330 THE EVOLUTION OF ANIMAL BEHAVIOUR 
organic development of the nervous system reaches a certain 
level and order of complexity consciousness emerges, how and 
whence we know not. The second is, that consciousness is 
developed from sentience, which is the concomitant of all 
organic behaviour ; which accompanies life wherever it occurs 
and therefore shares the continuity of the germinal substance. 
The difficulty inseparable from the first hypothesis, is that 
it is contrary to the analogy of all that we know or infer else- 
where throughout the realm of nature. Huxley * likened its 
emergence to the production of heat when an iron bar is 
struck by repeated blows of the hammer. But this analogy 
will not hold ; for heat is a mode cf energy, and only emerges 
through the transformation of other and pre-existing modes 
of energy. A certain amount of the energy of motion in the 
massive hammer-head is transferred to the iron rod, and 
assumes the form of that molecular vibration which we call 
heat. And by what amount the one is the gainer, by that 
amount is the other the loser. But we have no reason to 
suppose that the like takes place in the origin of the mental 
concomitants of neural changes. No portion of the brain’s 
store of physical energy is drained off to form the rivulet of 
consciousness. Now, whenever we speak of a product else- 
where in nature, we mean a specialized bit of something pre- 
existent. Water is the product of pre-existing oxygen and 
hydrogen. Heat is the product of other forms of energy. 
But this is not so on the first hypothesis, according to which 
consciousness emerges when the functional activity of the 
nervous system reaches a certain level and order of complexity. 
The mental concomitants are not “products,” in the recog- 
nized sense of the term. Furthermore, although on this 
hypothesis we may still speak of what was termed above 
evolutional continuity in the mental concomitants, there is 
nothing analogous to either developmental or germinal con- 
tinuity. 
On the second hypothesis, according to which sentience is 
the concomitant of all organic behaviour, such developmental 
* “Collected Essays,” vol. i., p. 239 
