Adoption studies definitively demonstrate the importance of genetic factors in the development of alcohol abuse and they also allow for the separation of the role of environmental factors and genetic factors in the development of 2 types of adult alcohol abuse.Individuals with adult onset of alcohol problems who have low criminality and low novelty seeking and high harm avoidance, reward dependence and guilt after drinking require both environmental and genetic factors to develop alcohol abuse.Individuals with high criminality and high novelty seeking and low harm avoidance, reward dependence and guilt need only genetic factors to increase the risk of developing alcohol abuse (although adverse environmental factors also increase the risk of alcohol abuse in this group).