The irrationality of disgust suggests it is unreliable as a source of moral insight. There may be good arguments against gay marriage, partial-birth abortions and human cloning, but the fact that some people find such acts to be disgusting should carry no weight.

Some scholars argue that although the brain might contain neural subsystems, or modules, specialized for tasks like recognizing faces and understanding language, it also contains a part that constitutes a person, a self: the chief executive of all the subsystems.

Morality is often seen as an innovation, like agriculture and writing. From this perspective, babies are pint-sized psychopaths, self-interested beings who need to be taught moral notions such as the wrongness of harming another person.

Part of the satisfaction of tattling surely comes from showing oneself to adults as a good moral agent, a responsible being who is sensitive to right and wrong. But I would bet that children would tattle even if they could do so only anonymously. They would do it just to have justice done.