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THE PHYSIOLOGICAL ASPECT 297 
conspire with sufficient unity of biological purpose. And 
when we pass to the higher creatures in which many cells 
unite to form one animal, the very word “unite” indicates 
that the vital processes of all must conspire with sufficient 
unity of biological purpose to insure the continued life of the 
whole. 
Now, in all the higher and more active animals a nervous 
system is developed, which has for its purpose and end the 
preservation and furtherance of unity amid circumstances of 
progressively increasing diversity. And in the course of its 
evolution an added means of preserving and furthering the 
essential unity is provided in consciousness, which, through the 
coalescence of scattered units of sentience, leads behaviour to 
acquire a new and higher unanimity of purpose. Thus a 
mental evolution is engrafted on the organic evolution which 
precedes it. But every step in this mental evolution presup- 
poses a step in organic evolution. And such is the complexity 
of structure and process in all the higher animals that much 
of the business of behaviour is relegated to quasi-independent 
nervous centres, which perform this business automatically, and 
will continue to perform it, with much subsidiary unity of end, 
when they are left to themselves and all connection with the 
supremely unifying sensorium has been severed. 
- Before proceeding to give some examples of this fact, and 
to indicate its bearing on our interpretation of behaviour, it 
may be well to state distinctly that no attempt is or will be 
here made to trace in detail the course of the evolution of 
animal behaviour through the ascending grades of life, nor, 
indeed, to prove that there has been any such evolution. 
Evolution by natural genesis is here assumed as the only 
hypothesis with which science has any concern. If it be false, 
then have the labours of workers and thinkers, since Darwin 
and Mr. Herbert Spencer worked and thought, been vain. 
Special creation is not a scientific hypothesis, but a reference 
of biological and mental phenomena to an ultimate cause, 
which lies beyond and altogether apart from the scope of 
scientific inquiry. The fundamental assumption of the man 
