It is argued that differences in response heritability may have important implications for the testing of general psychological theories, that is, responses that differ in heritability may function differently. For example, attitudes higher in heritability are shown to be responded to more quickly, to be more resistant to change, and to be more consequential in the attitude similarity attraction relationship. The substantive results are interpreted in terms of attitude strength and niche building. More generally, the implications of heritability for the generality and typicality of treatment effects are also discussed.