West, J. D.,Bergstrom, C. T.

Ideas are like fire, observed Thomas Jefferson in 1813—information can be passed on without relinquishing it (1). Indeed, the ease and benefit of sharing information select for individuals to aggregate into groups, driving the buildup of complexity in the biological world (2, 3). Once the members of some collective—whether cells of a fruit fly or citizens of a democratic society—have accumulated information, they must integrate that information and make decisions based upon it. When these members share a common interest, as do the stomata on the surface of a plant leaf (4), integrating distributed information may be a computational challenge. But when individuals do not have entirely coincident interests, strategic problems arise. Members of animal herds, for example, face a tension between aggregating information for the benefit of the herd as a whole, and avoiding manipulation by self-interested individuals in the herd. Which collective decision procedures are robust to manipulation by selfish players (5)? On page 1578 of this issue, Couzin et al. (6) show how the presence of uninformed agents can promote democratic outcomes in collective decision problems.