Morality might be hard-wired into the brain, like language. So say the cognitive neuroscientists investigating the neural basis of moral cognition. I couldn't find a link to the actual study for your reading pleasure, but another study by the same neuroscientists, Jorge Moll and Jordan Grafman, shows that making charitable donations activates the brain's reward system in the same way that receiving monetary rewards does.
I don't know about you, but I love finding out there's a physiological basis for stuff like moral behavior. This is why I'm a fan of the enteric nervous system, which is responsible for your gut feelings.