Soleron on 12 October 2012
Almost purely genetics. It is something that needs more study though.
It's certainly not a free choice, and if there was an environmental method to produce no or fewer homosexual people I'm sure religion would have found it.
It's not nearly as simple as binary gender preference. Even what people prefer in the opposite sex is wildly different, and there's more differences between possible body attributes/types than between the two genders.
