are far older than the city, and exist, at least in germ, in the most primitive communities of which we have knowledge.[227] III. _The Comparative-Sociological View_ As social classes belong to all society,[228] they cannot be explained by the peculiar conditions of any one community. The only scientific approach to this subject is through comparative study; the inferences of the ancient historians relative to primitive Rome are not to be displaced by purely subjective theories, but are to be tested by comparison with conditions in other communities of equal or less cultural advancement. Distinctions of rank depend ultimately upon physical, mental, and moral inequalities,[229] which differentiate the population of a community into leaders and followers.[230] The exhibition of physical strength and skill on the part of young men and of knowledge and wisdom on the part of the elders are often “the foundation of leadership and of that useful subordination in mutual aid which depends on voluntary deference.”[231] In an age in which men were largely under the control of religion the possession of an oracle or skill in divination or prophecy might contribute as much to the elevation of an individual above his fellows.[232] Leadership, once obtained, could display and strengthen itself in various ways. In primitive society the strong, brave, intelligent man was especially qualified to take command in war. Success brought the chief not only renown but a large share of the booty and in later time acquired land. The same result might be obtained by other means than by war;[233] but in any case wealth and influence inherited through several generations made nobility.[234] Primarily grounded on ability, wealth, and renown, this preëminence was often heightened by a claim to divine lineage or other close connection with the gods.[235] There was evidently a stage of development—before the association of the nobles into a class—in which chieftains alone held preëminence. This condition is common in primitive society, as among the American Indians.[236] Also among the Germans, who had advanced somewhat beyond this stage, each chief or lord appears to have been noble “less with reference to other noblemen than with reference to the other free tribesmen comprised in the same group with himself.”[237] From Brehon law we infer that the Irish lords were individually heads of their several groups of kinsmen or of vassals;[238] and in Wales the nobles were a hierarchy of chieftains.[239] As soon as leadership became hereditary there arose noble families, in which the younger members were often sub-chieftains;[240] and finally through intermarriage among these families, as well as through the discovery of common interests, the nobles associated themselves into a class.