In February, the New York University social psychologist Jonathan Haidt spoke at the Museum of Sex in New York City. At his website, YourMorals.org, he has asked 300,000 people a variety of questions about politics and personality. Following the speech—which was hosted by the Reason Foundation, the nonprofit that publishes this magazine—New York Times science columnist John Tierney interviewed Haidt about his research on political ideologies, his views on morals in politics, and why libertarians aren't easily disgusted.

Q: What distinguishes libertarians? You have probably the greatest database on the libertarian personality.

A: What we find is that libertarians are by far the highest on systemizing and by far the lowest on empathizing. [These characteristics are generally associated with sex differences; men are higher on systematizing and women are higher on empathizing.] And that's even true within sexes. Women who become libertarians are higher on systemizing and lower on empathizing than women who don't. Liberals and conservatives aren't actually that different on these. This explains the great strengths of libertarians and why they do so well in academics and in think tanks. They're very theoretical, logical, rational people. We also have some logic problems [on the battery of tests that we ask people to take]. Libertarians solve them better than anyone else.

Q: You also find that libertarians are low on disgust. Should libertarians be trying to figure out these disgust feelings to be able to understand [adversaries]?

A: Learning to empathize better—to "assume a virtue if you have it not, for use almost can change the stamp of nature"—might be strategically an effective way to be able to talk to people who are not dispositionally libertarian and get them to actually be involved in libertarian projects.

In a less Machiavellian vein, think about whether [disgust] actually does anything for us, or whether it's some ancient atavism that we might as well just ditch. To some extent, we do need to ditch it, or at least tone it down. Because it makes us believe things. Like miscegenation laws; a lot of disgust is just keeping things separate. It's this purity and pollution idea taken to an extreme. Gay marriage, it's exactly the same thing.

Q: You talk about society becoming decentralized and this revulsion against impure things diminishing in the West. Do you have any predictions on the future of the culture war? This impurity/disgust aspect of politics, what's going to happen to that?

A: Republicans have realized that they basically lost the battle over these social issues. And the reason they lost the battle is that the demographics are just taking care of it. I believe that the culture war has now shifted radically. Since the Tea Party has united libertarians and social conservatives, that unity has forced them to downplay the social issues. So for a variety of reasons—that alliance, plus the increasing demographic diversity—the Republicans can't possibly revive this purity stuff, this anti-gay stuff. It's a losing ticket. It'll be more losing every year.

Q: From the other side, though, Greens now have their own purity obsession with organic foods and pesticides. Is that where purity is going to end up going?

A: That's a good point. I've painted it as though it's conservatives that do all the purity stuff. Liberals do it too. It's commonly joked that conservatives are always moralizing sex and telling you what you can't do. But my God, just try to order breakfast with someone who is on the far left.