The importance of the Mutual Aid factor--"if its generality could only be demonstrated"--did not escape the naturalist's genius so manifest in Goethe. When Eckermann told once to Goethe--it was in 1827--that two little wren-fledglings, which had run away from him, were found by him next day in the nest of robin redbreasts (Rothkehlchen), which fed the little ones, together with their own youngsters, Goethe grew quite excited about this fact. He saw in it a confirmation of his pantheistic views, and said:--"If it be true that this feeding of a stranger goes through all Nature as something having the character of a general law--then many an enigma would be solved." He returned to this matter on the next day, and most earnestly entreated Eckermann (who was, as is known, a zoologist) to make a special study of the subject, adding that he would surely come "to quite invaluable treasuries of results" (Gespräche, edition of 1848, vol. iii. pp. 219, 221). Unfortunately, this study was never made, although it is very possible that Brehm, who has accumulated in his works such rich materials relative to mutual aid among animals, might have been inspired by Goethe's remark. Several works of importance were published in the years 1872-1886, dealing with the intelligence and the mental life of animals (they are mentioned in a footnote in Chapter I of this book), and three of them dealt more especially with the subject under consideration; namely, Les Societes animales, by Espinas (Paris, 1877); La Lutte pour l'existence et l'association pout la lutte, a lecture by J.L. Lanessan (April 1881); and Louis Buchner's book, Liebe und Liebes-Leben in der Thierwelt, of which the first edition appeared in 1882 or 1883, and a second, much enlarged, in 1885. But excellent though each of these works is, they leave ample room for a work in which Mutual Aid would be considered, not only as an argument in favour of a pre-human origin of moral instincts, but also as a law of Nature and a factor of evolution. Espinas devoted his main attention to such animal societies (ants, bees) as are established upon a physiological division of labour, and though his work is full of admirable hints in all possible directions, it was written at a time when the evolution of human societies could not yet be treated with the knowledge we now possess. Lanessan's lecture has more the character of a brilliantly laid-out general plan of a work, in which mutual support would be dealt with, beginning with rocks in the sea, and then passing in review the world of plants, of animals and men. As to Buchner's work, suggestive though it is and rich in facts, I could not agree with its leading idea. The book begins with a hymn to Love, and nearly all its illustrations are intended to prove the existence of love and sympathy among animals. However, to reduce animal sociability to love and sympathy means to reduce its generality and its importance,