. Darwin can be said to have established:

"That if the various kinds of lower animals have been evolved
one from the other by a process of natural generation or
evolution, then it becomes highly probable, _a priori_, that
man's body has been similarly evolved; but this, in such a
case, becomes equally probable from the admitted fact that he
is an animal at all" (p. 65).

From the principles laid down in the last sentence, it would follow
that if man were constructed upon a plan as different from that of any
other animal as that of a sea-urchin is from that of a whale, it
would be "equally probable" that he had been developed from some other
animal as it is now, when we know that for every bone, muscle, tooth,
and even pattern of tooth, in man, there is a corresponding bone,
muscle, tooth, and pattern of tooth, in an ape. And this shows one
of two things--either that the Quarterly Reviewer's notions of
probability are peculiar to himself; or, that he has such an
overpowering faith in the truth of evolution, that no extent of
structural break between one animal and another is sufficient to
destroy his conviction that evolution has taken place.

But this by the way. The importance of the admission that there is
nothing in man's physical structure to interfere with his having been
evolved from an ape, is not lessened because it is grudgingly made and
inconsistently qualified. And instead of jubilating over the extent of
the enemy's retreat, it will be more worth while to lay siege to his
last stronghold--the position that there is a distinction in kind
between the mental faculties of man and those of brutes; and that, in
consequence of this distinction in kind, no gradual progress from
the mental faculties of the one to those of the other can have taken
place.

The Quarterly Reviewer entrenches himself within formidable-looking
psychological outworks, and there is no getting at him without
attacking them one by one.

He begins by laying down the following proposition: "'Sensation' is
not 'thought,' and no amount of the former would constitute the most
rudimentary condition of the latter, though sensations supply the
conditions for the existence of 'thought' or 'knowledge'" (p. 67).

This proposition is true, or not, according to the sense in which the
word "thought" is employed. Thought is not uncommonly used in a sense
co-extensive with consciousness, and, especially, with those states
of c