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gladwell dot com - do parents matter?
In a series of careful and comprehensive studies (among them the famous Minnesota studies of twins separated at birth) behavioral geneticists have concluded that about fifty per cent of the personality differences among people--traits such as friendliness, extroversion, nervousness, openness, and so on--are attributable to our genes, which means that the other half must be attributable to the environment. Yet when researchers have set out to look for this environmental influence they haven't been able to find it. If the example of parents were important in a child's development, you'd expect to see a consistent difference between the children of anxious and inexperienced parents and the children of authoritative and competent parents, even after taking into account the influence of heredity. Children who spend two hours a day with their parents should be different from children who spend eight hours a day with their parents. A home with lots of books should result in a different kind of child from a home with very few books. In other words, researchers should have been able to find some causal link between the specific social environment parents create for their children and the way those children turn out. They haven't.
One of the largest and most rigorous studies of this kind is known as the Colorado Adoption Project. Between 1975 and 1982, a group of researchers at the University of Colorado, headed by Robert Plomin, one of the world's leading behavioral geneticists, recruited two hundred and forty-five pregnant women from the Denver area who planned to give up their children for adoption. The researchers then followed the children into their new homes, giving them a battery of personality and intelligence tests at regular intervals throughout their childhood and giving similar tests to their adoptive parents. For the sake of comparison, the group also ran the same set of tests on a control group of two hundred and forty-five parents and their biological children. For the latter group, the results were pretty much as one might expect: in intellectual ability and certain aspects of personality, the kids proved to be fairly similar to their parents. The scores of the adopted kids, however, had nothing whatsoever in common with the scores of their adoptive parents: these children were no more similar in personality or intellectual skills to the people who reared them, fed them, clothed them, read to them, taught them, and loved them all their lives than they were to any two adults taken at random off the street.
The children of smokers are more than twice as likely to smoke as the children of nonsmokers, so it's natural to conclude that parents who smoke around their children set an example that their kids follow. In fact, a lot of parents who smoke feel guilty about it for that very reason. But if parents really cause smoking there ought to be elevated rates of smoking among the adopted children of smokers, and there aren't. It turns out that nicotine addiction is heavily influenced by genes, and the reason that so many children of smokers smoke is that they have inherited a genetic susceptibility to tobacco from their parents. David C. Rowe, a professor of family studies at the University of Arizona (whose academic work on the limits of family influence Harris says was critical to her own thinking), has analyzed research into this genetic contribution, and he concludes that it accounts entirely for the elevated levels of cigarette use among the children of smokers. With smoking, as with niceness, what parents do seems to be nearly irrelevant.
