human beings that marks them off and
distinguishes them from the actions of animals and plants with which
human beings have so much in common?

The problem is the more difficult because, in some one or other of its
aspects, human behavior involves processes which are characteristic of
almost every form of nature. We sometimes speak, for example, of the
human machine. Indeed, from one point of view human beings may be
regarded as psycho-physical mechanisms for carrying on the vital
processes of nutrition, reproduction, and movement. The human body is,
in fact, an immensely complicated machine, whose operations involve an
enormous number of chemical and physical reactions, all of which may be
regarded as forms of human behavior.

Human beings are, however, not wholly or merely machines; they are
living organisms and as such share with the plants and the lower animals
certain forms of behavior which it has not thus far, at any rate, been
possible to reduce to the exact and lucid formulas of either chemistry
or physics.

Human beings are, however, not merely organisms: they are the home and
the habitat of minuter organisms. The human body is, in a certain sense,
an organization--a sort of social organization--of the minute and simple
organisms of which it is composed, namely, the cells, each of which has
its own characteristic mode of behavior. In fact, the life of human
beings, just as the life of all other creatures above the simple
unicellular organisms, may be said to consist of the corporate life of
the smaller organisms of which it is composed. In human beings, as in
some great city, the division of labor among the minuter organisms has
been carried further, the interdependence of the individual parts is
more complete, and the corporate life of the whole more complex.

It is not strange, therefore, that Lloyd Morgan begins his studies of
animal behavior by a description of the behavior of the cells and
Thorndike in his volume, _The Original Nature of Man_, is led to the
conclusion that the original tendencies of man have their basis in the
neurones, or nerve cells, and in the changes which these cells and their
ancestors have undergone, as a result of the necessity of carrying on
common and corporate existences as integral parts of the human organism.
All acquired characteristics of men, everything that they learn, is due
to mutual stimulations and associations of the neurones, just as
sociologists are now dispos