THE CAUSATION OF DISEASE. 247 



Our giant city affords an example of Social Evolution 

 pushed to the farthest limit yet attained, but at what a cost to 

 individual health ! Government is careful to educate the 

 rising generations of Londoners, oblivious of the fact that it 

 is educating a race which is continually travelling towards 

 extinction. Herbert Spencer, with his marvellous power of 

 detecting similarities, has likened a society to an animal or- 

 ganism. London is such an organism : as this process of ex- 

 tinction proceeds among its various family units, a fresh 

 stream of healthy country blood continually pours in to replace 

 them, and thus the great monster is kept alive. 



We have seen that the central parts of large towns neces- 

 sitate an E which is incompatible with the survival of more 

 than two or three generations of the same family, and that 

 the population of such towns is kept up by the continued influx 

 of healthy country-bred people. Some maintain that the 

 same argument applies with equal force to the modern American 

 race — that it, too, is only prevented from extinction by the 

 continued inpouring of fresh European blood. According to 

 this view, the E, as determined by the conditions of American 

 climate and society, is necessarily fatal to Europeans. Be 

 this as it may, there can be no doubt that the American, in 

 certain of the States, is undergoing a profound change, and it 

 is quite clear that this modification is not due to natural 

 selection, but to the action of E upon S, irrespective of any 

 selective process — i.e., by direct equilibrium. It must be remem- 

 bered the United States are of large extent, and that the E 

 •differs very much in different parts. In certain States the 

 immigrated European is undergoing marked deterioration, and 

 in these, I take it, the E is necessarily fatal, so far as the 

 'European is concerned ; but this is by no means true of all 

 parts of the country ; and it would be easy to find many where 

 the inhabitants are strong and vigorous. 



I may refer to one other example of necessarily fatal E. It is 

 well known that when the white man takes up his abode in an 

 uncivilized country the aborigines generally become extinct. In 

 certain cases, doubtless, they are actually destroyed by violence 

 or oppression, but it also very often happens that extinction 

 results from the inability of the aborigines to adapt themselves 



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