Panksepp et al. (2002) note the possibility that “narcotic addiction operates partially through mechanisms which ensured mammalian social bonding over the course of evolution” (p. 463). The relevance of the affiliative behaviors to the addiction risk is supported by the data related to the vasopressin–oxytocin system, including the arginine-vasopressin receptor 1A (AVPR1A) gene. Studies in prairie and montane voles showed that interspecies differences in mating behavior (monogamous and polygamous, respectively) are determined by the brain distribution of this receptor (Insel et al., 1994). This receptor, as well as the vasopressin–oxytocin system in general, has been shown to be involved in attachment, affiliation and parental and reproductive behavior (rev. in Insel, 2010). This involvement demonstrates sex dimorphism, in that vasopressin (AVP) is particularly influential in males, while oxytocin (OXT) in females (although it seems unlikely that this sex-specificity is absolute). Consistent with this dimorphism, association of polymorphisms in the AVPR1A gene with the risk for addiction has been observed in men but not women (Maher et al., 2011). Confirming the role of affiliative behaviors and pointing to a role of the
