The theory of evolution and homosexuality

The existence of homosexuality among a distinct percentage of the human population seems to contradict the theory of evolution. Most people are aware that the traits of organisms that reproduce, especially in high numbers, will come to dominate in future generations over the traits of organisms that don't reproduce, or reproduce far less than average. Thus sex is pleasurable: because organisms that devote energy enjoy towards having sex will tend to pass on that trait to future generations, while organisms that devote the same energy elsewhere will not pass on their proclivities. Why, then, does homosexuality exist in the animal kingdom? It would seem from the above that the opposite would be true. Organisms that show no desire for sexually reproductive activity would die without producing any offspring that shared the lack of desire. I can venture a few guesses at some answers but really don't have a clue what the honest answer is. According to this Wikipedia article, homosexuality is far more prevalent in the animal kingdom than had until recently been thought, probably because of observer bias. For example, the article says that 8% of male rams exhibit a preference for male partners, and that male penguin couples are known to mate for life together. Again, how does the theory of evolution explain these behavioral traits having survived? One possible answer lies in a "group selection" theory of evolution. For a controversial example of a popular writer who puts forward that type of theory see Howard Bloom's The Lucifer Principle. The basic idea is that groups compete, not just people, so that the traits of a successful group as a whole will be passed down to future generations, while unsuccessful groups will not pass on their traits. I see the process working but not necessarily on an evolutionary level, but more on an anthropological one. For example, let's take two cultures - one discourages homosexuality, and the other encourages it. Those two cultures compete, and the one that encourages homosexuality prevails, that is, it's cultural norms come to dominate. In that event, the social constructs that encouraged the homosexuality are passed down to descendant cultures. If we accept this model, then the current existence of homosexuality demonstrates a cultural construct that has contributed to the success of contemporary culture. The question then becomes, what about homosexuality has made it at least somewhat helpful? Check out Plato's The Symposium next time you're bored. Bloom though, and some others, while not denying the importance of anthropological explanations, somehow go further by saying that group selection can operate at a biological level. This I'm not persuaded of, and the prevailing theory, as expressed most popularly in Richard Dawkins's The Selfish Gene, is that group selection is not possible. All of this, of course, has enormous ramifications for the law in that the law is an omnipresent cultural construct that lends itself to study. As such, it is most interesting to note for its function ...