Question: hi thank you for answering my question on how different sexualities might come about, would you be able to provide more info?

Dan Taylor answered on 13 Mar 2019:

Not a problem! Thanks for following it up! So I what I would say is most research into sexual orientation has looked as gay men, so a lot of this will be focused on that, where possible I will try and talk about other sexual orientations in both men and women, but if the research doesn’t exist I don’t want to make any wild claims!

So i’ll start by talking about genetics. Whilst there is some evidence to suggest that having a relative who is homosexual increases your chances of being homosexual. However, the idea of a “gay gene” has been widely disputed, chances are a single gene is not the cause of homosexuality, but multiple. This seems to be the case for both gay men and women. There is a little evidence when examining other orientations, and again there does seem to be a link, but the research pool is tiny and I wouldn’t want to say for sure either way – but it’d make sense that genetics play a role here as well, it may be that there are genes for both same sex and opposite sex attraction, bisexuals may just have both.

Handedness (preference for using your left or right hand) is linked to homosexual men and women also. Homosexual people are more likely to be left handed – strange but quite cool if you ask me! One reason that homosexuals might be more likely to be left handed is down to something called brain organisation. In this case, what we can see is gay male brains are organised in a similar way to that of straight (or heterosexual) female brains, likewise there is some evidence (though not as much as with men) that gay female brains are similar to that of straight male brains. Gay men are more likely to use both sides of their brain in certain visual or memory tasks, similar to straight women; gay women are more likely to only use one side (similar to straight men). If you’re interested, this phenomenon is known as cerebral asymmetry (because only one side of the brain is being used – so its asymmetrical not symmetrical). In men, this was originally thought to be down to a “feminisation of the brain” however, this is most likely not the case as women do not show the opposite effect (a masculinisation of the brain). So the exact reasoning for this handedness isn’t really known yet.

One reason researchers thought this feminisation process may have been correct is due to the birth order effect. Gay men are more likely to have more older brothers when compared to straight men, it is thought this is due to the mother developing antibodies to male sex hormones. Whilst the birth order effect does seem to strongly predict gay male homosexuality, it does not do the same for female homosexuality. What’s quite interesting is it almost seems to reverse in left handed men. Left handed gay men tend to be the older sibling. So there’s clearly a complex interaction between handedness, the way your brain is organised and the birth order effect.

Another really interesting theory coming from evolutionary psychology talks about an idea of population control. If a population is left to increase rapidly in an enclosed space then eventually there won’t be enough resources (such as space to live or food) to contain the population, when this happens the incidence of homosexual mating behaviours goes up! Even in animals like insects! This might make sense when we think about birth order effects because it would allow larger families to control population easier, leading to survival. When combined with the “gay uncle” hypothesis which suggests that gay uncles actually invest more in their nieces and nephews than straight uncles, it might make sense that homosexuality (at least in men) may allow for families (or tribes when we think about our evolutionary past) to survive, by investing things like food and care into children without having any of their own!

I’m aware this post is getting quite long now, and as you can see I’ve only really covered gay men. Sexuality is very complex and it’s likely that there isn’t a single cause that fits, it’s likely that every homosexual (or hetero or bisexual) has multiple factors influencing their sexual orientation. If you’re interested, take a look on things like google scholar, or library books on human behaviour. There’s tonnes out there and there is still so much we need to find out!
I hope this at least answers some of your question! I could honestly go on for hours!