London

Stephen Mobley's defence at his trial for killing a pizza-store manager in Jackson, Georgia, was unusual. His lawyers had pointed to a family history of violence, and argued for leniency on the basis that genetic factors contributed to his crime.

Mobley's defence was rejected, and he is now on death row. But in a controversial study published this week — “Genetics and Human Behaviour: The Ethical Context” — a leading bioethics group says it may only be a matter of time before courts use genetic evidence to help determine punishments.

The London-based Nuffield Council on Bioethics says that genetic factors should sometimes be cited in mitigation for a crime, just as social factors, such as being a victim of child abuse, already are.

“If it is legitimate for a judge to take upbringing into account then it's legitimate to take genetics into account, providing the data are good enough,” says Martin Bobrow, who is head of the department of medical genetics at the University of Cambridge, and deputy chairman of the Nuffield Council.

Some researchers do claim links between a person's genes and antisocial behaviour. A certain form of a gene that breaks down neurotransmitter chemicals has been found to make men more likely to be violent, if they were maltreated as children (Science 297, 851–854; 2002). Before genetics can be used in courts, however, Bobrow says that such results would have to be successfully replicated and the magnitude of the effect quantified. For some associations this could be done “within a decade”, claims Andrew Wilkie, a medical-genetics researcher at the University of Oxford and a member of the working party that prepared the Nuffield Council report. He adds, however, that very few people would be affected.

But not everyone agrees that genetic influences should be used this way. Sceptics include Craig Venter, the former boss of Maryland-based Celera Genomics. Using genetics as mitigation in courts would be a “dangerous leap”, Venter said last week. “I don't see anything in the genetic code that forgives criminal activity,” he says.

Some also fear that using genetics in sentencing could lead to the use of gene therapy to try to 'cure' criminals, and the genetic screening of populations for likely offenders. “This poses some fundamental questions for the legal system,” says Margaret Somerville, director of the Centre for Medicine, Ethics and Law at McGill University in Montreal, Canada, “because the technology will surely improve.”