A study of 3,546 pairs of twins in the U.S. looked into the relationship between environment, genetics and alcohol problems. 85% of the sample - who were all between 18-29 - reported having at least one drink in their lifetimes, although only 7% became alcohol dependent. The researchers found that, overall, environmental factors were more important than genetic ones. Environmental factors, such as exposure to conflict between parents and alcohol use among peers in school, exerted the largest influence on initiation of alcohol use and the study found that women who had their first drink at an earlier age were more likely to develop serious alcohol problems. The influence of genetics became more marked in deciding who went on to develop alcohol problems but was still less influential than environmental factors.
You can read more about this research at