The biology of mental defect / by Lionel S. Penrose ; with a preface by J.B.S. Haldane.

  • Penrose, L. S. (Lionel Sharples)
Date:
[1954]
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: The biology of mental defect / by Lionel S. Penrose ; with a preface by J.B.S. Haldane. Source: Wellcome Collection.

    47/342 (page 29)
    INCIDENCE, DEFINITION AND MEASUREMENT 29 testing. As Thomson (1939) has repeatedly pointed out, it is the simplest assumption to make, but it is not the only explana¬ tion and probably not the correct one. The skill with which mental tasks are performed is due to a large number of small causes, some environmental and some hereditary. In discussing general intelHgence we must remember that its existence is only a convenient hypothesis. The facts are the test scores. To be precise, we should only speak of ability of each subject on a given test and not of his intelligence level. CULTURAL DIFFERENCES IN INTELLIGENCE The concept of general intelligence tends to become strained when people with very different cultural backgrounds are com¬ pared. The traditional idea of separating mankind into con¬ stituent races each endowed with a particular set of mental qualities has received little support from the findings of modem genetical research. Qualities known to be determined genetically are distributed throughout all groups of mankind. The question of distinguishing races genetically has been resolved into the identification of the same genes in different populations. The populations are then distinguished by differences in gene fre¬ quencies. The A.B.O. series of inherited antigens shows marked gene frequency differences in populations all over the world, but the M.N. types are more evenly distributed. No quahties have been found to occur in every member of one racial group and in no member of another. The differences between races in respect of measurable qualities are often found to be much less than might be commonly supposed. Morant (1939), for example, showed that differences between means of physical measurements among the so-called European races were small and often statistically negligible. Few people have attempted to justify Langdon Down's (1866) scheme for the ethnological classification of idiots. The clinical entity of mongolism was described, but it had nothing to do with racial MongoHans. Microcephalics were thought to be related to an Aztec race. A rather indefinite negroid type was included in the list, to which Davenport (1944) has recently drawn attention, and also a Malayan type. A tendency sometimes has appeared in modem times to reverse the direction of Down's philosophy and to suggest that