Just adding my 2 cents here and submitting an observation which I have yet to see in print.
Homosexuality does not exist in any other species simply because if there were such a gene in that species it would have been eliminated eons ago.
If human population were to procreate via the same internal instincts inherent in all other species, such homosexual gene would also have been eliminated eons ago.
However, the human species is the only species which copulates without any genetic predisposition to the survival of the species. We copulate and self gratificate merely for the pleasure of such activity but in the instances of married couples (or unmarried it really doesn't matter), such activity creates birth if that is their desire. In other words, the ability to create a newborn has evolved beyond species survival to personal choice.
Since homo-sapiens have evolved beyond the primitive instincts of mating when the female becomes fertile and have developed intelligence to the degree that sexual contact has now become a choice rather than a drive, the only logical explanation left is that sexual behavior is just what it is, behavior. Behavior which is totally controllable by the individual if he/she wishes because behavior is driven strictly by societal and psychological influences....
The hypothesis is wrong the gene for male homosexuality can be passed on the female chromosome. That way it wouldn't be effected by natural selection. Also there seems to be some indication that the environment in the uterus namely hormone levels might effect this. Baldness in men seems to be determined by this mechanism as well as fingerprints etc. Why argue the point. It doesn't matter one way or the other. Buying into the lie that because homosexuality is an inborn condition it follows that the behaviorshould be acceptable is the our first mistake. Whether gays can be reconditioned into heterosexuals only interests me in an academic way. Gay activists by making gayness synonomous with race or skin color have been quite successful. This is the "Big Lie". Suppose we find a gene for criminality does that infer that criminality in the case of some individuals who happen to have the gene should be tolerated. How about alcoholism, should the behavior be tolerated because they have the gene. How about pedophilia, if they have the gene they are only acting in accordance with their nature. Don't you realize that pedophilia is only a sexual orientation and therefore has nothing to do with perversion. As a free society I think it's probably incumbent to tolerate homosexual behavior between two consenting adults or maybe even three or four. But as long as society continues to buy into this lie this lobby will continue to make progress in such a manner as they have whereby you can toss all sexual mores out the window and we'll have every perversion imaginable protected by some civil right.