een discussing since the time of the Greek
philosophers. The hand of tradition, however, was heavy on them still.
They dreaded to run counter to authority, and did not dare think
unrestrainedly. Descartes shows us how we can understand things better
if we will imagine a few principles by which it will be easy to
account for things as they are. Then he carefully elaborates these
principles as they occur to him; but he has no sooner done so than he
takes care to add, "Of course, we know the earth was not made in this
way."

A little later the philosopher, Leibnitz, believed in an orderly
creation that had advanced by regular degrees, and that the lower
animals had thus developed into the higher. He adds interestingly that
there are probably on some other planets animals midway between the
ape and man, but that nature has kindly removed such animals from the
earth in order that man's superiority to the apes should be entirely
beyond question.

By the middle of the eighteenth century men had begun to think more
fearlessly. The great Emanuel Kant wrote in his younger and less timid
years, "The General History of Nature and Theory of the Heavens." The
great Newton had by his law of gravitation brought order into the
heavens. Kant looked longingly for a greater Newton, who should find a
similar unity in the animal world. He saw the wonderful likenesses
between animals that the anatomist, Buffon, had recently pointed out.
He believed there must somehow be blood relationship between all
animals. He tried hard to conceive of some underlying natural cause by
which all could have come about. As he grew older and his mind became
more cautious he came to think the matter deeper than the human mind
could ever fathom. He gave up the hope and believed the problem of
animal origin and derivation would forever remain insoluble. He
feared there was not in man the power to conceive his own origin.

If we ever wonder why it took so long before the thought of evolution
should have fully dawned upon the world, the answer is not far to
seek. No student of Natural History in ancient or medieval times had
the faintest conception of the enormous number of animals and of
plants in the world. The old Greek or Roman student of Natural History
gives no evidence of knowing more than a few hundred animals. Men have
named to-day, with systematic Latin names, hundreds of animals for
every one that Pliny ever knew, and he knew more than any other man of