Combining these three behavioral categories yields a figure of just over 20 percent: roughly one-fifth of all interactions, on average, are homosexual in mammal and bird species that have at least some form of same-sex courtship, sexual, and/or pair-bonding activities. If one figure could be said to represent the overall frequency of homosexual activity in animals, this would probably be the one—but it is virtually impossible to come up with a truly “representative” number. A figure such as this collapses a multiplicity of behaviors (both between and within species), it represents only a fraction of the animals in which homosexuality has been documented, it glosses over many observational and theoretical uncertainties (not the least of which is widely differing sample sizes), and it misleadingly equates often radically unlike phenomena (different forms of heterosexual and homosexual behaviors, disparate social contexts, and so on). A less satisfying, but ultimately more meaningful, “formula” for understanding frequency is to recognize that there is no one overall frequency, no single formula. As in all aspects of animal homosexuality, different species exhibit an extraordinary range of rates, quantities, periodicities, and proportions of same-sex behavior—a diversity that is equal to the variation in the behaviors themselves. We can make tallies for particular species, develop formulas for certain populations or behaviors, and calculate percentages, time budgets, and so on—thereby trying to gain some overall impressions regarding the prevalence of homosexuality in animals. In the end, though, we must acknowledge that our measures are at best imperfect—and what we are attempting to quantify is, in many senses, incalculable.
Within Genders, Without Genders, Across Genders
The traditional view of the animal kingdom—what one might call the Noah’s ark view—is that biology revolves around two sexes, male and female, with one of each to a pair. The range of genders and sexualities actually found in the animal world, however, is considerably richer than this. Animals with females that become males, animals with no males at all, animals that are both male and female simultaneously, animals where males resemble females, animals where females court other females and males court other males—Noah’s ark was never quite like this! Homosexuality represents but one of a wide variety of alternative sexualities and genders. Many people are familiar with transvestism or transsexuality only in humans, yet similar phenomena are also found in the animal kingdom. Although this book focuses primarily on homosexuality, it is helpful to compare this with related phenomena that are often confused with homosexuality, and to discuss some specific examples of each.
Many animals live without two distinct genders, or with multiple genders. In hermaphrodite species, for instance, all individuals are both male and female simultaneously, and hence there are not really two separate sexes; in parthenogenetic species, all individuals are female and they reproduce by virgin birth. A number of other phenomena in the animal kingdom—for which we will use the cover term transgender—involve the crossing or traversing of existing gender categories: for example, transvestism (imitating the opposite sex, either behaviorally, visually, or chemically), transsexuality (physically becoming the opposite sex), and intersexuality (combining physical characteristics of both sexes).46
Early descriptions of animal homosexuality often mistakenly called the animals “hermaphrodites,” since any “transgression” of gender categories (such as sexual behavior) was usually equated with physical gender-mixing. True hermaphroditism, however, involves animals that have both male and female reproductive organs at the same time. This phenomenon is found in many invertebrate organisms, such as slugs and worms, as well as in a number of fish species (for example, lantern fishes and some species of hamlets and deep-sea fishes). Some hermaphrodites can fertilize themselves, but mating in many hermaphroditic species involves two individuals having sex with each other in order to mutually exchange both eggs and sperm.47 Since both such individuals have identical biologies, i.e., are of the same (dual) sex, technically such behavior could be classified as homosexual. However, such activity differs from actual homosexuality because it occurs in a species that does not have two separate sexes, and because it typically does result in procreation. In species that do have two distinct sexes, there are other types of hermaphroditism or intersexuality, in which individuals combine various physical features of both sexes. These differ from species-wide, true hermaphroditism because such animals are not able to reproduce as both males and females simultaneously, and they usually comprise only a fraction of the otherwise nonhermaphroditic population. Further examples of this type of transgender will be discussed in chapter 6.
Virgin birth, or parthenogenesis, is not just the stuff of religions: it is actually found in over a thousand species worldwide and is a “natural” form of cloning. Each member of a parthenogenetic species is biologically female (that is, capable of producing eggs). Rather than requiring sperm to fertilize these eggs, however, she simply makes an exact copy of her own genetic code. Virgin birth is found in a number of fishes, lizards, insects, and other invertebrates. In most parthenogenetic species, individuals do not have sex with each other, but in some species, such as the Amazon Molly and Whiptail Lizards, females actually court and mate with one another, even though no eggs (or sperm) are exchanged in such encounters.
Whereas homosexuality and bisexuality involve activity within the same gender, hermaphroditism and parthenogenesis involve courtship and sexual behavior without genders (at least, without one class of individuals that are male and another class that are female). In contrast, transvestism and transsexuality are a kind of “crossing over” from one gender or sexual category to another, or the combining of elements from each category. In transvestism, individuals of one biological sex take on the characteristics of the other sex, either behaviorally or physically, without actually changing their own sex. In transsexuality, individuals actually become the opposite sex, so that a male turns into a female or vice versa (where male and female are used strictly in the reproductive sense to refer to animals that produce sperm or eggs, respectively).
Transvestism is widespread in the animal kingdom and takes a variety of forms.48 Both male-to-female and female-to-male transvestism occur: some female African swallowtail butterflies, for example, resemble males in their wing coloration and patterning, while in some species of squid, males imitate female arm postures during aggressive encounters.49 Physical transvestism can involve almost total physical resemblance between males and females, or mimicry of only certain primary or secondary sexual characteristics. For instance, in several species of North American perching birds, young males resemble adult females in their plumage—making them distinct from both adult males and juvenile females. In some birds, such as the painted bunting, the resemblance between adult females and juvenile males is nearly total, while in others, younger males are more intermediate between adult males and females in appearance.50 Several species of hoofed mammals show a different type of physical transvestism: female mimicry of the horns or tusks found in males.51 Female Chinese water deer, for example, grow special tufts of hairs on their jaws that resemble the tusks of the male, while female Musk-oxen have a patch of hair on their foreheads that mimics the males’ horn shield. Physical transvestism can also be chemical or scent-based: some male Common Garter Snakes, for example, produce a scent that resembles the female pheromone, causing males to mistake them for females and attempt to court and mate with them.