One of the most notable findings in contemporary behavior genetics is that children growing up in the same family are not very comparable. Findings suggest that in order to understand individual differences between siblings it is necessary to examine not only the shared experiences but also the differences in experiences of children growing up in the same family. In the past decade a group of investigators has begun to examine the contributions of genetics, and both shared and nonshared environment to development. As with many new research endeavors, this has proven to be a difficult task...