Chapter 9 No.9

The term "species" was at first used very loosely by scientific writers. It meant very little more than our vague word kind does at the present time. Not until the time of Linn?us (1707-1778) did the term acquire a definite and precise meaning. The aphorism of the great botanist, "species tot sunt divers? quot divers? form? ab initio sunt creat?"--"just so many species are to be reckoned as there were forms created in the beginning,"--was at least an attempt to use the term in a well-defined sense.

Of course, this definition assumed the "fixity" of species; but with the wide prevalence of the views of Darwin and his followers the term "species" has fallen into disrepute, and is now regarded by many as only an artificial rank in classification corresponding to no objective reality in the natural world. Some writers, as Lankester, have found so much fault with the term as to urge its complete abandonment in scientific literature. This is logical enough from the standpoint of Darwinism; for if the latter be true there ought indeed to be such a swamping of every incipient "species" as to make one kind blend with others all around it in the classification series.

But since the term has by no means been discarded, we must endeavor to determine the sense in which it continues to be used in good scientific literature.

"A species," says Huxley, "is the smallest group to which distinct and invariable characters can be assigned." The Standard Dictionary says that the term is used for "a classificatory group of animals or plants subordinate to a genus, and having members that differ among themselves only in minor details of proportion and color, and are capable of fertile interbreeding indefinitely."

The latter authority also adds:

"In the kingdoms of organic nature species is founded on identity of form and structure, and specifically characterized by the power of the individuals to produce beings like themselves, who are in turn productive."

To put the matter still more definitely before the reader, we quote the following from a well-known scientist whose writings on the subject of evolution have had a wide circulation:

"There are two bases on which species may be founded. Species may be based on form, morphological species; or they may be based on reproductive functions, physiological species. By the one method a certain amount of difference of form, structure, and habit, constitutes species; according to the other, if the two kinds breed freely with each other and the offspring is indefinitely fertile, the kinds are called varieties, but if they do not they are called species."[15]

This author adds that this physiological test, as to whether or not the kinds are cross fertile, "is regarded as a most important test of true species, as contrasted with varieties or races."