The New Mexico Supreme Court recently weighed in on an issue that will continue to be raised as scientists gain new knowledge about the impact of genetics on self-control. In State v. Yepez, the court held that a particular genome associated with violent behavior in victims of an abusive childhood cannot be the subject of expert testimony about a defendant’s intent to commit a violent crime.
An ongoing controversy in criminal law hinges on science and philosophy as much as precedent. When should individuals be held responsible for their misconduct?
Traditionally, convictions of serious crimes require proof that the accused offender intended to commit the crime. If the accused caused an accidental result and did not behave recklessly, the accused should not usually face serious punishment.
When it is clear that the offender caused harm that was not accidental, courts generally recognize only a state’s version of the “insanity” defense as negating intent. “Insanity” is an antiquated term that mental health experts have largely abandoned. While states formulate the defense in different ways, one version of the defense places the burden on the offender to prove that a mental disease or defect prevented the offender from conforming his or her conduct to the law.
Another version requires the offender to prove that, because of a mental disease or defect, he or she was incapable of appreciating the difference between lawful and unlawful conduct (or more fundamentally, the moral difference between “right and wrong”). Jurisdictions that have adopted that version of the defense do not allow experts to opine that an offender was incapable of controlling his actions, because lack of volitional control is not relevant to the defense.
The “insanity defense” has long been criticized as being divorced from medical science. Psychiatrists and other expert witnesses have difficulty applying a legal standard that is at odds with a medical understanding of mental health and volitional control.
Tradition has governed, in part because members of society tend to express outrage that an offender has “gotten away with” a crime when the offender is found not guilty due to a mental disease. The defense is rarely used and even more rarely successful. A few states have abolished it; in others, it is severely limited. But questions remain about the morality of holding people accountable for behavior that they cannot control.
Competing Views of Free Will
An ongoing debate in science and philosophy involves the degree to which individuals have any control over their actions at all. The debate between free will and determinism “is among philosophy’s oldest controversies.”
Some neuroscientists argue that free will may be an illusion. They suggest that we engage in an action, that our brain perceives the action, and that our brain convinces us that we willed the action to occur.
The notion that choice is not a matter of volition divides neuroscientists. Scientific studies approach the question indirectly and their results are open to interpretation.
Self-Control and Criminal Justice
Free will is the foundation for the criminal justice system. Criminal law assumes an individual’s ability to control his or her behavior. Criminal punishment (at least for serious crimes) is based on a volitional choice to disobey the law. If, in fact, offenders have no choice, punishment is based on a false premise.
There is room for middle ground in the debate between free will and determinism. It is possible that people generally have free will, but that some people, under some circumstances, are unable to exercise it. If, through no fault of your own, you are incapable of controlling your actions, whether you have free will is academic.
When intent is an element that must be proved to obtain a conviction, one might expect defense lawyers to call expert witnesses to prove that their client was incapable of choosing to break the law because the client was powerless to control his or her behavior. Courts have historically shut the door to that argument, in part because they do not want to undermine the rationale for criminal punishment. Apart from the insanity defense or its cousin, diminished capacity, the claim that “I couldn’t control my actions” is usually unavailable as a defense to criminal culpability, even if it happens to be true.
Expert Opinion in Yepez
Anthony Yepez killed George Ortiz during an argument, then set fire to Ortiz’s body. Yepez was charged with murder and tampering with evidence, among other crimes.
Yepez sought to admit evidence that he had “experienced maltreatment in childhood.” Yepez also wanted to admit expert evidence that he has “a genotype that confers low levels of monoamine oxidase A (MAOA) activity.” MAOA is an enzyme that affects the metabolism of neurotransmitters in the brain. According to Yepez’s experts, low levels of MAOA activity, combined with childhood maltreatment, produce maladaptive or violent behavior.
Yepez essentially hoped to defend the case with evidence that he was “born violent” and could not overcome traits that were part of his genetic makeup. He argued that the testimony was relevant because the condition caused him to kill without forming an intent to kill. He identified a neuropsychologist, James S. Walker, and a geneticist, David A. Lightfoot, as expert witnesses.
The prosecution argued that the proposed testimony was not relevant. It also argued that the expert opinions were insufficiently reliable to be admissible under New Mexico’s version of the Daubert test.
Walker testified at the Daubert hearing, as did two psychologists. All three experts based their opinions on research demonstrating “a relationship between childhood maltreatment combined with low MAOA activity and predisposition to antisocial aggressive behavior.” The research included a study of Brunner Syndrome (a condition that associates complete deficiency of MAOA with aggressive behavior) and a study by Avshalom Caspi and his colleagues in 2002.
The Caspi study attempted “to determine why some children who are maltreated grow up to develop antisocial behavior, whereas others do not.” The study found that MAOA moderates the effects of maltreatment. Maltreated children who have a genotype conferring high levels of MAOA are less likely to become antisocial than children with a genotype that confers low levels of MAOA.
Many studies have replicated the Caspi study’s findings but some have not. A meta-analysis of peer-reviewed studies found a “moderately reliable” interaction between certain environmental risk factors (including abuse during childhood) and levels of MAOA.
Based on Lightfoot’s testing, Walker testified that Yepez’s genotype produces extremely low levels of MAOA, although he could not be sure whether Yepez suffered from Brunner Syndrome. Walker also testified that Yepez’s “history of childhood abuse and … this low MAOA activity gene made him exceptionally predisposed to committing violent behavior.”
Rather confusingly, the trial judge first said “the Daubert factors are met,” then questioned the reliability of the defense evidence. The court said: “I’m really kind of iffy on whether — whether we’ve satisfied — whether it’s a scientific technique that’s reliable enough to prove what it [purports] to prove.” The court also noted that the defense relied on a thirty-year longitudinal study that the court deemed “inconclusive.” The judge observed that there is still “work to be done.”
The trial court ultimately excluded the expert testimony because Lightfoot’s testing could not determine a precise level of MAOA that Yepez’s genotype produced. The judge then faulted the defense for not calling Lightfoot as a witness at the Daubert hearing.
The defense moved for reconsideration, pointing out that New Mexico law allowed its experts to base their opinions on Lightfoot’s report without having Lightfoot testify. Those experts interpreted the facts cited in Lightfoot’s report as consistent with a genotype that produces very low levels of MAOA. The defense also provided an affidavit from Lightfoot that confirmed that interpretation.
The judge accepted the new information but shifted his reasoning. The judge decided that a propensity to behave violently is insufficient to establish New Mexico’s insanity defense — a defense that Yepez did not raise. The judge then decided that people with a propensity to violence can still form an intent to kill and that propensities do not, by themselves, negate intent.
Finally, the judge concluded that studies of low levels of MAOA combined with childhood maltreatment document “increased outcomes of aggressive and antisocial behavior — not impulsive behavior or impulsive violence as such.” The judge thus engaged in hair splitting to distinguish aggressive behavior from impulsively violent behavior, notwithstanding that impulsively violent behavior is by definition aggressive.
The New Mexico Supreme Court agreed that “since Yepez has a low-activity MAOA genotype, not a no-activity MAOA genotype, Walker’s testimony that Yepez is predisposed to impulsive violence was not based on reliable scientific knowledge.” The court agreed that the studies “identified outcomes of antisocial behavior, generally” rather than violence, specifically.
The court was apparently unimpressed by a study finding that low MAOA activity and childhood maltreatment “predict[ed] outcomes … of … both violent and non-violent antisocial behaviors.” The study authors noted that “the low-activity MAOA genotype heightens maltreatment-dependent risk for a range of conduct problems and not aggression or criminal violence specifically,” but that observation means that violence and aggression are not the only outcomes of low levels of MAOA. Both courts were stretching the evidence to conclude that low levels of MAOA do not cause violence.
The court also noted a conflict in the underlying studies about the impact of low levels of MAOA on impulse control. Yet the experts were entitled to rely on studies suggesting that low levels of MAOA diminish impulse control, and the experts are in a better position than judges to evaluate scientific studies. The supreme court essentially cherry-picked the studies underlying the expert testimony to produce the result it wanted.
The court was on firmer ground in concluding that low levels of MAOA do not inevitably produce impulsive violence. Perhaps Yepez killed because he could not control his impulses, or perhaps he formed an intent to kill. The science at this point is incapable of distinguishing between acts caused by an impulsive predisposition and acts taken with intent.
At best, the science can tell us about behaviors that are more common in groups of people who share genomes and childhood experiences. That information doesn’t tell us whether specific individuals within the group are more likely to behave violently. But a defendant only needs to create reasonable doubt about his intent. Whether the science is sufficient to create a reasonable doubt about a defendant’s intent might be a question best left for the jury to decide.
In the end, the court decided that the “mere genetic susceptibility to a given mental condition is not relevant on the issue of deliberate intent, at least in the absence of evidence that such susceptibility is so well understood and has such strong predictive value as to be clinically validated as an indicator of the mental condition.”
As science advances, it may be possible for an expert witness to testify with certainty that a person’s genetic makeup makes it more likely than not that an individual with a particular genome and a particular set of life experiences will engage in impulsive, uncontrollable acts of violence. If that happens, will courts admit expert testimony that a defendant could not form the requisite criminal intent?
In the interest of fairness, they should. Given the judicial tendency to hold people accountable for their behavior regardless of scientific debate about free will, gaining the admissibility of expert evidence about intent will continue to be an uphill battle.