Even genetic diseases sometimes need environmental influences to develop.
For example, some people are prone to alcoholism in a hereditary way. But if they live in a society that has zero alcohol, they won't ever become alcoholic. Upon moving to a society where alcohol is sold freely and frequently, they may sink into alcoholism without having any obviously alcoholic ancestor.
For example, some people are prone to alcoholism in a hereditary way. But if they live in a society that has zero alcohol, they won't ever become alcoholic. Upon moving to a society where alcohol is sold freely and frequently, they may sink into alcoholism without having any obviously alcoholic ancestor.