This from the New Scientist:
CultureLab: Can the biology of being gay combat bigotry?.
LeVay’s central claim is that “sexual orientation is an aspect of gender that emerges from the prenatal sexual differentiation of the brain”. A cocktail of sex hormones, genes and the womb environment, including factors such as stress during pregnancy, comes together to determine sexuality. That is, sexual orientation may not be determined at the moment of conception, but it’s pretty much locked down by the time we are born.
Gay, Straight, and the Reason Why: The science of sexual orientation
by Simon LeVay
Oxford University Press
Available from Amazon for $18.45