Social theorists have long argued that literacy is one of the principal causes and hallmark features of complex society. However, the relationship between literacy and social complexity remains poorly understood because the relevant data have not been assembled in a way that would allow competing hypotheses to be adjudicated. The project set out in this thesis provides a novel account of the multiple origins of literate behaviour around the globe, the principal mechanisms of its cultural transmission, and its relationship with the cultural evolution of large-group human cooperation and complex forms of socio-political organisation. A multi-method large-scale cross-cultural approach provided the data necessary to achieve these objectives. Evidence from the societies within which literate behaviour first emerged, and from a representative sample of ethnographically-attested societies worldwide (n=74), indicates that literate behaviour emerged through the routinization of rituals and pre-literate sign systems, eventually spreading more widely through classical religions. Cross-cultural evidence also suggests that literacy assumed a wide variety of forms and socio-political functions, particularly in large, complex groups, extending evolved psychological mechanisms for cooperation, which include reciprocity, reputation formation and maintenance systems, social norms and norm enforcement systems, and group identification. Finally, the results of a cross-cultural historical survey of first-generation states (n=10) reveal that simple models assuming single cause-and-effect relationships between literacy and complex forms of socio-political organisation must be rejected. Instead, literacy and first-generation state-level polities appear to have interacted in a complex positive feedback loop. This thesis contributes to the wider goal of transforming social and cultural anthropology into a cumulative and rapid-discovery science.