If, then, so little change of man’s mental constitution has been produced in the course of many thousand years, even though the growth of civilisation has so profoundly modified his mode of life and the nature of his pursuits, that is good evidence of the great persistency of racial mental qualities. But we have more direct evidence of their persistence. As Wallace points out, the negro and the yellow races are scattered over many parts of the earth, and, though these regions present great diversities of physical environment, men of either of the two races everywhere present the same mental peculiarities or strong similarities, for example, the Papuan and African and American negroes. And the characteristic differences between the two races are not diminished even where, as in the islands of the far East, they have been subjected to the same physical environment and modes of life for long periods of time. In the eastern Archipelago, Papuans and Malayans occupying the same or adjoining islands are cited by Wallace as illustrating the persistence of racial mental differences; and I can bear out his remarks from my own observations in that region. But we must beware of excess in the direction of the unalterability of race. The dogma of the non-transmissibility of acquired qualities is by no means established; it seems not improbable that mental acquisitions are so transmitted in some degree, though with only very slight effect in each generation. Even now, when the difficulties of the principle of transmission of acquired qualities are generally understood, almost all those who deal with the problem of the genesis of mental and physical peculiarities of races find themselves driven to postulate the principle in order to explain the facts. And this in itself constitutes evidence of a certain value in support of the validity of the principle. Again, we must beware of assuming that there are no selective processes operating among us. Although natural selection may be almost inoperative, there may well be at work other forms of selection, social selections; and these are specially powerful amongst populations of blended stocks. Summing up on the durability of racial peculiarities, we may say that racial qualities are extremely persistent; but that, nevertheless, they are subject to slow modifications when the conditions of life are greatly changed, as by emigration, or by changes of climate, or by social revolutions, and especially among populations of mixed origin.