The study of twins / Peter Mittler.

  • Mittler, Peter J.
Date:
[1971]
Catalogue details

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

Credit: The study of twins / Peter Mittler. Source: Wellcome Collection.

    29/196 (page 27)
    2 Twins as Individuals Until recently, twins have been used as pawns in the nature- nurture controversy to the neglect of more serious study of their individual psychological characteristics, or, with few exceptions, of the psychology of the twin pair. The few studies which have considered twins as individuals rather than as members of a pair have consistently indicated that they are anything but a typical sample of the population either biologically, intellectually or educationally. Before considering the contribution of twin studies to our know¬ ledge of human behaviour genetics, we must obviously con¬ sider the justification, both logical and psychological, of attempts to estimate the contribution of genetic factors in the normal population from studies based on samples of twins who may be atypical in respect of the characteristic being studied. Intellectual differences Although most studies concentrate on comparisons of identi¬ cal and fraternal pairs (Erlenmeyer-Kimling and Jarvik, 1963), very few have compared the mean scores of twins with those that might be expected in the general population. Evidence from several studies, however, indicates that twins achieve below average scores on intelligence tests. Merriman (1924), Wingfield (1928) and Lauterbach (1925) all reported IQs of around ninety-five on the 1916 version of the Stanford-Binet test, but three important studies will now be more fully discussed; the Scottish mental survey (Scottish Council for Research in Education, 1953), the French national study (Zazzo, 1960) and Koch's (1966) study of ninety-six five- and six-year-old twin pairs in Chicago.