THE DESCENT OF MAN. 
Pakt 1. 
being performed during many generations, become con- 
verted into instincts and are inherited. They may then 
be said to be degraded in character, for they are no 
longer performed through reason or from experience. 
But the greater number of the more complex instincts 
appear to have been gained in a wholly different man- 
ner, through the natural selection of variations of simpler 
instinctive actions. Such variations appear to arise from 
the same unknown causes acting on the cerebral organ- 
isation, which induce slight variations or individual dif- 
ferences in other parts of the body ; and these variations, 
owing to our ignorance, are often said to arise sponta- 
neously. We can, I think, come to no other conclusion 
with respect to the origin of the more complex instincts, 
when w r e reflect on the marvellous instincts of sterilo 
worker-ants and bees, which leave no offspring to inherit 
the effects of experience and of modified habits. 
Although a high degree of intelligence is certainly 
compatible with the existence of complex instincts, as 
we see in the insects just named and in the beaver, it is 
not improbable that they may to a certain extent inter- 
fere with each other’s development. Little is known 
about the functions of the brain, but we can perceive 
that as the intellectual powers become highly developed, 
the various parts of the brain must be connected by the 
most intricate channels of intercommunication ; and as 
a consequence each separate part would perhaps tend to 
become less well fitted to answer in a definite and uni- 
form, that is instinctive, manner to particular sensations 
or associations. 
I have thought this digression worth giving, because 
we may easily underrate the mental powers of the 
higher animals, and especially of man, when we com- 
pare their actions founded on the memory of past 
events, on foresight, reason, and imagination, with 
