use are largely influenced by common environmental factors (Hopfer et al., 2003). We know that dramatic changes occur in the relative importance of genetic and environmental influences on alcohol use across adolescence, as individuals move from initial experimentation to more established, regular patterns of use (Koopmans and Boomsma, 1996; Rose et al., 2001b). Genetic influences assume increasing influence (Pagan et al., 2006), as illustrated by the fact that they account for but 27% of the variance at age 14, but nearly 50% by age 18, based on data from older adolescent Finnish twins (Rose et al., 2001b). The considerable and dynamic changes that occur from early to late adolescence on influences on alcohol use are further echoed here, where neighborhood factors that play a significant role in moderating genetic susceptibility to alcohol use later in adolescence, do not show similar effects on alcohol use at age 14.
