It is curious, however, that Lamarck should insist so strongly
[5] as he has done, that circumstances never in any degree directly
modify the form or the organization of animals, but only operate by
changing their wants and consequently their actions; for he thereby
brings upon himself the obvious question, how, then, do plants, which
cannot be said to have wants or actions, become modified? To this
he replies, that they are modified by the changes in their nutritive
processes, which are effected by changing circumstances; and it does not
seem to have occurred to him that such changes might be as well supposed
to take place among animals.

When we have said that Lamarck felt that mere speculation was not the
way to arrive at the origin of species, but that it was necessary,
in order to the establishment of any sound theory on the subject, to
discover by observation or otherwise, some 'vera causa', competent to
give rise to them; that he affirmed the true order of classification to
coincide with the order of their development one from another; that he
insisted on the necessity of allowing sufficient time, very strongly;
and that all the varieties of instinct and reason were traced back by
him to the same cause as that which has given rise to species, we have
enumerated his chief contributions to the advance of the question. On
the other hand, from his ignorance of any power in Nature competent to
modify the structure of animals, except the development of parts, or
atrophy of them, in consequence of a change of needs, Lamarck was led
to attach infinitely greater weight than it deserves to this agency,
and the absurdities into which he was led have met with deserved
condemnation. Of the struggle for existence, on which, as we shall see,
Mr. Darwin lays such great stress, he had no conception; indeed, he
doubts whether there really are such things as extinct species, unless
they be such large animals as may have met their death at the hands of
man; and so little does he dream of there being any other destructive
causes at work, that, in discussing the possible existence of fossil
shells, he asks, "Pourquoi d'ailleurs seroient-ils perdues des que
l'homme n'a pu operer leur destruction?" ('Phil. Zool.,' vol. i. p. 77.)
Of the influence of selection Lamarck has as little notion, and he makes
no use of the wonderful phenomena which are exhibited by domesticated
animals, and illustrate its powers. The vast influence of Cuvier