The study of twins / Peter Mittler.

  • Mittler, Peter J.
Date:
[1971]
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Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

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

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    84 Cognitive Processes Despite these difficulties, comparisons of separated and non-separated twins do reveal some fairly consistent trends, which cannot be explained away as sampling arte¬ facts. These are conveniently illustrated by Jensen (1969) with a simple graph based on the median correlations re¬ ported by Erlenmeyer-Kimling and Jarvik (1963). degree of relatioriship Figure 3 Median values of all correlations reported in the literature up to 1963 for the indicated kinships (after Erlenmeyer-Kimling and Jarvik, 1963). Note consistency of difference in correlations for relatives reared together and reared apart Source: Jensen (1969) The graph indicates that the extent of the differences between people brought up together and apart is very similar at all degrees of kinship. We can also compare heritability estimates based on M Z twins reared apart (0-75) with those based on unrelated children reared together (0-23). The proportion of the variance attributable to environment is around 25 per cent in both cases estimated independently. Jensen (1969) goes further by suggesting that we can also