07/11/2009 05:12 am ET | Updated Nov 17, 2011

STUDY: Genes Can Predict Which Kids Join Gangs

How much power do genes hold over behavior? Can they predict, for example, whether a child will grow up to join a gang? Those are among the questions raised by a new Florida State University (FSU) study released June 5. (What Can Genetic Tests Tell You?)

Since the early 1990s, science has suggested a link between antisocial behavior and a defect in the gene that codes for an enzyme called monoamine oxidase A (MAO-A). A low level of activity on the MAO-A gene results in an excessive breakdown of neurotransmitters, such as serotonin, which helps keep humans calm and happy. The defect thereby increases the urge to react aggressively to threats or fears, leading MAO-A to be referred to as the "warrior" gene. (See 20 ways to get and stay happy.)

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