Well, I doubt there is "a" trigger. The development of homosexuality by the individuals we interviewed showed such a broad "variety" that I think, if there is a genetic predisposition, it's in most cases slowly developing in interaction with various small triggers provided by the environment, and not something that is caused by a single trigger, like an "event". I think it's more a slow process that for most of them takes place during and shortly after puberty. I say for "most", because some people reported that they already before puberty (!) felt attracted to their own gender, and we had cases where people reported that they developed such feelings in the second half of their life, even when married and having kids. I can imagine what causes it, but I am almost 100% sure that the sexual attraction to the same gender isn't caused by a single factor. I think nobody can say what is "dominant". These days people tend to attribute everything to gens. I doubt thought this is the right way to look at sexual orientation, or other such habits that we know can run through families. And I agree, sexual orientation is for sure fluid, it can change during life, and many people are anyway bisexual.