Evolutionary genetics / edited by D.L. Jameson.

Date:
[1977], ©1977
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Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Evolutionary genetics / edited by D.L. Jameson. Source: Wellcome Collection.

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    W. Weinberg daily habits. Thus the family history of diabetics and those suffering from gout (arthritis) does not implicitly demonstrate that these diseases have a genetic foundation. The influence of the external conditions of life on the mentally ill has been too little studied, although outer conditions are probably over valued in the case of tuberculosis. For all these diseases a genetic influence can be recognized only insofar as it involves a hereditary factor whose character is not yet known, and also only insofar as more than a familial burden remains even after excluding the influence of age and external conditions. In order to make this possible for tuberculosis patients I have compared the incidence of tuberculosis in affected persons with those of their spouses. I found familial evidence of tuberculosis among affected individuals to be 507o higher than in their spouses. Furthermore, familial evidence was 1007o higher for affected individuals within the group of well off persons. A certain inbreeding among tuberculosis patients is a necessary result of a definite, if not strong, effort on the part of the healthy to avoid marriage with affected individuals. Thus my figures representing the relative familial burden of tuberculosis may be too low, and for the same reason the incidence of mortality from phthisis among spouses of tuberculosis patients, which I also determined, may be too high. I hope that my remarks have now provided a picture of the difficulties encountered in deter¬ mining and evaluating the influence of pathological inheritance in man. Those characteristics whose inheritance is or seem more or less linked to a certain sex are of particular interest for the theory of heredity. Colorblindness and hemophilia belong in this group. According to the literature to date, both diseases are many times more common among men than women, who play an essential role in the hereditary transmission from grandfather to grandson. But recently some doubts have arisen, at least with regard to color blindness, whether it is not significantly more common among women than has been previously believed. It is now particularly recom¬ mended that school physicians look for it in their examinations. And one should not exclude the possibility that colorblindness among men is more frequently discovered precisely because it disturbs them in their occupations. Such demonstration would complicate the interpretation of colorblindness to the extent that in this case the question would no longer solely concern the carrier. Hemophilia is also not entirely limited to the male sex. And even here it might be asked whether men - in consequence of their professions and different modes of life - more frequently give the disease opportunity to become manifest. In contrast to these diseases, the ability to bear twins from two ova represents a trait in which man plays only the role of agent of transmission. According to my investigations (begun over 7 years ago), it is clear that this characteristic is inheri¬ table, just as Darwin assumed, although only on the basis of casuistic interpretation. For at least a portion of the mothers of non identical twins this trait is linked to a particular con¬ struction of the ovaries. Consequently the abundance of eggs 119