aims that it
is possible for the intelligent adaptations, or any sort of
"accommodations," made by the individuals of one generation, to set
the direction of subsequent evolution, even though there be no direct
inheritance of acquired characters from father to son. It proceeds in
the case of instinct somewhat thus:

Suppose we say, with the first theory given above, that the organism
has certain reflexes which show some degree of adaptation to the
environment; then suppose we admit the point, urged by the advocates
of the lapsed intelligence theory, that the gradual improvement of
these reflexes by variations in the endowment of successive
generations would not suffice for the origin of instinct, seeing that
partial instincts would not be useful; and, further, suppose we agree
that many of the complex instincts really involved intelligent
adaptation in their acquisition. These points carefully understood,
then one new and further principle will enable us to complete a theory
which will avoid the objections to both the others. This principle is
nothing else than what we have seen already--namely, that the
intelligence supplements the partial instincts in each generation and
makes them useful in the respects in which they are inadequate, and so
keeps the young alive in successive generations as long as the
instinct is imperfect. This gives the species time gradually to
supplement its instinctive endowment, in the course of many
generations each of which uses its intelligence in the same way: time
to accumulate, by the occurrence of variations among the offspring,
the changes in the nervous system which the perfect instinct requires.
Thus as time goes on the dependence of each generation upon the aid of
intelligence is less and less, until the nervous system becomes
capable of performing the function quite alone. The result then will
be the same as if the acquisitions made by each generation had been
inherited, while in reality they have not. All that this theory
requires in addition to what is admitted by both the historical views
is that the species be kept alive long enough by the aid of its
intelligence, which supplements imperfect instincts, to give it time
to produce sufficient variations in the right direction. The instinct
then achieves its independence, and intelligent supervision of it is
no longer necessary (see Fig. 1).

[Illustration: FIG. 1,--Origin of instinct by Organic Selection: _A
n_, perfect instinct