when genetic relationships are usually evaluated, i.e., when a disorder or a behavioral deviation can be observed, the role of this early-acting factor may be as difficult to detect as it is to find a match that started a forest fire. The relative rarity and problems with the reproducibility of positive findings in molecular genetic studies of behavioral traits are thus not surprising. The complex and interacting genetic mechanisms are at the very outset of the long developmental process, and their immediate contribution is modulated by epigenetic modifications and other factors influencing gene expression.
