In a recent issue of PNAS (
Just a moment...), Francisco Ayala lays out his view of morality as an exaptation, a new use for a faculty that evolved for another reason. He believes that humans alone evolved, through natural selection, a capacity for moral behavior. Specifically, they evolved high intelligence, which facilitated tool use. Once intelligence reached a certain level, it was coopted by moral behavior. From that point on, cultural evolution takes over. Ayala believes that moral codes evolve by a process of cultural group selection. The groups with the fittest moral codes outcompeted other groups.
Ayala’s hypothesis seems to depend on his assertion that morality is unique to humans. He dismisses research suggesting that incipient morality exists in non-human primates. I don’t know how valid this dismissal is. (Unfortunately the research on non-human primates appears to be in some turmoil because of the Marc Hauser affair.)
Ayala dismisses natural group selection because it is vulnerable to cheaters. I think his concept of cultural group selection is open to the same sort of criticism.