Mendelism and the problem of mental defect / by David Heron.

  • Heron, David
Date:
1913
Catalogue details

Licence: In copyright

Credit: Mendelism and the problem of mental defect / by David Heron. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    50/68 page 46
    Mating. Percentages of Defectives. Expected. High and low grades together. Low grade only. 1. DD X DD 0 0 0 2. DD X DR 0 0 2*7 3. DD X RR 0 37.5 14-3 4. DR X DR 25 33-2 30-7 6. DR X RR 50 53-6 33-7 6. RR X RR 100 77-3 52-6 Now it should be noted that the number of matings included in each group is not given nor are the numbers of offspring on which the percentages are based, and the actual matings are stated in only a few instances where it is necessary to explain away exceptional cases, and even these serve merely to show that either the description of the Hill folk, or the charts, or both, are inaccurate.' This is particularly unfortunate in groups 1,2, and 3, involving the mating of duplex (HD) individuals, since the authors seem unaware that it is not possible to assert definitely that any individual is duplex. Thus, those three groups must be rejected. In the same way groups 4 and 5 should be confined to cases where those who are classed as simplex (DR) have each one nulliplex (RR) parent. The sixth group thus provides the crucial test, and it is unfortunate that the numbers given do not agree with those found for the charts. Thus the authors state that 52’6 per cent, of the children of two low grade feeble-minded parents are ‘ defective ’, but on examining the charts we find only 9 matings of this kind, showing 19 classified children, 7 low grade feeble-minded, 7 high grade feeble-minded, 1 alcoholic, 1 epileptic, and 3 normal. No combination of these groups gives 52-6 per cent, of defectives. The authors’ own figures, however, show that there is no approach to the theoretical Mendelian 100 per cent., and they therefore throw overboard the statement, repeated by Dr. Davenport and his collabora- tors in so many publications, that two feeble-minded parents have only feeble-minded children, and proceed to invent a new theory. They state (p. 11): ‘The analysis of the data, then, gives statistical support to the conclusion abundantly justified from numerous other considerations, that feeble-mindedness is no elementary trait, but is a legal or sociological, rather than a biological term. Feeble-mindedness is due to the absence, now of one set of traits, now of quite a different 1 See, for instance, the mating ol A. III. 39, and C. III. 42 above.
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