„As we shall see in this book's chapters, traditional societies are far more diverse in many of their cultural practices than are modern industrial societies. […] Yet psychologists base most of their generalizations about human nature on studies of our own narrow and atypical slice of human diversity. […] That is, as social scientists Joseph Henrich, Steven Heine, and Ara Norenzayan express it, most of our understanding of human psychology is based on subjects who may be described by the acronym WEIRD: from Western, educated, industrialized, rich, and democratic societies. […] Hence if we wish to generalize about human nature, we need to broaden greatly our study sample from the usual WEIRD subjects […] to the whole range of traditional societies.“
Prologue, section "Why study traditional societies?"
The World Until Yesterday: What Can We Learn from Traditional Societies? (2012)