The contagious nature of antisocial behavior

Attention is called to several recently advanced lines of evidence undersco ring the role of contagion in antisocial behavior. One line of evidence con sists of findings that the onset of antisocial behavior in one sibling incr eases the risk to other siblings. A second line of evidence shows that the tendency of monozygotic twins to be more concordant for antisocial behavior than dizygotic twins can be explained by contagion as well as heredity. In addition, there are differences in prevalence between same-sexed and oppos ite-sexed twins that contagion can explain, but heredity cannot, at least n ot without numerous ad hoc auxiliary suppositions. Third, behavioral contag ion is also able to explain, and very precisely, the temporal course of agg regate delinquency through adolescence. Fourth, evidence has been presented that antisocial behavior is an equilibrial phenomenon, that is, that it de pends on a balance between antisocial and prosocial forces, a balance (or i mbalance) that would explain the sudden leaps and falls that crime statisti cs sometimes take. Finally, programs to combat drug use are often modestly successful and almost all such programs presuppose that drug use is contagi ous. The paper closes with two sections on the implications of these findin gs, first for theory and research and then for policy and practice.