Psychologists who have studied the Nature vs Nurture debate have found that people grow into who they are from a combination of both Nature (i.e, genetics) and nurture (life experience, the way you were raised by your parents, etc.)

Take for instance a child, raised by shy parents, who then grows up to be a shy adult. Was his shyness the result of genes inherited from his shy parents? Or was it a result of the way he was raised by his shy parents (not going to parties, not bringing friends over)? Most scientists believe that it is a combination of these two factors. The child would have been born with a genetic predispostion towards shyness, making it likely, though not absolutely certain that he would have characteristics of a shy person. When he is raised throughout his childhood by his shy parents, the genetic predispostition towards shyness is in a sense activated.

The same holds true for alcoholism. Children of alcoholic parents, even children raised apart from their alcoholic parents by non-alcoholic guardians possess the genetic predisposition to become alcoholics. However, this genetic predisposition won't count for much if the child never has a drink in his life. If, however, he drinks heavily throughout his life, then both genetics and environment (Nature and Nurture) play a role in possibly creating another alcoholic.