research suggests that none
of these hold the key. So what does? Jerome Burne reports.
To smack or not to smack? Is divorce harmful? Should mothers work? Don't worry about it. It may not matter, because however dedicated (or otherwise) your parenting is, it doesn't have much influence on shaping children's personalities.
"If you took all the children from a group who went to school together," she says, "and switched their parents round, their adult personality would develop in just the same way - provided they stayed in the same school, lived in the same neighbourhood and remained part of the same cultural or subcultural group. The parent's influence is minimal."
Home, she says, is just one of several environments in which children have to learn how to behave. You can affect behaviour in the home, but that doesn't necessarily affect it in other situations. Plenty of children are difficult at home and helpful at school. "This makes evolutionary sense," says Harris. "The parental home is not where children are likely to spend their future. They are already genetically similar to their parents. Adopting all their habits as well would give them much less flexibility for adapting to changing conditions in the outside world."
Harris is far from a lone voice. Her book The Nurture Assumption, due to be published in the US next year, is based on an article in the Psychological Review, and won an award from the American Psychological Society.
"Psychologists often marvel that children turn out all right," she remarks, "despite great differences in the way parents treat them." Her theory is an attempt to explain why.
Over the last decade the idea that genetics influences behaviour has moved from being unmentionable in polite scientific circles to virtually a truism - violence, homosexuality and alcoholism are all recent candidates.
Take eating, for instance. What could be more obvious than the fact that children in a family where both parents over-eat and comfort themselves with food, will do the same? But no. Adopted children, who don't share the over-eating parents' genes, don't copy their behaviour.
The same goes for television watching. Adopted children in a house which goes in for heavy TV viewing won't also sit glued to the box, unless TV watching is something their biological parents also like to do.
But even most radical geneticists aren't claiming that we're pre-programmed. It's obvious that genes and environment work together. But how, then, do we explain how children from the same household can turn out so differently? The most imaginative attempt at an answer comes from Professor Plomin, of the Institute of Psychiatry in South London, with his theory of non- shared environments. If the effect of the family as a whole isn't the answer, he says, then maybe the crucial influence comes from the micro- environment that is unique to each child - that illness, that special teacher. Or the position in the family - birth order. But literally thousands of studies haven't thrown up any evidence of clear patterns.
This is what triggered Harris's research and her theory of Group Socialisation (GS). "What I've found is that the lasting influence on children comes from the one group which is found with little variation in every society - the children's play group," she says.
Humans are essentially social animals; millions of years of evolution have designed us to be exquisitely responsive to the group. We know that groups instill a strong drive to conform. But the effect goes much deeper than being seen in the correct T-shirt.
A crucial piece of evidence suggesting that the children's group has a greater effect than the home comes from the study of language. One of Harris's supporters is the leading linguistics researcher Steven Pinker, author of the best-selling The Language Instinct.
"Research in my area throws up two strong bits of evidence in her favour," he says. "First, that children of immigrants pick up the accent of their peers - not their parents, not their teacher, not television announcers. Secondly, children in a group will quickly develop their own language, if they don't start out with one."
If the simple nurture idea were right, you would expect parents to have a crucial effect on sex roles. But Professor John Archer, of the University of Central Lancashire, another Harris supporter, has found that they do not.
"Parents have tried for the last 20 years to raise boys and girls in much the same way," he points out. "Yet, as every school and every parent knows, boys and girls automatically split themselves into single sex groups from an early age." Then, once in the groups, they develop quite distinct patterns of behaviour, and it's these, rather than those of the parent, that children pick up.
An obvious line of criticism is to point out that there is absolutely nothing new in claiming that peer pressure influences the way children behave. However what is new about GS theory is that it says that the long- term influence of children's groups is far greater than that of the home, and that it starts much earlier than is generally recognised. It also makes a number of new and testable predictions about how it works.
For instance, take the findings that when parents divorce the children's behaviour often deteriorates. To begin with, the children have probably inherited the conflict-prone personalities of the parents - divorce runs in families - but, more to the point, divorce messes up their position in the group. "Many of them move house, which means they lose their place in the local hierarchy and have to work to be accepted into a new group," says Harris. "They may well move to a poorer neighbourhood, and so have to deal with a group with different norms. The result is problem behaviour."
So does it matter how parents behave towards their children? Are regular cuddles really no more influential than cool indifference?
"Well, if you are cruel or indifferent it won't ruin your child's personality," says Harris, "but it can certainly ruin your relationship with him or her. If you want your kids to like you when they are grown up, you'd better be nice to them now."