What's the scientific explanation for some of the madness in the hood? The Warrior Gene

From LiveScience

Boys who have a so-called "warrior gene" are more likely to join gangs and also more likely to be among the most violent members and to use weapons, a new study finds.
"While gangs typically have been regarded as a sociological phenomenon, our investigation shows that variants of a specific MAOA gene, known as a 'low-activity 3-repeat allele,' play a significant role," said biosocial criminologist Kevin M. Beaver of Florida State University.
In 2006, the controversial warrior gene was implicated in the violence of the indigenous Maori people in New Zealand, a claim that Maori leaders dismissed.
But it's no surprise that genes would be involved in aggression. Aggression is a primal emotion like many others, experts say, and like cooperation, it is part of human nature, something that's passed down genetically. And almost all mammals are aggressive in some way or another, said Craig Kennedy, professor of special education and pediatrics at Vanderbilt University in Tennessee, whose research last year suggested that humans crave violence just like they do sex, food or drugs.
"Previous research has linked low-activity MAOA variants to a wide range of antisocial, even violent, behavior, but our study confirms that these variants can predict gang membership," says Beaver, the Florida State researcher. "Moreover, we found that variants of this gene could distinguish gang members who were markedly more likely to behave violently and use weapons from members who were less likely to do either."
The MAOA gene affects levels of neurotransmitters such as dopamine and serotonin that are related to mood and behavior, and those variants that are related to violence are hereditary, according to a statement from the university.
The new study examined DNA data and lifestyle information drawn from more than 2,500 respondents to the National Longitudinal Study of Adolescent Health. Beaver and colleagues from Florida State, Iowa State and Saint Louis universities will detail their findings in a forthcoming issue of the journal Comprehensive Psychiatry.
A separate study at Brown University from earlier this year found that individuals with the warrior gene display higher levels of aggression in response to provocation.
Over networked computers, 78 test subjects were asked to cause physical pain to an opponent they believed had taken money from them by administering varying amounts of hot sauce. While the results were not dramatic, low-activity MAOA subjects displayed slightly higher levels of aggression overall, the researchers said.
The Brown University results, published in the journal Proceedings of the National Academy of Sciences, support previous research suggesting that MAOA influences aggressive behavior, the scientists said.