The appeal of Darwin's theory of evolution — and the horror of it, for some theists — is that it expunges from biology the concept of purpose, of teleology, thereby converting biology into a mechanistic, canonical science. In this respect, the author of The Origin of Species may be said to be the combined Copernicus, Galileo, and Kepler of biology. Just as these astronomers gave us a view of the heavens in which no angels were required to propel the planets in their orbs and the earth was no longer the center of the celestial system, so Darwin showed that no God was needed to design the spider's intricate web and that man is in truth but another animal.
That's how the standard story goes, and it is pretty much what I used to believe, until I read Darwin's later book, his treatise on the evolution of the mental life of animals, including the human species: The Descent of Man. This is the work in which Darwin introduces one of the most powerful ideas in the study of human nature, one that can explain why the capacities of the human mind so extravagantly exceed what would have been required for hunter-gatherer survival on the Pleistocene savannahs. The idea is sexual selection, the process by which men and women in the Pleistocene chose mates according to varied physical and mental attributes, and in so doing "built" the human mind and body as we know it.
In Darwin's account, human sexual selection comes out looking like a kind of domestication. Just as human beings domesticated dogs and alpacas, roses and cabbages, through selective breeding, they also domesticated themselves as a species through the long process of mate selection. Describing sexual selection as human self-domestication should not seem strange. Every direct prehistoric ancestor of every person alive today at times faced critical survival choices: whether to run or hold ground against a predator, which road to take toward a green valley, whether to slake an intense thirst by drinking from some brackish pool. These choices were frequently instantaneous and intuitive and, needless to say, our direct ancestors were the ones with the better intuitions.
However, there was another kind of crucial intuitive choice faced by our ancestors: whether to choose this man or that woman as a mate with whom to rear children and share a life of mutual support. It is inconceivable that decisions of such emotional intimacy and magnitude were not made with an eye toward the character of the prospective mate, and that these decisions did not therefore figure in the evolution of the human personality — with its tastes, values, and interests. Our actual direct ancestors, male and female, were the ones who were chosen by each other.
Darwin's theory of sexual selection has disquieted and irritated many otherwise sympathetic evolutionary theorists because, I suspect, it allows purposes and intentions back into evolution through an unlocked side door. The slogan memorized by generations of students of natural selection is random mutation and selective retention. The "retention" in natural selection is strictly non-teleological, a matter of brute, physical survival. The retention process of sexual selection, however, is with human beings in large measure purposive and intentional. We may puzzle about whether, say, peahens have "purposes" in selecting peacocks with the largest tails. But other animals aside, it is absolutely clear that with the human race, sexual selection describes a revived evolutionary teleology. Though it is directed toward other human beings, it is as purposive as the domestication of those wolf descendents that became familiar household pets.
Every Pleistocene man who chose to bed, protect, and provision a woman because she struck him as, say, witty and healthy, and because her eyes lit up in the presence of children, along with every woman who chose a man because of his hunting skills, fine sense of humor, and generosity, was making a rational, intentional choice that in the end built much of the human personality as we now know it.
Darwinian evolution is therefore structured across a continuum. At one end are purely natural selective processes that give us, for instance, the internal organs and the autonomic processes that regulate our bodies. At the other end are rational decisions — adaptive and species-altering across tens of thousands of generations in prehistoric epochs. It is at this end of the continuum, where rational choice and innate intuitions can overlap and reinforce one another, that we find important adaptations that are relevant to understanding the human personality, including the innate value systems implicit in morality, sociality, politics, religion, and the arts. Prehistoric choices honed the human virtues as we now know them: the admiration of altruism, skill, strength, intelligence, industriousness, courage, imagination, eloquence, diligence, kindness, and so forth.
The revelations of Darwin's later work — beautifully explicated as well in books by Helena Cronin, Amotz and Avishag Zahavi, and Geoffrey Miller — have completely altered my thinking about the development of culture. It is not just survival in a natural environment that has made human beings what they are. In terms of our personalities we are, strange to say, a self-made species. For me this is a genuine revelation, as it puts in a new genetic light many human values that have hitherto been regarded as purely cultural.