Originally Posted by Jeff the Green
What Absol said. I'll add that it shouldn't
matter, though. Gay sex is no better or worse than straight sex and gay relationships are no better than straight relationships. It's only because of homophobes that it matters, in much the same way that homosexuality is a risk factor for suicide only because of homophobes.
More science stuff:
I did say by the time the infant weans, because the mother's hormones still affect the infants until then. Do these studies on identical twins take into account whether they're breastfed or whether they receive other food? That might be interesting to look into.
Going by the studies with identical twins, environment must factor in somehow, but when? Many children's sexualities are fairly clear at around six or eight.