Wolfsoul, your post made me remember something!

In animals that have litters, the position of the animal in the womb in relation to its siblings has an affect on the animal's behavior later in life.

A male mouse that is between two females in the womb will have more estrogen, and behave less aggressively towards other mice. A male between two males will be super-aggressive.

Conversely, a female positioned between two males will have high testosterone, making her more aggressive and defensive. One positioned between two females will be super mellow, and probably a great mother!

I don't know if this has anything to do with homosexuality is certain species or not, but it's interestering.