NATURAL SELECTION IN MAN 



FEW people show any hesitancy in 

 accepting the idea that Natural 

 Selection is constantly at work 

 among plants and the lower 

 animals, weeding out the weak and 

 unfit, and allowing only those to survive 

 who are by heredity adapted to survive 

 in their own particular environment. 



But when the same doctrine is applied 

 to man, a great many persons have 

 hesitated. It was something of a shock 

 to them to admit that the death of a 

 friend or relative might be due to 

 unfitness to survive. 



The biologist could accept the applica- 

 tion of natural selection to man without 

 hesitation, but many others felt that 

 they required proof, before they could 

 open their minds so far. 



It has therefore been a chosen 

 task of Professor Karl Pearson, of the 

 University of London, and his school of 

 biometricians, to bring together mathe- 

 matical proof of the operation of natural 

 selection in man. 



Pearson's first contribution to the 

 subject, some twenty years ago, was 

 in the form of a study of the inheritance 

 of longevity. He found, to put the 

 case very briefly, that there was a close 

 connection between length of life in 

 parent and length of life in child; and 

 from this fact, demonstrated in various 

 strata of the population, he was able 

 to draw the conclusion that about two- 

 thirds of all the deaths that occur 

 nowadays, are due to natural selection: 

 they are the deaths of those who, 

 through heredity, were not able to 

 survive in their environment. 



The rest of the deaths must be set 

 down to random causes. If a man is 

 struck by a moving train, for instance, 

 it is evident that his hereditary make-up 

 will have little to do with his chances of 

 survival. 



It should be noted that we can not 

 blame environment too much for deaths 

 which we credit to natural selection. 

 It is not wholly that the environment 



was bad. Dr. Alfred Ploetz, of Munich, 

 investigated the royal families of Europe, 

 where the environment may be fairly 

 supposed to be as good as possible for 

 every child, and found that even there 

 60% of all the deaths were due to 

 heredity. 



It shoLild further be noted that when 

 we ascribe a death to heredity, we do not 

 necessarily mean a congenital defect 

 in the ordinary sense of the term. A 

 congenital lack of resistance to some 

 specific disease is equally a matter 

 of heredity, and is often a cause of 

 death. 



INFANT MORTALITY 



In 1911 Dr. E. C. Snow published the 

 results of an investigation on the 

 infant mortality of parts of England 

 and Prussia, in which he showed that a 

 high death rate during infancy was 

 followed by a low death rate during 

 childhood, in the same group; and vice 

 versa. Here was another evidence of 

 the work of natural selection: Nature 

 was weeding out the weakest, and in 

 proportion to the stringency with which 

 she weeded them out at the start, there 

 were fewer weaklings left to die in the 

 succeeding years. 



Evidence from another source was 

 published by Pearson in 1912. He 

 dealt with material analogous to that of 

 Snow, and showed ' ' that when allowance 

 was made for change of environment in 

 the course of fifty years, a very high 

 association existed between the deaths 

 in the first year of life and the deaths in 

 childhood (1 to 5 years). This associa- 

 tion was such that if the infantile 

 death rate increased by 10% the child 

 death rate decreased by 5.3% in males, 

 while in females the fall in the child 

 deathrate was almost 1% for every rise 

 of 1% in the infantile death rate." 



To put the matter in the form of a 

 truism, part of the children born in any 

 district in a given year are doomed by 

 heredity to premature death; and if 



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