174 INTELLIGENT BEHAVIOUR 
of cases demonstrably modify the course of instinctive behaviour, 
the converse proposition does not hold good in the same sense. 
The animal acts at first instinctively, and subsequently in the 
light of experience reaches further accommodation ; and though 
in later life a dominating instinct may override the guidance 
of intelligence, still, even this is probably due to the fact that 
the instinct is more deeply seated in the constitution than any 
opposing habits of intelligent acquisition. 
We can, however, infer what is the influence of intelligence 
on instinct without basing our inferences on any assumption 
of the initial priority of instinct in the evolutionary sequence. 
Taking animals as we find them, they afford numberless ex- 
amples of behaviour at first instinctive but subsequently modi- 
fied, in greater or less degree, in accordance with the teachings 
of experience. Let us, first, assume that the environment is 
slowly changing, or has changed, in some definite manner. 
Such change would, of course, be relative, and might be due, 
either to new conditions brought to bear on the animal, or to 
the animal being itself brought, in the expansion of its life, 
within their influence. The old instinct is no longer quite 
adapted to the changed circumstances. If the change were 
sufficient in amount, and occurred somewhat suddenly, variations 
of instinct might not occur soon enough to enable the animal 
to reach adaptation by the gradual process of natural selection. 
If dependent on instinct alone the animal would, under these 
circumstances, be eliminated. But if intelligence were able to 
modify the behaviour to meet the new conditions this elimina- 
tion would be prevented. In successive generations intelligence 
would constantly modify behaviour in the same manner and in 
a definite direction. Meanwhile congenital variations in 
different directions would occur. Those which were in direc- 
tions antagonistic to that dictated by intelligence would tend 
to thwart accommodation and render it less effectual ; but 
those which were coincident in direction would conspire with 
accommodation and render it more effectual. The individuals 
in which variations of instinct tended to thwart intelligence 
would be eliminated ; while those in which coincident variations 
