nervous or mental processes. When they enter our bodies, they with other
foods replenish the various tissues, and among these the parts of the
brain. In a material sense they become actual living protoplasm, replacing
the worn-out substances destroyed during our previous thinking; and their
properties are combined to make brain and thought, to play for a time
their part in life, and to pass back into the world of dead, unthinking
things. Every one of us knows that hunger reduces our ability to think
clearly and fully, and every one knows also that mental vigor is renewed
when fresh supplies of nourishment reach the brain. What can be the source
of mentality, if it is not something brought in from the outer world along
with the chemical substances which taken singly are devoid of mind?
Scientific monism frankly replies that it is unable to find another
origin.

We are thus brought to recognize, not only the continuity taught by
organic evolution, but also the uniformity of the materials constituting
the entire sensible world, inasmuch as the ultimate unit of all nervous
phenomena is the reflex act of a protoplasmic mass, which itself is a
synthesis of properties inhering in the chemical elements making up living
matter. Among inorganic things the mind-stuff units are combined in
relatively simple ways, and the "stuff" does not give any outward
evidences of "mind" as such. Living things are almost infinitely complex
as regards their chemical organization, and even in the very lowest of
them we can discern a cell-reflex element which, combined with others like
it, forms the unit of the compounds we call instinct, intelligence, and
reason. Hence through an analysis of mental evolution we are enabled to
form the larger conception of a continuous universe whose ultimate
elements are the same everywhere.

VII

SOCIAL EVOLUTION AS A BIOLOGICAL PROCESS

We now reach a critical juncture in our study of the foundations of
evolutionary doctrine, for we must pass at this point to an inquiry into
the nature and origin of human social relations. In undertaking this task
we may seem to leave the field which is properly that of organic
evolution, and many perhaps will be unwilling to view such aspects of
human life as materials for purely biological analysis, arrangement, and
explanation. But even before the reasons for doing so may be made
apparent, every one must admit that the subject of mental evolution, which
comprise