of the arthropods reaches its culminating point in the insect, and in
particular in the hymenoptera, as that of the vertebrates in man. Now,
since instinct is nowhere so developed as in the insect world, and in no
group of insects so marvelously as in the hymenoptera, it may be said
that the whole evolution of the animal kingdom, apart from
retrogressions towards vegetative life, has taken place on two divergent
paths, one of which led to instinct and the other to intelligence.

Vegetative torpor, instinct, and intelligence--these, then, are the
elements that coincided in the vital impulsion common to plants and
animals, and which, in the course of a development in which they were
made manifest in the most unforeseen forms, have been dissociated by the
very fact of their growth. _The cardinal error which, from Aristotle
onwards, has vitiated most of the philosophies of nature, is to see in
vegetative, instinctive and rational life, three successive degrees of
the development of one and the same tendency, whereas they are three
divergent directions of an activity that has split up as it grew._ The
difference between them is not a difference of intensity, nor, more
generally, of degree, but of kind.

* * * * *

It is important to investigate this point. We have seen in the case of
vegetable and animal life how they are at once mutually complementary
and mutually antagonistic. Now we must show that intelligence and
instinct also are opposite and complementary. But let us first explain
why we are generally led to regard them as activities of which one is
superior to the other and based upon it, whereas in reality they are not
things of the same order: they have not succeeded one another, nor can
we assign to them different grades.

It is because intelligence and instinct, having originally been
interpenetrating, retain something of their common origin. Neither is
ever found in a pure state. We said that in the plant the consciousness
and mobility of the animal, which lie dormant, can be awakened; and that
the animal lives under the constant menace of being drawn aside to the
vegetative life. The two tendencies--that of the plant and that of the
animal--were so thoroughly interpenetrating, to begin with, that there
has never been a complete severance between them: they haunt each other
continually; everywhere we find them mingled; it is the proportion that
differs. So with intelligence and