"Where do moral rules come from? From reason, some philosophers say. From God, say believers. Seldom considered is a source now being advocated by some biologists, that of evolution.See also some of my previous posts:
At first glance, natural selection and the survival of the fittest may seem to reward only the most selfish values. But for animals that live in groups, selfishness must be strictly curbed or there will be no advantage to social living."
New York Times, September 18, 2007
This, this, this, and this.