Of all the sexual acts that are possible, only one will produce babies. There isn’t really a sliding scale here—conception is either possible or not. Due to the nature of organisms that require two differentiated sexes in two individuals, one guaranteed way to do sex and not have a baby is to do it with members of the same sex. In the future, there will be ways that eggs or sperm might be engineered to be genetically suitable to form a new conception. Both are cells that have reached a fully differentiated state—they are mature, have shuffled and halved their total DNA in preparation for meeting an equivalent cell to complete the full deck at the beginning of a new life. But we may soon be able to rewind some of that maturation process and then redirect either cell type to become something else, for example, a sperm rewound and then steered toward becoming an egg, or vice versa. That way, two women or two men could in theory conceive a child with half of each same-sex parent’s genome.
That’s not possible, yet. Until then, two men or two women together do not have the required genetic compatibility to fertilize an egg and produce a pregnancy. Homosexuality therefore is a sexual identity independent of the evolutionary imperative to reproduce.
I could quote dozens of different statistics here to address the question of how many people are homosexual—there is no consistent figure. Nor is there a consistent pattern of behavior that allows easy or clear definitions or demographics. Some people appear to be exclusively homosexual from a young age, and some exclusively heterosexual. Many are somewhere in between, in that they might be primarily one way or the other, but have had homosexual, bisexual or heterosexual experiences or thoughts once, sometimes or regularly. Some studies have shown that 20 percent of adults have been sexually attracted to members of the same sex, though the percentage of people who have enacted same-sex encounters is typically half of that.
Precision in these demographics doesn’t really matter when thinking about the broad sweep of evolution. Homosexuality exists, and hundreds of millions of people identify as homosexual. Conception remains an impossibility following homosexual sex, which superficially suggests that it might be maladaptive. That poses a potential problem when searching for an evolutionary exploration of a particular behavior. How can sexual behavior that cannot produce offspring persist at such a high frequency? Could this be an example of something that has delineated a boundary between human animals and non-human animals?
Apparently not. Homosexuality abounds in nature too. Some of the examples have been mentioned already, though perhaps bonobos are not a great comparison, as they have sexual encounters with all members of a group all the time for complex social reasons, rather like the English chat about the weather.
Consider the giraffe. Giraffes are beloved of evolutionary biologists for a number of reasons. They are, of course, the tallest of all living animals, and that elegant neck is the primary reason why. Its exaggerated form was historically given as an example of how evolution might occur under the auspices of a now abandoned theory. Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck, was not the first person to consider the concept of evolution—simply, how animals change over time—but he was one of the first to think, write and publish seriously on the matter. Giraffes, or camelopards* as they were referred to in the nineteenth century, were a big part of his scheme. In 1809, the year that Charles Darwin was born, Lamarck published Philosophie Zoologique, in which he espoused his theories on why animals change over time. The giraffe, he argued, became “gifted with a long flexible neck” by stretching to reach the juiciest acacia leaves.† In doing so, something akin to a “nervous fluid” would flow into the neck, which would grow in response. This incremental acquisition of length would be passed on to its children and the process repeated.
Fifty years later, On the Origin of Species was published, which fully supplanted the idea of the inheritance of acquired traits:‡ the experiences of a life does not change DNA in a way that can be passed on to the next generation, and so has little or no influence on the genes on which natural selection acts. Darwin relegated Lamarck to the category of important, meticulous, great scientific thinkers who were not right on their big idea. We sometimes scoff at Lamarck for being wrong these days, which is an appalling slight on his thoughtful work. His ideas were supplanted by the greatest of all scientific theories, by the greatest of all biologists. All scientists need to be wrong as often as they can be, for that is the place from which we discover what is correct, and inch ever closer toward truth. There is a statue in the Jardin des Plantes in Paris, where his daughter is seen addressing an aged, blind Lamarck. The engraving on the plinth says: “Posterity will admire you, and she will avenge you, my father.”
It was data that killed Lamarck’s theory of evolution. There are many reasons why the inheritance of acquired traits is wrong, primarily because we have never discovered a mechanism by which the information could be passed on to subsequent generations. We don’t actually see the modification of a trait in subsequent generations as a result of experience—polar bears in zoos remain white despite not spending a lot of time in snow. More prosaically, giraffes mostly forage at shoulder height, and stretching to eat higher and theoretically juicier leaves is not borne out by observation. Nevertheless, its neck is still wonderfully instructive for Darwinian evolution. Betraying its shared ancestry with other animals, it has the same number of vertebrae as both us and mice. Each one is, of course, very much bigger. That neck is also home to the recurrent laryngeal nerve—found in us and in much more distantly related fish—which innervates parts of the larynx. In giraffes, this nerve takes a preposterous fifteen-foot detour, a meandering loop around a major artery flowing directly from the top of the heart. Which is exactly what it does in us, only the length of the giraffe’s neck has stretched this loop all the way up and down rather wastefully. The fact that its anatomical position is exactly the same in us and them is a stamp, a hallmark of blind, inefficient evolution in nature, which Darwin himself described as “clumsy, wasteful, [and] blundering.”
The origin of that beautiful neck has also been attributed to sexual selection. It is extravagant and slightly absurd, like a peacock’s tail, so might be one of those runaway traits that we see exaggerated in males of so many sexual beasts. This is where the sex lives of giraffes gets interesting. The neck is certainly a major part of sexual and social behavior. Since 1958, the male-to-male wrestling that giraffes are often seen engaging in has been called “necking.” They curl their necks around each other and rut. It’s incredible to watch, the necks twisting and bending at almost right angles, the normal grace of these animals replaced by ungainly aggression and awkward legs, with none of the elegant power of two stags clashing antlers.
Necking, as with its human teenage counterpart, is often foreplay to some more serious sex. It looks similar to many male-to-male competitive behaviors that precede copulating with a female. They battle, and one comes out on top. The primary difference in giraffes seems to be that after a bout of heavy necking, the males will often have penetrative sex. As with so many of the interesting behaviors of wild animals that we observe and try to understand, there hasn’t been a great deal of work in this area. Numbers therefore are not huge, and robust conclusions are elusive. But it does appear that the majority of sexual encounters in giraffes involve two males necking, followed by anal sex.* Not all necking encounters result in attempted or successful mounting, but in many cases, the necking males spar with erect unsheathed penises.
Giraffes tend to segregate by sex most of the time. The necking behavior happens almost exclusively in male herds. In one report, recording more than 3,200 hours of observation over three years in national parks in Tanzania, sixteen male-on-male mountings were seen, nine of which featured an unsheathed penis. The naturalists assumed initially that this was an expression of dominance, but saw no activity (normally indicated by submission, or a particular posture) surrounding the act that supported that idea. In the same period, they only saw one male mount a female. Sixteen out of seventeen is about 94 percent.
We don’t know why they behave like this. Twenty-two calves were born in the same period, presumably following heterosexual action, so it follows that most mountings must have gone unobserved, but that also implies that more same-sex male mountings also happened. This data and other observations suggest that male giraffes don’t have sex with females very often. When they do, they lick and smell the urine of the female, and then follow her around for a couple of days. The females will repeatedly frustrate the attempted mount by a male via the impressively nonchalant tactic of simply walking forwards. They eventually stand still if they are in the mood.
Even with scientific caution in play, it seems safe to say that most giraffe sexual encounters are male homosexual. Logic dictates that a species that is exclusively homosexual will not survive for very long. However, one in ten is still enough for a species to continue, and indeed twenty-two calves born in a three-year period is a decent brood. Female giraffes appear to be fertile and receptive for only a couple of days a year, and with a gestation period of up to one and a quarter years, they’re not particularly prone to a quick generational turnaround. The homosexual encounters are clearly an activity that has some social meaning, though it’s not obviously the establishment of a hierarchy or dominance. We don’t know much more than that.
Many other animals also engage in homosexual sex, including rats, elephants, lions, macaques, and at least twenty species of bat. There are fewer documented examples of female homosexuality, but then there is much less data on female sexuality in humans and other animals in general. As with so many areas of science, there has been a historical skew toward understanding male behavior. Of the sapphic relations we do know about, we have a better understanding of biological principles that might be at work. Farmers are entirely untroubled by homosexual activity in goats, sheep, chickens, and even use cows mounting each other as a good sign that they are fertile. Whiptail lizards can reproduce using parthenogenesis, the virgin birth that we also see in Komodo dragons, and female-onfemale mounting may be a mechanism to induce ovulation. Like bonobos, hyenas live in a matriarchy. Females are dominant, more aggressive and more muscular than males. They also have an unusual set of genitalia: the clitoris is huge, erectile and only slightly smaller than the male penis. Females engage in clitoral licking frequently, to bond socially and to establish hierarchy.
Homosexuality does pose an evolutionary puzzle, though there are plenty of ideas as to how this behavior might persist through time. In humans, there has been some evidence of regions of DNA that associate with male homosexuality. This is not a “gay gene” as the media would have you think, as there are no genes “for” complex behaviors. Rather, it seems (though data is somewhat limited) that certain sections of genetic code occur in versions that are more frequently associated with homosexuality than by chance. If that sounds mealy-mouthed and painfully caveated, that is where we are currently at with genetics and complex social behaviors. Almost no human traits are determined by the flick of a DNA switch, but instead by many genetic factors interacting and contributing small effects in concert with the lived life of experience.*
Outside of straight genetics, there have been plenty of twin studies looking at homosexuality in men. Identical twins have (very nearly) identical DNA, so any behavioral differences are likely to be caused by non-genetic, that is, environmental, factors. The various studies have produced a raft of different percentages, but all suggest that if one identical twin is homosexual, the other is on average more likely to also be homosexual, compared to fraternal twins. There’s also the fact that studies show that having a homosexual older brother increases the chances of a younger brother being homosexual.
There is little doubt that homosexuality has a genetic component—all behaviors do. Many genes influence biological traits in concert with the environment in which they act. Genes that reduce reproductive success are eventually deleted, as the individuals who carry them will be outcompeted. The question for evolutionary biologists is why haven’t those genes driven themselves out of the gene pool? Homosexual males are less likely to have children, therefore at first glance the genes involved should be prone to purging from the genome.
The first potential answer is that exclusive homosexuality may have been historically rare. There is a terminology issue here, because we tend to look at sexual behavior through a modern and Western lens. The way we typically talk about homosexuality today tends to be representative of an identity, rather than simply a description of behavior. I’ve fudged that boundary in these pages, but cannot when talking about homosexuality in humans. Here, I’m talking about what we might today call gender or sexual nonconformity. Having sexual relationships with people of the same sex has not always been regarded in the same terms that it is today in our culture, and in many examples it may be better thought of as “something they did” rather than “something they are.” With this in mind, same-sex activity is described as occurring in the ancient Greeks, Romans, indigenous people of the Americas, Japan and many other historical societies, with a mixture of cultural acceptance.
In many of these examples, it may not have been an exclusive practice, and therefore procreation and perpetuation of a genetic basis for sexually diverse behaviors can persist without hindrance. Though homosexuality in animals is everywhere, it is also rarely exclusive. There are some cases of animals only being interested in same-sex partners: around 8 percent of domesticated rams appear to only have sexual relations with other rams. Multiple ideas have been suggested to explain this, and as so often is the case in science, the answer may well be a combination of all of them.
One of the key ideas in evolutionary biology is kin selection. It’s predicated on the notion that the gene—rather than the individual, group or even species—is what is being selected by nature. It just so happens that the best way for a gene to survive into the future is by conspiring in concert with a whole load of other genes with the same selfish motivation, all kept inside a body whose job it is to secure the reproduction of those genes. This is a cast-iron theory, a towering cornerstone of evolution, and it explains the behaviors of all sorts of social organisms, especially the bees, ants and wasps, the males of which mostly don’t get to reproduce at all. They do share all of their DNA with their mother, who reproduces by the bucketload, and so what has evolved is a system by which, mathematically, sterile males assisting a fecund female accommodates the survival and genetic propagation of both.
Kin selection has been suggested as a mechanism by which homosexuality might have continued in evolutionary history, despite its appearance of being maladaptive. There are two types of kin that have been explored in attempts to explain the persistent existence of homosexual men. The “gay uncle hypothesis” suggests that having a close family member who is a homosexual male will increase the survival of a nephew or niece by helping to raise, protect and nurture. The biological imperative is that they share a high proportion of their genes, and the gay uncle’s genes will survive regardless of not having children himself. It’s not dissimilar to other examples of reproductive support in sexual organisms, where individuals with shared genes aid the survival of offspring which are not their own. Gay uncles are similar in that regard to another possible example of family member being important for evolution: the “grandmother hypothesis” (which also serves as a means of explaining the existence of the menopause). As women become post-reproductive, they don’t just shuffle off and die, but instead stick around and may assist in the raising of their grandchildren, with whom they share one-quarter of their DNA. It’s a popular idea, and may be true, though data in humans is not very rich. It may also be true in killer whales, who operate complex social structures headed by older matriarchs, and are one of only three species that are known to have the menopause (short-finned pilot whales are the third).* The gay uncle idea is the homosexual equivalent to the grandmother hypothesis. The trouble is that there simply aren’t many data points that support either.
There’s another explanation for which the data is more persuasive. In 2012, one study indicated that the grandmothers and aunts of homosexual men had significantly more children than the grandmothers and aunts of heterosexual men. The increase in fecundity of these women appears to adequately compensate for the absence of fecundity of the men themselves. It suggests that a genetic basis that predisposes men toward homosexuality may also be the same code that facilitates increased fertility in their female relatives. It doesn’t necessarily mean it’s causing either, but may be tipping the scales in those directions, which is mathematically enough to compensate for the apparent loss of genetic legacy. It’s an interesting idea and the data is compelling, but it’s early days in this research. Though the sample size is ample, it is only one study, and much more work is needed. Whether this is the case in the exclusively homosexual rams is yet to be investigated.
In animals, homosexuality is rampant. The important thing to note here is that we don’t know why giraffes or any animal engage in homosexual behavior, but we shouldn’t assume that it is for reasons relevant to human sexuality. Even within human behavior, there are many examples of sexual acts between males that are ritualistic, rather than conforming to the sexual identities of men who describe themselves as gay. The Sambia are a tribe in the Eastern Highlands of Papua New Guinea who believe that semen ingestion is an essential rite for the passage into manhood. Boys approaching pubescence practice oral sex on an older man for many years, until the boy pairs with a young woman, who also performs fellatio on him for a period of a few years. Some men abandon their same-sex practices then, and others do not. Anthropologists have asserted that the male homosexual behavior is purely ritualistic and therefore not erotic, though this seems a weak argument to me, given that sexual arousal is a prerequisite for the act of releasing semen.
Men of the Marind-Anim people of New Guinea enjoy anal copulation with other men throughout their lives, associated with their belief that semen has magical properties: it is spread on arrow tips and spears to help them find their target, and ingested in concoctions by men, women and children. Taking in semen from anal sex is viewed as a means of increasing masculinity.
All the myriad versions of genital engagement in us and other animals shows that sex is very clearly not only for making babies. We sometimes make the error of assuming that, a behavior is an evolutionary antecedent to our own, or that, conversely, it has emerged in parallel because it is a good trick. The marvelous carnival in nature shows that sex is important, and that evolution finds ways to utilize what it has available to do what needs to be done. Many people know of the maxim said by the biologist François Jacob describing natural selection as a tinkerer. I like to think of the words of the US president Teddy Roosevelt: “Do what you can, with what you have, where you are.”
Evolution invented parts thrown together through error and trial, which can then be deployed to try new things to fit the ever-changing environment. Sexual reproduction is clearly a useful ability to have in one’s armory,* and has been with us for at least a billion years, from a time when complex life had yet to fill the oceans, the skies and the land. Since then, the basic function of making offspring from two parents has been co-opted countless times to further create endless opportunities to enhance survival. We could try to deconstruct the ontology of homosexual behavior in us. We could attempt to deconvolute and extract the biological and social cues that lead to a person having a preference or even a “type,” whether it involves blondes, or kindness, or athletic physiques, or kind blonde athletic types of the same sex, or even the Papuan cultural rites of passage into manhood. Like all behavior, sexuality is programmed, not simply by genes, or the environment, but by inscrutable interactions between biology and experience.
There is a political point that unavoidably emerges from this.
Homosexuality abounds in non-human animals. Superficially, it appears to run counter to the general principles of evolution, but the more we look at the ethology of sex, the more this doesn’t necessarily seem to be problematic for science.
Rather hilariously, in November 2017, a Kenyan official responded to reports and photos of two large male lions in Maasai Mara engaging in anal sex (as they frequently do), with the statement that they must have copied it from watching men do it.* Imagine what he’ll think when he finds out about the giraffes. Amusing though that might be, homosexual men and women are persecuted, jailed, tortured and murdered in many countries all around the world, including Kenya, and suffer prejudice everywhere. Historically, the assertion that it is contra naturam—against nature—has been made in order to justify that persecution. Whatever the nature of homophobic bigotry, science is not on your side. As we have seen, homosexuality is natural, and it’s everywhere.