Sex is probably one of the last forms of human expression to enjoy such a direct connection with nature. It might be the primary site of conflict between nature and culture. If one assumes that nature (or instinct) is repressed in a highly civilised society, then I think the conceptual dyad nature-culture is best preserved there, in the realm of sex.
Originality is a thing we constantly clamour for, and constantly quarrel with; as if, observes our author himself, any originality but our own could be expected to content us! In fact all strange thing are apt, without fault of theirs, to estrange us at first view, and unhappily scarcely anything is perfectly plain, but what is also perfectly common.