REPRODUCTION, PUBERTY AND LONGEVITY. 243 



dent or war. The reason for doing this is that this is an investiga- 

 tion of natural heredity and not an investigation of accidents. The 

 other reason is that the children of large families appear to live 

 longer, on an average, than children of small families. This arises 

 from the fact that parents do not usually rear large families of 

 children living to become adults unless they themselves have con- 

 siderable stamina. 



INFANT MORTALITY. 



Another peculiarity of this investigation is that infant mor- 

 tality increases with the age of the parents and is greatest with the 

 ' last child produced. The last child of a large family is the most 

 variable in natural longevity. When he survives to be 25 or 30 he 

 usually lives to a great age. The elder children live more uniformly 

 to a moderate age. 



The reasons for these differences is that as long as parents 

 retain their full health and vigor the older they are the longer their 

 children will live, but if parents lose their health or fail in bodily 

 vigor, then the later children will live a less length of time than 

 their earlier children. In this examination of large families there 

 were found many cases in which the relationship between infant 

 mortality and the longevity of the children born nearest in point 

 of time to those who died in infancy showed very plainly the rise 

 and fall in health of parents, principally the mother. 



REVIEW OF EVIDENCE. 



From the foregoing facts it is quite evident that man, within 

 a few generations, may, if he chooses, bring about a delay in the 

 arrival at puberty, the result of which will be the elimination of 

 the least intelligent and most vicious, the raising of the intellectual 



