The Tipping Point: How Little Things Can - By Gladwell, Malcolm Page 0,88

deal with the issue of contagion first. There are two possible strategies for stopping the spread of smoking. The first is to prevent the permission givers—the Maggies and Billy G.’s—from smoking in the first place. This is clearly the most difficult path of all: the most independent, precocious, rebellious teens are hardly likely to be the most susceptible to rational health advice. The second possibility is to convince all those who look to people like Maggie and Billy G. for permission that they should look elsewhere, to get their cues as to what is cool, in this instance, from adults.

But this too is not easy. In fact, it may well be an even more difficult strategy than the first, for the simple reason that parents simply don’t wield that kind of influence over children.

This is a hard fact to believe, of course. Parents are powerfully invested in the idea that they can shape their children’s personalities and behavior. But, as Judith Harris brilliantly argued in her 1998 book The Nurture Assumption, the evidence for this belief is sorely lacking. Consider, for example, the results of efforts undertaken by psychologists over the years to try and measure this very question—the effect parents have on their children. Obviously, they pass on genes to their offspring, and genes play a big role in who we are. Parents provide love and affection in the early years of childhood; deprived of early emotional sustenance, children will be irreparably harmed. Parents provide food and a home and protection and the basics of everyday life that children need to be safe and healthy and happy. This much is easy. But does it make a lasting difference to the personality of your child if you are an anxious and inexperienced parent, as opposed to being authoritative and competent? Are you more likely to create intellectually curious children by filling your house with books? Does it affect your child’s personality if you see him or her two hours a day, as opposed to eight hours a day? In other words, does the specific social environment that we create in our homes make a real difference in the way our children end up as adults? In a series of large and well designed studies of twins—particularly twins separated at birth and reared apart—geneticists have shown that most of the character traits that make us who we are—friendliness, extroversion, nervousness, openness, and so on—are about half determined by our genes and half determined by our environment, and the assumption has always been that this environment that makes such a big difference in our lives is the environment of the home. The problem is, however, that whenever psychologists have set out to look for this nurture effect, they can’t find it.

One of the largest and most rigorous studies of this kind, for example, is known as the Colorado Adoption Project. In the mid 1970s, a group of researchers at the University of Colorado led by Robert Plomin, one of the world’s leading behavioral geneticists, recruited 245 pregnant women from the Denver area who were about to give up their children for adoption. They 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 the same sets of tests to their adoptive parents. For the sake of comparison, the group also ran the same set of tests on a similar group of 245 parents and their biological children. For this comparison group, the results came out pretty much as one might expect. On things like measures of intellectual ability and certain aspects of personality, the biological children are fairly similar to their parents. For the adopted kids, however, the results are downright strange. Their scores have nothing whatsoever in common with their adoptive parents: these children are no more similar in their personality or intellectual skills to the people who raised them, fed them, clothed them, read to them, taught them, and loved them for sixteen years than they are to any two adults taken at random off the street.

This is, if you think about it, a rather extraordinary finding. Most of us believe that we are like our parents because of some combination of genes and, more important, of nurture—that parents, to a large extent, raise us in their own image. But if that is the case, if nurture matters so much, then why did the adopted kids not resemble their adoptive parents at all? The Colorado