INTRODUCTION 9 
the analysis of instinct into simpler processes, and the 
different views of the origin and evolution of instinct. 
Considerable space is devoted to the transition between in- 
stinct and intelligence, and to evolution along the lines 
of plasticity and ready modifiability of behavior which has 
prepared the way for the appearance of intelligence. This 
is followed by a general and confessedly incomplete sketch 
of the gradual evolution of intelligence in the animal king- 
dom, and a discussion of some of the evidences for the ex- 
istence in the higher animals of a certain power of making 
inferences which some modern psychologists have claimed 
is not found in any sentient creature below man. 
A comparative survey of the actions of animals shows us 
that behavior is very much the same sort of thing wherever 
found. It is one of the many valuable contributions of the 
great pioneer in genetic psychology, Herbert Spencer, to 
have shown the fundamental unity of biological and psycho- 
logical processes in all their varied manifestations. Instinct, 
memory, volition and reason are all parts of that general 
process of adjustment of the organism to its environment, 
in which life in all its stages essentially consists. As we 
pass from lower to higher forms we have an increase in the 
complexity and perfection of the adjustments; the corre- 
spondence increases in space and in time, in definiteness and 
in generality, but everywhere it is “the adjustment of 
internal relations to external relations.”” This conception 
of mental life marks an important advance upon the psy- 
chology current in Spencer’s early years; it set aside the 
arbitrary distinctions of the so-called “faculties” and pre- 
pared the way for a clearer insight into the gradual unfold- 
ing of mind which the labors of genetic psychologists are 
slowly giving us. 
