PRACTICAL CONSIDERATIONS 307 



tend continually to be " weeded out," and the standard of fitness 

 is thus kept from falling rapidly. When predispositions to 

 specific diseases accumulate [e.g. by in-breeding of similars), a 

 non-viable, sometimes a non-reproductive, type arises, and — 

 disappears for ever. Rotten twigs are always falling off the 

 tree of life. There is a continual irrecoverable precipitation of 

 incapables, who thus cease to muddy the stream. 



But while this is true, every one is aware that man is so 

 constituted that he cannot submit to Nature's winnowing. 

 For reasons that go to the very foundations of our social frame- 

 work, we can neither act as Spartan eliminators ourselves nor 

 allow Nature to have her way. That this does not prevent us 

 from being perhaps more cruel than either, is to be gravely 

 feared, but, in any case, the fact is that we consistently try to 

 conserve lives which natural selection would eliminate. This 

 may be for social reasons necessary, but it cannot be regarded 

 with satisfaction unless it is associated with positive selection of 

 the fitter types. 



It has often been said that modern hygiene, in tending to 

 eliminate our eliminators — the microbes — is destroying a most 

 valuable selective agency which has helped to make our race 

 what it is. This seems a Httle like saying that the destruction 

 of venomous snakes in India is eliminating a most valuable 

 selective agency which has helped to evolve the Wisdom of the 

 East. 



It is difficult to find justification for the enthusiastic confidence 

 which some seem to have in the value of microbes as ehminators. 

 Which microbe ? . Surely not that of plague, which strikes in- 

 differently, and is no more discriminatively selective than an 

 earthquake. Surely not that of typhus, which used to kill weak 

 and strong alike. Surely not that of typhoid, which may strike 

 anyone, and does not confer more than a passing immunity. 

 And so on through a long list. 



It would perhaps be a subtler and more convincing line of 



