Is Homosexuality unnatural?There was much debate in our Philosophy class.
I can't think of any good definition of "(un)natural" according to which it would be correct to say that homosexuality is unnatural. We should first recognize that defining "homosexuality" is itself a difficult task. I'll begin by distinguishing between being a homosexual person and homosexual acts, where the latter involves sexual activity between members of the same biological sex. An overly simplistic way of defining a homosexual person would be someone who identifies him or herself as wanting (when wanting to engage in sexual activity) primarily to engage in homosexual acts, but this definition neglects other important ways homosexuals think of themselves (e.g., as loving or wanting to marry someone of the same sex).
Now, how could it be that homosexual acts or homosexual persons are unnatural?
1. Perhaps one thinks that *hetero*sexual acts (and persons) are natural and any other type of sexual activity is (thereby?) unnatural. But this view just begs the question of what counts as natural (see below). And why can only one type of activity be natural? Breathing with lungs is natural, in some sense, but that doesn't mean breathing with gills is unnatural.
2. Perhaps one thinks that heterosexual acts are natural because they are "normal" in the sense that they are statistically more common among humans (as well as other animals), and homosexual acts are not as common. But lots of uncommon things are both part of nature (one way of thinking of "natural") and are considered good ("natural" misused to mean "normatively good"). Left-handed people, and the tallest 10% of giraffes, are uncommon, yet very much a part of nature. And the best violinists (and perhaps the fastest cheetahs) are uncommon yet are properly considered good (at what they do). Indeed, self-sacrificial heroes are rare, but they are part of nature and morally good. Regarding rarity, homosexual acts are relatively rare in non-human animals but they do occur in several species so they are "part of nature" in that sense, and even if humans were the only species to engage in homosexual acts, that wouldn't make them unnatural, unless complex language, cooking, and playing soccer are unnatural because only humans engage in those activities.
3. Perhaps one thinks that homosexual acts and persons are unnatural because they could not be selected for in the process of natural selection. But first of all, they could be, and perhaps were (e.g., one possibility is that homosexual persons or animals conferred greater fitness to their kin or their groups). And second, who cares? Lots of things are natural that were not selected for, including for instance, our ability to do calculus or dance the tango. And lest one think that whatever traits humans have that were selected for are traits we should think of as good (or part of our "purpose"), keep in mind that our traits of promiscuity and aggression towards out-groups (a likely source of racism) were likely selected for.
4. Alas, I suspect that most people who think and say that homosexuality is unnatural typically just want to use "unnatural" to mean "wrong"--or not what (they think) God wants or some equally improper (unnatural!) meaning of the word. And they typically think that for unjustifiable reasons. I've yet to see a compelling argument that homosexual acts, much less homosexual persons, are wrong, much less unnatural.