In naming organisms, biologists use binomial nomenclature, which Webster's Third International Dictionary defines as
For example, the house mouse has been assigned the two-part name Mus musculus, in which Mus is the genus name and musculus is the species name.
This system, in which the names are usually in Latin or Greek, was devised during the first half of the eighteenth century by Carolus Linnaeus, when the educated were still masters of those languages.
Because all existing classifications of living organisms were cast in terms of binomial nomenclature when biology first began, scientists kept using the same system even when the original motives for creating the system (which are rooted in the arcane doctrines of medieval philosophy) ceased to exist.
Also, the word species remained as prominent in scientific debate as it had been in the religious and philosophical discussions of old. Naturalists had always used the term and they continued to do so. In constructing their systems of classification, medieval schoolmen had wanted to be sure that they were correct when they used the word species to refer to a given type of organism. Modern scientists who construct such systems (taxonomists) want to be sure of the same thing.
However, debate has been endless over the question of what exact criteria are appropriate for making such determinations. If biologists are to carry out the process of naming organisms in an objective manner, they need a clear definition of species. But attempts to say which populations should be treated as species have always been, and continue to be, problematic.
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