THE NATURE OF SPECIES
than one species and several subspecies. Systematic botanists and zoologists have been divided into two schools — the "Splitters" and the "Lumpers." The "Splitters" establish species on differences which the "Lumpers" treat as mere individual and inconstant variations. Darwin represented Asa Gray, the famous American botanist, as a Splitter, and Sir Joseph Hooker, of Kew, as a Lumper. Herbert Spencer, in 1852, estimated that the number of species must amount to at least ten millions. The Splitters would multiply that number many times.
There has been no agreement as to what characteristics should be regarded as of specific rank—that is, as sufficient to justify a naturalist in founding a species—and as to what are of a lower systematic value. For example, there has been a long-continued controversy whether man is one species or whether the European, the Negro, and the Mongolian are distinct species. This difficulty has been partly overcome in practice by the introduction of minor units of classification, which have been called subspecies, and the subspecies have been divided into varieties, and these into subvarieties, and these in turn into races and subraces. The divisions are thus numerous, and the grounds for them are indefinite. Different groups of plants and animals have different grades of specific subdivision, according to the abundance of their members, or their variability, or the attention they have attracted. Thus the Flora of France uses in some genera six subdivisions lower than the genus. British botanists adopt more subdivisions of species in roses and brambles than in less variable plants. Some species of British land snails, such as the common Helix nemoralis, have undergone indefinite subdivision.
The extent to which experts differ as to whether certain variations are distinctive of species, varieties, or races shows that there are no such fixed limits to species as the pre-
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