title: Evolution of cooperation by multilevel selection.
abstract: We propose a minimalist stochastic model of multilevel (or group) selection. A population is subdivided into groups. Individuals interact with other members of the group in an evolutionary game that determines their fitness. Individuals reproduce, and offspring are added to the same group. If a group reaches a certain size, it can split into two. Faster reproducing individuals lead to larger groups that split more often. In our model, higher-level selection emerges as a byproduct of individual reproduction and population structure. We derive a fundamental condition for the evolution of cooperation by group selection: if b/c > 1 + n/m, then group selection favors cooperation. The parameters b and c denote the benefit and cost of the altruistic act, whereas n and m denote the maximum group size and the number of groups. The model can be extended to more than two levels of selection and to include migration.
authors.affiliation: Program for Evolutionary Dynamics, Departments of Organismic and Evolutionary Biology and Mathematics, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Arne
authors.initials: A
authors.lastname: Traulsen
authors.forename: Martin A
authors.initials: MA
authors.lastname: Nowak
mesh_terms: D000818:Animals; D005075:Biological Evolution; D006801:Humans; D008957:Models, Genetic; D012641:Selection, Genetic