Smoking and obesity are the top-two leading causes of preventable disease and death in the U.S. and significant sources of the substantial disparities in health between socioeconomic status (SES) groups. We utilize recent discoveries of genetic variants exhibiting credible and robust associations with smoking and obesity to study the effects of genetic predispositions, in interaction with the socioeconomic environment of the family during childhood, on risky health behavior and on health disparities. To interpret the analyses we develop a lifecycle theory of gene-by-SES interplay in unhealthy behavior. The theory provides a conceptual framework for analyzing the role of genetics in explaining health behaviors, such as smoking and overeating, and how SES moderates this process. The theory predicts rich interactions between genes, SES, health behavior, health and longevity. For example, SES increases the marginal value of health, thereby increasing the demand for health investment and reducing the demand for unhealthy consumption. Withdrawal, tolerance, and reinforcement, however drive unhealthy behaviors forward.These competing effects suggest SES protects individuals from detrimental genetic endowments by raising the value of health, reducing consumption and addiction. Joint with Laura Bierut, Pietro Biroli, and Kevin Thom.