Genetic

I completely feel that my orientation was not my choice.  It's not some kind of decision I made.  But I can't accept that there is a big genetic component to it, either.  Think about it for a bit.  If it was genetic, it should be entirely lost from the genome after just a few generations.  Gay guys are definitely less likely to have children.  They are more likely to join a monastery or other group in which they are not likely to procreate.  The orientation would simply go away by natural deselection. But it doesn't.

Some people have speculated that there are strong sociological benefits to have a portion of the population this way.  But others also point out that homosexuality is manifest in many different mammalian species.  If it was sociologically important, we should primarily see it in species with human-like sociology, but it seems far more general than that.  So that's not likely, either.

The only thing I can possibly think of is that there is some genetic component that is advantageous to females, for which the natural side-effect is that some guys turn out gay.  That would make male and female homosexuality very very different from each other.  Actually, there is some evidence that the mechanism for male homosexuality could be very different from the mechanism for female homosexuality, so this would be a possibility.  But unless this turns out to be the case, I just don't think that natural selection would allow a genetically caused homosexuality.

I give it as my opinion that orientation is not a predominantly genetic trait.