THE EVOLUTION OF CONSCIOUSNESS 61 
IV.—TuHE Evonution OF CONSCIOUSNESS 
The origin of consciousness, like that of matter or energy, 
appears to be beyond the pale of scientific discussion. The 
appearance of effective consciousness on the scene of life does 
indeed seem to justify the belief in the prior existence of sen- 
tience as the mere accompaniment of organic behaviour. Lv 
nihilo nihil fit. And since effective consciousness must, on this 
principle, be developed from something, it is reasonable to 
assume that this something is pre-existing sentience. Again, 
we may assume that this sentience is a concomitant of all life- 
processes, or only of some. But we have no criterion by which 
we can hope to determine which of these alternatives is the 
more probable. 
We appear, however, at all events to have evidence that 
when effective consciousness does enter on the scene and play 
its part in the guidance of behaviour, its progress is, in tech- 
nical phraseology, marked by that differentiation of conscious 
elements, and that integration of these differentiated items, 
which are seemingly the correlatives of the differentiation and 
integration of nervous systems. There is thus, presumably, a 
progressive development of orderly complexity in the conscious 
situations of which controlled or guided behaviour is the out- 
come. And when this has reached a certain stage—what stage 
it is most difficult to determine—the relationships, at first 
implicit in the conscious situations, as they naturally arise in 
the course of experience, begin to be rendered explicit with the 
dawn of reflection. Intentional abstraction and generalization 
to which data are afforded by the reiterated emphasis in ex- 
perience of the salient features in successive situations, supply 
new elements to the more highly developed situations of 
rational life. Ideal schemes and plans of action, the products 
of reflection and foresight, take form in the mind and enter 
into the conscious situation. And the intelligent animal, 
hitherto the creature of impulse, guided only by the pleasur- 
able or painful tone which gives colour to experience, becomes 
