Europe on the other hand was fortunate in that all the different peoples, or most of the peoples, from which its nations have been formed were of allied race; they were all, with few exceptions, of the white race, sufficiently nearly allied not to produce inferior cross-races but rather to produce some superior subraces. The conquered peoples have been so similar to their conquerors in physical type that crossing could take place without the cross-bred offspring bearing the indelible marks of inferior or mixed parentage, such as a dark skin or a woolly head. Hence, although caste systems were formed, they did not prove rigid; free intermarriage took place, and it was not impossible for individuals of the conquered race or of the mixed stock to rise into the superior ruling class. The importance of this may be seen, on reflecting how the merest trace of negro-blood in individuals of mixed origin in North America is apt to show itself in the physical features and how, even in that enlightened and Christian country, a trace so revealed suffices to condemn a man, no matter how great his powers or refined his character, to remain a member of the inferior caste. But, apart from the possible improvement of the racial qualities of the whole people, or of the average individuals in general, which may well have occurred in Europe, the biological blending of allied races may give important advantages to the resulting people in another way—namely, by increasing its variability, the variability of its mental qualities. If a people is extremely homogeneous in the racial sense, it may be expected to display little variability, its members will be of essentially similar mental qualities and of a uniform level of mental capacity; and this will tend to make them a very stable, but a very conservative unprogressive, nation. This seems to be true of China, and to be in large part the source of its extreme stability and extreme conservatism. Where, on the other hand, a people is formed by the intimate blending by intermarriage of two or more racial stocks, it is likely to be a variable one; there will be large departures in many directions from the average type of mental ability, and there will be individuals varying by excess of development of various capacities as well as others varying by defect of development. And a people of variable and therefore widely diversified mental capacities will, even though its average capacity is no greater than that of a more homogeneous people, be more likely to make progress in civilisation, and this for three reasons.