CHAPTER XII 



THE ARGUMENT FROM DISEASE 



The Lamarckian doctrine is certainly untrue It is equally untrue that 

 hereditary tendencies may be easily changed by the direct action of 

 external forces Professor Cossar Ewart's observations. 



261. JUDGED, then, by the test of racial change in relation 

 to disease, both the Lamarckian doctrine and the belief that 

 the environment acting directly on the germ-plasm is the 

 cause of variation would seem mistaken. The Lamarckian 

 doctrine, indeed, is certainly and obviously erroneous. The 

 very clinical evidence on which it is supposed to rest is 

 founded partly on a misuse of terms and partly on an abuse 

 of logic. Diseases acquired by the foetus in utero are spoken 

 of as congenital with the meaning implied that they are in- 

 born. Post hoc is confused with propter hoc. The exception 

 is supposed to prove the rule. Common experience is ignored, 

 and rare coincidences are given the evidential rank of regular 

 consequences. But the plain fact that diseases like tuber- 

 culosis do not render races degenerate, nor diseases like 

 measles render races immune, is decisive testimony that 

 acquirements are not even faintly -and fitfully transmitted. l 



262. The Lamarckian doctrine is not only untrue, it is 

 inherently improbable. But the doctrine that variations 



1 Formerly all the world believed in the transmission of acquirements, 

 and consequently all the world was constantly finding " conclusive " 

 evidence of its constant occurrence. To-day there is hardly a rag 

 of that evidence left ; and, with rare exceptions, only certain French 

 medical observers are able to discover fresh evidence. It is a remarkable 

 fact, however, that the problem of evolution of adaptation has excited 

 singularly little interest in France, and it is equally curious that these 

 French observations relate almost entirely to laboratory work which it 

 is not easy to repeat. In Great Britain or Germany, you may cut off 

 the tails of a thousand dogs, or amputate the limbs of a thousand men, 

 or observe the non-infected offspring of a thousand tuberculous patients, 

 and get no evidence of transmission. 



157 



