pressing forward unceasingly." Matters, however, were not destined to
remain long at this stage. As man's knowledge of the processes of nature
increased further, a twofold result followed. On the one hand, the sense
world of nature became increasingly absorbing in interest; on the other
hand, laws were formulated and nature was conceived of as being a chain
of cause and effect, a combination of mechanical elements whose
interactions were according to law, and could be foretold with the
utmost precision.

These two factors worked in the same direction, namely, that of
rendering less necessary the conception of a spiritual world. The
interest of mankind became so concentrated upon material things that the
interest in the invisible decreased, while the mechanical, soulless
elements with their ceaseless actions and reactions in definite order,
and according to inviolable law, were held sufficient to account for the
phenomena of nature. The keynote was "relation to environment"; a
constantly changing environment, changing according to law, called for
ceaseless readjustment, and the adaptation to environment was held to be
the stimulus to all activity in the natural world.

The later development of biology, and the doctrine of the evolution of
species, gradually extended this conception of nature to include man
himself.

What he had regarded as his distinctive characteristics were held to be
but the product of natural factors, and his life was regarded, too, as
under the domain of rigid, inviolable law. There was no room for, and no
need of, the conception of free, originative thought. Thought was
simply an answer to the demand that the sense world was making, entirely
dependent upon the external stimulus, just as any other activity was