Alcoholism is well studied. There is a clear genetic factor. In some people, it is determinative; these folks are drunks from the first drink. In most folks, it's more complicated but the genetic predisposition is clearly important. And some people can drink like a fish their entire life without a problem. These tend to be the people who insist that alcoholism is entirely a matter of character.
I think some mental disorders have some sort of genetic predisposition component as well. It wouldn’t shock me that there are absolutely some sort of predisposition component with homosexuality.
Freegards