Between 1935 and 1950, adoption studies involving 8,000 adoptees from three Scandinavian countries, showed conclusively that your chances of having a drug or alcohol problem were four times greater if you had a primary relative who was an alcoholic or a drug addict. So, we've known since 1950 that there is a strong genetic component in compulsivity problems. What we have since learned about brain chemistry has helped us to understand how much nature predominates over nurture. Children in the adoption studies developed alcohol problems, regardless of whether they had alcohol in their homes or not. It is a clear case of nature over nurture.