Biological Exuberance: Animal Homosexuality and Natural Diversity

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