It's hard to tell the absolutes in an individual, but my family members and I have discussed this in great depth on a couple of occasions. I had five brothers and one sister. One brother was killed while high on cocaine when he was eighteen, he was one year younger than I. My oldest brother had problems with alcohol, my next oldest had very little. I became a chronic alcoholic and all of my younger siblings became alcoholic and drug addicts. My mother drank and did drugs during her pregnancies, except when she was carrying my next oldest brother, the one who did not develop alcoholism. Who knows, but there seems to be some legitimacy to the conditions that produce alcoholics, at least in my family.