uman
progress came to be recognized in practice. And--to seek an illustration
at the other end of the scale--we know that the advanced thinkers of
Greece and Rome believed in the antiquity of the earth and in the
evolution of man two thousand years before the coming of Darwin. We have
but partly solved the mysteries of the progress of civilization, then,
when we have pointed out that each tangible stage of progress owed its
initiative to a new invention or discovery of science. To go to the root
of the matter we must needs explain how it came about that a given
generation of men was in mental mood to receive the new invention or
discovery.

The pursuit of this question would carry us farther into the realm of
communal and racial psychology--to say nothing of the realm of
conjecture--than comports with the purpose of this article. It must
suffice to point out that alertness of mind--that all mentality--is, in
the last analysis, a reaction to the influences of the environment. It
follows that man may subject himself to new influences and thus give his
mind a new stimulus by changing his habitat. A fundamental secret of
progress is revealed in this fact. Man probably never would have evolved
from savagery had he remained in the Tropics where he doubtless
originated. But successive scientific inventions enabled him, as has
been suggested, to migrate to distant latitudes, and thus more or less
involuntarily to become the recipient of new creative and progressive
impulses. After migrations in many directions had resulted in the
development of divers races, each with certain capacities and
acquirements due to its unique environment, there was opportunity for
the application of the principle of environmental stimulus in an
indirect way, through the mingling and physical intermixture of one race
with another. Each of the great localized civilizations of antiquity
appears to have owed its prominence in part at least--perhaps very
largely--to such intermingling of two or more races. Each of these
civilizations began to decay so soon as the nation had remained for a
considerable number of generations in its localized environment, and had
practically ceased to receive accretions from distant races at
approximately the same stage of development. There is a suggestive
lesson for present-day civilization in that thought-compelling fact.
Further evidence of the application of the principle of environmental
stimulus, operating through c