strongly at different stages of development and within different social contexts. We cannot allow ourselves to be lulled into the assumption of a constancy in either individuals' constitutions or the social environments they find themselves in. Human beings engage in dynamic transactions with their environments; and in the process, they change both themselves and their environments. Although genes play a role in determining the life course, there is no neat linear cryptography existing by which genes code for certain types of brains, which, in turn, code for different kinds of behavior. But genes do provide directions by which our development and our behavior are guided in ways favored over alternatives.