One in five people carry the 'reward gene': Dopamine D2 receptor A1. It could give murderers and miscreants the ultimate excuse
The criminal gene
by Professor Steve Jones whose BBC series on genetics begins next month
ON THE sacred island of Miyajima in Japan is a red box with four holes, labelled A, B, AB and O. Inside are messages bearing fortunes. Blood group O people are, they say, relaxed but they aspire to leadership. Bs are eccentric; As conservative; ABs, given their internal contradictions, moody and standoffish. Japanese couples often ask each other their blood groups, and some offices attempt to achieve the right mix, guaranteeing a harmonious working environment.
It is easy to laugh at the idea that blood group determines personality. It is, though, only an exaggerated version of a belief about what genes can do. Genes determine the colour of your hair and your propensity to disease: why then, should they not predispose you to act in a particular way? Say, a criminal way?
Geneticists discuss the case of the murderer Stephen Mobley, now in the Georgia Diagnosis and Classification Center; Death Row in other words. His defence against execution rests on his family history: he has, his lawyers claim, an inherited predisposition to crime. The case made headlines worldwide. Almost all referred to Mobley's "criminal gene". The press dismissed the idea as yet another attempt to excuse the inexcusable.
Even if such a gene existed, it could never be admitted into court. If crime was genetic, what would be the point of punishment? Inborn bias towards crime might indeed call for a lesser penalty. But not necessarily: in Texas, a jury must, when deciding on the death penalty, consider "whether there is a probability that the defendant would commit criminal acts of violence that would constitute a continuing threat to society". Any failed defence based on a criminal gene could be a highway to the chair.
Yet incredulity about a "gene for crime" is surprising, as nobody denies that crime is inherited. In the 1960s, criminologists began following a group of 400 children from Camberwell, south London. During the subsequent 30 years many committed misdeeds, ranging from shoplifting to robbery.
A good way of predicting who would err was to identify those with a parent found guilty of an offence. Of course, children who became criminals had other similarities. They failed in school, drank and took drugs. All this can be construed as due to social background. Perhaps it is, but the study does show that a tendency towards crime is passed from one generation to the next.
Everyone knows that many criminals come from deprived - even criminal - homes. Although crime runs in families it need not be coded into DNA. There is an association of tattoos with violence, and tattooed youngsters tend to have tattooed parents, but there is no gene for tattoos. Poverty, too, is inherited - but a poor home is not seen as an excuse for criminality.
And that is the question: what is an excuse? Much of the law comes from the 19th-century case of a Glasgow carpenter, Daniel M'Naghten. He became obsessed with the belief that he was victimised for not voting Tory. He decided to kill his chief oppressor, the Home Secretary, Sir Robert Peel. Unfortunately he shot the wrong man. M'Naghten's defence against the death penalty was that: "The Tories in my native city have compelled me to do this. They follow and persecute me wherever I go, and have entirely destroyed my peace of mind . . . It can be proved by evidence. That is all I have to say."
His plea succeeded. It has been restated in more scientific terms. They turn on whether an offender knew that what he did was wrong. More and more, the argument turns on genetics.
For any human attribute the question is not whether biology is involved but how. The brain, with its 10,000 million cells, is the most energetic organ in the body. All cells receive a complete set of genes but in most only a few are switched on. Sixty-six genes are doing something in red blood cells; the heart has 6,000 - but the brain, the master of the body's economy, has 30,000 genes at work: half the total. They are as liable to go wrong as any other.
The law accepts this. Ten years ago in Georgia a woman was imprisoned for killing her mother. In mitigation she claimed that she had a gene for Huntington's disease, a failure of the nervous system whose first signs include mental instability. Her father had died of it. The judge was unimpressed and she was sentenced to life. Soon, though, signs of the illness began to appear. The judge, recognising that the woman had not been responsible for her acts, ordered her release.
John Baker was a successful California lawyer. He is also an alcoholic. After embezzling clients' money, he was hauled before his Bar Association. The punishment is automatic - to be disbarred. Talking to his legal adviser, though, Baker mentioned that his father had American Indian blood. That race's drink problem is well documented. It arises in part because of genetics. Amerindians have a reduced ability to break down alcohol. Their form of a certain enzyme is less active and those who carry it are more susceptible to the effects of drink.
Baker used this in mitigation and, instead of being disbarred, was suspended. He no longer drinks and could have returned to his job but, because of the stress, decided not to. Instead, he runs a bingo supply company.
His case raises an issue that may limit the use of genes in court. Baker's defence was based not on a rare inherited disease but on a normal system of variation. Tens of millions of Americans - some with Indian ancestry, but many Europeans as well - share his inborn inability to deal with alcohol. Several genes are involved: some affect the machinery that breaks down the poison, others change the ability to evade its addictive effects.
Alcoholics are, some say, more likely to possess a certain variant of a gene active in the brain's "pleasure centre". As many as seven out of 10 might carry this gene, the Dopamine D2 receptor A1 gene, compared with one in five of the general population. Most people inheriting it do not become alcoholics, and many who do remain within the law. In principle though, each could ask that the gene be taken into consideration should they offend because of drinking.
This means that a defence based on biology may soon be open to all. The A1 gene is carried by 10 million Britons. It may be a "reward gene", favouring instant gratification. It is said to be frequent among cocaine addicts, among autistic children and even in people with withdrawn personalities. Most geneticists question whether a single gene could have such diverse effects but its widespread presence is bound to alter the relationship between genetics and the law.
With the new genetics, it is becoming easier to blame all bad conduct on DNA. Acts once thought of as the result of poor upbringing are more and more ascribed to inborn weakness.
Badly behaved children were once seen as free spirits, to be controlled when necessary. Now though, there is a disease known as attention deficit-hyperactivity disorder, ADHD. Its symptoms include poor concentration and a general tendency to run riot. In the US it is epidemic. In some classrooms, a quarter of the pupils are diagnosed as having it.
Why is the disease (if such it is) so common? Blame has been directed at everything from soft drinks to computer games. Some psychiatrists, though, think that genes - perhaps A1 - are involved. A difficult child is much more likely to get into trouble when adult. In Britain, a quarter of all juvenile crimes are carried out by a hard core of 3 per cent of all young offenders. Many continue their criminal careers as adults.
Childish bad behaviour and adult crime might, then, spring from the same source: a source that is, at least in part, genetic. Some enthusiasts suggest that half the prison population is there because their genes predispose them to ADHD. If this is true, prisons are as much institutions for the genetically unlucky as places of punishment.
Imagine the problems that will emerge as genetic arguments are used in court. If a child's outrageous conduct in school is excused because of an inherited flaw, it is hard not to permit the same excuse in adulthood. When, as in the US, more children are diagnosed with ADHD than there are adult criminals, then many of those who offend may soon be able to appeal to genes in mitigation.
The law cannot, it is clear, accept this. Although it may be obliged to admit that for many people free will is constrained by genes , their actions must be treated as intentional, because good order demands it. Even if most of those who offend do so because of an inborn weakness, the law must ignore the fact.
Society is not a product of genes but of people, and what they do must be judged by the law and not by science. There can be no universal defence for bad behaviour. If some are excused because of biology, then others become relatively more culpable. Predisposition is a double-edged sword. If most criminals offend because of the genes they carry, the scope for mitigation becomes so wide as to lose its meaning. For the law to survive it must ignore the defence of inherited frailty, in much the same way it ignores poverty, inborn or not.
'In The Blood', by Steve Jones, to be published by HarperCollins on May 13, price £20, accompanies the forthcoming BBC television series of the same name. Steve Jones is Galton professor of genetics at University College London. He writes a fortnightly column on Wednesday's science page.
