I read an article recently in a reputed magazine, sadly I can't remember which one, claiming one theory for homosexuality MIGHT be a reproductive ADVANTAGE in cases where one has more "masculine" (women) or more "femininin" traits (men).
Speaking as a guy, I'll confess I do actually get attracted to certain kinds of "male" traits; i.e., a girl with more interests in common with me and less "feminim" temperment might be more attrractive to me.
The article also discussed and dismissed the idea that the gay relatives might benefit their siblings, which is another theory going around.
Sorry that I have no references.
I'm curious if anybody has any scientific links on the subject.