HOW TO SEPERATE HEREDITY FROM ENVIRONMENT? Through twin studies of course! Particularly through the study of identicals reared apart. That has been the conventional wisdom in devlopmemtal psychology. But it now turns out to be not quite that simple. This article from the newsletter of the American Psychological Association is a good assesment of how and what we can learn from twin studies about the sources (genetic and environmental) of aggression, intelligence and other important aspects of the human repertoire.