Unselfishness is the soul of true friendship, yet it nevertheless remains true that all instincts are founded on the experience of benefits or injuries. During the rough transition period from beasthood to manhood, when our uncivilized ancestors roamed the forests of the foreworld, it must have been an incalculable advantage to the individual hunter or herder to secure the coöperation of a trusty companion, whose watchful eye would double his chance of finding food or avoiding danger, whose stout arm might parry a blow which unaided strength would have failed to avert. As in other circumstances of natural selection, those who most successfully availed themselves of such advantages had a superior chance of survival and consequently of transmitting their disposition to subsequent generations, and the habit of friendship thus became a hereditary instinct. The social system of civilized life has since devised manifold substitutes for the coöperation of elective affinities, but various unalienable advantages of the primitive plan have been more or less clearly recognized by all nations, especially by the manful and nature-abiding nations of pagan antiquity. The benefits secured by the mutual aid of sympathizing friends are not limited to the guarantee of civil rights, but extend to the realization of individual hopes and the indulgence of personal inclination and predilections, as well as to the higher privileges of a mental communion for which the panders of selfish wealth have as yet devised no equivalent. The power of approbativeness, the main stimulus of ambition, is infinitely intensified by the emulation of noble friendship, which, in the words of an ancient philosopher, “inspires to deeds heroic, and makes labor worth the toils that lead to success.” Such friendship inspired the heroism of Theseus and Pyrithous, of Harmodius and Aristogiton, of Nisus and Euryalus, and recorded its experience in proverbs which have few parallels in the languages of the Christianized nations: “Solem e mundo qui amicitiam e vita tollunt”—“They deprive the world of sunshine who deprive life of friendship.” “Amicum perdere damnorum est maximum”—“To lose a friend is the greatest of losses.” “Amicus magis necessarius quam ignis aut aqua”—“A friend is more needful than fire or water.”