H2 SEX AND HEREDITY 



discovery has done, and which should be the chief aim 

 of all scientific investigations of heredity, they possess 

 the great practical importance of emphasising the dangers 

 and possibilities which beset the human race. 



Infirmity and disease are so common among civilised 

 man that we have come to look upon them as part of the 

 order of nature. Under conditions more natural in 

 regard to natural selection, however, these afflictions 

 would not have the chronic influence in our lives that they 

 have at present. When a wild animal falls ill it generally 

 either makes a quick recovery or dies. Thus the deformed 

 and unfit, and those which are less resistant to disease, 

 die off more rapidly, and therefore leave fewer offspring 

 to inherit their weak constitution and poor powers of 

 resistance than do the more fit animals. 



In this way the power of resisting disease is maintained 

 and increased under a state of nature ; but in the case of 

 man, and especially civilised man, humane considerations 

 coupled with medical science keep alive large numbers 

 of those who under natural conditions would perish, 

 and thus the evolution against disease is impeded or even 

 altogether suspended. 



Now it cannot be denied that this is a very grave state 

 of affairs. Indeed it is doubtful whether any other 

 factor will affect more the welfare of the human race in 

 the future, and it is considerations such as these which 

 lead Eugenists to advocate the policy of a partial control 

 of the birth-rate, preventing the multiplication of the 

 obviously unfit (for example, the insane or feeble-minded) 

 and encouraging a high birth-rate among the vigorous 

 and intelligent. 



The fact that the birth-rate in this country (as in all 

 the highly-civilised ones) is diminishing has been so 



