The scientists-discover-new-gene genre is controversial. Recent genetic research concerns a socially significant stereotype, that of the black male thug.
The gene is called monoamine oxidase A, or MAOA. It produces an enzyme that breaks down neurotransmitters which activate many of the brain’s circuits. Back in the 1990s, scientists discovered a mutation of MAOA that completely switches off the activation. The result is called Brunner syndrome, which is only known to have afflicted 14 men, all of them related.1. What makes this extremely rare mutation so important is that it links MAOA to violence and criminality. A man with Brunner syndrome is what psychiatrists refer to as “a bad guy.” Five of these 14 men were arsonists; others were rapists or attempted killers. Four men with the mutation somehow escaped having the syndrome, but 10 out of 14 is still significant.
Then came a flood of follow-up research, and MAOA was relabeled the “warrior gene.” A pair of 2008 studies found that a certain type of MAOA (2-repeat allele) doubles a person’s rate of violence (without factoring child abuse into the equation). This allele is less powerful than Brunner syndrome but far more common.
Three studies over the past five years hint that the especially dangerous 2-repeat allele might be more common among African Americans. In one study, 6% of nonwhite subjects had this allele.2 In another, five of 37 (14%) African-American men possessed these rare MAOA alleles.3 Those percentages are remarkable given that in both studies, fewer than one percent of white men had this gene. A third study determined that 0.5% of white MAOA genes and 4.7% of African-American MAOA genes feature this 2-repeat allele—almost a tenfold difference.4
It makes perfect sense that evolution adapted humans to new cognitive demands. For certain groups, cognitive demands amounted to the most efficient and aggressive way of ending others’ lives.