As
one result of this, he does not learn from individual experience,
but one generation is like the preceding generations, with here and
there some slight modifications. But when you get the creature
that has arrived at the point where his experience has become
varied, he has got to do a good many things, and there is more or
less individuality about them; and many of them are not performed
with the same minuteness and regularity, so that there does not
begin to be that automatism within the period during which he is
being developed and his form is taking on its outlines. During
prenatal life there is not time enough for all these nervous
registrations, and so by degrees it comes about that he is born
with his nervous system perfectly capable only of making him
breathe and digest food,--of making him do the things absolutely
requisite for supporting life; instead of being born with a certain
number of definite developed capacities, he has a number of
potentialities which have got to be roused according to his own
individual experience. Pursuing that line of thought, it began
after a while to seem clear to me that the infancy of the animal in
a very undeveloped condition, with the larger part of his faculties
in potentiality rather than in actuality, was a direct result of
the increase of intelligence, and I began to see that now we have
two steps: first, natural selection goes on increasing the
intelligence; and secondly, when the intelligence goes far enough,
it makes a longer infancy, a creature is born less developed, and
therefore there comes this plastic period during which he is more
teachable.
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