I am grateful to Robin Corley for providing me with the Colorado IQ data, to Joseph M. Horn, the late Lee Willerman, and the Methodist Mission Home of San Antonio for the Texas data, and to three anonymous referees for helpful comments.

Conflict of Interest

John C. Loehlin have no conflict of interest.

Human and Animal Rights and Informed Consent

No data were gathered directly for this paper. The original studies were reviewed by the relevant institutional ethics committees, and the participants provided informed consent.