Читать книгу Applied Eugenics - Paul Popenoe - Страница 11
Fig. 3.—An unusually short and an unusually tall man, photographed beside extreme varieties of corn which, like the men, owe their differences in height indisputably to heredity rather than to environment. No imaginable environmental differences could reverse the positions of these two men, or of these two varieties of corn, the heredity in each case being what it is. The large one might be stunted, but the small one could not be made much larger. Photograph from A. F. Blakeslee.
ОглавлениеThis has actually been done,[6] and none of the conditions enumerated has been found to be closely related to myopia in school children. Correlations between 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 common heredity coefficient of .51.
Does this prove that the myopia is rather due to heredity? It would, by a process of exclusion, if every conceivable environmental factor had been measured and found wanting. That point in the investigation can never be reached, but a tremendously strong suspicion is at least justified. Now if the degree of resemblance between the prevalence of myopia in parents and that in children be directly measured, and if it be found that when the parent has eye trouble the child also has it, then it seems that a general knowledge of heredity should lead to the belief that the difficulty lies there, and that an environmental cause for the poor vision of the school child was being sought, when it was all the time due almost entirely to heredity. This final step has not yet been completed in an adequate way,[7] but the evidence, partly analogical, gives every reason to believe in the soundness of the conclusion stated, that in most cases the schoolboy must wear glasses because of his heredity, not because of overstudy or any neglect on the part of his parents to care for his eyes properly during his childhood.
WHY MEN GROW SHORT OR TALL
