It's thought that between 2 and 6 percent of people identify as same sex attracted – but the jury is still firmly out on the science on why and how it occurs.
Is being gay genetic, and if so, is there a gay gene?
Well, as the boys from AsapSCIENCE explain, having a specific gay gene that can be passed on doesn't make a lot of sense considering how few same sex couples have kids.
However, that being said, two studies in the 1990s found that gay men do have a higher number of homosexual relatives compared to heterosexual men.
This led the researchers to think that being gay had something to do with a linkage on their X chromosome.
As the video explains, this has also been found in newer studies – specifically a part of the X chromosome called Xq28.
But with 80 percent less children then straight couples, purely genetic inheritance of same sex attraction can be something of a paradox.
So it's obviously more complicated than that – and that means that epigenetics gets involved.
A recent study looked at whether the attachment of a type of a methyl group (a type of epigenetic DNA change) changes your likelihood of same sex attraction.
The team were able to use that methyl groups to predict the sexuality of men with 70 percent accuracy.
However, it was a small population size, and there has been some controversy about the research.
So where does this leave us?
Well, I'll let the AsapSCIENCE boys explain the rest in the video above, but there are quite a few interesting hypotheses about how being gay fits into the world.