Even same-sex activity that does have its genesis in the absence of opposite-sex partners—so called situational homosexuality—often shows remarkable longevity and durability, rarely conforming to the stereotype of being “fragile” or liable to disintegrate once heterosexual mates are available. Captive animals that bond sexually with one another when opposite-sex partners are completely unavailable often resist later attempts to “convert” them to heterosexuality. They may even exhibit a longer-term “preference” for same-sex mates that outlasts their initial “situational” introduction to homosexuality. A pair of male White-fronted Amazon Parrots, for example, vigorously refused the advances of female birds even though their homosexual bond was formed “because” no females were available, while two female Long-eared Hedgehogs who were sexually involved with each other in the absence of males refused to mate heterosexually for up to two and a half years after they were separated (as mentioned earlier). The bonding in same-sex pairs of male Steller’s Sea Eagles and female Barn Owls (housed without any heterosexual mates) was strong enough to enable successful coparenting of chicks, and in some cases the birds ignored subsequent introductions of opposite-sex partners. Male Rhesus Macaques, Crab-eating Macaques, Bottlenose Dolphins, Cheetahs, and Black-headed Gulls with homosexual bonds resist the attentions of opposite-sex partners or are clearly distressed when separated from one another, and/or they promptly renew their relationship on being reunited—often showing visible signs of affection and excitement when seeing their male partner again. This is also true for male Mallard Ducks that are raised together, in whom homosexual pairing typically becomes their lifetime “orientation.” They consistently seek the company of other males even when opposite-sex mates are available and maintain their homosexual bonds year after year (or re-pair with males after the death of a partner) in spite of persistent overtures from females.55
The Contamination of Homosexuality
Of all the scientists who have advocated a shortage explanation for homosexuality, not one has ever specified a critical sex ratio that will consistently “induce” homosexuality, or a crucial threshold of members of the opposite sex that must be present in order to unfailingly prevent individuals from “resorting” to homosexuality. Is a mere 5 percent surplus of one sex enough to tip the scales? Apparently, since a population of Ring-billed Gulls with only 55 percent females is claimed to have enough of a skew to “cause” homosexual pairing. Yet a 5 percent excess of males in other species such as Greylag Geese is apparently not sufficient to “precipitate” homosexual pairing.56 In fact, it is highly unlikely that a single critical sex ratio could ever be specified, because the proportion that “causes” homosexuality in one species (or population) has no such effect at all in other species, even where enormous “surpluses” (of, say, 80 percent or more of one sex) are concerned. More broadly, the underlying assumption behind the shortage hypothesis—that sex ratios actually determine a species’ mating habits and social systems—has already been shown to be false for other types of mating behaviors. Scientists now recognize that there is not a clear, one-way causal relationship between how many males or females are available in a population, and the form that their mating system takes (e.g., polygamy as opposed to monogamy). Rather, a complex interplay of many factors is at work.57 Unfortunately, the subtlety of this interaction is generally only recognized where heterosexual mating systems are concerned.
The shortage hypothesis is not only suspect on theoretical grounds, it is often applied to particular cases in a hasty or inconsistent fashion. Skewed sex ratios in animals exhibiting same-sex activity are often presumed without adequate supporting evidence, or else questionable “explanations” are proposed for the origin of such skewed ratios.58 This is best illustrated by the species in which the shortage explanation is most prominent: Gulls. In the late 1970s and early 1980s scientists noticed that high levels of DDT and other environmental contaminants seemed to be associated with some populations of Western and Herring Gulls where nests contained supernormal clutches (often belonging to lesbian pairs). The following chain of “causation” was proposed to explain the apparent correlation: toxins (such as DDT) cause “feminization” of male Gull embryos, which in turn leads to female-biased sex ratios, which in turn results in lesbian pairs, who then attempt to breed, ultimately laying supernormal clutches.59 Let’s set aside for the moment the fact that this explanation is only of limited applicability—homosexual pairing is not associated with environmental toxins in over 70 other bird species, including several Gulls (e.g., Ring-billed Gulls, Common Gulls, and Kittiwakes).60 Let’s also set aside the fact that it is only of limited explanatory value—even if it could be shown conclusively that same-sex pairing results from skewed sex ratios that in turn result from toxins, the fact that only some species (and only some individuals in each species) respond to such conditions with homosexuality would still need to be addressed. Even for the Gull species where this explanation is supposedly relevant, however, each link in the overall chain is weak.
First, although laboratory experiments have shown that some toxins may cause male bird embryos to develop some ovarian tissue, no “feminized” male chicks or adults have actually been found in the wild among Western Gulls (or other species) living in contaminated areas.61 Second, it is unlikely that toxin-induced feminization of males would result in populations with more breeding females than males (since it is most definitely not the case that toxins actually “convert” male embryos into female birds with fully functional ovaries). It would have to act either directly on the health of males, causing more deaths, or indirectly, by resulting in behavioral changes in males that would prevent them from mating with females. But there is no direct evidence that toxins cause anything beyond some physiological alterations in the reproductive organs of Gulls.62 A higher mortality rate among males exposed to toxins has never been demonstrated, nor have behavioral differences among such males been observed that might lead them to forgo mating or otherwise to be “unavailable” as mates.63 It has been suggested that “chemically sterilized” males simply fail to join the breeding colonies, or that such males are “no longer interested” in copulating heterosexually. Yet this begs the question of how or why sterility (or other physiological modifications) causes such males to exempt themselves from reproductive activities, or what exactly prevents them from pairing (or even copulating) with females even if they are sterile. Just because an animal is intersexed or transgendered (e.g., “feminized”) does not necessarily mean that it is asexual or that its reproductive organs or behavior are “dysfunctional.” “Masculinized” female Deer, Bears, and Spotted Hyenas, for example, regularly mate with males, give birth, and raise offspring—even though such individuals often have highly modified reproductive anatomies and hormonal profiles. Even when they are sterile, transgendered and intersexual animals in other species engage in courtship, copulation, and/or pair-bonding. Thus, it is overly simplistic to equate changes in reproductive physiology with an absence of sexual, pairing, or even procreative abilities. It should also be pointed out that a skewed sex ratio is not necessarily an “unnatural” result of environmental contamination: many Gull populations are in fact “naturally” biased in favor of females independently of the effects of toxins, owing to the overall higher survival rate of females (among other factors).64