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 which 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 hall 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 worlds 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 study isn't saying that genes explain everything and that environment doesn't matter. On the contrary, all of the results strongly suggest that our environment plays as big — if not bigger — a role as heredity in shaping personality and intelligence. What it is saying is that whatever that environmental influence is, it doesn't have a lot to do with parents. It's something else, and what Judith Harris argues is that that something else is the influence of peers.

Why, Harris asks, do the children of recent immigrants almost never retain the accent of their parents? How it is the children of deaf parents manage to learn how to speak as well and as quickly as children whose parents speak to them from the day they were born? The answer has always been that language is a skill acquired laterally — that what children pick up from other children is as, or more, important in the acquisition of language as what they pick up at home. What Harris argues is that this is also true more generally, that the environmental influence that helps children become who they are — that shapes their character and personality — is their peer group.

This argument has, understandably, sparked a great deal of controversy in the popular press. There are legitimate arguments about where — and how far — it can be applied. But there's no question that it has a great deal of relevance to the teenage smoking issue. The children of smokers are more than twice as likely to smoke as the children of nonsmokers. That's a well-known fact. But — to follow Harris's logic — that does not mean that parents who smoke around their children set an example that their kids follow. It simply means that smokers' children have inherited genes from their parents that predispose them toward nicotine addiction. Indeed studies of adopted children have shown that those raised by smokers are no more likely to end up as smokers themselves than those raised by nonsmokers. "In other words, effects of rearing variation (e.g. parents' lighting up or not, or having cigarettes in the home or not) were essentially nil by the time the children reached adulthood," the psychologist David Rowe writes in his 1994 book summarizing research on the question. The Limits of Family Influence. "The role of parents is a passive one — providing a set of genes at loci relevant to smoking risk, but not socially influencing their offspring."

To Rowe and Harris, the process by which teens get infected with the smoking habit is entirely bound up in the peer group. It's not about mimicking adult behavior, which is why teenage smoking is rising at a time when adult smoking is falling. Teenage smoking is about being a teenager, about sharing in the emotional experience and expressive language and rituals of adolescence, which are as impenetrable and irrational to outsiders as the rituals of adolescent suicide in Micronesia. How, under the circumstances, can we expect any adult intervention to make an impact?

"Telling teenagers about the health risks of smoking — it will make you wrinkled! It will make you impotent! It will make you dead! — is useless," Harris concludes. "This is adult propaganda; these are adult arguments. It is because adults don't approve of smoking — because there is something dangerous and disreputable about it — that teenagers want to do it."

If trying to thwart the efforts of Salesmen — if trying to intervene in the internal world of adolescents — doesn't seem like a particularly effective strategy against smoking, then what of stickiness? Here the search for Tipping Points is very different. We suspect, as I wrote previously, that one of the reasons some experimenters never smoke again and some turn into lifelong addicts is that human beings may have very different innate tolerances for nicotine. In a perfect world we would give heavy smokers a pill that lowered their tolerance to the level of, say, a chipper. That would be a wonderful way of stripping smoking of its stickiness. Unfortunately we don't know how to do that. What we do have is the nicotine patch, which delivers a slow and steady dose of nicotine so that smokers don't have to turn to the dangers of cigarettes to get their fix. That's an anti-sticky strategy that has helped millions of smokers. But it is fairly clear that the patch is far from perfect. The most exhilarating way for an addict to get his fix is in the form of a "hit" — a high dose delivered quickly, that overwhelms the senses. Heroin users don't put themselves on a heroin intravenous drip: they shoot up two or three or four times a day, injecting a huge dose all at once. Smokers, on a lesser scale, do the same. They get a jolt from a cigarette, then pause, then get another jolt. The patch, though, gives you a steady dose of the drug over the course of the day, which is a pretty boring way to ingest nicotine. The patch seems no more a Tipping Point in the fight against the smoking epidemic than SlimFast milkshakes are a Tipping Point in the fight against obesity. Is there a better candidate?