INHERITANCE IN MANKIND 53 



are yet available to determine how many of our paupers 

 are made so by circumstances and how many are un- 

 employable by nature. In some cases, such, for instance, 

 as the number who suffer from a zymotic disease like 

 enteric fever, the main influence must probably be 

 assigned to environment. On the other hand, we 

 should expect the incidence of deaf- mutism to be 

 almost entirely hereditary. But often there are no 

 reasons for looking for an overwhelming effect of 

 one of these influences rather than of the other, and 

 we have no evidence available for comparing their 

 results. 



The only quantitative study yet published of the 

 comparative influence of heredity and environment 

 seems to be the work of Harrington and Pearson on 

 keenness of vision and defects of eyesight. Here we 

 have a character which we might expect to be influenced 

 profoundly both by inheritance and by surroundings. 

 We should expect visual powers to be innate to some 

 extent, but to be affected largely by the surroundings 

 and occupations of childhood and youth. 



The Edinburgh Charity Organization Society has 

 published a report on the physical condition of fourteen 

 hundred school children in the city, together with an 

 account of their homes and surroundings. From this 

 report it is possible to examine the correlation of the 

 children's eyesight with the condition of their homes. 

 From an elaborate statistical investigation, it appears 

 that no measurable relation exists between powers of 

 vision and environment overcrowding, extreme 

 poverty, immoral surroundings, were equally without 

 effect. 



