2v^2 



The Journal of Heredity 



in school children. Correlations be- 

 tween fifteen environmental conditions 

 and the goodness of children's eyesight 

 were measured, and only in one case 

 was the correlation as high as .1. The 

 mean of these correlations was about 

 .04 — an absolutely negligible quantity 

 when compared with the heredity 

 coefficient of .51. Does this prove 

 that the myopia is rather due to hered- 

 ity '1 It would, by a process of exclusion, 

 if we could be sure that we had measured 

 every conceivable environmental factor 

 and found it wanting. We can never 

 reach that point in the investigation, 

 but we have at least reached, it seems 

 to me, a tremendously strong suspicion. 

 Now if we go on and measure the degree 

 of resemblance between the prevalence 

 of myopia in parents and that in chil- 

 dren, and if we find that when the 

 parent has eye trouble, the child also 

 has it, then it seems to me that our 

 general knowledge of heredity should 

 lead us to believe that we have put our 

 finger on the difficulty, and that we 

 were seeking an environmental cause 

 for the poor vision of the school child, 

 when it was all the time due almost 

 entirely to heredity. This final step 

 has not yet been completed in an 

 adequate way,^ but the evidence we 

 have, partly analogical, gives every 

 reason to believe in the soundness of the 

 conclusion I stated, that in most cases 

 the school-boy must wear glasses because 

 of his heredity, not because of over- 

 study or any neglect on the part of his 

 parents to care for his eyes properly 

 during his childhood. 



I have exi:)laincd this case at some 

 length, so you might understand clearly 

 the way in which we have i^roceeded 

 tf) pile up mathematical jjroof of the 

 prejjonderating importance of heredity 

 as com]mred with environment. I shall 



now run over several similar cases more 

 hastily. 



INTELLIGENCE OF SCHOOL CHILDREN 



The extent io which the intelligence 

 of school children is dependent on 

 defective physique and unfavorable 

 home environment is an imi:)ortant 

 practical question, which David Heron 

 of London attacked by the methods I 

 have outlined. He wanted to find out 

 whether the healthy children were the 

 most intelligent. We are constantly 

 hearing stories of how the intelligence 

 of school children has been improved 

 by some treatment which im])roved 

 their general health, but these stories 

 are rarely presented in such a way as to 

 constitute evidence of scientific value. 

 We wanted to know what exact measure- 

 ment would show : whether it was really 

 possible that the dullards became prodi- 

 gies as soon as their adenoids were 

 removed, whether hot lunches ' really 

 increased the brain jjower, and so on. 

 The intelligence of all the children in 

 fourteen schools was measured in its 

 correlation with weight and height, 

 condition of clothing and teeth, state 

 of nutrition, cleanliness, good hearing, 

 and the condition of the cervical glands, 

 tonsils and adenoids. It- could not be 

 found that mental capacit\' was closely 

 related to any of the characters dealt 

 with. The rather curious set of char- 

 acters measured was taken because it 

 happened to be furnished by data 

 collected for another purpose; the vari- 

 ous items are suggestive rather than 

 directly conclusive. Here again, the 

 correlation in most cases was less than 

 .1, as compared with llic heredity 

 correlation of .5. 



Next, take the very com])lex subject 

 of tuberculosis. Certainh- we would not 

 sav that it is inherited, ])ut there is 



^ Dr. James Al'-'xandiT Wilson, assistant .surgeon of the Optlialmie Institute, Glasgow, pub- 

 lished an finalysis of 1,.S00 cases of myopia in the British Medical Journal, p. 395, August 29, 

 1914. His methods are not above criticism, and too much imjjortance sliould not be attached 

 to his results, which show that in 58'/f, of the cases heredity can bv credited with the myojiia of 

 the i)atient. In 12% of the cases it was due to inflammation of the cornea (keratitis) while in 

 the remaining .^0% no hereditary influence could bi' proved, but various reasons made him feel 

 certain that in many cases it existed. The distribution of myopia l)y trades and ])r()fessions 

 among his j)atients is suggestive: 65% of the cases among scliool children sliowed myopic 

 heredity, M'/'o among housewives and domestic servants, 6S'^ among shoji and factory workers, 

 60% among clerks and typists, 60% among laborers and miners. If environment really played 

 an active part, one would not expect to find this i-imilarity in percentages between laborers and 

 clerks, between h(jusewives and school children, etc. 



