It is an error to regard the struggle for existence as the only power giving shape to the organic world. The struggle for existence is the main power that causes the origin of new species, but Darwin himself knew full well that other powers co-operate which give shape to the forms, habits, and peculiarities of animate things. In his “Descent of Man” Darwin elaborately treated sexual selection and showed that the competition of males for females gave rise to the gay colors of the birds and butterflies and also to the singing voices of birds. There he also devoted a chapter to social living. Many illustrations on this head are also to be found in Kropotkin’s book, “Mutual Aid as a Factor in Evolution.” The best representation of the effects of sociability are given in Kautsky’s “Ethics and the Materialistic Conception of History.” When a number of animals live in a group, herd or flock, they carry on the struggle for existence in common against the outside world; within such a group the struggle for existence ceases. The animals which live socially no longer wage a struggle against each other, wherein the weak succumb; just the reverse, the weak enjoy the same advantages as the strong. When some animals have the advantage by means of greater strength, sharper smell, or experience in finding the best pasture or in warding off the enemy, this advantage does not accrue only to these better fitted, but also to the entire group. This combining of the animals’ separate powers into one unit gives to the group a new and much stronger power than any one individual possessed, even the strongest. It is owing to this united strength that the defenseless plant-eaters can ward off rapacious animals. It is only by means of this unity that some animals are able to protect their young. A second advantage of sociability arises from the fact that where animals live socially, there is a possibility of the division of labor. Such animals send out scouts or place sentinels whose object it is to look after the safety of all, while others spend their time either in eating or in plucking, relying upon their guards to warn them of danger. Such an animal society becomes, in some respects, a unit, a single organism. Naturally, the relation remains much looser than the cells of a single animal body; nevertheless, the group becomes a coherent body, and there must be some power that holds together the individual members.