Obviously, I am going to have to write another article in due course about the phenomenon, because non-zoologists do not understand that many species of animals use sex in manners not easily referable to human sexuality - or, indeed, to that of other non-human species. Homosexuality as we know it is extremely rare outside of humans.There seems to be a lot of interest in this lately. The Wikipedia article on the subject, for example, is accurate as far as it goes, but misses the big picture entirely. The natural temptation is always to equate it with human homosexuality. Indeed, it is clear that many people cite it in order to validate the human activity. One wonders how many examples they need to validate it: a hundred, or just one? And how the same method would not validate monogamy, harems, promiscuity, infanticide, and cannibalism, all of which can be found in the lower animals. In point of fact, every species, including the human species, possesses a social system adapted to its way of life. The presence of a specific behaviour in some other species does not validate it for human beings, and its absence does not invalidate it. Whether homosexual practices are a legitimate activity for human beings is a legitimate subject for debate, but you won't find the arguments in this essay.
First Principles
It is important to mention certain things which a zoologist - and particularly an ethologist, or student of animal behaviour - takes for granted, but which may not be obvious to the outsider.
The first is, as mentioned before, that every species has its own social system, which is as hard-wired into its nature as its physical characteristics, and which allows its individuals to operate effectively within its ecological niche. In an earlier essay, I cited the well-known differences in personality between dogs and cats, and explained how the human niche as a large brained generalist led to a social organisation quite different from those of the apes.
Secondly, evolution proceeds by means of genes which allow the individual to maximise the number of surviving children. To the extent that an individual spends its time trying to mate with the wrong sex, its breeding success will be reduced. Therefore, the activity must be either abnormal, or else it provides some secondary, indirect selective advantage. As we shall see, when homosexual behaviour is widespread in a species, it does in fact provide an indirect advantage.
Thirdly, behaviour and anatomy go together. In play fighting and real fighting, lambs butt and kids strike upwards with their heads, although they do not as yet possess horns. They each possess an instinct to fight in a particular way because their natural weapons are designed to be used in different ways. If a lamb is fostered on a nanny goat, or a kid on a ewe, they will still instinctively use the fighting method of their own species. When it comes to sex, the organs of males and females are complementary. But there are no anatomical adjustments for homosexual behaviour.
Now let us examine the situations in detail.
One would assume that, if an individual were genuinely attracted to the same sex, it would nevertheless follow the instinctive mating pattern of its own sex. When an animal adopts the mating pattern of the opposite sex, this is known as "pseudomale" or "pseudofemale" behaviour. Thus, when a subordinate male presents his rump to the alpha male, and the latter mounts him, both are involved in a homosexual encounter, but the subordinate is performing pseudofemale behaviour, as distinct from the regular male response of the alpha. When a cow or female koala on heat mounts another female, she is performing pseudomale behaviour. The other female, however, is not performing any behaviour; she didn't choose to get involved.
How does this relate to human behaviour? Not very well. It might be argued that the passive partner in a homosexual encounter is engaged in pseudofemale female activity, but this is deceptive. Rear entry is not a common sex position for men and women. I'm not saying it is abnormal, just that it is uncommon. Indeed, although there are a few positions which most couples use most of the time as a matter of convenience, it would be hard to argue that there is a "natural" human method of copulation, because humans are given verbal instructions - though not always very detailed, I will admit. To ascertain "what comes naturally" among human beings, you would need to find a completely naive couple, like Richard and Emmeline in The Blue Lagoon. However, because Richard and Emmeline are rational beings, they are perfectly capable of working things out by trial and error. One thing is certain: as the homosexual raconteur, Quentin Crisp put it: when a man and a woman want to do it, they just do it, but every homosexual sex act has to commence with a conference.
The second was with a fellow zoologist involved in artificial insemination. "How do you know," I asked, "when a cow is on heat?" (Which would mean she was at the fertile stage of her cycle, and ready for mating.)
"When they mount other cows," she blithely replied.
In my earlier essay I also described how, when a female koala is on heat, she will mount, neck bite, and pelvic thrust another female, and also bellow, which is normally a male prerogative.
In neither case is it obvious how, or whether, it improves the female's reproductive fitness, and in the case of koalas, it would occur only rarely in the wild, because they are basically solitary. I suspect it is a side effect of the hormonal changes during heat. In any case, it is a regular, normal occurrence and does not indicate that the female is attracted to other females; it means she is desperate for a male to satisfy her.
Of course, penguins, like most birds, have next to no sense of smell. Since we humans are not much better, we tend to forget that it dominates the lives of most other mammals. The female signals her sexual receptibility during her fertile period by a distinct odour, and without it, males, by and large, do not find her sexy. It is what is referred to as a pheromone. An interesting feature of cats is that the female typically becomes attractive to males before she herself is ready to mate. This has the advantage (to her) of bringing together suitors to fight for her hand, so to speak, so that, when she is ready, she knows the toughest and strongest male is ready.
Now, Joy Adamson, who achieved fame with her book, Born Free, also rehabilitated a cheetah, Pippa into the wild, and followed up her litter into adulthood. When the female cub came into season, her brothers tried to mate with her. (If they hadn't been brothers, they would have fought.) When she ignored them, as often as not they would mount each other. The point of course is that their actions were not due to same-sex attraction, but were reactions to their sister's pheromone.
To a certain extent, a comparison might be made with the homosexual liaisons in such places as prisons, where people are denied normal sexual outlet. Although this can obviously become an acquired taste, it is not what most of us would call "normal" homosexuality. But even here the comparison falls down, because the human actions are based on reason, rather than confusion of signals. The lusting male convict does not mistake the "pretty boy" he rapes for a woman; he knows full well he isn't. Given a choice, he would much prefer a rough, "macho" woman with few feminine signals, but he has made a rational decision to make use of what - or rather whom - he has got.
Just the same, interspecific breeding ie mating between males and females of closely related species, are more common in captivity than attempted matings between members of the same sex. You have to remember that the dynamics of animal societies are not all the same. What has just been described can more easily happen if the species normally lives in moderately sized groups of both sexes, with a recognizable dominance hierarchy. But many species are normally solitary, or live in small, narrowly restricted groups. Even big, anonymous herds are often aggregations of individuals of a more-or-less solitary disposition. Such individuals will be more likely to view a member of the same sex - or even the opposite sex during the non-mating season - as an enemy than a lover.
Also, as pointed out earlier, mammals are dominated by scent. Thus, if a new jackass is placed in an enclosure with another jackass, the resident will be more likely to attack him. Even if that didn't happen, they are hardly likely to see each other as potential sex objects. No matter how much a jackass may resemble a she-ass to the human eye, it will never, ever smell like one. On the other hand, a mare on heat will have enough of the characteristics of a she-ass to act as a reasonable proxy. That's how mules are made.
Agonistic interactions are those involving fighting, threats, or potential fights. Suppose you are being attacked or threatened by a big, hulking alpha male, and you cannot escape, or do not wish to run away, because you belong to a group. What do you do? Well, the first option is to reverse all your own aggressive signals. Instead of standing upright, bristling, and roaring, you hunch down, flatten your fur and ears, pull your tail between your legs, and utter high pitched sounds - in other words, cringe, cower, whimper, and squeal.
Another option is to distract your opponent by inciting another urge. You might, for instance, act like a child, and thus evoke his parental, protective, or at least non-aggressive instincts. This is not unknown among humans; witness the wife who bursts into tears during an argument with her husband. But it is more often used to avoid provoking aggression in the first place, for example, by a subordinate ape who approaches a dominant by holding out his hand in the child's begging gesture - not because he wants to be given something, but just to avoid being chased away.
Otherwise, you can attempt to arouse his sexual urges, say by presenting your rump to him as would a female. You might think that an intelligent animal such as a baboon would know the difference between a female and a male pretending to be a female. But, as one primatologist pointed out, human advertisers will use a photograph of an attractive woman in order to sell a car. A photo, of course, is not the real thing, but it possesses some of the features of the real thing, and the ad-men use the slight arousal induced by the photo in order to produce a positive feeling towards the adjacent object. Similarly, the subordinate baboon distracts the angry alpha by producing some of the feelings normally produced by a female. The result is that, in species where this behaviour occurs, it has become ritualised. The subordinate presents his rump, the dominant mounts him, usually perfunctorily, and without penetration or ejaculation, and the ritual is over. Both of them have established, or reaffirmed, the dominance hierarchy, and they can go back to their normal business.
This pattern of behaviour has obviously evolved more than once, because the ingredients are the same all over. It is common, for example, for male dogs to mount another male as a display of dominance. It is particularly common among ungulates. Dominant rams, for instance, will mount subordinates in order to demonstrate their dominance. Interestingly, when a ewe comes into heat, she also mounts other females. I read in one popular science blog how, after the mating season, the rams get together in homosexual groups. I shall not repeat the author's name. He is a very brilliant paleontologist, but not an ethologist, and his interpretation is bizarre. Mountain rams don't have their special Brokeback Mountain when they are finished mountin' ewes. These are not sexual encounters per se, but dominance-submission rituals. When the mating season recommences, they go back to bashing their heads together. Thus, when you read how one or two percent of rams (not 10%, as is often quoted) are "gay", you should understand that the anomaly is their disinterest in females, not the fact that they are carrying out normal agonistic activities with other males. One experimenter presented some "gay" rams with rams and ewes confined so that their rear ends were available to "rape". It seems painful to have to point out that the scientist, being a member of a species with a poor sense of smell, failed to recognize that, unless the ewe were on heat, and smelled appropriately, even the most heterosexual of rams would have little interest in her.
The behaviour is also quite common among monkeys, particularly macaques and baboons but, interestingly, it is practically unknown among our nearest relatives, the great apes. The one big exception is the bonobo, a type of chimpanzee which lives south of the Congo River. Bonobos have taken it to a whole new level. They use sexual activity, between opposite sexes, members of the same sex, and even between adults and young as a social lubricant, applied to any situation which might arouse tension, or even to display friendship. These activities hardly ever result in orgasm, unlike real matings when the female is on heat.
To begin with, it is best to lay to rest some of the very simplistic ideas held by many non-scientists. As I pointed out in my earlier post, there is no such thing as a gene for monogamy, polygamy, promiscuity, or the like. What the genes affect are such things as the amount of hormone, the response to hormones, the response to specific stimuli, the rate of maturing of certain behaviours, and the ability to learn specific things. As a result, they push the individual, and ultimately the species, in a particular direction.
You should not be surprised, therefore, that the heritability of homosexuality is less than 20% (similar to church going and political affiliation, believe it or not), and that if a homosexual has an identical twin, raised in the same family environment, that twin will be homosexual in only one case out of nine. You should also not be surprised that all the other simplistic explanations, involving hormones, immune responses and the like, have turned out negative. Specialists have been trying for years to discover a simple cause for homosexuality, but there isn't one. It is almost certainly due to a large complex of factors, not all of which will be operative in any single case. However, it is not my aim to re-open this can of worms, but to point out the human exceptionalism.
As a starting point, we might consider the much rarer, but nevertheless related condition of transsexualism or gender dysphoria. The victim of such a disorder feels he is "really" a woman trapped in a man's body, or a man trapped in a woman's body. The point is, it is almost certainly unique to humans. I cannot imagine a bull going around thinking, "I'm really a cow trapped in a bull's body." In fact, I cannot imagine a bull thinking, "I'm a bull, not a cow." Indeed, I cannot even imagine a bull thinking - at least not in a manner with which we would use the term. Before you have an identity crisis, you have to have an identity.
The more complex a machine or an organism, the more things which can go wrong. There must, therefore, be mental or emotional disorders to which only a rational animal, such a humans, can fall victim.
In their excellent book, My Genes Made Me Do It! (which can be read, downloaded, or purchased here), Whitehead and Whitehead include a third chapter (in PDF format) entitled, "Are Heterosexuals "Born That Way"? (something which is not often asked). They state (with references):
I would highly recommend that you read that chapter, because it explains in detail the process of psycho-sexual development in human beings. Turtles may come into the world with the whole of their limited social repertoire written in their brains, but that is not the way the higher mammals develop. Just as a baby' first smile elicits a smile from its parent, and its parent's smile makes it respond in kind, so we are programmed to develop our personalities by means of interactions with other people. Our responses to their actions, and their responses to us, are conditioned by certain basic instincts which push us in one direction or another. Added to this are the specific features of the human family: a lengthy childhood, and the involvement of both parents. By and large, a boy identifies with his father, a girl with her mother. All of this means that, in the vast majority of cases, the pre-programmed result is reached. But sometimes the system breaks down and goes awry.
However, that is not the topic of this essay, and I shall leave the further reading up to you.
Secondly, evolution proceeds by means of genes which allow the individual to maximise the number of surviving children. To the extent that an individual spends its time trying to mate with the wrong sex, its breeding success will be reduced. Therefore, the activity must be either abnormal, or else it provides some secondary, indirect selective advantage. As we shall see, when homosexual behaviour is widespread in a species, it does in fact provide an indirect advantage.
Thirdly, behaviour and anatomy go together. In play fighting and real fighting, lambs butt and kids strike upwards with their heads, although they do not as yet possess horns. They each possess an instinct to fight in a particular way because their natural weapons are designed to be used in different ways. If a lamb is fostered on a nanny goat, or a kid on a ewe, they will still instinctively use the fighting method of their own species. When it comes to sex, the organs of males and females are complementary. But there are no anatomical adjustments for homosexual behaviour.
Now let us examine the situations in detail.
Manifestation
This is something which always get missed in discussions, because people always see things from a human point of view. Every species has a stereotypical mating pattern, and while the more intelligent species are able to vary it, the lower species are forced to stick to it more or less rigidly. Typically, it involves the female crouching somewhat, and raising her rump - "presenting" is the usual term - and the male mounting her. However, it can be more complex. A typical example is the way a tom cat grasps the female by the nape of her neck with his jaws. It is a variation of the way a mother cat carries her kitten, and just as the neck bite induces passivity in the kitten, it induces passivity in the she cat. A zoologist once watched the interspecific mating, in captivity, of two different species of cats, of which the male was shorter than the female. Once he had gripped her neck with his teeth, he couldn't get the parts that count to line up. He therefore started moving his teeth back down her spine until they were able to get their genitals aligned. The point was, instinct forced him to first go through with the neck bite ritual; it couldn't be omitted.One would assume that, if an individual were genuinely attracted to the same sex, it would nevertheless follow the instinctive mating pattern of its own sex. When an animal adopts the mating pattern of the opposite sex, this is known as "pseudomale" or "pseudofemale" behaviour. Thus, when a subordinate male presents his rump to the alpha male, and the latter mounts him, both are involved in a homosexual encounter, but the subordinate is performing pseudofemale behaviour, as distinct from the regular male response of the alpha. When a cow or female koala on heat mounts another female, she is performing pseudomale behaviour. The other female, however, is not performing any behaviour; she didn't choose to get involved.
How does this relate to human behaviour? Not very well. It might be argued that the passive partner in a homosexual encounter is engaged in pseudofemale female activity, but this is deceptive. Rear entry is not a common sex position for men and women. I'm not saying it is abnormal, just that it is uncommon. Indeed, although there are a few positions which most couples use most of the time as a matter of convenience, it would be hard to argue that there is a "natural" human method of copulation, because humans are given verbal instructions - though not always very detailed, I will admit. To ascertain "what comes naturally" among human beings, you would need to find a completely naive couple, like Richard and Emmeline in The Blue Lagoon. However, because Richard and Emmeline are rational beings, they are perfectly capable of working things out by trial and error. One thing is certain: as the homosexual raconteur, Quentin Crisp put it: when a man and a woman want to do it, they just do it, but every homosexual sex act has to commence with a conference.
Manifestation in Heterosexual Mating
Surprisingly enough, pseudomale behaviour might actually be part of normal heterosexual mating patterns. For this, I shall relate two conversations I had. They first was with a workmate, who declared: "Of course, homosexuality is common among animals. You only have to watch cows."The second was with a fellow zoologist involved in artificial insemination. "How do you know," I asked, "when a cow is on heat?" (Which would mean she was at the fertile stage of her cycle, and ready for mating.)
"When they mount other cows," she blithely replied.
In my earlier essay I also described how, when a female koala is on heat, she will mount, neck bite, and pelvic thrust another female, and also bellow, which is normally a male prerogative.
In neither case is it obvious how, or whether, it improves the female's reproductive fitness, and in the case of koalas, it would occur only rarely in the wild, because they are basically solitary. I suspect it is a side effect of the hormonal changes during heat. In any case, it is a regular, normal occurrence and does not indicate that the female is attracted to other females; it means she is desperate for a male to satisfy her.
Confusion of Signals and Sexual Substitution
Animals are programmed to react to social signals. Humans, of course, are no exception - recall how we all think babies are "cute" - but we are able to modify our interpretation of the situation by use of reason. In sexual situations, the physical appearance, smell, and behaviour of another individual signal its sexual status. And an animal can make a mistake. Thus, for example, a scientist on Scott's expedition was shocked at the "depravity" of Adélie penguins. But, as the ornithologist, Douglas Russell pointed out:"Adélies gather at their colonies in October to start to breed. They have only a few weeks to do that and young adults simply have no experience of how to behave. Many respond to inappropriate cues. Hence the seeming depravity of their behaviour. For example, a dead penguin, lying with its eyes half-open, is very similar in appearance to a compliant female. The result is the so-called necrophilia that Levick witnessed and which so disgusted him."At the same time, if an individual is deprived of a member of the opposite sex of its own species, it may settle for something which produces only some, but not all, of the required sexual signals ie a member of a related species, or the same sex. Of course, the most famous case was the two "gay" chinstrap penguins at Central Park Zoo, New York, whose relationship was ended once a real female was introduced. Confusing the issue, at least in the popular mind, was the way they hatched an egg provided by the staff. This was a behaviour pattern independent of mating and bonding. The egg sitting drive is so strong among penguins that unattached individuals, or same-sex pairs, will attempt to hatch an egg - even stealing one from its parents - or occasionally a stone, if nothing else will suffice.
Of course, penguins, like most birds, have next to no sense of smell. Since we humans are not much better, we tend to forget that it dominates the lives of most other mammals. The female signals her sexual receptibility during her fertile period by a distinct odour, and without it, males, by and large, do not find her sexy. It is what is referred to as a pheromone. An interesting feature of cats is that the female typically becomes attractive to males before she herself is ready to mate. This has the advantage (to her) of bringing together suitors to fight for her hand, so to speak, so that, when she is ready, she knows the toughest and strongest male is ready.
Now, Joy Adamson, who achieved fame with her book, Born Free, also rehabilitated a cheetah, Pippa into the wild, and followed up her litter into adulthood. When the female cub came into season, her brothers tried to mate with her. (If they hadn't been brothers, they would have fought.) When she ignored them, as often as not they would mount each other. The point of course is that their actions were not due to same-sex attraction, but were reactions to their sister's pheromone.
To a certain extent, a comparison might be made with the homosexual liaisons in such places as prisons, where people are denied normal sexual outlet. Although this can obviously become an acquired taste, it is not what most of us would call "normal" homosexuality. But even here the comparison falls down, because the human actions are based on reason, rather than confusion of signals. The lusting male convict does not mistake the "pretty boy" he rapes for a woman; he knows full well he isn't. Given a choice, he would much prefer a rough, "macho" woman with few feminine signals, but he has made a rational decision to make use of what - or rather whom - he has got.
Just the same, interspecific breeding ie mating between males and females of closely related species, are more common in captivity than attempted matings between members of the same sex. You have to remember that the dynamics of animal societies are not all the same. What has just been described can more easily happen if the species normally lives in moderately sized groups of both sexes, with a recognizable dominance hierarchy. But many species are normally solitary, or live in small, narrowly restricted groups. Even big, anonymous herds are often aggregations of individuals of a more-or-less solitary disposition. Such individuals will be more likely to view a member of the same sex - or even the opposite sex during the non-mating season - as an enemy than a lover.
Also, as pointed out earlier, mammals are dominated by scent. Thus, if a new jackass is placed in an enclosure with another jackass, the resident will be more likely to attack him. Even if that didn't happen, they are hardly likely to see each other as potential sex objects. No matter how much a jackass may resemble a she-ass to the human eye, it will never, ever smell like one. On the other hand, a mare on heat will have enough of the characteristics of a she-ass to act as a reasonable proxy. That's how mules are made.
Agonistic Interactions
This fairly common behaviour pattern is completely outside the imagination of most people, because it does not occur among human beings at all - not even among those who are genuinely attracted to the opposite sex.Agonistic interactions are those involving fighting, threats, or potential fights. Suppose you are being attacked or threatened by a big, hulking alpha male, and you cannot escape, or do not wish to run away, because you belong to a group. What do you do? Well, the first option is to reverse all your own aggressive signals. Instead of standing upright, bristling, and roaring, you hunch down, flatten your fur and ears, pull your tail between your legs, and utter high pitched sounds - in other words, cringe, cower, whimper, and squeal.
Another option is to distract your opponent by inciting another urge. You might, for instance, act like a child, and thus evoke his parental, protective, or at least non-aggressive instincts. This is not unknown among humans; witness the wife who bursts into tears during an argument with her husband. But it is more often used to avoid provoking aggression in the first place, for example, by a subordinate ape who approaches a dominant by holding out his hand in the child's begging gesture - not because he wants to be given something, but just to avoid being chased away.
Otherwise, you can attempt to arouse his sexual urges, say by presenting your rump to him as would a female. You might think that an intelligent animal such as a baboon would know the difference between a female and a male pretending to be a female. But, as one primatologist pointed out, human advertisers will use a photograph of an attractive woman in order to sell a car. A photo, of course, is not the real thing, but it possesses some of the features of the real thing, and the ad-men use the slight arousal induced by the photo in order to produce a positive feeling towards the adjacent object. Similarly, the subordinate baboon distracts the angry alpha by producing some of the feelings normally produced by a female. The result is that, in species where this behaviour occurs, it has become ritualised. The subordinate presents his rump, the dominant mounts him, usually perfunctorily, and without penetration or ejaculation, and the ritual is over. Both of them have established, or reaffirmed, the dominance hierarchy, and they can go back to their normal business.
This pattern of behaviour has obviously evolved more than once, because the ingredients are the same all over. It is common, for example, for male dogs to mount another male as a display of dominance. It is particularly common among ungulates. Dominant rams, for instance, will mount subordinates in order to demonstrate their dominance. Interestingly, when a ewe comes into heat, she also mounts other females. I read in one popular science blog how, after the mating season, the rams get together in homosexual groups. I shall not repeat the author's name. He is a very brilliant paleontologist, but not an ethologist, and his interpretation is bizarre. Mountain rams don't have their special Brokeback Mountain when they are finished mountin' ewes. These are not sexual encounters per se, but dominance-submission rituals. When the mating season recommences, they go back to bashing their heads together. Thus, when you read how one or two percent of rams (not 10%, as is often quoted) are "gay", you should understand that the anomaly is their disinterest in females, not the fact that they are carrying out normal agonistic activities with other males. One experimenter presented some "gay" rams with rams and ewes confined so that their rear ends were available to "rape". It seems painful to have to point out that the scientist, being a member of a species with a poor sense of smell, failed to recognize that, unless the ewe were on heat, and smelled appropriately, even the most heterosexual of rams would have little interest in her.
The behaviour is also quite common among monkeys, particularly macaques and baboons but, interestingly, it is practically unknown among our nearest relatives, the great apes. The one big exception is the bonobo, a type of chimpanzee which lives south of the Congo River. Bonobos have taken it to a whole new level. They use sexual activity, between opposite sexes, members of the same sex, and even between adults and young as a social lubricant, applied to any situation which might arouse tension, or even to display friendship. These activities hardly ever result in orgasm, unlike real matings when the female is on heat.
Human Exceptionalism
As you can see, the patterns described above are not easily referable to anything in human society. The converse is also the case. Homosexuality in humans belongs to a small minority (2 - 3%) with a dominant and, in about half the cases, an exclusive attraction to the same sex, and it does not appear to have any selective advantage ie it does not improve their reproductive success. I won't say that this never occurs in other animals, only that it is extremely rare. Perhaps, one might argue, it has been overlooked. After all, most studies on the social life of animals involve much fewer than 100 individuals, so if it is present in the same proportion as in human beings, it may not have been noticed. Nevertheless, there is one subset of animals which have been observed in their millions, and their breeding activities have been of prime concern. They are domesticated animals. And the only one where "homosexuality" is an issue involves sheep - and I have already pointed out that this is a manifestation of a different behaviour. Perhaps, therefore, we should really be discussing why humans are so different.To begin with, it is best to lay to rest some of the very simplistic ideas held by many non-scientists. As I pointed out in my earlier post, there is no such thing as a gene for monogamy, polygamy, promiscuity, or the like. What the genes affect are such things as the amount of hormone, the response to hormones, the response to specific stimuli, the rate of maturing of certain behaviours, and the ability to learn specific things. As a result, they push the individual, and ultimately the species, in a particular direction.
You should not be surprised, therefore, that the heritability of homosexuality is less than 20% (similar to church going and political affiliation, believe it or not), and that if a homosexual has an identical twin, raised in the same family environment, that twin will be homosexual in only one case out of nine. You should also not be surprised that all the other simplistic explanations, involving hormones, immune responses and the like, have turned out negative. Specialists have been trying for years to discover a simple cause for homosexuality, but there isn't one. It is almost certainly due to a large complex of factors, not all of which will be operative in any single case. However, it is not my aim to re-open this can of worms, but to point out the human exceptionalism.
As a starting point, we might consider the much rarer, but nevertheless related condition of transsexualism or gender dysphoria. The victim of such a disorder feels he is "really" a woman trapped in a man's body, or a man trapped in a woman's body. The point is, it is almost certainly unique to humans. I cannot imagine a bull going around thinking, "I'm really a cow trapped in a bull's body." In fact, I cannot imagine a bull thinking, "I'm a bull, not a cow." Indeed, I cannot even imagine a bull thinking - at least not in a manner with which we would use the term. Before you have an identity crisis, you have to have an identity.
The more complex a machine or an organism, the more things which can go wrong. There must, therefore, be mental or emotional disorders to which only a rational animal, such a humans, can fall victim.
In their excellent book, My Genes Made Me Do It! (which can be read, downloaded, or purchased here), Whitehead and Whitehead include a third chapter (in PDF format) entitled, "Are Heterosexuals "Born That Way"? (something which is not often asked). They state (with references):
By the age of three, 65-75% of children correctly identify themselves as a boy or a girl, but most do not at age two and a half. ... Kindergarten age children already know from pictures of toys what a boy would like to play with and what a girl would. They can also identify the sex of dolls correctly. They will not be persuaded to change these opinion, even with the offer of a reward! But they are still not clear what male and female really is, and categories and their properties are still very fluid and fuzzy at ages three to six. Before the age of six, children tend to believe in a form of magic; they believe a car could change into a truck under the right circumstances, or a boy into a girl. [pp 67-68]It is hard to imagine these sorts of ideas going through the mind of a young chimpanzee. So you get the picture: in a rational animal speech, imagination, and learning reinforce, and occasionally get in the way of, processes which in the lower animals "just come naturally".
I would highly recommend that you read that chapter, because it explains in detail the process of psycho-sexual development in human beings. Turtles may come into the world with the whole of their limited social repertoire written in their brains, but that is not the way the higher mammals develop. Just as a baby' first smile elicits a smile from its parent, and its parent's smile makes it respond in kind, so we are programmed to develop our personalities by means of interactions with other people. Our responses to their actions, and their responses to us, are conditioned by certain basic instincts which push us in one direction or another. Added to this are the specific features of the human family: a lengthy childhood, and the involvement of both parents. By and large, a boy identifies with his father, a girl with her mother. All of this means that, in the vast majority of cases, the pre-programmed result is reached. But sometimes the system breaks down and goes awry.
However, that is not the topic of this essay, and I shall leave the further reading up to you.
