Second, estimates from Heath and colleagues (in press) have been remarkably consistent across groups born in different time periods—that is, whether one compares U.S. male twins born in the 1920’s who served in World War II or U.S. adoptees born in the 1940’s, 1950’s, and 1960’s, or whether one compares Swedish female adoptees born from 1930 to 1949 and Swedish female twins born as late as 1967. Given the changes that occur over time in the levels of alcohol consumption and the rates of alcohol problems, it is somewhat surprising that the importance of genetic factors has not changed, although a similar finding has been observed for genetic influences on smoking behavior (Heath et al. 1993; Heath and Madden 1995). It could have been anticipated that increasing exposure to alcohol would make genetic factors become more important.
