In an article written for the New York Times on January 13th, Steven Pinker makes his case for the biological and evolutionary source of our morality.
Pinker concludes that since certain moral ideals (murder, incest, etc...) are held universally and can be made to fit in the story of evolution, morals are all a product of evolution. At the articles conclusion, he argues that while morals are not absolute (since they are merely biological) we should strive to improve our morals--thus making the oddly elementary mistake of suggesting that we should adjust our (non-transcendent) "moral instinct" to the transcendent moral law exists outside of our biology while denying that transcendent moral laws exist.
What moral law is it that he appeals to?
Read it and see for yourself: Moral Instinct