In summary, the first period is characterized by the social trigger model in which the rise of smoking is primarily among those with genetic predispositions; the second period of rising social push reflects the rise of smoking among those with social motivations and the declining statistical importance of genetic influences; the third period of declining social push reflects the fall of smoking among those with social motivations and the growing statistical importance of genetic influences; and the fourth period of increasing social control reflects an actual drop in smoking among genetically motivated smokers and the declining importance of genetic influences. These predictions involve something more than claims about steady and small upward or downward trends in heritability. Rather, they involve changes in heritability that match specific events, occur relatively quickly, and involve directional shifts—all making for an original and highly falsifiable test of the value of an integrative gene–environment interaction approach to understanding health behavior.
