cherished intellectual possessions have received no attention, so that we
might learn how evolution works in the lower fields of organic life in
general and human life in particular without being disturbed by them. No
doubt, however, the conviction has grown with each step in our progress
that the principles we have learned must cause us to readjust our views of
the highest elements in human thought to a degree that must be inversely
proportional to our previous acquaintance with the laws and processes of
nature. But the seeker after truth is fearless of consequences. He knows
that truth cannot contradict itself; and if those to whom he looks for
authority give him conflicting accounts of nature's history, he knows that
one of these must be less surely grounded than the other. The investigator
soon learns to withhold final judgment, realizing that the primary
conditions for intellectual development are the plasticity and openness of
mind that dogmatism and finality destroy. He knows that while his
researches may be, and indeed must be, iconoclastic, they provide him with
better icons in place of the old.

Let us recall the steps in our progress through one and another field of
knowledge, from which representative facts have been chosen for
classification and summary. We began with the basic principles of organic
structure and workings, and then we examined serially the larger
categories of the evidences relating to evolution as a fact, and to the
mode of its accomplishment by natural factors. Proceeding to the special
case of our own species, we learned that human beings are inevitably a
part of nature and not outside it; in structure, development, and
palaeontological history, mankind is subject to the control of the uniform
laws which operate throughout the entire range of living things. Finally,
the mental characters and the social relations of human organisms were
derived from beginnings lower down in the scale, and were proved to be no
more exceptional than the physical constitution of a single human being.

Are we to forget all of these things when we try to put in order our ideas
belonging to the categories of higher thought? Can we hope to find the
truth if we fail to employ the methods of scientific common-sense which
only yield sure results? It is no more justifiable to discard our
hard-earned knowledge than it would be for an advocate to undertake the
conduct of a case in deliberate disregard of what he had l