Should a criminal defendant be allowed to argue that a specific gene rendered him unable to control his violent behavior? [A New Mexico] court concluded that the answer was no, in this instance: It upheld the second-degree murder conviction of Anthony Blas Yepez, who killed a man in 2012. Yepez had sought at trial to introduce evidence that he had what’s been called the “warrior gene” — a version of a gene known as MAOA, which has been linked to violence in some studies.
The state Supreme Court, however, missed an important opportunity: It did not go nearly far enough in batting down the scientifically suspect claim that there is a gene for violence. More broadly, it failed to relay the view of contemporary experts that the very idea of a “warrior gene” is based on obsolete science.
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The court’s failure puts more pressure on scientists and scientifically informed lawyers to spread the word that there is no gene — or combination of genes — yet identified that predisposes people to violence. If such genes are eventually discovered, that will create thorny ethical (and judicial) questions about the limits of personal responsibility. But for now… we can’t be punishing people, or excusing behavior, based on studies that simply have not held up.
