ur tools. Our
individual and even social habits survive a good while the circumstances
for which they were made, so that the ultimate effects of an invention
are not observed until its novelty is already out of sight. A century
has elapsed since the invention of the steam-engine, and we are only
just beginning to feel the depths of the shock it gave us. But the
revolution it has effected in industry has nevertheless upset human
relations altogether. New ideas are arising, new feelings are on the way
to flower. In thousands of years, when, seen from the distance, only the
broad lines of the present age will still be visible, our wars and our
revolutions will count for little, even supposing they are remembered
at all; but the steam-engine, and the procession of inventions of every
kind that accompanied it, will perhaps be spoken of as we speak of the
bronze or of the chipped stone of prehistoric times: it will serve to
define an age.[62] If we could rid ourselves of all pride, if, to define
our species, we kept strictly to what the historic and the prehistoric
periods show us to be the constant characteristic of man and of
intelligence, we should say not _Homo sapiens_, but _Homo faber_. In
short, _intelligence, considered in what seems to be its original
feature, is the faculty of manufacturing artificial objects, especially
tools to make tools, and of indefinitely varying the manufacture_.

Now, does an unintelligent animal also possess tools or machines? Yes,
certainly, but here the instrument forms a part of the body that uses
it; and, corresponding to this instrument, there is an _instinct_ that
knows how to use it. True, it cannot be maintained that _all_ instincts
consist in a natural ability to use an inborn mechanism. Such a
definition would not apply to the instincts which Romanes called
"secondary"; and more than one "primary" instinct would not come under
it. But this definition, like that which we have provisionally given of
intelligence, determines at least the ideal limit toward which the very
numerous forms of instinct are traveling. Indeed, it has often been
pointed out that most instincts are only the continuance, or rather the
consummation, of the work of organization itself. Where does the
activity of instinct begin? and where does that of nature end? We cannot
tell. In the metamorphoses of the larva into the nymph and into the
perfect insect, metamorphoses that often require appropriate action and
a