The nature of a thing, from an Aristotelian point of view, is the form or essence it instantiates. Ex.: it is of the essence, nature, or form of a triangle to have three perfectly straight sides.
In biological organs, we have things whose natures or essences more obviously involve certain final causes or purposes. Ex.: the function or final cause of eyeballs is to enable us to see. Objections: Ex.: if it is wrong to go against nature, then it is wrong to wear glasses. Again: If homosexuality is genetic, doesn’t that show that it’s natural too.?
To wear eyeglasses isn’t contrary to the natural function of eyeballs; rather, it quite obviously restores to the eyeballs their ability to carry out their natural function. The question of homosexuality’s genetic basis is quite irrelevant; it does not by itself prove anything about whether it is natural. The possibility of a genetic basis for clubfoot doesn’t show that having clubfeet is “natural”. It is obviously unnatural in the Aristotelian sense of failing perfectly to conform to the essence or nature of a thing. No one who has a clubfoot would take offense at someone’s noting this obvious matter of fact, or find it convincing that the existence of a genetic basis for his affliction shows that it is something he should “embrace” and “celebrate”.
Of course, that by itself does not show that homosexuality is immoral either. After all, having a clubfoot is not immoral, and neither is being born blind or with a predisposition for alcoholism.
