192 THE CAUSATION OF DISEASE. 



There can be no doubt that the above propositions of Spencer 

 are in the main correct. Man will advance in the future 

 chiefly by a process of direct equilibration. Nevertheless, 

 natural selection plays a very important part, even in the case 

 of civilized man — a part, too, which, viewed from a pathological 

 standpoint, is of the utmost iiuportance. It demands, there- 

 fore, our serious study. 



In 1 8 8 1 I read a paper at the Abernethian Society * on 

 "Instinct and Reason," wherein I had occasion to draw 

 certain contrasts between man and the dumb animals, and one 

 of these was founded on the very small part played by natural 

 selection among men as compared with the brutes. On re- 

 considering the subject, after fuller investigation, I have found 

 that my conclusion was immature, but I propose here to give 

 certain extracts from the paper, because, in the first place, I 

 shall thereby avoid having to deal separately with " Instinct 

 and Reason," a subject closely connected with the causation of 

 disease ; and, in the next place, because this proceeding will 

 serve to emphasize certain important facts. 



The grand purpose of instinct and reason is to place the 

 individual in proper connection with the outer world. They 

 are both the outcome of nervous action, and it is interesting 

 to note that the nervous system develops from the epiblast or 

 outer part of the ovum, thus clearly showing that its first and 

 primordial function was to regulate the relations of the indivi- 

 dual with the outer world. 



Put scientifically, we may say that the essential purpose of 

 instinct and reason is to regulate the E of the individual, to 

 surround him by such conditions as are best suited to his 

 existence. No doubt reason — I use the term in its widest 

 sense, to include all the higher faculties of the mind — has 

 advanced to a stage altogether beyond this ; but its essential 

 function is, and ever will be, to regulate the environment of 

 the individual, whether he be a Shakespeare or only "common 

 clay." 



Every animal, indeed, every organism, has its particular E. 

 * St. Bartholomew's Hospital. 



