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Binomial system

The method of classification in taxonomy (from Greek taxis order, nomia law) is used in the form devised by Linnaeus. It is called the binomial system because each plant or animal is known by two names. The first, defining the group within which it has natural affinities, is its genus. The second, including only those creatures with which it can interbreed, is its species.

The original task of classification seems impossibly difficult, if one imagines Linnaeus surveying the vast animal kingdom. But there are obvious places where one can start. To take an easy example, the wolf, the jackal, the dingo and the domestic dog share certain evident characteristics. Yet they are different animals.

They therefore become a genus, which is given by Linnaeus the name Canis (Latin for dog). Thereafter it is simply a matter of choosing a species name within this genus. The wolf becomes Canis lupus (Latin for wolf). The jackal exists in many forms in different parts of the world, and so is variously Canis aureus, Canis mesomelas, Canis adjustus and so on. The Australian dingo, unknown to Europeans in Linnaeus' time, goes now by its aboriginal name as Canis dingo.

The domestic dog, infinitely variable in colour, shape and size but in all cases technically capable of interbreeding, becomes Canis familiaris.

Where a particular creature at the time of naming seems the most common example of its kind, the species name is sometime the same as that of the genus. Thus the common toad of Europe is Bufo bufo (sometimes also called Bufo vulgaris), even though the genus has some 250 species.

The system is flexible, in that subspecies can be added to eliminate confusion. Neanderthal man, when first discovered, is called Homo Neanderthalensis - recognizing him as part of the human genus, but as a distinct species from ourselves (Homo sapiens). When subsequent research suggests a closer link, we become related subspecies - as Homo sapiens Neanderthalensis and Homo sapiens sapiens.

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