To call the former varieties of the
same species, and the latter distinct species, is altogether arbitrary.
Nevertheless, notwithstanding the arbitrary classifications of
naturalists, it remains true that there are what Professor Dana calls
"units" of the organic world. "When individuals multiply from generation
to generation, it is but a repetition of the primordial type-idea, and
the true notion of the species is not in the resulting group, but in
the idea or potential element which is the basis of every individual of
the group."[50] Dr. Morton's definition of species as "primordial
organic forms," agrees with that given by Professor Dana; and both agree
with the Bible, which says that God created plants and animals each
after its kind. A primordial form is a form which was not evolved out of
some other form, but which began to be in the form--subject to such
varieties as we see in the dog, horse, and man--in which it continued
during the whole period of its existence.
The criteria of these primordial forms or species of nature, are, (1.)
Morphological. Animals, however, may approach very nearly in their
structure, and yet belong to different species. It is only when the
peculiarities of structure are indicative of specialty of design, that
they form a safe ground of classification. If the teeth of one animal
are formed to fit it to feed on flesh, and those of another to fit it to
feed on plants; if one has webbed feet and another not; then, in all
such cases, difference of structure proves difference of kind.
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