On that same note, if there IS a genetic component to homosexuality, the expression of it could be highly variable depending on the social environment that the individual was a part of. Present day expression, with the desire of gays to have pair bonding, is relatively new historically speaking. Trying to figure out in what way this genetic component (if it exists) was expressed in early Man is probably not possible.
IIRC, the Persians of Alexander's time maintained a regiment composed solely of homosexual men and their lovers, the idea being that no man would want to appear cowardly in the presence of his significant other.