The new experiment focused on sentencing by judges, not jury verdicts. It found that neurobiological evidence reduced judges’ sentences by an average of about 7 percent for a fictional defendant convicted of battery and identified as a psychopath.
In the study, three researchers at the University of Utah tracked down 181 state judges from 19 states who agreed to read a fictional case file and assign a sentence to an offender, “Jonathan Donahue,” convicted of beating a restaurant manager senseless with the butt of a gun. All of the judges learned in their files that Mr. Donahue had been identified as a psychopath based on a standard interview — that is, he had a history of aggressive acts without showing empathy.
The case files distributed to the judges were identical, except that half included testimony from a scientist described as “a neurobiologist and renowned expert on the causes of psychopathy,” who said that the defendant had inherited a gene linked to violent, aggressive behavior. This testimony described how the gene variant altered the development of brain areas that generate and manage emotion.
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The judges who read this testimony gave Mr. Donahue sentences that ranged from one to 41 years in prison, a number that varied with state guidelines. But the average was 13 years — a full year less than the average sentence issued by the judges who had not seen the testimony about genetics and the brain.
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“But then those who read about the biological mechanism subtracted a year, as if to say, ‘This guy is really dangerous and scary, and we should treat him as such, but the biological evidence suggests that we can’t hold him as responsible for the behavior,’ ” said James Tabery, an assistant professor of philosophy at Utah.
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This mixed result — added punishment for the defendant’s being identified as a psychopath, tempered by empathy for his having a possible genetic predisposition — provides a good illustration of what legal researchers call the double-edged sword of biobehavioral evidence. On one hand, a biological predisposition suggests that a person is likely to be dangerous in the future and should get a longer sentence; on the other, it implies a lower threshold of responsibility. The evidence could cut either way, depending on the judge.