70 WARFARE IN THE HUMAN BODY 



compensated for. Is there any reason for believing that 

 variation in the structure of living organisms follows 

 exactly the same principle ? Are we entitled to say that 

 the mammal, for instance, with all its complexity, is the 

 result of infinite ages of functional failure or disease which 

 was met by processes of repair and reaction ? In a word, 

 can we speak of the evolutionary value of disease, of im- 

 paired function, of disadvantageous variations ? It seems 

 possible to do so, if what is true of one structure is roughly 

 true of another. 



It may seem absurd to talk of the value of dis- 

 advantageous variation; but it is no more absurd than 

 to imply that all variation is advantageous because it is 

 perpetuated. What is useful at one period may be harmful 

 at another, and embryologists thoroughly understand that 

 developments useful in fcetal or larval life may open up 

 many dangers for the adult. The real point to be con- 

 sidered is whether organisms as a species do not vary and 

 run great, even largely destructive, risks by an increased 

 pressure of function which, in the few that finally react, or 

 whose descendants react, to such stress, results at last in 

 structure that is advantageous as altered. The given 

 variation in itself may be a failure of what was normal 

 function in the species, and we should therefore as patho- 

 logists or physiologists speak of it as a disease ; but if 

 the few that recover become a new species, a mended race, 

 it is no longer disease. After many generations it may be 

 truly advantageous to individuals. Have such processes 

 occurred in the evolution of organisms, as they undoubtedly 

 have in the arts and social progress, where we often observe 

 political failure of organization result in ad hoc reaction 

 which leads to a changed social form ? I have no doubt 

 that they do, and many organs in mammals, to speak only 



