The Nature of Nurture: Parents or Peers?

Dear Jerry,

       You wouldn’t know it from the way it has been depicted in the media, but my book The Nurture Assumption covers a diversity of topics. I talk about how cultures are passed on and what makes them change, and why girls and boys behave differently in some circumstances, and how adolescents turn into adults and lose their annoying ways, and why humans have such a strong tendency to identify with a group and to hate the members of other groups, and why the “me” that looks out at the world from behind my eyes still feels 20 even though the eyes are 60 years old. But none of this gets mentioned in the media storm surrounding my book. All the attention is focused on one idea, which journalists insist on overstating as “Parents Don’t Matter.”
       Yes, I’m the terrible grandmother from New Jersey–the gadfly who has taken on the academic establishment and has been ferociously attacked by some of its members (few of whom have actually read the book). I’m the one who says that parents have no power to mold their child’s personality–that parents have no important long-term effects on the way their children behave when they’re not at home. And I should tell you right off, Jerry, I’m not here to repent of my sins. My head is bloody but unbowed.
       In your attacks on me on National Public Radio and in the Boston Globe, you accused me of ignoring all the evidence that indicates that parents do have important long-term effects on their children. You implied that I must be ignorant of that evidence. But I’ve spent almost 20 years studying it. As a writer of textbooks in developmental psychology (the senior author of a text that went through three editions), I spent many years telling credulous college students about that evidence. I told them about your work, too, Jerry!
       But now I’ve looked more closely at the evidence–looked at it under a microscope, to turn one of your metaphors around–and I’ve seen that it is full of holes. It isn’t just that there is ample evidence against the nurture assumption, it’s that the evidence supporting the nurture assumption is so embarrassingly weak. If it weren’t for the fact that researchers take the idea of parental influence as a “given,” they would never accept evidence of this sort as proof of anything. Yes, there is an awful lot of it, but no matter how high you pile it, horse manure never turns into gold.
       Developmental psychology rests upon data that come almost entirely in the form of correlations, and correlations are ambiguous. Epidemiology has the same problem. When epidemiologists find a correlation between exercise and good health, they like to think it shows that exercising causes good health. They know there is a possibility that the connection works the other way–that healthy people may be more likely to exercise–but they assume that at least some of the correlation must be due to what they’re looking for: an effect of exercise on health.
       But assuming just isn’t good enough. Ambiguous results must be backed up with evidence from other kinds of studies. When all you’ve got is correlations, you have to home in on the truth from different directions, using a variety of techniques.
       In developmental psychology, all you’ve got is correlations. And when I look at other kinds of studies, they do not back up your interpretation of the correlations. Take, for example, the correlation you mentioned in the Boston Globe: “that the best predictor of a child’s verbal talent is the frequency with which the parents talk and read to the child.”
       It is perfectly true that talkative, bookish parents tend to have children who score high on vocabulary tests. But this is an ambiguous result, because correlations don’t come with labels saying, “X caused Y.” Parents and children tend to be alike partly for biological reasons–children inherit some of their characteristics from their parents. Although most developmental psychologists admit this, they nevertheless make the assumption that some of the correlation between verbal parents and verbal children must be due to what the children learned at home.
       The problem is, if we do a different kind of study–look at adopted children, for example–we find no support for this assumption. On the contrary. By the time they reach late adolescence, adopted children do not resemble their adoptive parents in any measure of intelligence. The adolescent reared by talkative adoptive parents is no more verbal, on the average, than the one reared by taciturn parents.
       The problem with your evidence, Jerry, is that a whole bunch of causes and effects are tangled together, and the methods of developmental psychology provide no way to tease them apart. Before you can conclude that the parents are influencing the children, you have to separate parental influence from other possible explanations of your results. Children resemble, for genetic reasons, their biological parents. Parents are more likely to read to children who want to be read to. Children and parents are usually members of the same culture or subculture, and the culture influences both the parents and the kids.
       Like you, I believe that kids are influenced by their culture. But you assume they get their culture from their parents, and that’s an assumption I don’t buy. I hope to take this up with you in the next round of our debate.

Till then,

Judy Harris