Against nature? Homosexuality and evolution

Dave Weston reports on a Lunch Hour Lecture guaranteed to generate robust debate.

Same-sex sexual behaviour is often condemned on the grounds that it’s ‘against nature’. Indeed, biology tells us that selection favours those who leave more offspring. But then, homosexual behaviour is widespread – not only among humans, but also throughout the animal kingdom.

So, does that constitute a paradox for Darwinian theory? And is there a connection between what goes on in nature and what is morally desirable? These were the tricky questions that Professor Volker Sommer set out to address in a Lunch Hour Lecture on 17 November.

I’ve heard Volker speak several times before. His official title is Professor of Evolutionary Anthropology at UCL and he’s an expert in behavioural ecology, having spent many years studying the behaviour of monkeys, apes… and people. The combination of an eminently quotable and engaging speaker with a live audience and potentially controversial subject matter meant this was always going to be a popular lecture.

Sure enough, when I rolled up to the Darwin Building, the queue was already snaking onto Malet Place (NOTE TO SELF: arrive a few minutes early for the next Lunch Hour Lecture or you might not get in!).

The talk began with some context about the number of homosexual people in the world. With a global population in excess of 7 billion, and an estimated four per cent of men and one to three per cent of women believed to be homosexual, Volker put the combined total in the region of 350 million people – more than the entire population of the USA.

Now, I think his sums were a little off and the figure should be around the 210 million mark, but who am I to quibble? The point remains that there are plenty of gay people all over the world – something that Darwinists might not expect, because homosexuals rarely make babies.

We’ll return to the idea of natural selection in a minute, but first Volker spent a few minutes systematically shooting down the arguments of famed liberals such as Zimbabwe’s Robert Mugabe and Israel’s Ezer Weizman, who are both on record as saying that homosexual sex is not ‘natural’. What quickly became apparent is that whether you’re looking at monkeys, gorillas, grey-legged geese, flamingos, meerkats, sheep or a dozen other species, nature is full of examples of homosexual animals.

So, if homosexual behaviour can be observed in both the human and animal worlds, how does that tally with our understanding of evolutionary theory? Volker cited a few statistics that suggest there is a genetic component to homosexuality. Apparently, an identical twin with a gay sibling has a 50% chance of also being gay. A non-identical twin has a 20% chance of sharing the same sexuality as their twin, while ‘normal’ (i.e. non-twin) siblings have a 10% chance. All of these incidences are higher than the average chance of an individual being gay.

If we accept that there is a genetic component at work, how are non-breeding gay couples able to pass on the gene? Well, it turns out that copies of genes can be passed down by relatives if the gene’s traits benefit the relative. For example, in communities of bees, termites, birds, wild dogs and meerkats, there are non-breeding individuals who help the collective, so copies of their non-breeding genes are passed on to the next generation by their relatives.

This raises the question: what are the potential functions, in evolutionary terms, of homosexual sex? Volker pointed out various hypotheses, including the idea that in early human evolution non-reproducing males could have helped acquire meat for the group. More recently, studies have shown gay men to have higher IQs and to earn more money than heterosexual men – potentially passing on their wealth to their families.

Having shown how Darwinian theory can help to explain the continuation of homosexual sex, Volker returned to the question of whether or not it is ‘morally desirable’. He’d already disproved the argument that there are no examples of homosexual behaviour in nature and went on to target those who hold up ‘nature’ as a paragon of virtue.

Zoomorphising human sexual behaviour doesn’t work, he argued, and we shouldn’t be fooled into thinking that animals are exemplars of monogamy, responsible parenting or other desirable human traits.

In fact, the animal kingdom is rife with incest, cannibalism, infanticide and a host of other behaviour that would not be tolerated in civilised human society. Indeed, as James Weinrich (1992) said: “If animals do what we like, we call it natural. If they do what we don’t like, we call it animalistic.”

Dave Weston is Media Relations Manager in UCL Communications & Marketing.

Watch the full lecture here: