In the animal world we have seen that the vast majority of species live in societies, and that they find in association the best arms for the struggle for life: understood, of course, in its wide Darwinian sense--not as a struggle for the sheer means of existence, but as a struggle against all natural conditions unfavourable to the species. The animal species, in which individual struggle has been reduced to its narrowest limits, and the practice of mutual aid has attained the greatest development, are invariably the most numerous, the most prosperous, and the most open to further progress. The mutual protection which is obtained in this case, the possibility of attaining old age and of accumulating experience, the higher intellectual development, and the further growth of sociable habits, secure the maintenance of the species, its extension, and its further progressive evolution. The unsociable species, on the contrary, are doomed to decay. Going next over to man, we found him living in clans and tribes at the very dawn of the stone age; we saw a wide series of social institutions developed already in the lower savage stage, in the clan and the tribe; and we found that the earliest tribal customs and habits gave to mankind the embryo of all the institutions which made later on the leading aspects of further progress. Out of the savage tribe grew up the barbarian village community; and a new, still wider, circle of social customs, habits, and institutions, numbers of which are still alive among ourselves, was developed under the principles of common possession of a given territory and common defence of it, under the jurisdiction of the village folkmote, and in the federation of villages belonging, or supposed to belong, to one stem. And when new requirements induced men to make a new start, they made it in the city, which represented a double network of territorial units (village communities), connected with guilds these latter arising out of the common prosecution of a given art or craft, or for mutual support and defence. And finally, in the last two chapters facts were produced to show that although the growth of the State on the pattern of Imperial Rome had put a violent end to all medieval institutions for mutual support, this new aspect of civilization could not last. The State, based upon loose aggregations of individuals and undertaking to be their only bond of union, did not answer its purpose. The mutual-aid tendency finally broke down its iron rules; it reappeared and reasserted itself in an infinity of associations which now tend to embrace all aspects of life and to take possession of all that is required by man for life and for reproducing the waste occasioned by life.