in the group, altruistic behavior toward the gang members may be consistent with the induced genetic correlations between non-relatives and the extension of inclusive fitness to them. It is noteworthy that this group behavior has been shown to depend on the oxytocin–vasopressin system. In particular, administration of oxytocin in males (only males were studied) elevated in-group cooperation and defensive aggression (De Dreu et al., 2010). It seems likely that other components of the stress-socialization system subserved by vasopressin, oxytocin and stress-reactivity mechanisms participate in both the formation and individual variation of social behavior.
