Group selection

Group selection is the process by which natural selection operates on groups of organisms — populations, colonies, or species — rather than on individuals alone. A trait that reduces the fitness of individuals within a group may nonetheless spread if groups containing the trait outcompete groups lacking it, particularly when groups are small, genetically related, and subject to frequent extinction and recolonization. The concept has been one of the most contentious in evolutionary biology, with critics arguing that individual-level selection will almost always overwhelm group-level effects, and defenders pointing to cases — from the evolution of multicellularity to human cooperation — where group-level processes appear indispensable.

The modern resolution, articulated through multilevel selection theory and inclusive fitness theory, is that selection operates at multiple nested scales simultaneously. The question is not whether group selection exists but under what conditions it is strong enough to produce traits that cannot be explained by individual selection alone.