In the last two chapters we have seen evidence that males are uniformly more antisocial than females. In this chapter we turn our attention more specifically to sex differences in physical violence and aggression. We examine physical violence at different ages and in different settings as measured via multiple data sources: parent and teacher reports of fighting during childhood, informant reports of fighting, self-reports of violent delinquent offending, and official records of convictions for violent offences in adolescence and young adulthood.

Females have long been demonstrated to be less violent than males at every age and in every setting. This is true in research conducted by criminologists studying violent crime (Greenfield and Snell, 1999; Kruttschnitt, 1994) and by psychologists studying aggression (Bettencourt and Miller, 1996). This sex difference implicitly has been interpreted to mean that women differ fundamentally from men by lacking the underlying motivation or capacity for violence that men have. Following from this interpretation is the deduction that uncovering the source of the sex difference in antisocial behaviour is the key that will also unlock the secret of what causes male violence. This deduction has directed much scientific attention toward explanatory variables on which men and women differ in fundamental ways, primarily physical strength (Felson, 1996), or hormones such as testosterone (Dabbs and Morris, 1990; Mazur and Booth, 1998).