Causal presumptions to the effect that the living world categorically divides into well-bounded types, regardless of the deree of morphological variation that may actually exist or be observed within or between different kinds. Importantly, though, categorization used by people maps well onto the notion of biological species. This is consistent with Atran's rationalism. For example, people who have a category for tigers generally believe that tigers are quadrupedal animals that roar and have stripes and tawny fur because of their intrinsic species-nature. Nonetheless, most people haven't the foggiest idea of the underlying causal mechanisms that are actually responsible for the tiger's legs, roar, stripes, and fur.
All humans classify animals and plants into folk species.
These species are useful for understanding local situations, and making local predictions. But from a scientific vantage, the concept of folk species is woefuly inadequate for capturing the graded relationships that characterize the evolution of species over geologically vast dimensions of time and space. Folk Taxonomy Folk species are fit into a hierarchy. Many different cultures exhibit a number of special purpose hieararchies. Taxa are mutually exclusive.