Stephen Pinker has a fantastic piece in the New York Times today on The Moral Instinct. It's a good explanation of what evolutionary psychologists, neuroscientists and philosophers (well, those who aren't fundamentally opposed to an empirical investigation of ethics) have learned about our moral sense and conflicting moral impulses.
As for what it means, Pinker points out that those impulses are no the be-all and end-all of morality, and that reason plays a role well beyond just filling in the gaps. Morality is, in the words of Plato, "no small matter, but how we ought to live". In a world where people have different values and different weightings on their moral impulses, reason and impartiality becomes the arbiter, at least if we wish to have any hope of living together.
What science tells us is the roots of our moral impulses, why we are predisposed to think in a certain way. It doesn't tell us how to resolve conflicts between these impulses, which (if any) we should privilege or listen to, or why. Like any other sense, or moral senses are falliable, and prone to misfiring; this means we must always question them and assess whether our natural reaction is justified. So, we still need to keep on thinking, and keep on arguing. The difference is that we'll know ourselves a little better.
