Having the low-activity version of MAO-A tripled the likelihood … but only in people with a history of severe childhood abuse. And if there was no such history, the variant was not predictive of anything. This is the essence of gene/environment interaction. What does having a particular variant of the MAO-A gene have to do with antisocial behavior? It depends on the environment.
( Robert M. Sapolsky )
[ Behave: The Biology of Humans ]
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