WHAT IS A "SPECIES"?


I

We have seen that there is no way to account for the origin of matter,
of energy, or of life, except by postulating a real Creation.

We have seen that cells continue to maintain their identity, and
reproduce only "after their kind."

We must now deal with the higher forms of cell aggregates, which we call
plants and animals. It has long been held that these at least are
mutable, that one kind of plant or of animal may in the course of ages
be transformed into a distinctly different type; and of late years there
has accumulated a very voluminous literature dealing with the various
intricacies of this problem of the origin of species. How can we deal
with such a large subject in a brief way? It seems best to confine our
attention in this chapter to an attempt to answer the question, What is
a species? and are "species" natural groups clearly delimited by nature?


II

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 Linnæus (1707-1778) did the term
acquire a definite and precise meaning. The aphorism of the great
botanist, "_species tot sunt diversæ quot diversæ formæ ab initio sunt
creatæ_"--"just so many species are to be reckoned as there were forms