I am sure many of you wondered about the impact of age on biometric estimates when we discussed general cognitive ability last week. Indeed some of you asked about this issue on the Forums. You were right to raise the question because this is an important issue in the behavioral genetic literature. Given its importance, I thought it might work best to place the question of age moderation in a larger context, which we do this week. We will begin the week by returning to the distinction between shared and non-shared environmental influences, an important distinction in the behavioral genetic literature. You will see that while shared environmental influences are not important for most behavioral phenotypes, there are a few exceptions (including general cognitive ability). However, in all of these exceptional cases, the magnitude of shared environmental influences decreases with age as the heritability increases. To understand this developmental pattern, at least from a behavioral genetic perspective, it is helpful to consider mechanisms of gene-environment correlation as well as behavioral genetic perspectives on family socialization. We end this unit with an overview of behavioral genetic research on aging.