Relying on the face might be human nature - even babies prefer to look at attractive people. But, of course, judging someone based on the geometry of his features is, from a moral and legal standpoint, no better than judging him based on the color of his skin.

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.

Natural selection shaped the human brain to be drawn toward aspects of nature that enhance our survival and reproduction, like verdant landscapes and docile creatures. There is no payoff to getting the warm fuzzies in the presence of rats, snakes, mosquitoes, cockroaches, herpes simplex and the rabies virus.

We are constituted so that simple acts of kindness, such as giving to charity or expressing gratitude, have a positive effect on our long-term moods. The key to the happy life, it seems, is the good life: a life with sustained relationships, challenging work, and connections to community.

We know that young babies, as they become capable of moving voluntarily, will share. They will share food, for instance, with their siblings and with kids that are around. They will sooth. If they see somebody else in pain, even the youngest of toddlers will try to reach out and pat the person.