Biological Exuberance: Animal Homosexuality and Natural Diversity

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.