Others point to heredity as the cause since many times alcoholism tends to occur in families, sometimes extending over several generations. In the 1980's C. Robert Cloninger conducted a study in Sweden that examined the occurrence of alcoholism in adopted children of alcoholic parents. Type I. Many children of Type II alcoholics themselves become Type II alcoholics, regardless of their environment. I alcoholics tend to become Type I alcoholics. However, many of these children, influenced by environmental factors, become Type II alcoholics.
Males are much more likely to become alcoholics than females.
In l987, Cloninger proposed a theory based on his findings. His theory suggested that three personality types make up the two types of alcoholics and that the traits shown by these have a biological basis. Gene regulated activation of chemicals in the nervous system controls each trait. These alcohol-susceptibility genes determine how the central nervous system reacts to the environment. For one individual, a stimulus may activate one chemical, but in another person a different chemical may be activated.