334 THE EVOLUTION OF ANIMAL BEHAVIOUR 
a clearer light. This is what is generally meant by the state- 
ment that animals have probably not reached the level of 
rational beings. 
But even if they have not reached this level, their perceptual 
processes supply the antecedent conditions which are necessary 
if this level is to be attained in the course of further evolution. 
We have seen that, even in relatively simple cases, where con- 
scious situations mark only the beginnings of intelligence, there 
is a biological emphasis of some, rather than others, among 
what we call the qualities of objects, and there is a grouping, 
on biological grounds, of certain things which have some 
quality in common—such, for example, as being fit for food. 
Here we have at the outset of perceptual development the 
germs of processes which are the precursors of the abstraction 
and generalization of ideational thought. And in the more 
complex conscious situations of the higher animals these pro- 
cesses attain to such degree of development as is necessary to 
secure more difficult and more remote biological ends, until all 
that is necessary, for their rational use, is the quickening touch 
of a new purpose, that of explanation. 
We have seen that, through what Dr. Stout terms 
“manipulation,” and Professor Groos “ experimentation ”— 
names applied to a type of behaviour widely exemplified 
among the higher animals,—things, as the nuclei of conscious 
situations, become differentiated from the environment. One 
can hardly question that a fly to the trout, a ball to the kitten, 
a bone to the puppy are things distinguished from their 
surroundings, and that they become marked off as special 
centres of interest. Here on the perceptual plane is a process 
which is the antecedent of the conception of quasi-independent 
objects on the ideational plane.’ For rational thought the 
thing, as object, is not only the centre of a practical 
situation leading to behaviour of direct or indirect biological 
value, but is the nucleus around which we build all the qualities 
which are ascertained by more elaborate manipulation and 
experimentation carried out deliberately and of set purpose 
for rational ends. It becomes capable of definition with 
