For the past five years, he has been working with children referred to his Sydney clinic for sustained rages, continual aggression, calculated violence and, occasionally, cruelty to animals. Robert Thompson and Jon Venables killed UK toddler James Bulger. These are children with some of the worst behavioural problems, who score highly for ''callous, unemotional'' traits. In his studies in both Sydney and London, it was these children who did not meet their mother's gaze, even when told they were loved. People marvel at the resilience of children who overcome appalling family backgrounds to make good lives. We understand when childhood trauma sends a child off the rails. But we also have to accept that even good parents can have mean children - how else to explain families where only one child seems to be callous and unemotional, while the siblings are not? Dadds distinguishes between children who are emotionally ''hot'' - those who lash out at the world - and the much smaller subset of ''cold'' children - the ones who don't react emotionally, don't care about others' feelings and don't show remorse.

Disciplining them doesn't have much effect, he says, and even the most souped-up, hands-on therapeutic parenting programs can have trouble reaching them. Dadds calculates only one in 200 children would behave like this, but they're a troubling group whose behaviour, unchecked, turns into violence, criminality and isolation as they grow older. Studies suggest these are the children who could grow up to be psychopaths. ''Your garden-variety child that causes problems at home and school tends to be impulsive, highly emotional and disregulated, and they see hostility everywhere. They hit out, their aggression is a reaction to what they perceive,'' he says. ''But there's a much smaller group, whose aggression is proactive or predatory. And they don't respond as well to our standard parenting programs.'' Dadds's work with these ''cold'' children contributes to a body of research trying to map what Harvard experimental psychologist Steven Pinker calls ''the moral instinct'' - finding the neurological clues that switch on empathy. In his 2002 book The Blank Slate, an ironic title, for no child is that, Pinker says ''genetics and neuroscience are showing that a heart of darkness cannot always be blamed on parents or society''. In The Science of Evil, Cambridge psychiatrist Professor Simon Baron-Cohen proposes that evil is the absence of empathy, and that ''zero-negative'' types - narcissists, borderline personalities, psychopaths- share a neurological disability that short-circuits their empathetic responses.

When babies gaze at their mothers, it's the fundamental moment that sets the stage for the development of empathy and morality in humans. This in turn clicks with the twin studies produced by Dr Essi Viding, a colleague of Professor Dadds. When she was at Kings College, her 2005 analysis of 3,687 pairs of seven-year-old twins found that children with early psychopathic tendencies - the ''cold'' children - most likely inherited these traits, whereas the garden-variety aggression of the ''hot'' children was caused by environmental factors, such as family violence or neglect. This is sensitive stuff, and the scientists are all keen to stress that the children they work with are not ''born evil''. Dadds is at pains to emphasise that ''psychopathy'' does not mean ''serial killer'' but callous disregard for the feelings of others - they could, as psychologist Robert Hare says in his book Sharks in Suits, find their place as easily in the corporate world as in the criminal. Indeed, the emphasis of much of the studies has been in finding the best ways to teach these boys - they're overwhelmingly, though not always, boys - how to love and care for others before they harden their hearts forever. More than 100 boys aged five to 16 in Sydney, and 24 children aged four to eight in London, took part in Dadds's studies. Both studies screened out mothers with histories of mental illness, drug or child abuse, or children with other significant behaviour issues such as hyperactivity or disabilities such as autism.

They were referred by parents or schools for what's called Oppositional Defiant Disorder, a sustained and exhausting defiance thought to affect between 3 and 5 per cent of children. Within this group were the children who'd scored highly for ''callous, unemotional'' traits. Control groups of children with no history of bad behaviour were included in both studies. In Sydney, mothers and sons sat together for 30 minutes playing with toys and drawing family pictures. Then the mothers would be prompted to discuss a happy time and a sad time they'd recently shared with their son. Many of the fathers completed personality tests separately. In London, mothers played with their children and then told them that they loved them. Most, but not all, of the children in London were boys. Some of the fathers completed personality tests to see if they had similar traits to their children. In all cases, the mothers of the cold children were able to express their love as directly as mothers of the children with no behaviour problems. All the mothers, regardless of the challenges they faced in their day-to-day parenting, could provide their child with a direct dose of love when asked to do so. But in both cities, the cold children did not return their mother's gaze, and did not seem to respond to their love - and it was apparent even in children as young as four.

Both studies concluded this reluctance to look into the mother's eyes was not the result of poor parenting or chaotic family lives but ''a trait characteristic of the male side of the family''. Yes, the biological fathers of the cold children - but not stepfathers - were much more likely to display the fearlessness and low-level eye contact also seen in adult psychopaths. But Dadds says it is too soon, and the results too sketchy, to say for sure if this is because the fathers and sons share some genetically inherited neurological deficits. ''Gazing into the eyes is hard-wired into the human brain, and it's the first thing babies will detect in their environment,'' Dadds says. ''When they gaze at their mothers, it's the fundamental moment that sets the stage for the development of empathy and morality in humans. Some of the earliest evolved parts of our brains are dedicated to driving our attention to the eyes of other people.'' Studies of adult psychopaths have noted their lack of focus on the eyes of others, and it's associated with two other markers: an inability to recognise fear and a lack of empathy. The absence of eye contact also helps to explain why the cold children don't respond well to the intensive parenting programs that have proved effective for other children with conduct disorders: perhaps they're missing the positive feedback the other children get when things are going well.

Dadds's studies investigate whether the lack of eye contact is a neurological deficit, more specific than the broad spectrum difficulties faced by autistic children, and yet more disturbing. The failure to gaze may be the start of what could become ''cascading errors in the development of moral conscience and empathetic concern'', the studies conclude: the baby doesn't look in his mother's eyes, the mother never feels the baby's love, the toddler is remote, the mother is stressed, the child is aggressive, the parents are angry, the child shows no remorse, the family fights all the time, the teenager becomes aggressive and destructive. Finally, the adult is callous and calculating, as he's never understood or cared for the feelings of others. The families Dadds sees for psychopathic behavioural issues ''tend to be pretty good parents: motivated, engaged and loving, not high rates of abuse,'' he says. ''The evidence so far is this is not something we can blame on the parents.'' Indeed, many families he sees have other children with different temperaments. The new wave of genetic and neurological research into these ''remorseless'' children is finally shifting the burden of blame from the mothers, says Warren Cann, director of the Parenting Research Centre in Melbourne. ''It's like autism, that was once thought to be a parental deficiency, the cold mother. We went through it with schizophrenia, too. It's always been blamed on mothers and the way they treated kids. What our genetic studies are showing is that parenting is not a level playing field. When you've got a kid who is really oppositional, you fall back to negative strategies or feel helpless and defeated.''

But the new studies are also suggesting ways to reach these most difficult of children. If the love feedback loop begins with the eyes, Dadds thinks these children could be taught to return the gaze that will rewire the empathetic pathways through the brain. Researchers in the US have reported that psychopathic prisoners can be taught to recognise the signs of fear in others. Dadds has seen similar results with the cold boys. Usually, they have trouble recognising fear in other people, but when they're asked to focus on the eyes they learn to recognise the signs. Teaching children to look and understand can be part of a specialised parenting program that could steer them towards a better life, Dadds says. He intends to study the effect of these parenting programs as his subjects grow up. ''Give them as much positive parenting as you can, enhancing the standard programs with extra dollops of love and engagement and eye contact to get these kids into the zone.''

Loading Michelle Griffin is social affairs editor. We Need to Talk about Kevin screens in Australia from November 10.