excluded. Heritability was found to explain 65%, shared environment explained 5%, and the nonshared environment explained the remaining 30% of the variance in aggressive behavior (Burt, 2009). Both Burt (2009) and Rhee and Waldman (2002) examined nonadditive genetic effects, but only Rhee and Waldman (2002) found significant nonadditive genetic effects for antisocial behavior. It is noteworthy that genetic influences are consistently found across these reviews, while shared environmental influences are comparatively small or nonexistent. Family similarity in aggressive and antisocial behavior, therefore, is primarily the result of shared genes, not environment.
