Do your genes make you a criminal?In the US a murderer is claiming his crime was the tragic consequence of being born a killer. Steve Connor reports on new arguments over whether some people are destined to be badSTEPHEN "Tony" Mobley has all the attributes of a natural born killer. Nobody could blame his upbringing - he came from an affluent, white, middle-class American family and he was not abused or mistreated as a child. Yet as he grew up he became increasingly violent, and at the age of 25 he walked into a pizza store and casually shot the manager in the neck after robbing the till and joking that he would apply for the job vacancy when the man was dead.That was in 1991. Now Mobley is waiting on Death Row in Georgia to hear whether his appointment with the electric chair is to be confirmed. His last chance of a reprieve rests with a plea from his lawyer that the murder was not the evil result of free will but the tragic consequence of a genetic predisposition. The genes of Tony Mobley, his lawyers argue, meant he was born to kill.

The chief witness for the defence is Mobley's aunt, Joyce Childers, who has testified that various members of the Mobley family over the past four generations have inexplicably been very violent, aggressive and criminal, although most of them "mellowed" in middle age.

``There is no legal defence to his crime,'' says Daniel Summer, Mobley's attorney. ``There is only the mitigating factor of his family history. His actions may not have been a product of totally free will." Murder, rape, robbery, suicide, "you name it", the Mobley family has had it, he says.

The idea of invoking the Mobley genes as mitigation for the brutal murder of the pizza manager came to Mr Summer after reading about genetics research in the Netherlands. Scientists studying the history of a particular Dutch family had identified a specific genetic mutation that resulted in a chemical imbalance in the brains of some of the males in the family. This, they said, could explain why the same men were prone to unusually violent outbursts.

"We applied for $1,000 from the court to see if Mobley had a similar chemical imbalance, but we were refused. However, our appeal to the Supreme Court against the death sentence still rests on his family history of violent behaviour," Mr Summer says.

This week, at a closed meeting of scientists at the Ciba Foundation in London, Mobley's family tree will again come under intense scrutiny, this time by researchers studying the link between genes and violence. Deborah Denno, a genetics expert at the law school of Fordham University, New York, will end the conference by saying that it is not a question of whether genetic evidence will ever be admitted to court, but when and under what circumstances.

THERE is nothing new about the notion that criminals are born rather than made; it has cropped up repeatedly over the past century in the continuing debate over nature versus nurture.

This is, however, the gateway to a moral minefield. If it could be proved that the criminal urge might be traced to genes, then, some would argue, crime could no longer be blamed on parents, or society, or unemployment, or bad housing, or anything else that is capable of improvement. It would simply be a fact of life for which nobody was to blame, but which would be traceable to a minority of individuals.

This has uncomfortable overtones of eugenics, the pseudo-science which held that mankind could be improved by breeding out the bad, and which the Nazis took a step further by their policy of exterminating the Untermenschen. Even if it stopped there, the idea of the "criminal gene" would be controversial enough, but it does not, for modern science opens up new and different possibilities. If there are genes conferring on certain people a genetic predisposition to crime, could they and their carriers be identified, perhaps as early as the womb? What should happen to those embryos? Moreover, if someone is born with a criminal mind, what else should be done with them other than to lock them away for as long as possible?

The arguments date back at least to 1870, when Cesare Lombroso, an Italian doctor, devised his theory of the criminal man. The idea came to him in a "flash of inspiration" on a gloomy day in December when he was studying the skull of a notorious brigand: "At the sight of that skull, I seemed to see all of a sudden, lighted up as a vast plain under a flaming sky, the problem of the nature of the criminal - an atavistic being who reproduces in his person the ferocious instincts of primitive humanity and the inferior animals." Enormous jaws, huge eye sockets and handle-shaped ears were the sort of inherent features to be found in "criminals, savages and apes", Lombroso wrote.

Throughout the 20th century further attempts have been made to refine what Lombroso started. Many did little to improve on his nonsensical ramblings.

As recently as 1968, for instance, scientists thought they had stumbled across another physical marker for criminal behaviour. They found that 3 per cent of the male inmates in a hospital for mentally abnormal offenders had an extra Y chromosome. Enterprising lawyers seized upon this information and used it as defence evidence in court: "My client has the extra Y chromosome; he couldn't help himself." But it was soon discredited when it was shown that the majority of XYY men had no obvious abnormality and were no more likely to be involved in serious crime than normal XY men.

The more durable research into the genetics of crime has its roots in 1931, when psychologists began looking at nature's own "experiment" in genetics - twins. Identical twins share exactly the same genes, whereas non-identical twins share about 50 per cent of their genes, just like other brothers and sisters. Comparing the fates of pairs of identical twins and non-identical twins, it was clear, could offer some idea of how much a behavioural trait was due to genes (nature) and how much to upbringing (nurture).

Thus the results of twin studies have been at the forefront of the evidence for a genetic component to criminal and antisocial behaviour. Chief of these is the Danish twin study, which has been running for the past quarter- century.

Denmark has become a magnet for social psychologists interested in criminal genetics. Not only is it racially homogeneous, with a good health care system (both of which help to standardise data), but every pair of twins born since 1870 has been registered with the authorities, as has every criminal.

The Danish twin study has cross-checked criminal records for pairs of identical and non-identical twins to compare their fate. The broad conclusion is that a Danish man with an identical twin who has a criminal record is about 50 per cent more likely to have been in prison himself compared with the average Danish male. Non-identical twins are between 15 and 30 per cent more likely to both have criminal records.

Irving Gottesman, a psychologist at the University of Virginia who has worked on the Danish twin study, believes the results show that "criminals are not born, but the odds at the moment of birth of becoming one are not even".

Another Danish study, this time of identical twins who are reared apart in different families, appears to support the notion of being born with a criminal disposition. According to Sarnoff Mednick, a psychologist at the University of California at Santa Barbara, a child whose biological parents are criminals is more likely than other children to begin a criminal career himself even if his adopted parents are law abiding.

Yet another Scandinavian adoption study, this time in Sweden, found a link between criminality, genes and alcohol abuse. Michael Bohman, professor of child psychiatry at Umea University, says the results show a clear genetic predisposition to alcohol abuse which leads to a rising tendency towards anti-social or criminal behaviour. "Of course if there was no alcohol in the environment then there would be no alcoholism," he says. "The risk is related to your genes and the amount of alcohol you're swimming in, but not everyone, of course, drowns."

Studies on twins and adopted children have always suffered from a basic problem. They can only indicate a possible genetic component to a trait. They cannot find the genes involved, nor can they say much about the mechanisms by which environment or upbringing could overcome the genetic predisposition. Every geneticist knows that even if a trait is 100 per cent genetically determined, that does not necessarily mean that nothing can be done about it. The classic example here is the inherited disease phenylketonuria, which can lead to mental retardation. A simple change in the infant's environment, in this case a diet free of the amino acid phenylalanine, can completely override its genetic "destiny" and the disorder is overcome.

The history of studies such as these, especially in relation to the debate over IQ and genetics, is littered with controversy. Conclusions from such work have usually been fiercely challenged and some have had to be withdrawn after other researchers had identified methodological flaws. Today, however, there is a new dimension.

ALTHOUGH twin studies go on much as they always have, genetics has become transformed over the past 10 to 15 years. New techniques in molecular biology have enabled scientists to identify specific inherited defects in DNA, the genetic blueprint. One of the most startling pieces of research into the genetics of violence has come out of the Department of Human Genetics at the University Hospital in Nijmegen. This was the work that inspired the unusual plea of mitigation from Tony Mobley's lawyers.

The scientists at Nijmegen studied the apparent inherited aggression of the Dutch family. Han Brunner, who led the research team and who will also be attending this week's Ciba conference, has, however, distanced himself from suggestions that he has found a "gene for aggression".

"The notion of an `aggression gene' does not make sense," he says, and it would be wrong to suggest that any one gene or collection of genes can account for something as complex as aggressive human behaviour. He emphasises that his research has only demonstrated how a very specific genetic defect can result in a fairly specific behavioural abnormality in one particular family, not society at large. The family spanned four generations and almost a century in time. He found that at various times 14 men in the family had displayed mental retardation combined with unusually aggressive posturing, verbal abuse and sometimes physical violence. There was one instance of rape, two of arson and one of attempted murder.

Professor Brunner's investigation soon found that the trait was "sex linked" like the blood disorder haemophilia, which affects only males but is transmitted through the maternal line. Further work identified the gene itself, which is responsible for an enzyme called monoamine oxidase- A.

Defects in the gene of the aggressive men prevent the enzyme from working, so causing a build-up of neuro-transmitters in the brain, perhaps resulting in over-excitation of the nerves in stressful situations.

Although this sounded a neat solution to the problem, Professor Brunner was presented with some logical inconsistencies in that drugs blocking monoamine oxidase-A have been used extensively to treat patients with depression, with no apparent increase in violent tendencies. Furthermore, one of the neurotransmitters building up in the men was serotonin, which other researchers have found to depress, rather than increase, the propensity for aggression.

Such contradictions serve to reinforce the difficulties of explaining complex emotions in biological terms. Nevertheless, psychologists keep pointing to a clear biological basis for criminal or antisocial behaviour on the basis of their studies on twins and adopted children.

Even if there does appear to be a genetic basis to some types of behaviour that lead to criminality, psychologists are almost unanimous in their belief that it does not mean some children are doomed to a life of crime. "Just because it's genetic it doesn't mean to say it's not amenable to environmental intervention," says Judy Silberg, a clinical psychologist at the Virginia Commonwealth University. "If weapons are available and you have kids with, say, attention deficit disorder, it's a set-up. You're setting up a situation to happen."

THERE are some bitter opponents of what has become known as "neurogenetic determinism". Steven Rose, a brain researcher at the Open University, is a long-standing critic of those who believe that individual differences in human behaviour, notably IQ, have a genetic rather than environmental basis.

He lambastes the "reductionists" who believe there is a raw genetic basis for criminality and violence. The rise in genetic determinism offers no solutions to what are essentially society's problems, he wrote this month in the journal Nature.

"Although only the most extreme reductionists would suggest that we should seek the origins of the Bosnian war in deficiencies in serotonin-reuptake mechanisms in Dr

Karadzic's brain, and its cure by the mass prescription of Prozac, many of the arguments offered by neurogenetic determinism are not far removed from such extremes."

Professor Rose is particularly scathing about a recent attempt by some US researchers to establish a "violence initiative" which would investigate the biological basis of ghetto crime. "As an approach to diminishing the violence of city streets, it would seem unlikely to achieve as significant an impact as would measures to reduce the estimated 280 million handguns currently in personal possession in the United States."

This issue excites strong emotions. Two years ago there was public outrage in the US over a federal anti-violence initiative, conceived by Louis Sullivan, a black physician and then secretary of the US department of health and human services. The idea was to help young black people, who are disproportionately involved in violent crime. Part of the initiative involved investigating the ``biological'' basis of violent crime.

Civil rights leaders and others became deeply suspicious, especially after one leading scientist cited monkey violence and sexuality as the research rationale. "Maybe it isn't just the careless use of the word when people call certain areas of certain cities `jungles'," he said. Amid uproar, the project was shelved.

The notion that crime, genetics and race might be linked has particularly inflamed both proponents and opponents of "genetic determinism". Because skin colour is a genetic trait, because crime statistics show that blacks are more likely to end up in jail than whites, and because an increasing number of researchers appear to believe in a genetic basis of crime and violence, some commentators have jumped to the conclusion that black people are more likely to be involved in crime because of their genes.

The water has been further muddied by the recent publication in the US of a book called The Bell Curve by two right-wing social scientists, Richard Hernstein and Charles Murray. The book argues that IQ has a genetic basis and this accounts for an inherent difference between the IQs of the races. Low IQ people, the book says, are more likely to commit crimes because they lack foresight and cannot understand that robbing someone is wrong.

Few, if any, of the psychologists and geneticists at this week's Ciba conference would agree with Hernstein and Murray. They might, however, be persuaded that cold-blooded murderers such as Tony Mobley can have a genetic predisposition to violence and antisocial behaviour which they are born with.

The problem for Mobley, and others like him, is that judges and juries may be all too ready to agree and conclude that the only treatment is to lock them up and throw away the key, or, in the case of Mobley, throw the switch on the electric chair.

Criminologist’s Research Shows Genes Influence Criminal Behavior

Jan. 24, 2012

Dr. J.C. Barnes is an assistant professor of criminology in the School of Economic,

Political and Policy Sciences at UT Dallas.

Your genes could be a strong predictor of whether you stray into a life of crime, according to a

research paper co-written by UT Dallas criminologist Dr. J.C. Barnes.

“Examining the Genetic Underpinnings to Moffitt’s Developmental Taxonomy: A Behavior Genetic

Analysis” detailed the study’s findings in a recent issue of Criminology. The paper was written

with Dr. Kevin M. Beaver from Florida State University and Dr. Brian B. Boutwell at Sam Houston

State University.

The study focused on whether genes are likely to cause a person to become a life-course persistent

offender, which is characterized by antisocial behavior during childhood that can later progress to

violent or serious criminal acts later in life.

The framework for the research was based on the developmental taxonomy of anti-social behavior, a

theory derived by Dr. Terri Moffitt, who identified three groups, or pathways, found in the population:

life-course persistent offenders, adolescent-limited offenders and abstainers. Moffitt suggested that

environmental, biological and, perhaps, genetic factors could cause a person to fall into one of the

paths.

Genes Show Connection to Crime

UT Dallas criminologist Dr. J.C. Barnes has researched connections between

genes and an individual’s propensity for crime. Shown is the percentage that

genetic factors were found to have influenced whether people became “life

course persistent” offenders, “adolescent-limited” offenders, or those who

never engaged in deviant behaviors, called “abstainers.”

 

“That was the motivation for this paper. No one had actually considered the possibility that genetic

factors could be a strong predictor of which path you end up on,” said Barnes, who is an assistant

professor of criminology in the School of Economic, Political and Policy Sciences at UT Dallas. “In her

(Moffitt’s) theory, she seems to highlight and suggest that genetic factors will play a larger role for

the life-course persistent offender pathway as compared to the adolescence-limited pathway.”

Adolescent-limited offenders exhibit behaviors such as alcohol and drug use and minor property

crime during adolescence. Abstainers represent a smaller number of people who don’t engage in any

deviant behavior.

Barnes and his co-researchers relied on data from 4,000 people drawn from the National

Longitudinal Study of Adolescent Health to identify how people fell into each of the three groups. The

researchers then compared the information using what is known as the twin methodology, a study

design that analyzed to what extent genetic and environmental factors influenced a trait.

“The overarching conclusions were that genetic influences in life-course persistent offending were

larger than environmental influences,” he said. “For abstainers, it was roughly an equal split: genetic

factors played a large role and so too did the environment. For adolescent-limited offenders, the

environment appeared to be most important.”

The analysis doesn’t identify the specific genes that underlie the different pathways, which Barnes

said would be an interesting area for further research.

 “If we’re showing that genes have an overwhelming influence on who gets put onto the life-course

persistent pathway, then that would suggest we need to know which genes are involved and at the

same time, how they’re interacting with the environment so we can tailor interventions,” he said.

Barnes said there is no gene for criminal behavior. He said crime is a learned behavior.

“But there are likely to be hundreds, if not thousands, of genes that will incrementally increase your

likelihood of being involved in a crime even if it only ratchets that probability by 1 percent,” he said.

“It still is a genetic effect. And it’s still important.”

The link between genes and crime is a divisive issue in the criminology discipline, which has

primarily focused on environmental and social factors that cause or influence deviant behavior.

“Honestly, I hope people when they read this, take issue and start to debate it and raise criticisms

because that means people are considering it and people are thinking about it,” Barnes said.

The idea crime could be in part genetic is extremely controversial because most criminologists argue

the root causes of crime are environmental factors such as poverty.

But now a group of researchers claims that the genes we are born with could play an even more

significant role in our chances of turning to a criminal lifestyle in later years.

A University of Texas study published in the Criminology journal found that although there is no

single gene which causes criminal behaviour, there are probably a wide range which play a small

part in raising or lowering our chance of offending.

Dr J.C. Barnes, one of the co-authors, said: "There are likely to be hundreds, if not thousands, of

genes that will incrementally increase your likelihood of being involved in a crime even if it only

ratchets that probability by 1 per cent,” he said. “It still is a genetic effect. And it’s still important.”

Researchers looked at three broad groups of people: those who persistently offend throughout their

lives, those who only commit crimes in their teens, and those who always obey the law.

They focused on so-called life-course persistent offenders, who are typically guilty of anti-social behaviour during adolescence before progressing to violent or more serious crimes in adult life.Using data on 4,000 people from the National Longitudinal Study of Adolescent Health, the researchers found that while adolescent offenders appeared to be more influenced by the environment, the same was not true of those who became lifelong criminals.The twin methodology used to determine the relative influence of environmental and lifestyle factors did not identify which particular genes were responsible, but suggested what up to 70 per cent of our chance of lifelong criminality could be genetic.Dr Barnes said: "The overarching conclusions were that genetic influences in life-course persistent offending were larger than environmental influences."For abstainers, it was roughly an equal split: genetic factors played a large role and so too did the environment. For adolescent-limited offenders, the environment appeared to be most important.”

A U S T R A L I A N I N S T I T U T E

O F C R I M I N O L O G Y

t r e n d s

&

i s s u e s

No. 263

Is There a Genetic

Susceptibility to Engage

in Criminal Acts?

Katherine I. Morley and Wayne D. Hall

in crime and criminal justice

October 2003

ISSN 0817-8542

ISBN 0 642 53816 6

Australian Institute

of Criminology

GPO Box 2944

Canberra ACT 2601

Australia

Tel: 02 6260 9221

Fax: 02 6260 9201

For a complete list and the full text of the

papers in the Trends and Issues in

Crime and Criminal Justice series, visit

the AIC web site at:

http://www.aic.gov.au

Disclaimer: This research paper does not

necessarily reflect the policy position of the

Australian Government.

G

enetic theories of the origins of criminal behaviour have

been a source of contention for over a century since

Lombroso proposed quasi-biological explanations of criminal

behaviour (Pick 1989; Andrews 1999). Genetic theories of

criminality have been especially controversial within the field of

criminology because of the eugenic policies that they inspired

that were implemented during the Nazi era (Kevles 1985).

The sequencing of the human genome has created a

renewed interest in the contribution of genetics to socially

disapproved behaviour such as addiction, mental disorders and

criminal behaviour. Both the media and the public have shown

significant interest in stories relating genes to such disorders and

their presumed implications for policy. Criminologists, lawyers

and policy makers in the criminal justice field need to be well

informed about the results of research on genetics of criminal

behaviour and its limitations, a need that will only increase as

genetic research on behaviour becomes more sophisticated.

There is an understandable fear among criminologists that

information on increased genetic risks of engaging in criminal

Toni Makkai

Acting Director

Debates about criminality have long focussed on the relative contributions

of environment and genetics as components of antisocial and destructive

behaviour. Although genetic explanations for criminal behaviour have

been circulated since the emergence of modern criminology in the 1700s,

until recently, there has not been the scientific evidence to substantiate or

refute any claims. The past decade or so has seen an increase in research

on the genetics of behaviour, including antisocial behaviour. The findings

of some of this research have inspired media speculation about its policy

implications. Many criminologists are understandably concerned about

the potential misuse of this research given the earlier historical

experiences with the eugenic use made of biological explanations of crime,

and of genetic explanations in particular.

This brief paper summarises this evidence. Recent twin studies show

persuasive evidence that both genetic and environmental factors

contribute to antisocial behaviour. However the genetic evidence indicates

that there is no single gene, or even a small number of genes, that predict

an increased risk of antisocial behaviour. Where there have been some

effects the increase in risk associated with antisocial behaviour is modest..

A technical appendix to this paper discussing candidate genes for

antisocial behaviour is available on the AIC website <http://

www.aic.gov.au/publications/tandi2/tandi263.html>.Australian Institute of Criminology

2

acts may adversely affect

strategies used to prevent and

deal with people who commit

crimes. Some commentators fear

that genetic information on

criminal predisposition may be

used by policy makers to justify

reduced funding for programs

directed at environmental causes

of crime (Wasserman & Wachbroit

2001). More speculatively, there is

a concern that the identification of

genetic susceptibility to

criminality may lead to proposals

for genetic screening of the

population for susceptibility to

criminal behaviour (Rowe 2002).

These programmes would aim to

identify persons at increased risk

of engaging in criminal activities

and then intervene in some ways

to reduce their risk. Such

proposals understandably raise

fears of a return to the type of

state-sponsored intervention in

reproduction, pre-emptive

incarceration or medication, and

scientifically sanctioned racism

that earlier enthusiasms for

biological explanations of crime

have prompted (Comings 1996;

Andrews 1999; Rowe 2002).

Before the policy implications

of genetic research are addressed

we believe that it is essential to

critically examine the current state

of research on this topic. Such an

examination provides the

necessary basis for evaluating the

validity and ethical acceptability

of speculative proposals for the

preventive use of genetic

information about individual risks

of engaging in criminal behaviour.

In this paper we accordingly

review current knowledge of

genetic influences on criminal

behaviour and make some

tentative predictions about its

future direction. This is a

preliminary to a more detailed

analysis. The potential preventive

uses of such information by

society and the criminal justice

system will be the subject of a

separate paper.

Defining criminal behaviour

One of the major challenges in

researching the causes of criminal

behaviour — whether these be

genetic or environmental — is

how we should define it. Criminal

behaviour is defined by statute

and as such is necessarily a social

and legal concept rather than a

biological one. In light of this fact,

some researchers have argued

that criminal behaviours should

be examined within the wider

context of antisocial behaviour

(Rutter et al. 1998). This is the

approach we follow in this paper.

Three ways of defining

antisocial behaviour can be

distinguished. The first approach

equates it with criminality and

delinquency. Criminality is

defined as engaging in activities

that result in criminal prosecution

or incarceration, while

delinquency is defined as

engagement in unlawful activities

while under the age of 18 (Rhee &

Waldman 2002). Information on

these types of antisocial behaviour

can be collected either through

police and court records of

criminal offences or via

anonymous self-reports of

participation in activities that

would be considered criminal if

they had resulted in arrest and

conviction (Rhee & Waldman

2002). This categorisation of

criminal behaviours is

problematic because it means that

what constitutes criminal

behaviour is defined by statue and

therefore changes over time and

varies between countries (Rutter

et al. 1998).

The second approach that is

often used in genetic studies is to

use diagnostic criteria for various

personality disorders that are

associated with an increased risk

of criminal activity, namely,

Antisocial Personality Disorder

(ASPD). ASPD is characterised by

a persistent disregard for, and

violation of, the rights of others. It

can only be diagnosed in

individuals over the age of 18

(First 2000). Three childhood

disorders — Attention Deficit

Hyperactivity Disorder (ADHD),

Conduct Disorder (CD) and

Oppositional Defiant Disorder

(ODD) — are also often assessed

because they have been identified

as risk factors for development of

ASPD. ADHD is distinguished by

frequent inattention and/or

hyperactivity-impulsivity, while

individuals with CD display

behavioural characteristics that

are comparable to ASPD

(violation of societal norms or

rules) (First 2000). ODD is similar

to CD in that it involves

disobedient or hostile behaviour,

but if more serious forms of

behaviour are present, the

diagnosis of CD takes precedence

(First 2000).

A third approach to antisocial

behaviour has been to investigate

personality traits that may be risk

factors for engaging in criminal

behaviour. Aggressiveness and

impulsivity have been the most

heavily researched traits, usually

assessed by personality

questionnaires (Rhee & Waldman

2002). Adult hyperactivity, often

appearing as ADHD, may also be

of interest because individuals

who exhibit both antisocial and

hyperactive behaviour are more

likely to engage in criminal

behaviour (Rutter et al. 1998).

These three broad approaches

to measurement overlap and are

interrelated. For example, a prior

diagnosis of CD is part of the

criteria for ASPD and

approximately half of all children

clinically diagnosed with ADHD

also have ODD or CD (First 2000).

Additionally, childhood

aggression has been found to

predict adult criminality, and

criminality, aggressiveness and

impulsivity are also part of the

criteria for ASPD (Rhee &

Waldman 2002).

A number of limitations

should be highlighted before

considering studies that use these

three approaches to investigate

the role of genetics in antisocial

behaviour. Firstly, these studies

are primarily concerned with

more serious crimes against

property or person. They are not

thought to have any significantAustralian Institute of Criminology

3

influence on criminal behaviours

such as fraud, embezzlement, or

other “white collar” crimes

(Rutter et al. 1998). Secondly, the

correlation between these

disorders and crime is not perfect.

Not all individuals who are

diagnosed with ASPD and related

disorders will engage in criminal

behaviour and not all convicted

criminals will meet the criteria for

one or more of these disorders

(Rhee & Waldman 2002). Finally,

most of this research does not aim

to identify genetic influences on

criminal behaviour per se. Rather

these studies aim to find gene

variants that increase the risk of

developing a particular

psychological disorder, which

may in turn increase the risk of

engaging in criminal behaviour.

Heritability and antisocial

behaviours

Antisocial behaviour often

clusters within families,

suggesting that both inherited

genetic factors and family

environment are risk factors for

this behaviour. Twin and adoption

studies have been used to separate

genetic and environmental

influences and to assess the

contribution that these factors

make to the liability to engage in

antisocial behaviour.

Adoption studies are those in

which individuals with a family

history of antisocial behaviour are

adopted out to families without

such a history. If the majority of

adoptees later engage in antisocial

behaviour, this suggests that

genetic background has more

influence on liability than family

environment. Twin studies

compare the occurrence of the

behaviour in monozygotic (MZ)

and dizygotic (DZ) twin pairs. If

more MZ than DZ twin pairs both

have the disorder, this indicates a

genetic contribution to the

development of the trait.

Statistical models are used to

determine the “heritability of the

trait”, that is the contributions

made by shared genes as well as

the contributions of shared (e.g.

family) and non-shared

environment.

Rhee and Waldman (2002)

recently conducted a review of

the majority of the twin and

adoption studies on antisocial

behaviour that have been carried

out. They found that although

genetic background has a strong

influence on whether an

individual will engage in

antisocial behaviour, the

influence of environmental

factors is even stronger. These

results highlight the fact that even

if individuals have a strong

genetic predisposition, they may

never engage in any antisocial

behaviours if they are not

exposed to the necessary

environmental factors.

Mode of inheritance

The manner in which the

personality disorders and

behavioural traits associated with

criminal behaviour are inherited

has important implications for

research and the potential policy

uses of the research. First, all of

these behavioural characteristics

are determined by many different

factors. An individual’s risk of

developing these disorders or

displaying these traits is not

determined simply by their

genotype; environmental

influences such as parenting

style, socioeconomic status, and

peer groups also play a role

(Rutter et al. 1998; Gatzke &

Raine 2000). Additionally,

interactions between genetic and

environmental factors, and

between different genes, probably

influence the development of

these traits and disorders.

Although they have some

genetic basis, ASPD and related

disorders are not influenced by a

single gene, and are not inherited

in one of the simple patterns of

inheritance identified by Mendel.

The consensus view is that these

traits are influenced by the

additive effects of many different

gene variants that are widely

distributed throughout the

general population rather than

confined to a small proportion of

individuals. Individuals engage in

antisocial behaviour when they

inherit a sufficient number of

variant genes and are exposed to

the right (or wrong) social

environment (Comings 2000).

Candidate genes

Candidate genes are specific

genes that are thought to

contribute to an increased risk of

engaging in antisocial behaviour.

They are usually selected on the

basis of information about the

brain-related bases of behaviour

and personality traits. Association

studies are usually used to

investigate candidate genes. These

studies examine whether one

variant of a candidate gene occurs

more often in individuals who

display antisocial behaviour than

in some comparison group.

As has been true in studies of

many other personality traits,

research on candidate genes for

antisocial behaviour has primarily

focused on genes that influence

the ways in which nerve impulses

are transmitted and received in

the brain. Three such pathways

have been investigated in relation

to antisocial behaviours.

The serotonergic pathway

The serotonergic pathway is

involved in brain development

and dysfunction in this system is

thought to increase aggressiveness

and impulsivity (Reif & Lesch

2003). Associations have been

found between a number of genes

involved in this pathway and

antisocial behaviours, namely

impulsivity, aggression and

ADHD (see Table 1).

The dopaminergic pathway

The dopaminergic system is

involved in “reward pathways” in

the brain (Reif & Lesch 2003).

Genes involved in this pathway

have primarily been investigated

for involvement in ADHD,

although one study did find an

association with impulsivity and

ADHD-related symptoms in

violent offenders (see Table 1).Australian Institute of Criminology

4

The noradrenergic pathway

The noradrenergic system

functions as a central arousal

system (Reif & Lesch 2003).

Disruptions to the regulation of

the noradrenergic pathway have

been implicated in psychological

disorders such as anxiety and

depression. Only two genes

involved in this pathway have

been examined for a relationship

with antisocial behaviours. They

have been found to be associated

with ADHD and also impulsivity

and hostility (see Table 1).

Genes involved in two or more

pathways

Dopa decarboxylase (DDC) is

involved in both the serotonergic

and dopaminergic systems. Two

studies have provided evidence

that suggests the involvement of

this gene in ADHD.

Monoamine oxidase A

(MAOA) is involved in the

serotonergic, dopaminergic and

noradrenergic pathways. MAOA

has become the focus of much

genetic research on criminal or

antisocial behaviour because the

study by Brunner et al. (1993)

identified an association between

a mutation in MAOA and

impulsive aggression. Although

this relationship has not been

confirmed outside the family

examined in the original study,

MAOA has been the focus of a

number of studies, some of which

suggest that the gene has some

influence upon antisocial

behaviours.

Multi-gene studies

The inconclusive results from

studies of individual candidate

genes for antisocial behaviour

reflect the fact that these

behaviours are likely to be

influenced by the interaction of

multiple genes. Each genetic

variant that influences antisocial

behaviour will only have only a

small impact on an individual’s

overall predisposition to such

behaviour. It is therefore

unsurprising that individual

studies of single candidate genes

do not always produce the same

result (Ioannidis et al. 2001). Some

researchers have begun to address

this problem by studying multiple

susceptibility genes for

behavioural traits and disorders

that increase the risk of engaging

in antisocial behaviour.

Comings et al. have

simultaneously examined

multiple candidate genes for their

involvement in ADHD, CD and

ODD. These studies suggest that

some of the genes in the serotonin,

dopamine and noradrenergic

pathways do influence the

development of these disorders

(Comings 2000; Comings et al.

2000a; Comings et al. 2000b).

However, some of the results of

these studies conflict with the

results of some single-gene

studies. The authors found that

the noradrenergic genes had a

stronger influence than other

groups, but only single-gene

studies of DBH have produced

relatively consistent positive

results. It remains to be seen

whether this inconsistency is due

to different research methods, or

the fact that the noradrenergic

pathway has not been as well

investigated in single-gene

studies.

How much can genes tell us?

Genetic research is beginning to

identify genetic variants that may

have some bearing on an

individual’s liability to develop

antisocial behavioural

characteristics. In keeping with

the polygenic pattern of

inheritance proposed for

antisocial behaviours, the amount

that each individual gene

contributes to an individual’s

overall liability is likely to be

small. This is evident in Table 1

which summarises the relative

risks (RR) and odds ratios (OR)

for the candidate genes reviewed

above.

These measures of risk

indicate that an individual with a

susceptibility variant of one of

these genes will only have ~1.5

times the risk of antisocial

behaviour compared to an

individual from the general

population. Thus an individual

will only have a significantly

increased risk of engaging in

antisocial behaviour if they carry a

large number of variant genes.

This average RR is consistent with

the results of meta-analyses of

associations between individual

genes and risk of developing a

range of disorders and diseases

(Ioannidis 2003).

Implications and some tentative

predictions

This review of genetic research on

antisocial behaviour has

summarised growing evidence for

Table 1: Relative risks, odds ratios and associated behaviours for candidate genes

Gene Risk Behaviour

Serotonergic system

Tryptophan hydroxylase Not available Impulsivity, aggression

Serotonin receptors RR=1.24 Impulsivity (males), ADHD

Solute carrier family 6, member 4 RR=1.29 ADHD

Dopaminergic system

Dopamine receptor D4 RR=1.5; OR=1.4 ADHD

Dopamine receptor D5 RR=1.57-1.67 ADHD

Dopamine receptor D3 Not available Impulsivity, ADHD

Solute carrier family 6, member 3 RR=1.2; OR=1.5 ADHD

Noradrenergic system

Dopamine-beta-hydroxylase RR=1.31 ADHD

Alpha adrenergic receptor 2A Not available Impulsivity, hostility

Other genes

Dopa decarboxylase RR=1.48; 1.63 ADHD

Monoamine oxidase A OR=2.8 Impulsivity, aggression, CD,

criminal convictionAustralian Institute of Criminology

5

a genetic contribution to antisocial

behaviour but it has also indicated

that it is highly unlikely that

variants of single genes will be

found that very substantially

increase the risk of engaging in

criminal behaviour. Instead, it is

much more likely that a large

number of genetic variants will be

identified that, in the presence of

the necessary environmental

factors, will increase the

likelihood that some individuals

develop behavioural traits that

will make them more likely to

engage in criminal activities. This

review has a number of

implications for proposed uses of

genetic information in crime

prevention and offender

rehabilitation that we will briefly

sketch here and develop in more

detail elsewhere.

Firstly, adoption and twin

studies of antisocial behaviours

suggest that there are significant

environmental, as well as genetic,

risk factors for these behaviours.

Research such as that of Capsi et

al. (2002) has also shown that

genetic studies are likely to

provide information about both

types of risk factors. We believe

that genetic research is more likely

to refine social policies by better

specification of environmental

risk factors than to divert funds

from environmental crime

prevention strategies.

Secondly, susceptibility alleles

for antisocial behaviours only

increase risk. They are not

deterministic and only poorly

predict the likelihood that an

individual will engage in such

behaviour. Additionally, the

presence or absence of

environmental risk factors cannot

be identified by a genetic test.

Taking this information into

account, proposals for populationwide genetic screening for

criminality do not appear to be

feasible. We believe that eugenic

governmental policies such as preemptive incarceration are

unethical. Such policies are also

impractical because they require

genetic tests with high predictive

value that do not exist and are

unlikely to be found.

Thirdly, the majority of genetic

research on antisocial behaviours

has been conducted on Caucasian

populations, and does not aim to

identify race-specific susceptibility

alleles for antisocial behaviour.

The polygenic nature of antisocial

behaviour also means that even if

a susceptibility allele is found at a

high frequency in a particular

ethnic group, it is likely that a

different susceptibility allele will

be found at a similarly high

frequency in another ethnic

group. We believe it is unlikely

that genetic research in this area

will lead to or inspire racist crime

policies, but anxieties about this

issue need to be addressed by

behavioural geneticists.

Genetic research on criminal

behaviour may, however, have

some uses in offender treatment

and rehabilitation. Information

from genetic studies may be used

to develop new treatments for

personality disorders such as

ASPD, CD, ADHD and ODD that

are risk factors for criminal

behaviour. Genetic information

could also be used to assist in

diagnosing offenders who have

treatable psychological disorders.

Comings et al. (2000b) have

suggested that their multi-gene

tests could have such diagnostic

applications in the future. It is less

certain what the consequences of

such genetic diagnostic tests may

be for criminal cases in which

they may be cited as empirical

evidence of a defendant’s

diminished responsibility. Many

issues need to be examined in

more detail before genetic

information could be used in legal

settings to assess guilt and to

decide upon penalties for criminal

acts.

An analysis of candidate

genes for antisocial behaviours

and a glossary is available on the

AIC website <http://www.aic.gov.

au/publications/tandi2/tandi263.

html>.

References

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criminal justice system might use

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