Milinski, Manfred Department Evolutionary Ecology, Max Planck Institute for Evolutionary Biology, Max Planck Society;
https://link.springer.com/article/10.1007/s40750-015-0026-4#citeas (Publisher version)
Centorrino, S., Djemai, E., Hopfensitz, A., Milinski, M., & Seabright, P. (2015). A model of smiling as a costly signal of cooperation opportunities. Adaptive Human Behavior and Physiology, 1(3), 325-340. doi:10.1007/s40750-015-0026-4.