EVOLUTION OF INTELLIGENT BEHAVIOUR 167 
salient features in experience by reiterated emphasis in 
association with natural needs, and the development of generic 
in place of merely particular re-presentations will afford the 
appropriate material for abstraction on the one hand, and 
generalization on the other. Intelligence supplies the em- 
bryonic mental structures from which, under the quickening 
influence of a rational purpose, abstract and general ideas may 
be evolved. 
The essential features of the evolution of intelligence seem, 
then, to be, first, the development of controlling nerve-centres, 
by which the responsive action of reflex automatic or instinc- 
tive centres may be checked, augmented, or modified ; secondly, 
the increased differentiation and integration of these control 
centres with extension of the range and complexity of experi- 
ence in close touch with practical needs; thirdly, the con- 
densation and concentration of experience by the formation of 
generic products through the reiterated emphasis begotten of 
recurrent situations having certain salient features in common, 
though differing in details; and fourthly, an increased 
plasticity of behaviour, especially in early life, enabling an 
animal to deal effectually with an environment more com- 
plicated than that to which the more stereotyped instinctive 
behaviour is fitted by inheritance to respond. And this 
evolution of intelligent behaviour is working its way up to, 
though as such it cannot reach, the succeeding phase of mental 
evolution in which the data, supplied by intelligence, are 
treated with a new purpose for higher ends in the rational 
thought which seeks to explain the phenomena, and frame an 
ideal scheme of their relations and interconnections. 
Two further points may be noticed. First, that it is during 
the early and plastic days or months of life that intelligence is 
setting its seal on animal behaviour, and stamping it with its 
distinctive character. Adult life is very much what youth has 
made it; and old age is stereotyped through habit. In times 
of progress, the character of the race is determined by plastic 
possibilities of the young. Among them it is that the incidence 
of elimination makes itself felt, resulting in the survival of those 
