"What gives people the ability to tell right from wrong? Is the moral sense instilled in us by God? Is it inculcated through religious training? Or does moral judgment vary according to the culture in which we were raised?
Another important building block in the evolution of a moral sense is cooperation, which takes three different forms in the animal world. The first is cooperation based on kinship. An animal that sacrifices to benefit its offspring, for example, helps to protect their shared genes. In the second type, both individuals receive some cost, but both benefit. Cooperative hunting behavior is an example of this type. The third and rarest type is reciprocity, where an individual gives something up with the expectation that it will receive benefit in the future. The Golden Rule, Hauser said, is a formulation in human terms of this adaptation."
Harvard University Gazette, May 3, 2007
If you've read "The God Delusion" by Richard Dawkins then this is familiar, because he refers to Hauser's work there (on page 222 and onwards to be exact).
Update: Another interview with Marc Hauser