Some debates are so entwined with people’s moral identity that one might despair that they can ever be resolved by reason and evidence. Social psychologists have found that with divisive moral issues, especially those on which liberals and conservatives disagree, all combatants are intuitively certain they are correct and that their opponents have ugly ulterior motives. They argue out of respect for the social convention that one should always provide reasons for one’s opinions, but when an argument is refuted, they don’t change their minds but work harder to find a replacement argument. Moral debates, far from resolving hostilities, can escalate them, because when people on the other side don’t immediately capitulate, it only proves they are impervious to reason. 1

Nowhere is this more obvious than in the topics I will explore in this part of the book. People’s opinions on politics, violence, gender, children, and the arts help define the kind of person they think they are and the kind of person they want to be. They prove that the person is opposed to oppression, violence, sexism, philistinism, and the abuse or neglect of children. Unfortunately, folded into these opinions are assumptions about the psychological makeup of Homo sapiens. Conscientious people may thus find themselves unwittingly staked to positions on empirical questions in biology or psychology. When scientific facts come in they rarely conform exactly to our expectations; if they did, we would not have to do science in the first place. So when facts tip over a sacred cow, people are tempted to suppress the facts and to clamp down on debate because the facts threaten everything they hold sacred. And this can leave us unequipped to deal with just those problems for which new facts and analyses are most needed.

The landscape of the sciences of human nature is strewn with these third rails, hot zones, black holes, and Chernobyls. I have picked five of them to explore in the next few chapters, while necessarily leaving out many others (for instance, race, sexual orientation, education, drug abuse, and mental illness). Social psychologists have discovered that even in heated ideological battles, common ground can sometimes be found. 2 Each side must acknowledge that the other is arguing out of principle, too, and that they both share certain values and disagree only over which to emphasize in cases where they conflict. Finding such common ground is my goal in the discussions to follow.