It is a picture that sums up perfectly the dilemma of the well-meaning politician confronted by the disaffected young. David Cameron leans forward earnestly, brow slightly furrowed, as he addresses questions to his distracted audience. The distracted audience, a youth in a shell suit, lounges back, legs stretched out indolently, eyes semi-focused on the ceiling. No need to fill in the conversational details. They were almost certainly one-sided.

How to make contact with a generation that seems to grow steadily more detached from society’s mainstream is a cause of much soul-searching for all political parties, and it is driving Labour and Conservative into unexpected areas. Mr Cameron has moved back from the punitive stance of his predecessors. He says that antisocial behaviour is ultimately a matter of raising standards, and that, instead of interfering with parenting, schooling or social engineering, a “revolution in responsibility” should be launched, with people encouraged to take charge of their lives and those of their children rather than looking to government for the answers.

Tony Blair reaches for the big stick. He says you can spot problem children from an early age, and take action where it matters — in the family. Parenting orders, monitored by youth offending teams, mean that problem parents can be ordered to attend counselling sessions if their children become disruptive. They may be forced to attend meeting with teachers, and can be prosecuted if they fail to turn up. ASBOs crack down on young offenders, get them off the street corner and away from the areas where they are creating trouble. Mr Blair believes in interference — the earlier the better; he is a latterday Jesuit: “Give me the child until he is 7, and I will give you the man.”

Both agree on one thing: all trouble starts with the family. The more children grow up in a stable environment, the more they are likely to turn into model citizens. Restore family life and you restore the well-adjusted child. But what if that theory is wrong? What if the family has nothing to do with the way the young turn out, and the influences, for bad or good, lie elsewhere? What, in short, if the nurture part of the nature/nurture debate has been looking in the wrong place all this time?

That is the subversive argument that Judith Rich Harris, the American psychologist, has been pursuing for the past ten years or so, and which she has built into two books, The Nurture Assumption and No Two Alike. The theory she advances is that what influences behaviour is not so much the home or the family, or even the genetic make-up of a child, but the peer group in which they grow up. The survival instinct, which teaches the young either to conform with their contemporaries or to become their leader, kicks in early on and can result in huge variations in behaviour. One child may turn into a model conformist, while another, brought up in the same household, becomes a tearaway. To explain why, you have to look outside the family not inside it.

Ms Harris refines her case in the latest issue of Prospect magazine, in the course of which she challenges head-on the assumptions behind Professor Robert Winston’s BBC documentary series Child of Our Times, which is following 25 children from birth to the age of 20. She claims it will shed no light at all on the nature versus nurture argument because it is asking the wrong questions: “Observing children at home or in school, individually or in groups, is not the way to answer the question of why they turn out the way they do,” she writes. “Nor is interviewing their parents.”

She accepts that the genetic make-up of a child is important; she concedes that the home environment has a part to play. But neither on its own explains why identical twins, for instance, brought up in the same family, sharing the same genes and the same care and attention, can develop in completely different ways. She cites a case, ironically from the BBC series, where one male twin is developing into a macho character who is only interested in playing with boys, while the other is happiest with girls, and likes games involving dolls.

“The differences between them are nongenetic,” she says. “In fact, the nongenetic differences between them are as wide as the nongenetic differences between ordinary siblings.” What has influenced them more than the home, their parents, or their genes, has been their need to conform to the standards of their friends, their school mates, the role models they want to emulate.

It is not an easy conclusion to accept. It means that however much work is put into the home or school environment, it is the influence of life outside — on the streets or in the homes of friends and neighbours — that is ultimately the decisive influence. It can take two forms, according to Harris: “The socialisation system makes us want to fit in — to conform to our peers,” she says. “What I call the status system makes us want to stand out — to be better than our peers. We can see these motivations in people of all ages.”

For children this is the art of survival. It means that they must get along in the culture they are reared in rather than the one their elders and betters would like to instil; it means they pick up the accents and attitudes of their peers rather than their parents; it means they will compare themselves — their size, looks, behaviour and outlook — with their contemporaries rather than their teachers; it means that the outside influences to which they are subjected, such as pop culture, club life or street gangs, are likely to have a greater effect on them than anything learnt in the home.

This may be dispiriting for parents. It is even more so for politicians. It means that influencing the behaviour of a nonconformist generation is a far greater task than anyone had expected. It means that if you are to change the youth of today you have to begin with society itself.

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