CHAPTER XXXI 



PHYSICAL AND MENTAL INHERITANCE IN MAN 



The same laws govern inheritance in man as in other animals 

 and in plants, but our knowledge of human heredity is less 

 accurate than that of animals and plants, because we are in 

 the human field debarred from experiment. The best we 

 can do is to observe and compare the traits of individuals in 

 successive generations and thus to ascertain with what known 

 laws of heredity these cases best agree. For the discovery of 

 new laws of heredity, human data can have little value be- 

 cause of our inability to experiment. Nevertheless the inter- 

 est in human heredity is so general and the number of 

 competent observers so large, including as it does a great 

 many physicians and other men of science, that we may look 

 forward to a very complete cataloguing of human heredity 

 as fast as general categories of inheritance phenomena are 

 established by the experimental study of other organisms. 

 Already we have in hand a great amount of material bearing 

 on human heredity, gathered chiefly by medical men, much 

 of it within the last fifteen years. A considerable part of this 

 is unreliable because of the careless or biased way in which it 

 has been gathered, or the uncritical treatment which it has 

 received in publication. But still there remains a consider- 

 able body of valuable infonnation, which shows that man is 

 subject to heredity in every aspect of his physical and 

 mental make-up. 



Two comprehensive attempts have been made to gather 

 and analyze data concerning human inheritance, one in Eng- 

 land at the Eugenics Laboratory of the University of London, 

 founded by Galton and presided over by Karl Pearson, the 

 other and more recent one at the Eugenics Record Office, 

 Cold Spring Harbor, New York, directed by Dr. C. B. 

 Davenport. Pearson's data are recorded in the " Treasury 



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