 Trait group was introduced by D.S. Wilson, by contrast, specifically to name a type of group that he thought was pervasive in nature, one that could be a unit of selection just as individual organisms were. The intuitive idea behind a trait group is that populations can feature evolutionarily relevant structure wherein organisms belonging to one part of the population are subject to causal influences on fitness that do not extend to the population as a whole. A population of such structured demes would then function as a metapopulation, with natural selection operating between the trait groups that make up that metapopulation. The individuals in a trait group could thus be seen as evolutionary individuals, being the agents for evolutionary change over time.