as these processes are carried on by the
peculiar tissues of the nervous system they cannot be finally
distinguished from the functional products or accompaniments of the same
kind of active tissues and organs in lower creatures. Thus the subject of
mental evolution becomes much clarified at the outset by understanding
that nervous processes and nervous systems evolve together.

In the direct treatment of the facts and principles of mental evolution we
can use exactly the same classification and subdivisions of the materials
of study as heretofore, because psychological data are the correlates of
material organic systems, and also because the former, being natural
phenomena, are subject to the methods of analysis which can be employed
for any series of objects that have undergone evolution. Separating the
matter of fact from the question as to the method, and recalling the main
bodies of evidence as to the reality of evolution, we may establish four
sections of the subject before us: these are (1) the anatomy, (2) the
embryology, and (3) "palaeontology" of mind, and (4) an inquiry into the
way nature deals with the psychical characteristics of organisms in
accomplishing their evolution. To specify more particularly, it is
possible in the first place to compare the activities belonging to the
category of mental and nervous operations, displayed by man and other
organisms, and the results form the subject of comparative descriptive
psychology; the second division, namely, developmental or genetic
psychology, deals with the sequence of events in the life of a single
individual by which the infantile and adolescent types of mind become
adult intellectuality; in the third place, in speaking of the palaeontology
of mind, the phrase is used to refer to the varied and changing mental
abilities of human races in historic and prehistoric times as they may be
demonstrated and determined by the evidences of the culture of such
earlier epochs. In considering the matter of method, the questions are
whether variation, inheritance, and selection are as real in the world of
mental phenomena as they are in the material world, and whether the laws
are the same or similar in the two cases. We shall learn how the results
of such studies prove with convincing clearness, first, that the contents
of the individual mind and of the minds of various human races are truly
the products of natural evolution, and second, that the human mind differs
on