The idea that learned behavior is specific to the situation in which it is learned may be the most important idea in my book, because it resolves so many discrepancies in the research data, and so many discrepancies between the data and people's everyday observations. It explains why you do find birth order effects if you ask people to compare themselves to their siblings, but you don't find them if you give people a neutral kind of test — a test free of family associations.

It also explains why most people believe in birth order effects. You aren't likely to know someone's birth order unless you've seen them in the context of their family. When people think about birth order, they think about the families they know well: their own brothers and sisters, other relatives, the kids next door. But these are people they've seen mainly in a family context, behaving the way they behave with their siblings and parents. Try guessing the birth order of people you know fairly well but haven't seen in a family setting. I'll bet you do no better than chance!

The idea of context-specific learning can also explain why people believe so strongly in parental influence. After all, when you see a parent and a child together you can see that the parent is influencing the child! You can see the child responding to the parent's praise or criticism or method of discipline or lack thereof. What you're less likely to see is that this child will behave differently in environments that aren't associated with the parent. Or, if you do notice that the child behaves differently, the nurture assumption causes you to believe that the way the child behaves with the parent must somehow be more important or more lasting.

JB: Whereas just the opposite is the case?

HARRIS: Well, the way children behave outside their parents' home is certainly more lasting, because that's where they're going to spend their adult lives. But I'm not saying that the way they behave at home is unimportant. This is one of the ways that parents do have an influence: they can determine, to a large extent, how their children will behave at home. But they can't determine how their children will behave when they're not at home. It may look as though they can, but I believe the correlations that we notice are due mainly to genetic effects. Children carry their genes along with them wherever they go, and they got their genes from their parents. If an aggressive parent has an aggressive child, you can't conclude that the child learned to be aggressive from the parent until you've eliminated genetic effects.

JB: How does this idea resolve discrepancies in the research data?

HARRIS: A couple of years ago, two articles appeared in the same issue of Archives of Pediatrics and Adolescent Medicine. The first got into all the newspapers: the researchers reported that children who were spanked by their parents became more aggressive. The second went unnoticed: the researchers reported that children who were spanked by their parents did not become more aggressive. It turned out that the two groups of researchers were measuring different things: the first group looked at how the children behaved at home, the second at how they behaved at school. Spanking at home apparently makes kids act up more at home (or maybe kids who act up at home get more spankings), but it doesn't make the child more aggressive outside the home. The widely quoted conclusion of the first group of researchers — that if parents stopped hitting their kids it could "reduce the level of violence in American society" — was nothing but hot air.

JB: I take it you don't think spanking makes kids more violent?

HARRIS: I used to but I don't anymore. Look, in the early part of this century, American parents routinely spanked their kids. They considered it their duty to spank a kid if the kid did something wrong. That's where we got the expression, "This is going to hurt me more than it's going to hurt you." What the parent meant by this bizarre statement was, "I don't really want to spank you, but the experts tell me I'm supposed to." In those days, the advice-givers didn't warn parents against damaging their child's self-esteem — they warned against "spoiling" the child. Too much attention and affection were thought to be bad for kids.