By the second half of the 20th century, social scientists had erased most signs of overt sexism and racism from their disciplines. They also continued to hold onto the idea of the Blank Slate, ignoring evidence that supported, for example, the physical process involved in thinking and possible differences among the sexes. Social scientists feared that discoveries about human nature would reverse social progress. In this part of the book, Pinker investigates the political reasons people reject new scientific discoveries regarding human nature.

The author recalls the first lecture he went to as a graduate student at Harvard by computer scientist Joseph Weizenbaum in 1976 to illustrate that the scientific dialogue on human nature could be highly politicized, particularly in the 1970s. For example, the arguments of Richard Herrnstein, a psychologist who predicted that as nongenetic factors influencing IQ scores (such as lack of access to opportunities) decreased in importance, genetic factors would become more important. He was denounced by protesters as a Fascist. Scientists such as Paul Ekman (a psychologist who spoke about innate commonalities among people, such as the similar facial expressions displayed and understood worldwide) were also attacked.

Pinker discusses the reaction to E.