One of the best ways we have of determining if something has a genetic component is twin studies. If homosexuality was caused in part by genes, then you would expect that the identical twins of homosexuals would be more likely to be homosexual themselves than fraternal (non-identical) twins.
By using twins in this way we rule out environment as a factor, since in both groups the environment is the same, it’s just that in one group the genes are also the same, and in the other group the genes are somewhat different.
The conclusion for males is that yes, genetics plays a significant (but not complete) role in sexuality. The evidence for females isn’t as strong mostly due to not as much research being done, but leads in the same direction.
As Drew said twin studies are a good way of looking at the genetic component of things. However there are a few issues with this in that you have to be careful of your sample set. That means what twins you use. Because you are doing a study in humans you have to gain consent and you may find that the twins who volunteer for such studies are more likely to both be homosexual or both be heterosexual…of course this might not be true but you have to try and pick your sample set as randomly as possible and make it as large as possible to get a true representation.
Because of the findings of the twin studies that Drew told you about it is highly probable that some people are born with a genetic pre-disposition to being gay – but this does not necessarily mean that they are “born gay”. If it was just to do with the DNA twins that share the same DNA should always both be gay if one of them is…but this is not always the case. There are a lot of other factors involved – i.e. it is a multifactorial thing (which is like most things). A person’s environment, experiences and perceived norms can also affect sexual predispositions and behaviour. So really it’s a complex issue! There is no evidence for homosexuality being completely genetic – but there is no doubt some sort of genetic component to it.
Hi annabellake and james! I like Julia’s answer! I think there are biological and environmental factors that come into play. Hereditary mechanisms may certainly be a contributor. There are animals in the wild that exhibit homosexual behaviors, so I think it is definitely a natural biological response. Cultural perspectives can play a role as well, but I wouldn’t say that this means people necessarily choose to be homosexual. There could be social and cultural influences that come into play without the person ever being aware. So I think it is a complex mixture – mostly biology but also a little bit of social influence. In any case I think the diversity is a wonderful thing!