Howard T. Welser is an Assistant Professor of Sociology at Ohio University. He investigates how micro-level processes generate collective outcomes in contemporary and historical populations. Recent projects include “Cultural Evolution, Disproportionate Prior Exposure and the Problem of Cooperation” (Rationality and Society) and “Visualizing the Signatures of Social Roles in Online Discussion Groups” (Journal of Social Structure). Currently he is focusing on how network structure and reference groups influence retention, contribution, and diffusion in computer mediated social spaces.