This ambitious, highly theoretical book provides a capstone for the careers of two very distinguished scholars. It begins with an analysis of what functions and systems must exist for any organism or machine to perform an unlearned act, that is, with an analysis of what must be "wired into" the organism or machine. Once the basics of unlearned responding have been established, the authors then systematically show how learning mechanisms can be layered onto that foundation in ways that account for the performance of new, learned operations that eventually culminate in the acquisition of...