Your new book argues the importance of human nature in the way we think about ourselves. Why have you called it ''The Blank Slate''?

The common belief is that the mind is just that, a blank slate -- that people are born with no talents or temperaments and that the entire mind is a product of culture and socialization. More specifically, the book is an attempt to confront the phobia that people have of discussions of human nature.

What's at the heart of that phobia?

That a biological understanding of human nature threatens fundamental values of political equality, social progress, personal responsibility and meaning and purpose. And you can't advance research in psychology without confronting these often unspoken but very powerful feelings. There are fears that if you acknowledge that people are born with anything, it implies that some people have more of it than others, and therefore it would open the door to political inequality or oppression, for example.

Which makes it more comfortable to think of humans as characterless meatloaves imprinted by culture.

I don't think anyone who's had more than one child believes that children are indistinguishable lumps of putty waiting to be shaped. There's this enormous body of work on parenting that looks at the correlation of what parents do and how children turn out: parents who speak to their children have children with advanced language skills, parents who spank have children that grow up to be more violent and so on. This could be, but correlation does not prove causation. The fact is that parents provide their children not just with an environment but also with genes. The same genes that make parents talkative could make their children more advanced in language skills. The original studies are rarely done with adopted children.

Is even nurture an outgrowth of nature, then? Is all of it, even culture itself, reducible to evolutionary biology?

I prefer the word unification to reduction. An analogy is that even though we know that sand and mountains and dirt and so on are nothing but molecules -- they're not special kinds of stuff -- a physicist couldn't explain the geography of Europe, even though Europe is nothing but a bunch of protons, neutrons and electrons. Likewise, with human history and politics and cultural affairs, that level of analysis isn't going to tell you the best way to organize a society or how to change a law or try to influence a social value. An understanding of history and culture can only benefit from a better understanding of human emotion and thought. But you don't get much insight into day-to-day behavior by thinking about a person as a hundred billion neurons firing in complicated patterns. It doesn't buy you anything in figuring out how to please your boss or how to get a date or how to win friends and influence people.

Where does that leave our sense of agency and free will?

Agency, personal responsibility and so on can all be tied to brain function, but these are brain functions that are so staggeringly complex that there is no danger that they're going to be reduced to some simple reflex anytime soon, if ever. It's a fallacy to think that hunger and thirst and a sex drive are biological but that reasoning and decision making and learning are something else, something nonbiological. They're just a different kind of biology.

I think that would be a big leap. Rather than constructing a bomb, I hope the book is about how to defuse it. The explosiveness comes from a fear that certain empirical possibilities open the door to social and political evils. That's not the case. We can have an honest science of human nature without a Pandora's box of negative consequences. Anyone who's read the book can't attack it by saying, ''If we accept what you're saying about human nature, then all hell will break loose.'' The point of the book is that all hell won't break loose.