The first legislative efforts to limit or ban smoking in public places occurred during the early and mid-1970s. According to our hypotheses, the genetic contributions to regular smoking will decrease under noncausal changes due to the social composition or if there are causal social forces (normative, institutional, or both) that act to control the behaviors of individuals. For those born after the mid-1950s, entry into regular smoking took part under increasingly strict and formal social control. These controls, we argue, are responsible for the measured decline in the heritability of regular smoking that is seen in Figure 2. This period extends until the mid-1990s and is characterized by an increasing number of federal, state, and local laws that controlled the advertisement, sale, distribution, and smoking of tobacco. In other words, changes in the social orientation of smoking did not causally influence genetic factors related to smoking onset or persistence until laws were developed and enforced that placed physical limits on this behavior. These legislative efforts reflect the forces described by Shanahan and Hofer (2005) that restrict the variation of genetic factors, and the steep drop in the genetic influences on regular smoking fits the social control perspective on gene–environment interactions.
