308 THE EVOLUTION OF ANIMAL BEHAVIOUR 
Huxley seems to have been carried too far by the force of his own 
attack. So long as he held to the position that every conscious 
state has, as its concomitant, a molecular change in the brain, 
he had all the forces of evolution on his side. But when he 
said that consciousness is merely the steam-whistle of life’s 
locomotive, or merely answers to the sound which the animal- 
bell gives out when it is struck, he takes up another position 
of far less strategical strength. For whereas the frog from 
which the physical centres of consciousness have been removed 
sits crouched and motionless, and ‘“‘ will starve sooner than 
feed itself, although food put into its mouth is swallowed ;” 
the frog in which conscious situations can take form in 
unmutilated cerebral hemispheres behaves in a very different 
manner. It is nothing less than pure assumption to say 
that the consciousness, which is admitted to be present, has 
practically no effect whatever upon the behaviour. And we 
must ask any evolutionist who accepts this conclusion, how 
he accounts on evolutionary grounds for the existence of a 
useless adjunct to neural processes. 
“Tt is,” says Huxley,* “ experimentally demonstrable—any 
one who cares to run a pin into himself may perform a 
sufficient demonstration of the fact—that a mode of motion 
of the nervous system is the immediate antecedent of a state 
of consciousness. We have as much reason for regarding the 
mode of motion as the cause of the state of consciousness, as 
we have for regarding any event as the cause of another. 
How the one phenomenon causes the other we know as much, 
or as little, as in any other case of causation ; but we have 
as much right to believe that the sensation is an effect of the 
molecular change, as we have to believe that motion is an 
effect of impact; and there is as much propriety in saying 
that the brain evolves sensation, as there is in saying that 
an iron rod, when hammered, evolves heat.” But if we speak 
of the related antecedent as the cause, it is not obvious why 
we should not describe the desire to demonstrate the supposed 
fact as the cause of running in the pin. Weseem to have just 
* Op. cit., pp. 238, 239. 
