Junk Science: How the “Warrior Gene” Myth Led to a Death Sentence
Why the Science was Wrong.
At the heart of Amos’ death sentence was a theory scientists had already largely debunked. The “warrior gene” idea came from a single, small study that included just 13 people, too few to support broad claims about human behavior. Later research involving more than 1,000 men found no support for the original results, and by the time of Amos’ trial, the scientific consensus had moved away from the notion that one gene could meaningfully predict who would become violent, a theory with roots in eugenics, not modern behavioral science.
Despite this, Amos’ defense team inexplicably built their case around that theory. In so doing they gave the state a powerful tool to argue Amos would always be dangerous, despite lack of evidence to back up the claim.
What the theory actually says
The gene at issue, MAOA, helps the brain process certain chemical signals. Some people carry a version that works at a lower level. Early researchers suggested that, in men who had also endured severe childhood adversity, this combination might be associated with an increased risk of aggression.¹
Those findings, even on their own terms, were about patterns in groups, not destiny for any one person. They also came from narrow samples, mostly white men in specific settings, making the findings a poor fit for predicting the future of any particular individual, let alone in a capital trial.
The “Warrior Gene” in Amos’ case: how the “science” was weaponized against him.
In Amos’ case, his lawyers presented this theory to a Texas jury asked to decide whether he would be dangerous in the future. Their expert testified that Amos was more likely than the average person to be violent and framed this as a scientific conclusion. The prosecution then echoed that testimony in its closing argument, telling jurors that even the defense’s own expert had confirmed future dangerousness.
What the jury did not hear with equal weight was the rest of Amos’ story: severe psychotic depression, PTSD, brain damage consistent with chronic childhood trauma, and a long history of untreated mental illness. Those factors, well supported by clinical evidence, were overshadowed by a genetic narrative that sounded authoritative but was contradictory to accepted science.
The Racial Stakes
Media and commentators have used the “warrior gene” theory to feed racist myths about inherent violence, particularly in Black men. They seize on the idea to suggest that some groups are naturally more dangerous, despite scientists warning that this is not what the research shows.
Almost all of the early MAOA studies were conducted on men of European descent. The defense expert in Amos’ case acknowledged before trial that the findings were less reliable for people from other backgrounds and specifically asked whether Amos was Black or white. Even with that warning, the defense told the jury that race did not matter to the analysis. Presenting a the theory of a “warrior gene” as accepted science amplified harmful racial stereotypes in a courtroom where a Black man’s life was at stake.
In Amos’ case, his own lawyers introduced this theory about a Black man in a capital trial. They then reinforced damaging stereotypes in closing arguments by referring to their client using terms that echoed the very myths their expert had put into evidence. The U.S. Supreme Court has recognized that when a defense lawyer introduces race-linked evidence of future dangerousness, it can be even more harmful than if the prosecution had done so, because jurors view it as an admission rather than as an accusation. (Buck v. Davis, 2017.)
Why it Never Should Have Reached the Jury.
The scientists who first studied MAOA cautioned against using their research to label individual people as violent or irredeemable. Their work was about understanding risk factors in populations, not predicting the fate of a single defendant.
Courts are supposed to keep unreliable or misapplied science away from juries, especially in death penalty cases. In Amos’ trial, no one enforced that safeguard it. A discredited, racially fraught theory that did not meet the demands of sound science was presented as proof that he would always be dangerous, and it helped send him to death row.