Nested hierarchy

A nested hierarchy is the name given to the hierarchical structure of "groups within groups" or "branches from a trunk" used to classify organisms. For example, a species is a subset of a genus, which is a subset of a family, which is a subset of an order - and so on.
This structure is assumed to reflect the evolutionary pattern of descent with modification.

The system is hierarchical and tree-like because it consists of a single, all-inclusive category (the tree trunk) progressively dividing into non-overlapping categories (the branches). It will not permit, for example, the genera in one family being members of another family. Such straddling would be an example of heterarchy which is more like a network than a tree.

Initially described by Carl Linnaeus (Carolus Linnaeus) a Swedish Botanist, Physician, and Zoologist in the "Systema Naturae", published in 1735.

This system of classification uses the physical characteristics of organisms to group them according to shared similarities. It is still used to this day, although the original has been greatly expanded to account for new organisms and new evidence.

See also