Originally Posted by TheDave
I still think it's a combination of genetics and environment...
Yes it most likely is. What you've pointed out is the "Diathesis/Stress Model" which is a fairly solid psychological theory on the development of adult behaviors and the impact of genetics v. environment on them.
The analogy that is widely used is in reference to alcoholism. Understanding that there is a genetic predisposition for alcoholism doesn't necessarily mean an individual with a history of alcoholism in the family is going to be an alcoholic if they begin drinking. Consider, for simplicity's sake, a glass half full. The glass represents the disease and the it's being half full represents the pre-existing genetic predispostion to alcoholism. The behaviors of an individual will begin to fill, or empty the glass. If the glass overflows then the behaviors, in combination with the genetid pre-disposition, have created an alcoholic. However, if the drinking can be kept in check the individual can lead a normal life while being able to enjoy a beer or two. I think the same can be said of most behaviors.