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FIGURE II-8 Plot of support for attacks (Y1) and number of perpetrated attacks (Y2) over time.
SOURCE: Victoroff and Adelman, 2012.

Violence waxes and wanes in part because of innovation and imitation. Yet it is vital to acknowledge the multiplicity of other factors that may contribute to or cause major changes in community rates of individual or collective violence. Innumerable such factors have been proposed or identified—from the population density of proaggressive genetic polymorphisms, to the occurrence of harsh discipline or parental abuse, to the rate of childhood heavy metal neurotoxicity, to the cohesiveness of the community, and to the structural stresses of deprivation and income inequality.

The neurobiological mechanisms by which these factors influence the central nervous systems of participants in violence are slowly being elucidated. At this point, it is premature to propose a weighting of factors or tight localization of systems, circuits, neurons, and neurohumors contributing to the causal pathway. Yet one conclusion has become inescapable: People do not simply choose to become violent by the rational exercise of free will.

That is, according to the discipline of behavioral economics, all decisions are rational. Humans are assumed to have evolved rational decision-making nervous systems, and indeed, the primate brain appears to contain systems that internally represent values, calculate risks and benefits, and make useful behavioral choices.

But classical microeconomic algorithms fail to provide accurate predictions of real human decision making for several reasons. First, contrary to



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