Did 'warrior gene' predispose man to violence? Top New Mexico court to consider evidence issue

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The New Mexico Supreme Court has agreed to consider whether a judge improperly barred evidence of a genetic variation linked to impulsive violence in a man’s murder trial.

Lawyers for Anthony Blas Yepez contend his genetic predisposition negated the intent required for a murder conviction, report the Santa Fe New Mexican and the Associated Press. Yepez says he is entitled to a new trial because jurors who convicted him of second-degree murder weren’t allowed to hear the evidence.

Jurors had convicted Yepez in 2015 for the death of the 75-year-old man who raised Yepez’s girlfriend. Evidence showed that Yepez killed the man, George Ortiz, after Ortiz hit Yepez’s girlfriend during a night of drinking in 2012. Yepez and Ortiz had struggled during the fight, and Ortiz’s recliner fell over. When Ortiz appeared to be dead, Yepez set fire to his body.

The so-called warrior gene theory has been used only twice as a defense to murder in the United States, according to a 2017 International Journal of Law Psychiatry article cited by the Santa Fe New Mexican. In seven other cases, the theory was introduced as a mitigating factor in sentencing.

Yepez had the gene, which lowers activity of an enzyme called monoamine oxidase A, or MAOA. The enzyme breaks down serotonin and other neurotransmitters. A normal level is 5; Yepez’s level was about 1. The gene is associated with impulsive aggression in people who were mistreated in childhood, according to Yepez’s experts.

The New Mexico Court of Appeals ruled in July that the trial court abused its discretion by excluding the expert testimony. But the appeals court said the exclusion was harmless because the evidence had been offered to negate the intent for first-degree murder—and jurors acquitted Yepez on that charge. He was instead convicted of second-degree murder, which requires a showing that Yepez knew his acts created a strong probability of death or bodily harm.

Prosecutors and Yepez’s lawyer both asked the state supreme court to hear the case.

Hat tip How Appealing.

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