On the radio I heard someone reference a study done in 2002 by Peter S. Bearman and Hannah Bruckner. Even though it is ten years old, I've not heard it mentioned in any context, by either conservative or liberal news media. This 2002 study supports, if not outright proves, that homosexuality is not genetic. Identical twins have identical genes. If homosexuality is caused genetically, wouldn't identical twins have the same "sexual orientation"? Yet, in their study Bearman and Bruckner found concordance rates (both twins being homosexual) of only 7.7% for male identical twins and 5.3% for females identical twins. Bearman was with Columbia and Bruckner with Yale, so this isn't just a couple of conservatives trying to prove a point.
The study's "working papers" can be found online HERE.