INFLUENCE OF INTELLIGENCE ON INSTINCT 169 
a life of dull and unprogressive monotony. Strength without 
cunning made these big-framed animals for a while masters 
of the situation. But among those existing animals whose 
skeletons indicate an analogous zoological position, there is 
none which exhibits a cerebral development so poor. And we 
may fairly conclude that the fact that these huge creatures have 
left no lineal descendants may be taken as evidence of the 
importance and value, in evolution, of that cerebral tissue 
which is the organic basis of intelligence. The higher brain 
contains the potentiality of that experience without which 
the evolution of intelligent behaviour in any race of vertebrate 
animals is impossible. 
V.—TuHeE INFLUENCE OF INTELLIGENCE ON INSTINCT 
We have seen that the relation of instinct to intelligence is 
essentially that of congenital to acquired behaviour. We have 
seen, too, that in the Lamarckian interpretation what is 
acquired in the course of life may be transmitted through 
inheritance, and thus the intelligent behaviour of one genera- 
tion may become instinctive and congenital in the next. But 
serious biological difficulties stand in the way of the acceptance 
of this interpretation ; there is, moreover, little or no evidence 
of the assumed transmission to offspring of any acquired 
modifications of structure or behaviour. We have, therefore, 
been led to infer that instinctive behaviour has been evolved 
through the selection of adaptive variations of germinal origin, 
the influence of intelligence being restricted to the fosterage 
of co-incident variations, that is to say, of those congenital 
variations which coincide in direction with the acquired 
modifications of behaviour due to intelligence. It is clear 
that on this interpretation the influence of intelligence on 
instinct is more indirect and less simple than that implied by 
the Lamarckian hypothesis. Intelligence and instinct are in 
large degree independent, though there is continual interaction 
