From Edge:
What we regard as the modern human personality evolved during the Pleistocene, between 1.6 million and 10,000 years ago. If you encountered one of your direct ancestors from the beginning of the Pleistocene moseying down the street today, you would probably call the SPCA and ask for a crew with tranquilizer darts and nets to cart the beast off to the zoo. If you saw somebody from the end of the Pleistocene, 10,000 years ago, you'd call the Immigration & Naturalization Service—by that time our ancestors wouldn't have appeared much different from any of us today. It is that crucial period, those 80,000 generations of the Pleistocene before the modern period, which is the key to understanding the evolution of human psychology. Features of life that makes us most human—language, religion, charm, seduction, social status-seeking, and the arts—came to be in this period, no doubt especially in the last 100,000 years.
The human personality—including those aspects of it that are imaginative, expressive, and creative—cries out for a Darwinian explanation. If we're going to treat aspects of the personality, including the aesthetic expression, as adaptations, we've got to do it in terms of three factors.
The first is pleasure: the arts give us direct pleasure. A British study a few years ago showed that six percent of all waking life of the average British adult is spent enjoying fictions, in movies, plays, and on television. And that didn't even include fictional books—bodice-rippers, airport novels, high literature, and so forth. That kind of devotion of time and its pleasure-payoff demands some kind of explanation.
More here.
