278 PROBLEMS OF HUMAN EVOLUTION 



of births would in process of time lead to a physiological 

 limitation, since the fertility of a race is maintained only through 

 the fact that in each generation the offspring of prolific parents 

 outnumber the offspring of the less prolific. When this is 

 prevented, the race must lose its power of rapid multiplication. 

 This necessarily follows if we assume that fertility is hereditary. 

 The matter will be perfectly clear if we take an extreme case. 

 Let us imagine six married pairs, three of which under natural 

 condition's would have each two children, while the other three 

 would each have ten. In this case five-sixths of the younger 

 generation would be the offspring of fertile mothers. But if 

 through artificial restriction the number of children is limited 

 to two, then only half of the next generation will be sprung 

 from a fertile stock. And thus a physiological limitation will 

 follow in the wake of an artificial one. 



IX 



POSSIBLE MEANS OF CHECKING DEGENERATION 



improve- In the last resort there seems to be no means of improving a race 

 onditions exce P t selection. The improvement of the environment so that 

 not a real the component individuals may attain their full development is a 

 remedy Different matter. And if we wish to think clearly on the subject, 

 it is important to keep the two quite distinct. Practically a great 

 deal remains to be done that would tend towards what would in 

 popular language count as race improvement. In particular an 

 enormous gain in vigour would result from an improvement in 

 the health of mothers. During pregnancy the mother is the 

 child's entire environment. It is only through her that he comes 

 into contact with the world. He may be described as parasitic 

 upon her, receiving, as he does, food that has already been 

 assimilated. Even respiration is done for him, since he is 

 nourished with blood that has already been oxidised. It follows, 

 then, that the health of the mother is of supreme importance dur- 

 ing pregnancy. During this time the child may gain or fail to 



