not mechanical in the sense at least in which we usually employ
the word mechanical. For Bergson claims that the one chief feature of
living material is that it responds favorably to the situation in which it
finds itself; at least so far as lies within the possible physical
limitations of its organization. Evolution has followed no preordained
plan; it has had no creator; it has brought about its own creation by
responding adaptively to each situation as it arose.

But note: the man of science believes that the organism responds today as
it does, because at present it has a chemical and physical constitution
that gives this response. We find a specific chemical composition and
generally a specific physical structure already existing. We have no reason
to suppose that such particular reactions would take place until a specific
chemical configuration had been acquired. Where did this constitution come
from? This is the question that the scientist asks himself. I suppose
Bergson would have to reply that it came into existence at the moment that
the first specific stimulus was applied. But if this is the answer we have
passed at once from the realm of observation to the realm of fancy--to a
realm that is foreign to our experience; for such a view assumes that
chemical and physical reactions are guided by the needs of the organism
when the reactions take place inside living beings.

USE AND DISUSE

_From Lamarck to Weismann_

The second of the four great historical explanations appeals to a change
not immediately connected with the outer world, but to one within the
organism itself.

Practice makes perfect is a familiar adage. Not only in human affairs do we
find that a part through use becomes a better tool for performing its task,
and through disuse degenerates; but in the field of animal behavior we find
that many of the most essential types of behavior have been learned through
repeated associations formed by contact with the outside.

It was not so long ago that we were taught that the instincts of animals
are the inherited experience of their ancestors--lapsed intelligence was
the current phrase.

Lamarck's name is always associated with the application of the theory of
the inheritance of acquired characters. Darwin fully endorsed this view and
made use of it as an explanation in all of his writings about animals.
Today the theory has few followers amongst trained investigators, but it
still has a popular vogue