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 biology of socialization in addiction, this association was mediated by indicators of the quality of mates’ relationship. Interestingly, a flip-flop of alleles of the associated polymorphism was observed for this gene as well, possibly explained by phenotypic differences in the samples related to the dual role (and respective differences in the severity) of drug use: as a prosocial facilitator and as an indicator of antisociality. The epigenetic process of DNA methylation may control the persistent behavioral effects of environmental factors mediated by the AVP receptor expression (Murgatroyd et al., 2009). The ability of the organism to retain such effects for a long time is shared with memory and learning. The mechanistic data, from the genetic level to higher nervous activity to complex behaviors, point at the connections of drug use behavior and addiction in the general framework of behavioral evolution.
