As every beginning graduate student in Biology knows, it is important to distinguish between Taxonomy and Systematics. Taxonomy is a naive way of organizing the characteristics of living creatures so that they can be easily recognized, without any imputation of underlying reltiaonships. Systematics is the science of classification which is based on Evolutionary descent.
The oldest scientific system of classification is the Linnaean system, which classifies organisms by genus and species. As scientists have come to understand the diversity of biology more clearly, their system of classifying it has changed to reflect that increased understanding. Where there was once the Two Kingdom system (Plants and Animals), which gave way to the Five Kingdom system (Prokaryotes, Protista, Fungi, Plants and Animals), the discovery of an entire realm of new organisms in the deep-sea vents, thousand of feet below the surface of the ocean, has given rise to the Three Domain system.
The most recent system for classification of biological organisms is the Three Domain system introduced by Carl Woese in 1990. The three domains are:
- Archaea (Archaebacteria)
- Bacteria (Eubacteria)
- Eukarya (Eukaryota).
The Eukarya have well-organized nuclei, and their genetic material is condensed with histones into highly structured chromosomes. Most often they are multi-cellular. The Eukarya are composed of 4 Kingdoms:
- Protista (protozoans or single-celled eukaryotes)
- Fungi
- Plantae
- Animalia
Humans for example, are classified as follows:
