A STUDY OF INHERITANCE OF HUMAN INTELLIGENCE

Similarities regarding both physical and psychological characters between relatives, and above all between parents and children, have been observed for a very long time. Such observations no doubt formed the basis for the theories on the inheritance of human qualities developed as early as classical times (cf. Johannsen, 1918). It was not until the development of correlation technique by Pearson and the analysis of variance by Fisher that the problem of inheritance of quantitatively varying characters could be attacked in a scientifically fruitful way. It is of interest that a long series of early investigations, which arc now, owing to insufficient psychometric methods or the fact that they were based on rough estimation, only of historical interest, nevertheless showed correlations of about 0.5 between sibs. Correlations of the same order of magnitude had been found in a number of anthropological studies. The anthropological character which came first to mind for comparison with “intelligence” was stature, and when psychometric test scales became available, the analogies as regards both correlation and particularly the form of the distribution seemed striking 1. Of such early investigations may be mentioned those of Pearson (1919) , Gordon (1919) and Elderfon (1923) . In view of the fact that in those times it was considered self-evident that height, for example, was wholly determined by “heredity”, and broadly speaking not affected by environmental differences, it can be understood that the same was thought to apply to intelligence. Elderton, for instance, claimed to show that a number of various social circumstances, such as “drinking of father, of mother, morality of parents, physical conditions of parents, economic condition of the home, overcrowding”, etc., were not correlated with the intelligence of the children. The determination of intelligence was based on estimates made by teachers, “but there seems no reason to suppose that the I.Q. will yield different results for en-

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