Since the Gay Pride movement began just over ten decades ago, we have come far in our acceptance and understanding of ‘non-standard’ sexual orientations. In 1967 we finally began the amendment to Biritsh law to decriminalise sex between men. In 2001, the age of consent was equalised and in 2003 and 2005, same-sex couples were allowed to adopt and enter into civil partnerships respectively.

Though same-sex marriage is not yet legal, we appear to be heading in that direction with some recent polls indicating up to 61% of the public in favour. And in spite of the occasional bigoted Jan-Moir-esque article, the straight majority has come to recognise the validity of the ‘alternative’ sexual orientation as a natural inclination rather than as a ‘life choice’.

We still have a way to go, no doubt, but perhaps part of the plateau of approval can be blamed on science not quite keeping up with our cultural bounds. But science does, in fact, hold some of the answers.

Most people have heard rumour of the ‘gay gene’ and some Daily-Mail-reading-uber-traditional-Tory-types may even lose sleep over its pattern of inheritance (though as an interesting aside, it is intriguing to note that it is, in fact, Labour supporters – 12% versus 11% for Conservatives and 8% for Liberal Democrats – who would reject their gay child on the grounds of the orientation being ‘unnatural’ according to a 2009 Populus poll). Those of us of a biological persuasion, however, are excited to be able to finally draw some – albeit still rudimentary – conclusions about the nature of the ‘gay gene’.

As homosexuality has become more accepted in recent years, one might have expected a decline in the number of forced mariages (and fornications) and thus a reduced chance of inheriting any ‘gay genes’. The notion of inheritance poses a problem – how could such a gene persist in the population so that people are effectively born gay? The change in the number of in-the-idiomatic-closet homosexuals is unknown, thus we cannot make any conclusive statements. All we can say is that, if for any reason we suspect this mythical gene may be troubled by the thought of finding its way into the next generation, science offers many solutions to its predicament.

Ever since Richard Dawkins’ book The Selfish Gene made the case for genes as elements whose sole purpose is to maximise their own chance of being passed on to the next generation, most biologists have adopted an attitude towards evolutionary conundrums that assumes genes are the basic unit that natural selection acts upon. The consequence is that we can think of a ‘gene’ as a character leaping (often invoking intercourse) from one oddly-suspended platform (a generation) to another on the screen of a newfangled games console (the environment) of your choosing… Not the perfect analogy, but hopefully you get the idea. The point is this: in every individual of every organism there are genes and each of these genes wants nothing more than to make it into as many of the next generation as possible.

To the non-geneticist the idea of a ‘gay gene’ may be difficult to fathom. Indeed, if homosexuality is in any way inherited, it is unlikely to be due to just one gene and it may well be that the trait is influenced by the environment.

There are examples of animals that display homosexual behaviours as a matter of course and some of these cases may even suggest a sound evolutionary reason for some humans to be gay.In the bluegill sunfish, three different mating strategies exist among males. The ‘parentals’ mature slowly and invest time and effort into both looking good (they are brightly coloured in the breeding season) and courting the females. The ‘sneakers’ however, do as their name suggests – they mature quickly, invest the most in sperm and sneak between parentals and females when they are mating to fertilise as many of the female’s eggs as possible as she releases them. Finally, the ‘satellite’ males use a more bizarre tactic – they grow up to look like females and, while mimicking them, can come between parentals and their real female mate and fertilise the eggs, while the parental is fooled into continuing to mate with both – presumably thinking he’s got lucky and has two females at his disposal. These tactics are not unique to this species either – while most prevalent in fish, female mimicry exists in many taxa and sneaking behaviour is commonplace throughout the animal kingdom.

The ways this applies to homosexuality in humans are two-fold. Firstly, it is conceivable that homosexuality first evolved as a tactic for getting closer to females – a theory that has the potential to ruffle some politically correct feathers. This may only explain how the behaviour initially arose – perhaps later the genes controlling the traits mutated as homosexuality became sustainable for some other reason. There is another way this hypothetical ‘gay gene’ could avoid extinction – X-linkage.

Like baldness in men, a ‘gay gene’ may be something carried down the maternal line so that the females can still pass the gene on to their offspring without being gay themselves. This pattern of inheritance may even account for the notable discrepancy between the number of gay men and les

bian women in the population (about double the percentage of men than women according to NATSAL data).

Alternatively, the bluegill story may simply be a lesson for us – in our search for an explanation we should take heed of the tendency for evolution to produce behaviours that are ‘by-products’ of something else. No one would argue that the parental male chooses to mate with the mimic in that he ought to be trying to maximise his offspring by mating with the true female – but animals do not act directly on evolutionary concepts. A male bluegill sunfish does not ‘know’ he wants to make baby fish – he just ‘feels’ compelled to mate. It is quite simply possible that a gene that is important for some other function produces homosexuality as a consequence – which was in our ancestors and is still neither detrimental (except in that it prevents reproduction) or advantageous (except in that it is the by-product of something useful). The two cancel out so that the gene persists.

Many other potential explanations exist that are beyond the scope of this article. What is exciting is that we may soon have an answer. DNA sequencing has revolutionised genetics and given rise to the biologist’s playground that is genomics. Anyone reading this who hoped for ‘straight’ answers will now be disappointed by both the cringe-worthy pun and the inconclusive nature of the above. However, the point is not that there is a scientific answer currently available, but rather it is work in progress and, far more importantly, that a genetic basis for homosexuality is neither totally out of reach nor a logical impossibility.