I seek to make three separate contributions to the anthropological study of culture. Metatheoretically, I present the evolutionary psychological perspective within which to study culture and generate specific theories of the origins, constancy, and variations in human culture. Theoretically, I provide a concrete evolutionary psychological theory of son-daughter preference, why people in some societies prefer sons to daughters and practice female infanticide, while those in others prefer daughters to sons and practice male infanticide (killing of boys). Empirically, I test and support my evolutionary psychological theory of son-daughter preference with large, international quantitative data both at the micro and macro levels.