People pricked up their ears last December when actor Will Smith said Hitler probably considered himself a good person. Smith raised an age-old question that the “science of the moral sense” tries to answer: What is morality, and how should it affect our actions?

In a meaty article for the New York Times, Harvard professor Steven Pinker says the science of morality uses psychology, neuroscience and evolutionary biology to explain our reactions to certain moral actions.

Pinker first explains the difference between a moralization and an opinion: 1) People see morality as universal; 2) People say immoral people deserve to be punished. Modern moralizations are always in flux. Smoking (once a lifestyle choice) has become a moral issue, and homosexuality (once a moral issue) has become a lifestyle choice.

How do we decide what’s moral and what’s not? Neuroscience says our brain plays a role. People with certain types of brain damage sometimes display moral callousness. When we make a non-utilitarian decision, it’s an emotional impulse triumphing over our rational side.

Do we have an innate moral sense? Pinker says we seem to know innately that we shouldn’t harm others and that we should practice fairness, preserve community, respect authority and guard purity. We prioritize these values differently, leading to our cultural and political divides.

How did we get this moral sense? Pinker says evolutionary biology explains it. Rhesus monkeys show the same reluctance to harm each other. We see respect for authority in the pecking order of the animal kingdom. Community protects our survival.

So is morality objective or a figment of our imagination? Pinker says evolutionary biology doesn’t debunk morality. He discounts God as a source for morality and says perhaps moral truths are like mathematical truths – objective, there for us to discover.

Does the science of morality kill morality dissecting it? Pinker says no; it actually advances morality “by allowing us to see through the illusions that evolution and culture have saddled us with and to focus on goals we can share and defend.”