Pardon my lack of eloquence compared to the rest of you, but I just wanted to point this out: reproduction isn't the only necessity of a species survival. Social and emotional needs are also VERY important. In some cultures, even now, a woman is for making babies and not pleasure and therefore homosexuality is what is actually indulged in for pleasure. Regardless of what is natural (the majority of humanity does unnatural things, sorry to say), the main thing to remember is that marriage is supposed to be the union of two people who love each other enough that they want to spend the rest of their lives together. If two men or two women marry with that intention, wouldn't they be an excellent example to their children, adopted or otherwise, of how two people should treat each other and how love and other positive emotions can and should be exhibited?