Before I go too far into the science regarding gays, I best give my general view.
The nature/nurture debate is relatively unimportant to me, personally. Why should it matter? You don’t hear this sort of debate with, say, handedness ;-), even though it’s far more out of the genetic category. What if someone did choose to only be attracted to their same sex, a choice as simple as one to, say, date a brunet or practice a particular religion? If a person wants to date a man I don’t see why they want that should matter, be they a man or a woman.
But it does matter to many minds. Gay-rights opponents hope to control other’s agency, coerce them into not having relations with men, either remain celibate or marry women, and so on. They best gain that control over their neighbors, politically and socially, by posing gay attraction as chosen or alterable. Gay’s just have to want to be good, bad enough. Then, because nurture strikes most as more alterable than nature, nurture is their favored cause of gayness.
Of course, because they don’t want to be coerced or controlled, most gays tend to be biased to favor nature.
But, nature or nurture, it’s fuzzy territory.
What is the practical difference between an event that causes a person’s sexuality occurring one week before birth, and one occurring one week after? What’s the important difference between an event that occurred in an egg ten years ago, a sperm yesterday, or in a newborn boy 10 months from now? The effect is undeniably there; gay people are there. To me, the causes of being attracted to men are only important from the standpoint of discovery, be they in the genes, prenatal hormone exposure, the actions of siblings, birth order, family size, or any other event in a person's life.
An infinite web of events come together to make a person who they are, from their eye color to their religion, but there is no real need to segregate these events into post and pre-birth or pre-conception slots. A hormone or gene combination, for example, can be just as valid an effect on a person as being orphaned or losing their arm in an accident. In fact all such events, which we categorize as either nurture or nature, may be enduring or alterable (even, someday, the genetics).
So “nature”, “nurture”, “narture”, whatever; they are all merely causes. As to the more potent of them, I do favor what most would call nature for homosexuality and I feel those causes may be sufficient (I’ll go into why in my other posts on the topic in great detail, as I have in a small part here). But I don’t discount nurture, nor do I disbelieve it may be a cause for some gay men. If there’s one thing I’m sure of, there are many causes for human sexual orientation.
One last thing I want to point out is that, regardless, all sexual attraction has a very natural cause. All our wants, if traced back far enough, have to come from outside us: nature, god, the teachings of others, space aliens ;-) and so on. The debate here is over the desire’s focus, which, again, must originate from outside us, in nurture or nature. Hunger, for example is undeniably natural. It is the basis of the human act of eating and without that innate drive of achieving the pleasure in eating or avoiding the pain of hunger (and the drive to live) we’d not eat. What you want to eat, though, is certainly a mix of nature and nurture, but it all remains contingent upon the nature of hunger with which we all come pre-programmed.
Sexuality is one area where children in general are much less ridiculous than adults, by far :-); most never even think about it, let alone make awful decisions because of it. But, come puberty and the new, very natural expression of our once dormant genes, that all changes. No one would attribute puberty to early childhood upbringing. All sexual attraction, even mine, is and was brought on by the very natural effects of some well known chemicals. But when my switch was flipped, I got more of a surprise than most; I got what the female half of the population gets, and, unfortunately, that’s important in these days (though, gratefully, not as important as it was centuries past).