  This is a programmatic paper, marking out two directions in which the study
of social media can contribute to broader problems of social science:
understanding cultural evolution and understanding collective cognition. Under
the first heading, I discuss some difficulties with the usual, adaptationist
explanations of cultural phenomena, alternative explanations involving network
diffusion effects, and some ways these could be tested using social-media data.
Under the second I describe some of the ways in which social media could be
used to study how the social organization of an epistemic community supports
its collective cognitive performance.
