These
also produce their like and never produce each other or intermingle, and
they were therefore each supposed to have sprung from a single
individual whose "origin" was unknown. But besides the crow and the rook
there are about thirty other kinds of birds in various parts of the
world, all so much like our species that they receive the common name of
crows; and some of them differ less from each other than does our crow
from our rook. These are all _species_ of the genus Corvus, and were
therefore believed to have been always as distinct as they are now,
neither more nor less, and to have each descended from one pair of
ancestral crows of the same identical species, which themselves had an
unknown "origin." Of violets there are more than a hundred different
kinds in various parts of the world, all differing very slightly from
each other and forming distinct _species_ of the genus Viola. But, as
these also each produce their like and do not intermingle, it was
believed that every one of them had always been as distinct from all the
others as it is now, that all the individuals of each kind had descended
from one ancestor, but that the "origin" of these hundred slightly
differing ancestors was unknown. In the words of Sir John Herschel,
quoted by Mr. Darwin, the origin of such species was "the mystery of
mysteries."

_The Early Transmutationists_.

A few great naturalists, struck by the very slight difference between
many of these species, and the numerous links that exist between the
most different forms of animals and plants, and also observing that a
great many species do vary considerably in their forms, colours, and
habits, conceived the idea that they might be all produced one from the
other. The most eminent of these writers was a great French naturalist,
Lamarck, who published an elaborate work, the _Philosophie Zoologique_,
in which he endeavoured to prove that all animals whatever are descended
from other species of animals. He attributed the change of species
chiefly to the effect of changes in the conditions of life--such as
climate, food, etc.--and especially to the desires and efforts of the
animals themselves to improve their condition, leading to a modification
of form or size in certain parts, owing to the well-known physiological
law that all organs are strengthened by constant use, while they are
weakened or even completely lost by disuse. The arguments of Lamarck did
not, however, satisfy natura