Heredity, race, and society.

  • Leslie Clarence Dunn
Date:
1947
Catalogue details

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

Credit: Heredity, race, and society. Source: Wellcome Collection.

    32/148 page 30
    other general still serves as a sergeant, or that he has become tired of army life altogether. Newman, Freeman, and Holzinger compared the mental abilities of twins by means of various intelli gence tests. On one of these I.Q. tests (Binet's) the average difference between one-egg twins reared to gether amounted to 5.3 points, but when they were reared apart the difference increased to 8.2 points. Two-egg twins reared together showed an average dif ference of 9.9 points. It follows that mental ability, though undoubtedly influenced by heredity, is less fixed and more liable to modification by environment than most physical traits. In different achievement tests, sup posedly measuring educational performance, the role of environment proved to be greater still. The Stanford achievement test showed the average difference between one-egg twins reared apart to be even greater than that between two-egg twins reared together. In spelling, the one-egg twins were more alike than the two-egg ones, while in arithmetic environment was much more im portant. In tests of motor ability and emotional balance, environment assumed the major role, more than half of the differences between twins being due to experi ence, training, and other environmental factors and less than half to heredity. It must also be pointed out that the environments of the separated twins studied by Newman, Freeman and Holzinger were not very different. The twins were reared in the same country and generally in a similar class of society and exposed to the same educational system. We do not know how different the twins might have been if one of them were to grow up, say, in a city slum and the other in surroundings of comfort and refinement; or else, if one were to grow up in an American town and the other in a tribe of Asiatic nomads. In fact, where the differences in living condi tions were most marked, real differences in personality, in scores on mental tests, and in educational achieve ment did develop among the twins actually examined, while their physical traits remained closely alike.
    digitised image 1
    digitised image 2
    digitised image 3