Zoologists, again, will hardly accept without question Prince Kropotkine’s assertion that “life in societies is no exception in the animal world, but is the rule, the law of nature.” Many will contend, on the other hand, that life in societies with anything like division of labour, or with mutual aid (and this seldom carried far), is, taking the animal kingdom as a whole, of comparatively rare occurrence, though none the less noteworthy where it exists. And, in any case, it seems somewhat extravagant to say that sociability is the chief factor in evolution. No doubt it might be plausibly urged that human society is, from man’s point of view, the highest product of evolution; that in attaining to this end sociability has been the leading factor; and that obviously the leading factor in the evolution of the highest product may properly be called the chief factor in evolution. But Prince Kropotkine apparently means that sociability is the chief factor, not only in this evolution, but in all organic, or, at least, all animal evolution. In this he will receive the support of but few zoologists. By some extravagance of statement he has weakened his own case, which is otherwise not lacking in points of weakness. The legitimate inferences from animal behaviour are, that co-operation is in some cases a factor in the evolution of a successful species, that in human progress it has been an important factor giving strength to a creature weak in tooth and claw, and that this factor has co-existed, and still coexists, with that of competition, in the absence of which the race would be dragged down to lower levels of efficiency by the incubus of weaklings.