part of the
mental make-up of thinking persons that they can hold in common. The form
and method of science are fully set forth by these definitions, and the
purpose also is clearly revealed. For the results of investigation are not
merely formulae which summarize experience as so much "conceptual
shorthand," as Karl Pearson puts it, but they must serve also to describe
what will probably be the orderly workings of nature as future experience
unfolds. Human endeavor based upon a knowledge of scientific principles
must be far more reliable than where it is guided by mere intuition or
unreasoned belief, which may or may not harmonize with the everyday world
laws. Just as the law of gravitation based upon past experience provides
the bridge builder and the architect with a statement of conditions to be
met, so we shall find that the principles of evolution demonstrate the
best means of meeting the circumstances of life.

Evolution has developed, like all sciences, as the method we have
described has been employed. Alchemy became chemistry when the so-called
facts of the medievalist were scrutinized and the false were discarded.
Astrology was reorganized into astronomy when real facts about the planets
and stars were separated from the belief that human lives were influenced
by the heavenly bodies. Likewise the science of life has undergone
far-reaching changes in coming down to its present form. All the principles
of these sciences are complete only in so far as they sum up in the best
way the whole range of facts that they describe. They cannot be final until
all that can be known is known,--until the end of all knowledge and of
time. It is because he feels so sure of what has been gained that the man
of science seems to the unscientific to claim finality for his results. He
himself is the first to point out that dogmatism is unjustified when its
assertions are not so thoroughly grounded in reasonable fact as to render
their contrary unthinkable. He seeks only for truth, realizing that new
discoveries must oblige him to amend his statement of the laws of nature
with every decade. But the great bulk of knowledge concerning life and
living forms is so sure that science asserts, with a decision often
mistaken for dogmatism, that evolution is a real natural process.

* * * * *

The conception of evolution in its turn now demands a definite
description. How are we to regard the material things o