The earliest cohort in our study, those born in the 1920s through the mid-1930s, were in their late teens and young adulthood as smoking emerged from a disreputable activity limited to marginalized groups (lower-class bohemians and upper-class dandies, according to Sobel [1978]) to one accepted in more conventional middle-class groups. Early in the century normative sanctions limited the expression of genetic influences, but the growing acceptance of smoking in the 1920s and 1930s allowed, and possibly encouraged, the expression of genetic influences. Therefore, we believe that genetic influences on smoking will increase and remain quite high for those born during this time. This association is consistent with the social trigger model.2
