On adaptive success and theories of homosexuality…


The latest issue of New Scientist contains an article – “The In Crowd” – that is both profoundly interesting and yet totally unavailable online. Gradually, I’m delighted to say, this situation is becoming more rare and more of a surprise each time it occurs.

Anyway, the article – written by Joan Roughgarden – contends that: “Same-sex relationships are not a biological dead end. They are a glue that helps hold many animal societies together, and a fatal flaw in one of Darwin’s central ideas.” Here are a few choice chunks of the article that I think encompass most of the article:

Author Bruce Bahemihl, in his book Biological Exuberance: Animal Homosexuality and natural diversity, has catalogued over 200 vertebrate species in which same-sex genital contact regularly occurs. In some species, homosexuality is not very common – around 1 to 10 per cent of all mating. In others, such a bonobos, homosexual mating occurs as often as heterosexual mating. In some species only males participate, in others only females, in still others both sexes. Sometimes homosexuality is associated with pair bonds that last for years, and in others with short-term courtships. This broad occurrence of homosexuality among vertebrates raises the possibility that if it has a genetic basis at all, it has some broad adaptive significance, and is not an aberrant condition just a few species happen to be stuck with.

In humans, moreover, homosexuality is much too common for it to be considered a genetic aberration. Real genetic diseases are really rare, and their frequency inevitably depends on their severity. A disease that is uniformly lethal must arise anew each generation, so its frequency is equal to the mutation rate, say one in 1 million. A disease that causes only a 10 per cent drop in offspring production (fitness) is 10 times more common than a lethal disease – about one in 100,000. Similarly, a mere 1 per cent drop in fitness leads to a frequency of one in 10,000. If homosexuality has a frequency of 1 in 10, the fitness loss could be no more than 0.001 per cent, which is completely undetectable. A “common genetic disease” is a contradiction in terms, and homosexuality is three to four orders of magnitude more common than true genetic diseases such as Huntington’s disease.

All this seems eminently reasonable to me so far. I mean, clearly I’m no expert in evolutionary biology, so my opinion really counts for less than nothing. But on the other hand, as an engaged reader and a gay man I’ve at least got a legitimate interest in the subject and have found myself relatively compelled by the idea that if homosexual behaviour has a genetic component, that at least some of the genes that result in it must have some adaptive utility. The most commonly cited example is that perhaps a gene might exist that in an heterosexual adult provided a significant reproductive advantage of some kind – but which had the side effect of producing a certain proportion of children who were gay. As long as the cumulative effect was to mean that – on average – the familial line would produce more sexually productive offspring than a line which did not have the gene, then it would be clear that the genes that result in gay people had a reproductive advantage.

Of course while that theory has a certain compelling logic to it, it doesn’t (perhaps shouldn’t) have anything to say about what it means to be gay in this context. In other words – it makes no statement that homosexual behaviour is itself somehow useful or positive with regard to human behaviour, survival or evolution. Homosexual behaviour then, is not considered adaptively useful.

Now back to Joan Roughgarden’s piece (carrying on directly from what was written above):

Indeed, I challenge the presumption that homosexuality leads to any reduction in fitness whatever. Throughout history and across cultures, homoerotic attraction has not precluded heteroerotic attraction. And there is little evidence that people who feel homoerotic attraction have, as a group, any less Darwinian fitness than those who don’t. After all, many exclusively heterosexual people do not have offspring either. Even if those with homoerotic attraction did have marginally fewed children, they might make up for it by a better chance of survival – during wars, for example, when homoerotic bonds might lead soldiers to protect one another more vigorously.

So what then, is the adaptive significance of homosexuality? Homosexuality has many uses, much as the ability to speak does. Homosexual contact is a way to communicate pleasure. And I suggest that homosexuality is a social inclusionary trait – that is, it provides animals, including perhaps humans at times, with admission to social groups. It evolves, I suggest, whenever same-sex cooperation helps achieve an evolutionary successful life: to survive, find mates and protect one’s young from harm. This plays out in different ways in different sexes and species. Sometimes, as with bonobos, same-sex cooperation provides group security and access to food that females need to successfully rear their young. For others, such as male Savanna baboons and probably some whales, it provides the allies they need to survive conflicts so that they may later mate. But the unifying principle is the same – homosexuality cements relationships that are crucial for a successful life.

At which point, I’m afraid, I think my scepticism comes to the fore. It seems to me that any theory of homosexuality that operates in direct opposition to people’s experience of contemporary human sexuality seems to be at least flawed. While bonobo homosexuality might be seen to be useful in the creation of social inclusion, often exactly the opposite occurs in human society. Eve Kosofsky Sedgwick’s classic book Between Men specifically talks about the continual need to disavow sexual components to male homosocial relationships (ie. male-on-male friendship / bonding relationships). We’re all familiar with this kind of experience – that the most common and most potent sources of anti-gay tirades are tightly-bound social groups of men. At the very least more is going on in those situations than simple homoeroticism bringing those men together to express solidarity and closeness. Even at our most open-minded, surely we have to state that in those circumstances, the fact that any vestigial or situational erotics have to be so vigorously denied makes it clear that there’s a distinction to be drawn between homoerotic behaviour, homosexual behaviour and homosexual identities that is much more complex than anything that Roughgarden supplies us with.

I will of course give her the benefit of the doubt in this case – the article is evidently a truncation of a body of work that no doubt includes a massive set of sample data from which to draw conclusions as well as the applied expertise of a lifetime of training. If I get the chance to read any more of her work, I will make sure that I do so vigorously. But in the meantime, I’m afraid I must remain interested but unconvinced.