, snowshoe hares, lemmings, voles, and some species of finches, sandpipers, falcons, and grouse.¹⁵ If homosexuality were correlated with population size, one might expect that it would feature prominently in such species. One might also predict that its occurrence would “shadow” or fluctuate along with the population cycles, becoming more prevalent when population size or growth rate reaches its maximum, and less prevalent or nonexistent when the population is at its ebb. In fact, homosexual behavior has not been reported for most such species, and in the few cases where it has—Scottish Crossbills, Kestrels, and Grouse, for example—it does not appear to be related to either the cyclic or the irregular population increases (“eruptions,” as they are sometimes known) that occur in these species.¹⁶

Similarly, if homosexuality actually resulted in a significant decrease in population growth, one might expect it to be disproportionately represented among animals that are suffering a severe decline in numbers, i.e., in endangered species. However, of the 2,203 mammals and birds in the world that are currently classified as threatened (either critically endangered, endangered, or vulnerable), homosexuality has been documented in just over 2 percent of these.¹⁷ Moreover, the distribution of homosexuality across different species clearly has nothing to do with their endangered status: there are examples of two closely related species, such as the Pukeko and the takahe—two birds of New Zealand—in which homosexuality only occurs in the nonendangered one (the Pukeko); or animals in which one subspecies is endangered (e.g., the Asiatic Lion) yet homosexuality is not restricted to this subspecies; or else cases in which one or more subspecies are threatened (e.g., the Baja California and Sonoran Pronghorns), yet homosexual behavior is found in the nonthreatened subspecies of the same animal (the American Pronghorn); or two closely related species, in one of which homosexuality is common yet the species is not endangered (Hanuman Langur), the other in which homosexuality is much less common but the species is threatened (Nilgiri Langur). Conversely, if homosexuality were a form of self-preservation for a species as a whole—a “safety-valve,” as it were, activated in times of overpopulation—one would not expect to find it at all in animals suffering severe population declines. Nevertheless, same-sex activity is reported in at least 50 endangered species. Perhaps the most dramatic example is the nearly extinct Black Stilt: less than 50 of these birds are left in the wild, yet some individuals still form lesbian pairs.¹⁸

Animals are perfectly capable of “regulating” their population size with far more efficient and effective strategies than homosexuality. A wide variety of mechanisms for reducing density and/or growth rates have been documented, including emigration, stress-induced hormonal changes that inhibit reproduction, decreased fertility, delayed maturation or slowed development, infanticide, and cannibalism (not to mention “outside” checks on population size such as predators).¹⁹ In summary, then, it appears that homosexuality is neither useful to the species as a way of controlling population growth, nor useful to individual families as a mechanism whereby breeding animals are supplied with nonbreeding “helpers.”