Selection does not work by cutthroat competition between individuals, but by favouring whatever behavior is useful to the group. People with crude no… - Mary Midgley

Speaking of an institution such as marriage as natural is, of course, paying it a compliment, the compliment of saying that it meets a fairly central human need. The fact that it is found in some form in every human society is in a way enough to show. But it might be thought that marriage became thus widespread only because it was, like adequate sanitation, a means to an end. This is pretty certainly what Hume thought, as evidenced by his very confused contrast of natural with artificial virtues. He regarded human sagacity simply as the power to calculate consequences, and counted chastity and fidelity, with justice, as artificial virtues, devices designed merely to produce safety and promote utility. In a species as emotionally interdependent as man this view of marriage is nonsense. Pair-formation could never have entered anybody's head as a device deliberately designated to promote utility.

People did not proceed, as the theory of evolution really requires by demythologizing their symbolism about animals and the downward direction. Instead they resisted evolution at all costs, or accepted it with the provisio that the future was to lift them out of the degrading company that admittedly contaminated their past. The Future was seen as leading many away from the rest of nature as fast as possible, as giving him the hope of escaping continuity with it after all. Those who felt a sense of pollution at the thought of kinship with other animals could dwell on the hope of becoming less like them.

In fact, the whole idea of illusion seems to make sense only if we accept the reality of the illusory experience as an experience and question only what it seems to be telling us about the outside world. Optical illusions do really hapen. What they can’t do is provide accurate measurements of the outside world. The idea of having, so to speak, two successive layers of illusion here is unworkable.