Not by Genes Alone

Not by Genes Alone: How Culture Transformed Human Evolution (2005) is a book by Peter Richerson and Robert Boyd that presents Dual Inheritance Theory to a general audience. The book argues that human evolution cannot be understood through genetics alone because culture constitutes a second inheritance system operating under its own rules. Culture is not merely a product of human biology; it is a cause of human biology, shaping the selective environment in which genes evolve. The book's central thesis — that cultural evolution is as real and consequential as genetic evolution — has become a foundational text for the field of cultural evolution.

The book also develops the argument for cultural group selection in accessible form, explaining how prosocial norms and institutions spread because they enabled group-level competition. It connects to Ara Norenzayan's later work on the evolution of religion and to the broader Extended Evolutionary Synthesis. Richerson and Boyd argue that social learning strategies — when to copy others, who to copy, and how much to rely on individual exploration — are themselves adaptations shaped by natural selection.