Other examples present themselves. The aristocracy of Siam regard all forms of work as so degrading that they allow their finger-nails to grow five or six inches in length to prove that their hands have never been soiled with labour. Needless to say that this disuse of their muscles is followed by atrophy of their brain-cells, so that they are an emasculate and enfeebled group. The theory of concentration and disuse of faculties in the group led to the system of castes, the most striking example of which is in India, where they are divided upon race lines. The white Brahmans are the priests, legislators, scholars, and diplomats; the red Rajpoots are the warriors and chieftains; the yellow Mongols are the commercial and agricultural class; while the black Dravidians are the mechanics and herdsmen. Each caste adopts its special branch of activity and avoids that traditionally belonging to another caste. Although a similar theory has been widely popular in many states, such a division of labour and responsibility has in it elements of debility which in the long run must bring about social disintegration. It conflicts with the unity of the ethnic mind. 3. _Reaction from Natural Limitations._—As there is a difference in the mental aptitudes of individuals which no training can equalise, so there is in those of human groups. Its causes do not concern us here. The fact remains and must be faced. There are natural limitations to each mind and to each group of minds. Compared with the most highly gifted, the less so stand in the physiological relation of “rudimentary organs.” When brought into contact, the latter will either succumb or accept a subordinate position. The American Indians, as a race, were comparatively highly gifted. They created an order of architecture and even devised a system of phonetic writing; but none of their states was of long duration, and none of their so-called “empires” rose above the level of a temporary confederacy. The limitations of the racial mind were such that a complex social organisation was impossible for them. In the forms of their highest governments, those of the Aztecs, Mayas, and Peruvians, we see repeated on a large scale the simple and insufficient models of the rude hunting tribes of the plains. This is also true of the black race of Africa. The powerful monarchies which at times have been erected in that continent over the dead bodies of myriads of victims have lasted but a generation or two. The natural limitations of the racial mind prevented it. Many other examples could be cited. Indeed, the law of “thus far shalt thou go and no farther” tells the story of most of the failures of races and peoples. They fell through mental inability to succeed. They had reached the natural limit of their activities.