Interesting ... as I'm the oldest of 6 - all same mom, but they're all my half brothers and sisters. 4 brothers - all apparently straight (but I reeeeallly think 2 of them - middle boy and youngest - are closet gay), while my sister and I are both lesbian. I think it has more to do with long range big family effect ... my mom also came from a large family ... perhaps genetics steps in as a "normal" birth control way of controlling the population? Especially since we see it in the animal kingdom as well. That might be a more viable way to test the theory if "gayness" kicks in when the population threatens to over extend the availability of food/land to support the species.