Arne Traulsen and Martin A. Nowak propose a minimalist stochastic model of multilevel (or group) selection, where a population is divided into groups, and individuals within the same group interact in an evolutionary game. Individuals reproduce, and their offspring are added to the same group. If a group reaches a certain size, it splits into two new groups. This model demonstrates that higher-level selection emerges as a byproduct of individual reproduction and population structure. The authors derive a fundamental condition for the evolution of cooperation by group selection: if the benefit-to-cost ratio of the altruistic act exceeds 1 plus the ratio of group size to the number of groups ($b/c > 1 + n/m$), then group selection favors cooperation. The model can be extended to more than two levels of selection and to include migration. The study highlights the importance of group selection as an organizing principle in evolutionary processes.Arne Traulsen and Martin A. Nowak propose a minimalist stochastic model of multilevel (or group) selection, where a population is divided into groups, and individuals within the same group interact in an evolutionary game. Individuals reproduce, and their offspring are added to the same group. If a group reaches a certain size, it splits into two new groups. This model demonstrates that higher-level selection emerges as a byproduct of individual reproduction and population structure. The authors derive a fundamental condition for the evolution of cooperation by group selection: if the benefit-to-cost ratio of the altruistic act exceeds 1 plus the ratio of group size to the number of groups ($b/c > 1 + n/m$), then group selection favors cooperation. The model can be extended to more than two levels of selection and to include migration. The study highlights the importance of group selection as an organizing principle in evolutionary processes.