ACCLIMATIZATION 263 



capacity of making the acquirement, of recovering from infection. 

 On the other hand, races that have been exposed to non-lethal 

 diseases (e.g. chicken-pox), are neither more nor less resistant, 

 neither more nor less degenerate than races that have had no 

 previous experience of them. Apparently they are in no way 

 changed. The sufferings of races have not altered them at all. 

 Only the elimination of the un fittest has altered them. 



436. Clearly both the Lamarckian doctrine of the transmission 

 of acquirements and the doctrine that variations are normally 

 caused by the direct action of the environment on the germ-plasm 

 are erroneous. The theory that the mass of variations are spon- 

 taneous is just as clearly correct. Only in that case can Natural 

 Selection, the actuality of which as regards disease is obvious to 

 every observer, have produced the particular racial changes that 

 have resulted. We constantly speak of the acclimatization of an 

 individual or a race. As applied to individuals, the term is a 

 synonym for use-acquirement, for protective development, for a 

 becoming accustomed or habituated to the new conditions a 

 habitation which may be ' active ' (i.e. due to recovery from actual 

 disease), or ' passive ' (i.e. due to experience of microbes and toxins 

 in doses too small to cause disease). As applied to races, it is a 

 synonym for protective evolution, which, in the case of diseases 

 against which immunity cannot be acquired, implies the increase of 

 a power of resisting infection, and in the case of diseases against 

 which immunity can be acquired, implies the increase of a power 

 of recovering from infection and resisting it subsequently. When 

 we talk of the deadly climate of West Africa and the healthy climate 

 of England, we think only of ourselves. Not less deadly to the 

 African negro, to whom the West Coast is healthy, is the climate 

 of London with its prevalent tuberculosis. To the Polynesian or 

 Red Indian, whose race has had even less experience of this disease, 

 a residence in any one of our great cities is usually equivalent to a 

 sentence of death. 



437. All educated men know more or less clearly that every 

 race that has long dwelt in any environment is especially well 

 adapted to the conditions of that environment, including its 

 diseases. Medical men share this knowledge. But most doctors 

 believe a/so that races tend to deteriorate when exposed to injurious 

 conditions. The two beliefs are utterly incompatible, and afford a 

 good example of the confusion of thought that arises when the 

 duty of making a rigorous deductive inference of consequences 

 is neglected. The latter belief (that variations are commonly 



