Until comparatively recently, living organisms were divided into two kingdoms: animal and vegetable, or the Animalia and the Plantae. In the 19th century, evidence began to accumulate that these were insufficient to express the diversity of life, and various schemes were proposed with three, four, or more kingdoms. The scheme in widest current use divides all living organisms into five kingdoms: Monera (bacteria), Protista, Fungi, Plantae, and Animalia. This coexisted with a scheme dividing life into two main divisions: the Prokaryotae (bacteria, etc.) and the Eukaryotae (animals, plants, fungi, and protists.

Recent work, however, has shown that what were once called "prokaryotes" are far more diverse than anyone had suspected. The Prokaryotae are now divided into two domains, the Bacteria and the Archaea, as different from each other as either is from the Eucarya, or eukaryotes.

A fourth group of biological entities, the viruses, are not organisms in the same sense that eukaryotes, archaeans, and bacteria are. However, they are of considerable biological importance.

To start moving through the phylogeny of life on Earth, click inside the boxes at the branch tips. If there is a picture within the box, that means we have an exhibit on the taxon. If your favorite organisms aren't here yet, keep trying: since there may be as many as 100 million living and fossil species of organism, it may take us a little while to cover all the highlights.