Originally Posted by Play The Man
Both. Not a satisfying answer, but likely the truth.
There are twin study databases that can shed light on the matter. The databases include information on identical twins raised together and raised apart (due to separation in adoption situations). Identical twins are more likely to both be homosexual than regular siblings; however, it is not perfect concordance. In some cases, one identical twin is homosexual and one is heterosexual, suggesting that it is not completely genetic.
There are animal and population-based studies that suggest homosexuality can be caused by environmental exposures. For example, about 50 years ago Calhoun did studies on rats concerning crowding into the behavioral sink. In brief, if a large population of rats is kept in a living space too small for the population size, pathological behaviors will occur in the rats - homosexual behavior, cannibalism, fighting, killing infants, etc.
There were studies of post-war Europe that suggested that mothers who faced starvation and extreme stress from bombing during their pregnancy were more likely to have a homosexual offspring.
In the DSM-I and DSM-II homosexuality was considered a psychological disorder by the American Psychiatric Association. It was dropped in 1973. That decision had as much to do with political correctness as science. In the current political environment, it would be career suicide to study homosexuality, unless you were specifically looking to find a strictly genetic basis.
Bassically, you have no idea. Its alright to say "we dont know, tests are inconclusive."
This isnt about why gays are gay...this is about gays in the military.