Biological Exuberance: Animal Homosexuality and Natural Diversity

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