Folk biology (or folkbiology) is the cognitive study of how people classify and reason about the organic world. Humans everywhere classify animals and plants into obvious species-like groups. The relationship between a folk taxonomy and a scientific classification can assist in understanding how evolutionary theory deals with the apparent constancy of "common species" and the organic processes centering on them. From the vantage of evolutionary psychology, such natural systems are arguably routine "habits of mind", a sort of heuristic used to make sense of the natural world.