Of works dealing with nearly the same subject, which have been published since the publication of my articles on Mutual Aid among Animals, I must mention The Lowell Lectures on the Ascent of Man, by Henry Drummond (London, 1894), and The Origin and Growth of the Moral Instinct, by A. Sutherland (London, 1898). Both are constructed chiefly on the lines taken in Buchner's Love, and in the second work the parental and familial feeling as the sole influence at work in the development of the moral feelings has been dealt with at some length. A third work dealing with man and written on similar lines is The Principles of Sociology, by Prof. F.A. Giddings, the first edition of which was published in 1896 at New York and London, and the leading ideas of which were sketched by the author in a pamphlet in 1894. I must leave, however, to literary critics the task of discussing the points of contact, resemblance, or divergence between these works and mine. The different chapters of this book were published first in the Nineteenth Century ("Mutual Aid among Animals," in September and November 1890; "Mutual Aid among Savages," in April 1891; "Mutual Aid among the Barbarians," in January 1892; "Mutual Aid in the Medieval City," in August and September 1894; and "Mutual Aid amongst Modern Men," in January and June 1896). In bringing them out in a book form my first intention was to embody in an Appendix the mass of materials, as well as the discussion of several secondary points, which had to be omitted in the review articles. It appeared, however, that the Appendix would double the size of the book, and I was compelled to abandon, or, at least, to postpone its publication. The present Appendix includes the discussion of only a few points which have been the matter of scientific controversy during the last few years; and into the text I have introduced only such matter as could be introduced without altering the structure of the work. I am glad of this opportunity for expressing to the editor of the Nineteenth Century, Mr. James Knowles, my very best thanks, both for the kind hospitality which he offered to these papers in his review, as soon as he knew their general idea, and the permission he kindly gave me to reprint them. Bromley, Kent, 1902. CHAPTER I MUTUAL AID AMONG ANIMALS Struggle for existence. Mutual Aid a law of Nature and chief factor of progressive evolution. Invertebrates. Ants and Bees. Birds, hunting and fishing associations. Sociability. Mutual protection among small birds. Cranes, parrots.