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Code rage: The "warrior gene" makes me mad! (Whether I have it or not)

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Mel Gibson in the film BraveheartJust when you think the blame-it-on-our-genes craze can't get worse, the "warrior gene" goes viral. The latest media outlet to flog it is the Dr. Phil show, which on April 4 broadcast "Born to Rage?". From the promo: "Scientists believe they may know why some people are quicker to anger than others. A new study suggests that inside a rageaholic's DNA, 'a warrior gene' may be pulling the strings. Could today's guests be genetically predisposed to fits of fury?"


Dr. Phil, a psychologist whose real name is Phil McGraw, presented three "rageaholics"—including Lori, a self-described "Tasmanian devil," and Scott, a reality-TV star and "bully"—as well as Rose McDermott, a political scientist at Brown University and warrior gene researcher. McDermott claimed that the warrior gene, which occurs in about 30 percent of the population, makes you more likely to engage in "physical aggression".


Dr. Phil had the rageaholics tested, and guess what? They all had the warrior gene! "This is information to know that you are more susceptible, at risk for, and predisposed—like someone who is fair-skinned and will burn more readily in the sun," Dr. Phil sagely informed his guests. "It doesn't mean they need to go through life sunburned. They take precautions to protect against that." The Tasmanian devil sighed, "It's a relief there's something linked to this anger, and it's not brought on because I want to do it."


Dr. Phil's Web site links to a company called FamilyTreeDNA, "the leading direct-to-consumer DNA testing company in the world. " Send a cheek scraping to the company and it will tell you if you have the warrior gene for $69—$99 if you don't go through Dr. Phil's Web site.


This cheesy talk show is hardly alone in hyping the warrior gene. In fact, Dr. Phil borrowed his headline from a recent National Geographic broadcast, "Born to Rage?", which also explores "the disturbing possibility that some people are born to rage." The show follows Henry Rollins, a self-described former punk rocker with a nasty temper, as he interviews "outlaw bikers, mixed–martial arts fighters" and other tough guys and, once again, McDermott. ABC News jumped on the bandwagon last December with an interview with McDermott, who stated: "In many, many studies [the warrior gene] appears implicated in behaviors that look like they're related to physical aggression or some kind of conduct disorder."


The story of the warrior gene dates back to the early 1990s, when several groups reported a link between violent aggression and a gene on the X chromosome that encodes for an enzyme called monoamine oxidase A (MAOA), which regulates the function of the neurotransmitters such as dopamine and serotonin. The correlation first emerged from studies of a large Dutch family whose male members were mildly retarded and extremely violent. Two were arsonists, one tried to run over an employer with a car, another raped his sister and tried to stab the warden of a mental hospital with a pitchfork. The men all lacked monoamine oxidase A, suggesting that they possessed a defective version of the MAOA gene.


Later, other researchers reported a correlation between violent aggression and an allele of the MAOA gene, MAOA-L, that produces low levels of the MAOA enzyme; the correlation was reportedly stronger if carriers had experienced some sort of trauma as children. The MAOA allele occurs in apes and Old World monkeys as well as in humans, leading to speculation that the allele arose 25 million years ago in the common ancestor of these primates and was subsequently favored by natural selection. In a May 4, 2004, article reviewing all this research, Science dubbed the MAOA allele "the warrior gene," the oldest reference I have found to the term.


Race, inevitably, reared its head. In 2007 Rod Lea and Geoffrey Chambers, researchers at Victoria University of Wellington in New Zealand, reported that MAOA-L occurs in 56 percent of Maori men. "It is well recognized," the researchers commented in The New Zealand Medical Journal, "that historically Maori were fearless warriors." The researchers' racial profiling was based on a study of 46 men, who needed to have only one Maori parent to be defined as Maori. Lea and Chambers reported that MAOA-L was less common among Caucasians (34 percent) and Hispanics (29 percent) but even more common among Africans (59 percent) and Chinese (77 percent).


In 2009 Kevin Beaver, a criminologist at Florida State University, claimed that males with MAOA-L are more likely to report being gang members (pdf). But his study also showed that the vast majority of MAOA-L carriers are not gang members; moreover, about 40 percent of the gang members were not MAOA-L carriers. Like McDermott, Beaver was featured on the National Geographic show "Born to Rage?"


The 2009 study by McDermott and four colleagues, "Monoamine Oxidase A Gene (MAOA) Predicts Behavioral Aggression Following Provocation," which triggered much of the recent publicity given to the warrior gene, was published in Proceedings of the National Academy of Sciences (PNAS). The article claimed that MAOA-L carriers were more likely than noncarriers to respond with "behavioral aggression" toward someone they thought had cheated them out of money they had earned in a laboratory test. "Behavioral aggression" was defined as making the putative cheater consume hot sauce.


Even disregarding the issue of whether giving someone hot sauce counts as "physical aggression," McDermott's study provides little to no evidence for the warrior gene, because the difference between carriers and noncarriers was minuscule. McDermott et al. examined 70 subjects, half of whom carried the warrior gene. The researchers found that 75 percent of the warrior gene carriers "meted out aggression" when cheated—but so did 62 percent of the noncarriers. Moreover, when subjects were cheated out of smaller amounts of money, "there was no difference" between the two groups.


Obviously, the warrior gene cannot possibly live up to its name. If it did, the whole world—and China in particular, if the racial statistics cited above are remotely accurate—would be wracked by violence. The warrior gene resembles other pseudo-discoveries to emerge from behavioral genetics, like the gay gene, the God gene, the high-IQ gene, the alcoholism gene, the gambling gene and the liberal gene. (See my previous columns on the liberal gene and gay gene.)


The abysmal record of behavioral genetics stems from two factors. First, the quest for correlations between thousands of genes and thousands of traits and disorders is prone to false positives, especially when traits are as squishy as "aggression" and "childhood trauma" (the variable that helps some researchers link MAOA-L to violent behavior). Second, the media—including respected scientific journals like Science and PNAS as well as shows like Dr. Phil—are prone to hyping "discoveries" that will attract attention.


The media's fascination with the warrior gene recalls the lurid claims made decades ago concerning "XYY syndrome," in which men are born with two Y chromosomes instead of one; the syndrome affects about one in a thousand men. In the 1960s British researchers identified nine men who had an extra Y chromosome and had a record of violent outbursts. This correlation was not surprising, because the men were all incarcerated in a mental hospital for violent patients. Other researchers, also focusing on institutionalized patients and criminals, quickly claimed to have found evidence that XYY men were hyperaggressive "supermales" at risk of becoming violent criminals.


The XYY-supermale claim was propagated by The New York Times and other mainstream media, enshrined in biology and social science textbooks, and even written into plots for films, novels and television shows (as Wikipedia's excellent entry on XYY syndrome documents). Meanwhile, follow-up studies of noninstitutionalized XYY men failed to corroborate the initial claims. In a 1993 report "Understanding and Preventing Violence" the National Academy of Sciences concluded that there is no correlation between the XYY syndrome and violent behavior. In 2007 CSI: Miami nonetheless broadcast a show, titled "Born to Kill," which featured a serial killer with an extra Y chromosome.


Unlike, say, multiverse theories, unsubstantiated claims about human genetics can have real-world consequences. Racists have seized on warrior gene research as evidence that blacks are innately more violent than whites. In 2010 defense attorneys for Bradley Waldroup, a Tennessee man who in a drunken rage hacked and shot a woman to death, urged a jury to show him mercy because he carried the warrior gene. According to National Public Radio, the jury bought this "scientific" argument, convicting Waldroup of manslaughter rather than murder. A prosecutor called the "warrior gene" testimony "smoke and mirrors." He was right.


Photo of Mel Gibson in the film Braveheart courtesy of Wiki Commons

The views expressed are those of the author and are not necessarily those of Scientific American.

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