"constitution" plainly indicated to him the conduct appropriate to a
human being.

Such appeals to man's nature we are apt to listen to with a good deal of
sympathy. Manifestly, man differs from the brutes, and they differ, in
their kind, from each other. To each kind, a life of a certain sort seems
appropriate. The rational being is expected to act rationally, to some
degree, at least. In our dealings with creatures on a lower plane, we
pitch our expectations much lower.

And the behavior we expect from each is that appropriate to its kind. The
bee and the ant follow unswervingly their own law, and live their own
complicated community life. However the behavior of the brute may vary in
the presence of varying conditions, the degree of the variation seems to
be determined by rather narrow limits. These we recognize as the limits
of the nature of the creature. It dictates to itself, unconsciously, its
own law of action, and it follows that law simply and without revolt.

When we turn to man, "the crown and glory of the universe," as Darwin
calls him, we find him, too, endowed with a certain nature in an
analogous sense of the word. He has capacities for which we look in vain
elsewhere. The type of conduct we expect of him has its root in these
capacities. Human nature can definitely be expected to express itself in
a human life,--one lower or higher, but, in every case, distinguishable
from the life of the brute. It means something to speak of the physical
and mental constitution of man, that mysterious reservoir from which his
emotions and actions are supposed to flow. We feel that we have a right
to use the expression, even while admitting that the brain of man is, as
far as psychology is concerned, almost unexplored territory, and that the
relation of mind to brain is, and is long likely to remain, a subject of