The question of whether a given trait qualifies as an adaptation must be answered on a case-by-case basis. Nevertheless, a strong case can be made for species as primarily adapted to their environments. A similar argument can be made for human cultures as primarily adapted to their environments at the group level. The reason that human cultures are primarily adaptive at the group level is because the capacity for culture is itself a group-level adaptation. Establishing a consensus on human cultures as primarily adapted at the group level will enable human cultural diversity to be studied in the same way as biological diversity.