222 SCIENCE AND IMMORTALITY 



animal can he change his habitat, his food, his 

 clothing, according to his needs ; and this power 

 he possesses of choosing and arranging his environ- 

 ment prevents environment from freely choosing 

 and arranging and varying him. 



Further, the multitudinous and interrelated 

 nature of his adaptations render improbable the 

 perpetuation of any single corporeal variation, 

 and make for the stability of the species. The 

 chief factors in modern life of much evolutionary 

 force are microbes and marriage : microbes, as a 

 selector of obscure variations ; marriage, both as a 

 producer and selector of variations. These two 

 factors it is which will make the man of the future, 

 and their selection probably will not much affect 

 the present physical type of man. 



Let us look first at microbes. 



Nature, as we have seen, has brought man's 

 body so far into correspondence with its environ- 

 ment that it is difficult to see how it can be much 

 further evolved ; but in one respect it is certainly 

 still lacking — it has little or no power to resist 

 certain microbes of disease ; and probably during 

 the next few thousand years breeds of men will 

 be evolved, by the weeding out of the vulnerable, 

 which will be immune to certain microbic diseases. 

 Already such a process of immunisation by selec- 

 tion has commenced. We find, for instance, among 



