To show the general conformity of the whole body of facts to such
assumption, and also to adduce instances explicable by it and inexplicable
by the received view, so perhaps winning our assent to the doctrine,
through its competency to harmonize all the facts, even though the cause of
the assumed variation remain as occult as that of the transformation of
tadpoles into frogs, or that of Coryne into Sarzia.

The first line of proof, successfully carried out, would establish
derivation as a true physical theory; the second, as a sufficient
hypothesis.

Lamarck mainly undertook the first line, in a theory which has been so
assailed by ridicule that it rarely receives the credit for ability to
which in its day it was entitled, But he assigned partly unreal, partly
insufficient causes; and the attempt to account for a progressive change in
species through the direct influence of physical agencies, and through the
appetencies and habits of animals reacting upon their structure, thus
causing the production and the successive modification of organs, is a
conceded and total failure. The shadowy author of the "Vestiges of the
Natural History of Creation" can hardly be said to have undertaken either
line, in a scientific way. He would explain the whole progressive evolution
of Nature by virtue of an inherent tendency to development, thus giving us
an idea or a word in place of a natural cause, a restatement of the
proposition instead of an explanation. Mr. Darwin attempts both lines of
proof, and in a strictly scientific spirit; but the stress falls mainly upon
the first, for, as he does assign real causes, he is bound to prove their
adequacy.

It should be kept in mind that, while all direct proof of independent
origination is attainable from the nature of the case, the overthrow of