But, when, under the influence of Welshman's theories, the majority of biologists came to the conclusion that acquired qualities are not transmitted, the position of the 'race theorisers' was immensely strengthened. For selection, natural or social or artificial, remained as the only recognised cause of change of racial qualities; and, since it is clear that the development of civilisation tends to bring to an end the operation of natural selection, owing to the more efficient shielding of the weaker by the stronger members of societies, and since no other form of selection seems to have operated forcibly to change race qualities, it was inferred that race qualities endure throughout long ages with very little change.
Another revolution of opinion has had a similar effect. One of the old assumptions which seemed to justify the belief in rapid modifiability of race qualities was that the difference of culture between ourselves and our savage ancestors corresponds to, and is the expression of, an almost equally great difference of innate capacities, intellectual and moral. But this was in the main a misunderstanding. One well established fact suffices to show its improbability--namely, the larger size of the brains of Palæolithic men as compared with our own. Our superiority of civilisation is due to slow accumulation, each generation adding comparatively little to the mass of intellectual and moral tradition which it inherits and passes on to later coming generations. In so far as differences of cultural level are associated with differences of level of innate intellectual and moral qualities, cultural superiority must be regarded as the effect, rather than the cause, of innate mental superiority. There are strong grounds for holding that, in so far as Europeans are innately superior to negroes, that superiority was achieved not by means of, and in the process of, the development of, civilisation; but rather before civilisation began; and that the principal mental differences of the various human stocks were, like their principal physical differences, produced in the course of the immensely long ages of human life that preceded the dawn of civilisation, or at any rate of history, ages compared with which the historic period is but a very brief span.