I96 THE CAUSATION OF DISEASE. 



chemico-physical nature. Now for the first time there occurs 

 the clashing of two great systems — chemico-physical nature 

 on the one hand, mind on the other. The former is no longer 

 able to pursue her unchecked course, for man is capable 

 of modifying the processes of physical nature at will. He 

 cannot, indeed, suspend them — he must, as Bacon observes, 

 rule by obeying, but in this way he can compel natural 

 laws to work together towards a definite end, and thus not 

 only the inanimate but the animate world is largely under 

 his control. Man's influence over the brutes is not, be it noted, 

 one of mere personal mastery : he can mould both plant and 

 animal forms at will, namely, by modifying their environ- 

 ment and by artificial selection. For these reasons, if for no 

 other, the appearance of mature reason, such as we find it in 

 man, marks an important epoch in the history of evolution. 

 But two other noteworthy effects must be mentioned, and they 

 relate to man alone. (1) Reason being a far less perfect 

 guide than instinct, man, forsaken by the all-wise guide, but 

 too often finds himself plunging in the dark, and unwittingly 

 rushing into destruction. (2) Owing to the evolution of reason 

 in man, he is to a very large extent exempt from the opera- 

 tion of natural selection, and, inasmuch as this process is 

 continually weeding out the inferiors and securing the survival 

 of the fittest alone, the effect on the human race must be 

 injurious. I will consider the latter propositions presently. 

 Meanwhile, let us examine the former, namely — Reason is a 

 less perfect guide than instinct. 



conclusions is altogether correct. In the first place, the distinction above drawn, 

 between "chemico-physical nature" and the voluntary operations of the mind, 

 though useful, is arbitrary. Now that I have become better acquainted with 

 psychology, I cannot do otherwise than accept the doctrine of necessity, and 

 hence the sharp distinction I have drawn between a voluntary mental impulse 

 and a chemico-physical process does not exist. The apparently voluntary 

 efforts of the mind are nothing else than the expression of chemico-physical 

 nerve change, the "voluntariness" being a delusive creation of the mind. 

 It is quite obvious, in fact, that the doctrine of necessity is inconsistent 

 with my assertion that " with the evolution of reason we have a something 

 quite distinct from chemico-physical nature." Secondly, although doubt- 

 less there is some interference with the operation of natural selection among 

 men, I cannot doubt, on maturer thought, that natural selection here still 

 operates very potently, as I shall show hereafter. 



