THE NATURAL HISTORY OF MAN 35 



more resistant to it. Moreover, since resisting 

 power against one disease does not imply resisting 

 power against any other, for example, since resisting 

 power against consumption does not imply resisting 

 power against malaria, every race should grow 

 resistant only against the particular death-dealing 

 diseases by which it is afflicted. 



Now there are some diseases, of which consump- 

 tion is an example, against which no resisting powers 

 can be acquired. One attack of consumption, the 

 most death-dealing of all diseases, weakens rather 

 than strengthens, against subsequent attacks. If, 

 therefore, the acquired effects of disease were 

 transmissible, races afflicted by tuberculosis should 

 grow less and less resistant to it. The exact 

 opposite is true. For very many centuries consump- 

 tion has ravaged the Old World, especially such 

 crowded parts of it as England. But Englishmen 

 now increase and multiply in cities and towns, the 

 natural breeding-places of consumption ; whereas, 

 under like conditions, the inhabitants of the New 

 World, where consumption was unknown until 

 recently, perish. When infected with consumption 

 by white men they tend to extinction everywhere, 

 even in rural districts. Plainly there has been great 

 evolution, but as plainly it has resulted solely from 

 the survival of the fittest, not in the least from the 

 transmission of acquirements. On the other hand. 



