Classification
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There are some 10 million species of living organisms (mostly insects), and many more extinct ones, so they need to be classified in a systematic way. In 1753 the Swede Carolus Linnaeus introduced the binomial nomenclature for naming organisms. This consists of two parts: a generic name (with a capital letter) and a specific name (with a small letter), e.g. Panthera leo (lion) and Panthera tigris (tiger). This system replaced non-standard common names, and is still in use today.

A group of similar organisms is called a taxon, and the science of classification is called taxonomy. In taxonomy groups are based on similar physical or molecular properties, and groups are contained within larger composite groups with no overlap. The smallest group of similar organisms is the species; closely related species are grouped into genera (singular genus), genera into families, families into orders, orders into classes, classes into phyla (singular phylum), and phyla into kingdoms. So you need to remember KPCOFGS.

This shows how the seven taxons are used to classify humans. As we go through the taxon hierarchy from kingdom to species, the groups get smaller and the animals are more closely related.

	Kingdom Animalia	Phylum Chordata	Class Mammalia	Order Primates	Family Hominidae	Genus Homo	Species sapiens
Sponge	P
Earthworm	P
Insect	P
Fish	P	P
Dinosaur E	P	P
Bird	P	P
Mouse	P	P	P
Cat	P	P	P
Elephant	P	P	P
Lemur	P	P	P	P
Monkey	P	P	P	P
Orang-utan	P	P	P	P
Gorilla	P	P	P	P	P
Chimpanzee	P	P	P	P	P
Australopithecus E	P	P	P	P	P
Homo Habilis E	P	P	P	P	P	P
Neanderthal Man E	P	P	P	P	P	P	P
Modern Human	P	P	P	P	P	P	P
E = Extinct

This shows the complete classification of some other species:

Earthworm

Mushroom

Garlic

Kingdom

Phylum

Class

Order

Family

Genus

Species

Animalia

Annelida

Oligochaeta

Terricolae

Lumbricidae

Lumbricus

terrestris

Fungi

Mycota

Basidiomycota

Agaricales

Agaricacae

Agaricus

campestris

Plantae

Angiospermophyta

Monocotyledonea

Liliales

Liliaceae

Allium

sativum

The aim of taxonomists today is to develop phylogenies, family trees representing true evolutionary relationships. Historically classification was based on easily observable structures, and gradually this was extended to microscopic and electron-microscopic detail. The recent advances in embryology and molecular biology have given new tools such as patterns of life cycle, larval development, and gene sequences. These have often led to radically different phylogenies (e.g. humans should really be the "third chimpanzee").

The Five Kingdoms [back to top]

Until the middle of this century, life was divided into two kingdoms, plants and animals. With the greater understanding gained from new techniques this has been revised, and modern classifications recognise far more diversity and are less zoocentric. The classification system used today is that of Whittaker (1959, modified by Margulis), and contains five kingdoms: prokaryotae, protoctista, fungi, plantae and animalia. The greatest division now recognised is not between plants and animals (which are relatively similar), but between the prokaryotes (cells without nuclei) and eukaryotes (cells with nuclei). The three "higher" kingdoms are distinguished by their ecological strategies: absorption (fungi), consumption (animals) and production (plants).

Classification [back to top]

The Five Kingdoms [back to top]

Classification
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