Differences in genders can be cultural and biological, and the specifics can be difficult to know because culture is so deeply embedded in all of us. When looking across cultures we do see certain commonalities, such as differing interests. What is interesting is that sexuality is moderately correlated with these differences such that men can often share typically female traits if attracted to other men. Samoa goes so far as to recognise gay men as a third gender; Fa’afafine. They are effectively raised as women but don’t change their physical appearance.

Evolutionarily there may be an advantage to homosexuality because these gay individuals will not reproduce but will help care for the next generation. We do know from a vast amount of research across many cultures that some number of individuals are gay as a result of the environment of their mother’s womb. In what is known as the fraternal birth order effect, each successive male in the sibling chain is more likely to be gay. This looks to be a side effect of the mother’s immune system reacting to male hormones and dampening them down and as such it only occurs in males born from the same womb.