Species and Varieties, Their Origin by Mutation | Page 4

THEORIES OF EVOLUTION AND METHODS OF
INVESTIGATION
Newton convinced his contemporaries that natural laws rule the whole
universe. Lyell showed, by his principle of slow and gradual evolution,
that natural laws have reigned since the beginning of time. To Darwin
we owe the almost universal acceptance of the theory of descent.
This doctrine is one of the most noted landmarks in the advance of
science. It teaches the validity of natural laws of life in its broadest
sense, and crowns the philosophy founded by Newton and Lyell.
Lamarck proposed the hypothesis of a common origin of all living
beings and this ingenious and thoroughly philosophical conception was
warmly welcomed by his partisans, but was not widely accepted owing
to lack of supporting evidence. To Darwin was reserved the task of [2]
bringing the theory of common descent to its present high rank in
scientific and social philosophy.
Two main features in his work have contributed to this early and
unexpected victory. One of them is the almost unlimited amount of
comparative evidence, the other is his demonstration of the possibility
of a physiological explanation of the process of descent itself.
The universal belief in the independent creation of living organisms
was revised by Linnaeus and was put upon a new foundation. Before
him the genera were supposed to be created, the species and minor
forms having arisen from them through the agency of external
conditions. In his first book Linnaeus adhered to this belief, but later
changed his mind and maintained the principle of the separate creation
of species. The weight of his authority soon brought this conception to
universal acceptance, and up to the present time the prevailing
conception of a species has been chiefly based on the definition given
by Linnaeus. His species comprised subspecies and varieties, which
were in their turn, supposed to have evolved from species by the
common method.
Darwin tried to show that the links which bind species to genera are of
the same nature as those which determine the relationship of [3]
subspecies and varieties. If an origin by natural laws is conceded for the

latter, it must on this ground be granted for the first also. In this
discussion he simply returned to the pre-Linnean attitude. But his
material was such as to allow him to go one step further, and this step
was an important and decisive one. He showed that the relation
between the various genera of a family does not exhibit any features of
a nature other than that between the species of a genus. What has been
conceded for the one must needs be accepted for the other. The same
holds good for the large groups.
The conviction of the common origin of closely allied forms
necessarily leads to the conception of a similar descent even in remote
relationships.
The origin of subspecies and varieties as found in nature was not
proved, but only generally recognized as evident. A broader knowledge
has brought about the same state of opinion for greater groups of
relationships. Systematic affinities find their one possible explanation
by the aid of this principle; without it, all similarity is only apparent
and accidental. Geographic and paleontologic facts, brought together
by Darwin and others on a previously unequalled scale, point clearly in
the same direction. The vast amount of evidence of all [4] comparative
sciences compels us to accept the idea. To deny it, is to give up all
opportunity of conceiving Nature in her true form.
The general features of the theory of descent are now accepted as the
basis of all biological science. Half a century of discussion and
investigation has cleared up the minor points and brought out an
abundance of facts; but they have not changed the principle. Descent
with modification is now universally accepted as the chief law of nature
in the organic world. In honor of him, who with unsurpassed genius,
and by unlimited labor has made it the basis of modern thought, this
law is called the "Darwinian theory of descent."
Darwin's second contribution to this attainment was his proof of the
possibility of a physiological explanation of the process of descent
itself. Of this possibility he fully convinced his contemporaries, but in
indicating the particular means by which the change of species has been
brought about, he has not succeeded in securing universal acceptation.
Quite on the contrary, objections have been raised from the very outset,
and with such force as to compel Darwin himself to change his views
in his later writings. This however, was of no avail, and objections and

criticisms have since steadily accumulated. Physiologic facts
concerning the origin of [5] species in nature were unknown in the time
of Darwin. It was a happy idea to choose the experience of the breeders
in the production of