evidence of change and development, of rise and fall, in the
tide of animal life, in its geographical range, in its anatomical
organization, and in its adjustability to the major features of
environment. One of the lectures in this series has in particu-
lar been devoted to evidence of this character as it applies to
the changes brought about in the nervous system of various
forms of animal life. The development of man himself and of
the society within which he lives has also been passed in review
and convincing demonstration has been offered of the extensive
changes which have, throughout the ages, come to pass in both.
Evolution having been thus convincingly exhibited in a number
of important fields, it behooves us, in discussing the present
problem, to secure impressions as clear as possible of the char-
acter of the evidence upon which we are to base our inferences
and conclusions regarding the development of intelligence.

In the case of animal life, the only available information is
to be gained by the direct observation of animal behavior as
that is found among the creatures surviving in our age of the
world. Whether there may have been creatures in the past
possessing forms of intelligence substantially different from
that of any animals now living can neither be denied nor as-
serted with absolute confidence. But such evidence as we have
is at least all against the inference that animals superior to
those now living have ever been developed. So great is the
similarity of existing forms to such extinct forms as are known
to us, that it seems highly improbable there should have oc-
curred developments of intelligence widely different from those
represented in the animal life of to-day. This inference,
to be sure, rests upon the hypothesis which most scientists re-
gard as conclusively established, to wit, that intelligence is

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