It will probably be remarked that mutual aid, even though it may represent one of the factors of evolution, covers nevertheless one aspect only of human relations; that by the side of this current, powerful though it may be, there is, and always has been, the other current--the self-assertion of the individual, not only in its efforts to attain personal or caste superiority, economical, political, and spiritual, but also in its much more important although less evident function of breaking through the bonds, always prone to become crystallized, which the tribe, the village community, the city, and the State impose upon the individual. In other words, there is the self-assertion of the individual taken as a progressive element. It is evident that no review of evolution can be complete, unless these two dominant currents are analyzed. However, the self-assertion of the individual or of groups of individuals, their struggles for superiority, and the conflicts which resulted therefrom, have already been analyzed, described, and glorified from time immemorial. In fact, up to the present time, this current alone has received attention from the epical poet, the annalist, the historian, and the sociologist. History, such as it has hitherto been written, is almost entirely a description of the ways and means by which theocracy, military power, autocracy, and, later on, the richer classes' rule have been promoted, established, and maintained. The struggles between these forces make, in fact, the substance of history. We may thus take the knowledge of the individual factor in human history as granted--even though there is full room for a new study of the subject on the lines just alluded to; while, on the other side, the mutual-aid factor has been hitherto totally lost sight of; it was simply denied, or even scoffed at, by the writers of the present and past generation. It was therefore necessary to show, first of all, the immense part which this factor plays in the evolution of both the animal world and human societies. Only after this has been fully recognized will it be possible to proceed to a comparison between the two factors.