What makes a criminal?

Our attitudes towards crime and punishment are highly political. They

often come down to how much we believe a person’s particular life

circumstances should be taken into account when deciding whether their

punishment fits the crime they committed. But criminal justice isn’t an

evidence-free zone. Behavioural scientist Terrie Moffitt at King’s College

London has spent her career trying to uncover biological and

environmental roots to criminal behaviour. Now she has evidence from

brain imaging and genetics to support her idea that there are generally

two groups of people who commit crime, each with different causes for

their behaviour and different prospects for reform. Dan Jones: How has the nature-nurture debate influenced views on criminal behaviour? Terrie Moffitt: Our thinking about the roots of

antisocial behaviour has followed pendulum swings between putting

nature or nurture centre stage. Writing in the late 17th century,

philosopher John Locke came down on the side of nurture, arguing thatwe are born as blank slates and learn all our behaviours, bad ones

included. Then in the 19th century, Cesare Lombroso, the founder of

criminology, suggested that bad people were born that way and could be

identified by the shape of their eyes, ears, teeth and eyebrows. By the

1960s, after John Watson and B. F. Skinner developed behaviourism, the

pendulum had swung back to nurture.

Everything changed in the 1980s and 90s, and the debates really heated

up. Scientists started reporting studies of crime drawing on thousands of

twins and adoptees in Scandinavian registers, which seemed to point to

genetic transmission of criminal behaviour from parent to child. This was

like pouring petrol on a fire, and the nature- nurture debate got vicious.

But these studies also made clear that over half the variation in antisocial

and criminal behaviour couldn’t be explained by genetics, and provided

some of the first really solid evidence for the social transmission of crime

in families. Since then, nearly everyone has come to agree that crime

involves both nature and nurture.

But you think they have been missing something. Can you explain

what?

Back in the early 1990s, criminologists knew that male antisocial

behaviour is concentrated in adolescence: when you plot crime against age, you get a crime curve that peaks between 16 and 20 years of age,

and tapers off into the thirties and forties. They also knew that fewer than

10 per cent of males commit more than 50 per cent of crimes.

In 1993, I published a hypothesis that the peak of the crime curve conceals

two different groups, with different causes for their criminal behaviour. I

called one group “life-course persistent offenders”. These are people who

show extreme and often violent antisocial behaviour that begins in early

childhood and continues through adulthood. I thought they would be a

minority, at less than 10 per cent, and biological factors along with bad

childhoods would play a big role for them. The other group, which

I called “adolescence-limited delinquents”, show a similar level of

antisocial behaviour when they are around 18 years old but

grow out of it. I suggested that biology wasn’t part of the story for this

group. And I expected them to be very common, with teenagers who

abstain from offending altogether being the rare ones.

How do you go about testing an idea like this?

You need to follow people for years to identify life-course persistent and

adolescence- limited criminals, ideally from birth to their fifties, measuringantisocial behaviours all along the way. We have been able to do this in the Dunedin Cohort Study, which has followed 1000 New Zealanders from their birth in 1972/73 and who are now in their late forties. And in the

past few years, we have used brain imaging and new techniques of wholegenome analysis to look deeper into the biology of crime.

What have you discovered from the brains studies?

When we scanned the brains of the Dunedin study members last year, we

found that most of those who were offenders didn’t have unusual brains.

But people whose antisocial behaviour started in childhood and persisted

into adulthood – the life-course persistent group – showed less grey

matter in some regions of the cortex, most of which have previously been

linked to antisocial behaviour through their involvement in goal-directed

behaviour, regulation of emotions and motivation.

Are you saying these people were born with different brains?

It is difficult to say. Had we done the scans when they were small children,

we could say whether the brain-structure abnormalities were there before their lives of crime, but the technology wasn’t available then. More recent brain imaging of children with callous or unemotional kinds of behaviour – children who hurt other children and apparently lack remorse –has revealed similar brain abnormalities to those we are finding.

So it is possible for such brain-structure abnormalities to have been there

all along. The persistent offenders in our study also tended to have bad

childhoods, which might alter brain development. That muddies the

picture.

Are some people destined for a life of crime?

No. People will turn out just fine as long as they have good parents who

provide warm, sensitive, stimulating parenting and lots of consistent,

loving discipline, plus the necessary resources for child development, such

as nutritious food and encouragement at school. But great childhoods can

be in short supply. Deprivation, abuse and neglect allow a child’s own

personal vulnerability to grow into antisocial and criminal behaviour.