CLASS DIFFERENCES IN GENERAL INTELLIGENCE: III

The argument put forward in the following paper is based on three main premises, for which ample evidence is now available: (i) individual differences in ‘general intelligence’ are transmitted in accordance with the multifactorial theory of inheritance; (ii) in our own country for thirty generations or more, there has been a discernible tendency for individuals endowed with high intelligence to rise to a higher social class and for those of low intelligence to drop to a lower; (iii) with minor fluctuations, this twofold movement has increased at an accelerated rate from almost negligible amounts to the comparatively large proportions reported in recent sociological surveys. From these three propositions it is concluded that there must now be appreciable differences in the genetic composition of different social classes, and that these differences will show themselves most plainly in differences between the mean level of intelligence obtaining within each class. But it also follows that, within each class, there will be wide individual variations, so that each class remains highly heterogeneous; and these differences in innate ability will be still further magnified by environmental differences and by innate differences in temperament. The conclusions thus deduced appear to be fully confirmed by surveys carried out with tests of intelligence and other devices. But the test‐results themselves by no means form the only ground, as is so often supposed, for accepting the conclusions thus reached. The various objections urged against the foregoing arguments are discussed; and their practical consequences briefly indicated.