Secondary analyses reveal that the findings are more significant in females. All males, irrespective of genotype, showed a greater increase in drunkenness associated with the transition to adulthood. A number of previous studies have documented higher rates of risky drinking behaviors in males as compared to females at this age (White, Kraus et al. 2006; White and Swartzwelder 2009), and our data support this. It is possible that this leads to a heightened culture of accepted drunken behavior in males, and that under these environmental pressures, genotypic effects are attenuated. None of the twin studies, reviewed above, showing that genetic effects are more evident in environments with less social control, have tested for sex differences. Our study illustrates the complexity of understanding how genetic predispositions interact with contextual influences and suggests that examining environmental circumstances and pressures that may differ for males and females at the transition to adulthood is an important area to pursue.
