About 20 percent of those defendants had a favorable outcome of some kind, such as a new hearing to consider whether to include the evidence at trial or the reversal of a prior ruling. The crimes ranged from fraud and kidnapping to drugs and murder. She found more than 2,800 judicial decisions from 2005 to 2015 in which defendants had cited neuroscience in their arguments.
A psychologist also administered a series of tests on Yepez, who said he’d been mistreated as a child, including beatings with a belt buckle, according to Loyd.Ī few years ago, Nita Farahany, a law and philosophy professor at Duke University, set out to measure neuroscience’s growing influence in the criminal justice system. The geneticist, David Lightfoot, concluded that there was “no doubt” that Yepez had the MAO-A mutation, according to court filings. The consumer test wouldn’t hold up in court, so Loyd called Bernet, a professor emeritus at Vanderbilt University School of Medicine, who suggested getting a geneticist to perform a more comprehensive test. Anthony Yepez New Mexico Corrections Dept. “This is the defense I want to pursue,” Loyd told Yepez. A few weeks later, the results came back positive. He had one of his investigators visit Yepez at the Santa Fe County jail, where he swabbed Yepez’s cheek for cells. Loyd went online and found a commercial genetic testing company, FamilyTreeDNA, that charges $99 to determine if someone has the MAO-A deficiency. “Maybe he’s got this gene too,” Loyd recalled thinking. Loyd frantically scribbled notes, thinking of Yepez. Some researchers began dubbing MAO-A the “warrior gene,” a term that was picked up by documentary filmmakers, talk show hosts and consumer-DNA testing companies. There are less extreme, and less rare, versions that have been linked to an increased risk of criminal convictions - but only among men who also suffered from abuse as children. The mutation’s impact on criminal behavior was first documented in 1993 in members of a Dutch family with a severe version that has since been found in a handful of families worldwide. The defendant had argued that a genetic deficiency - a variant of a gene named MAO-A, which regulates aggressive behavior in men - along with abuse he had suffered as a child were partly to blame for his crime. Bernet told the story of a Tennessee murder defendant, facing the possibility of the death penalty, who persuaded a jury in 2009 that he deserved a less severe punishment. One of the speakers was forensic psychiatrist William Bernet. He seemed bewildered at what he had done, according to Ian Loyd, a public defender who was assigned to represent him.Ī few months later, as they prepared for trial, Loyd attended a conference in Washington. But he said he could not remember much of it, and could not explain why he’d reacted so violently. He admitted to attacking the 75-year-old victim during a drunken dispute. In October 2012, he was charged with first-degree murder for beating to death the boyfriend of his girlfriend's mother. Yepez’s journey to this frontier began with a mail-order DNA test. “But how do you know when, and how much?” A test for brain science “The law at the moment exists in this gray zone where everyone acknowledges that both genetic and environmental factors could affect culpability,” said Owen Jones, a Vanderbilt University law professor who directs the Research Network on Law and Neuroscience. That is troubling to researchers who fear some of the tactics push the boundaries of science. But some - about 20 percent, according to one study - have worked, winning defendants new hearings or reversals. Most of those attempts to use neuroscience as a defense have failed, researchers say. This cutting-edge evidence, collected through brain scans, psychological exams and genetic sequencing, has been deployed in a range of ways: to challenge whether a defendant was capable of premeditated murder, whether a defendant was competent to stand trial, whether a defendant should be put to death. The rapidly developing field is forcing officials to confront new questions about how changes in the brain influence behavior - leading some to rethink notions about guilt and punishment. The court’s decision - still months away - could accelerate a trend in the criminal justice system: the use of behavioral genetics and other neuroscience research, including the analysis of tumors and chemical imbalances, to explain why criminals break the law. But Yepez took it to the New Mexico Supreme Court, which agreed to consider it. The claim seemed like a stretch to the judge, prosecutors and some scientists.