he same in kind with
those of man, though so different in degree, are capable of advancement.
Thus the interval between the mental powers of one of the higher apes
and of a fish, or between those of an ant and scale-insect, is immense;
yet their development does not offer any special difficulty, for with
our domesticated animals the mental faculties are certainly variable,
and the variations are inherited. No one doubts that their mental
faculties are of the utmost importance to animals in a state of nature.
Therefore the conditions are favorable for their development through
natural selection. The same conclusion may be extended to man; the
intellect must have been all-important to him, even at a very remote
period, as enabling him to invent and use language, to make weapons,
tools, traps, etc., whereby, with the aid of his social habits, he long
ago became the most dominant of all living creatures."

It is further pointed out that a great stride in the development of
man's intellect must have followed as soon as the half-art and
half-instinct of language came into use; for the continued use of
language must have reacted on the brain, and produced an inherited
effect, and this again will have reacted on the improvement of language.
The largeness of the brain in man relatively to his body, compared with
the size of that organ in the lower animals, is attributable in chief
part to the early use of some simple form of language, that engine which
affixes signs to all sorts of objects and qualities, and excites trains
of thought which would never arise from the mere impression of the
senses, or, if they did arise, could not be followed out. The higher
intellectual powers of man, such as those of ratiocination, abstraction,
self-consciousness, etc., probably follow from the continued improvement
and exercise of the other mental faculties.

How man's moral qualities came to be developed is an interesting problem
which is considered by Darwin at some length. He holds that their
foundation lies in the social instincts under which term are included
family ties. These instincts are highly complex, and, in the case of the
lower animals, give special tendencies toward certain definite actions.
But the more important elements are love and the distinct emotion of
sympathy. Animals endowed with the social instincts take pleasure in one
another's company, warn one another of danger, defend and aid one
another in many ways. These insti