162 INTELLIGENT BEHAVIOUR 
When we compare, however, the several grades of intelli- 
gence which observation discloses, and when we watch the 
conscious development of the more intelligent animals, we seem 
to find evidence of the growth of a system of experience, at 
first in very close touch with inherited modes of procedure, 
but gradually acquiring more of independence and freedom. 
Increase of the range and complexity of behaviour brings with 
it, not only increase in the range and complexity of experience, 
but also—what is, perhaps, even more essential to effective 
progress—greater unity and closer connection into a well-knit 
whole. And with this greater unity and closer connection 
there goes what one may term a condensation of experience by 
an elimination of detail and the survival of essential features 
repeatedly emphasized. This is analogous in the development 
of intelligence to the generalization and abstraction which play 
so important a part in the development of reason. It affords, 
in fact, the data which reflection utilizes in the purposive and 
intentional condensation and concentration of knowledge at a 
higher stage of mental development. 
The omission of detail and the survival of the salient 
features is well known to us in the familiar facts of memory. 
We have seen thousands of sheep and oxen, no two of which 
are probably alike in all their external details as presented to 
vision. But we remember what a sheep or an ox looks like, 
and many of us can form a visualized image of either of these 
animals, This, however, is not the re-presentative image of any 
particular sheep or ox. It is what psychologists term a generic 
image. It is like a composite photograph made by superimpos- 
ing on the same plate a number of individual images so that the 
salient features which all possess in common stand out clearly 
by their coincidence on the plate, while the distinctive details 
are but dimly presented. Thus does memory preserve the 
essentials common to many impressions while the distinguishing 
details are lost and fade, eliminated by forgetfulness. And 
thus in the experience which intelligence practically utilizes 
are the net results of a thousand particular impressions con- 
densed in one effective image. 
