No science is a better exponent of this radical and important change than that which has to do with the principles of morals; for by no science was the theory of evolution assailed, in the beginning, with more vehemence and indefatigability. Not only did the zealous adherents of Christian dogma fear to find, in the destruction of all distinct barriers between the different forms of animal life, a ground for the denial of God's especial favor to man, and the worshippers of emotional morals become indignant at the unveiling of the divine Mystic (as if only ignorance were reverence, and only the Unknown worthy of homage), but even the less conservative schools of philosophy often showed themselves unfavorable or hesitant towards the new ideas, dreading their implications. All this is changed. If England's most popular living philosopher was among the first to declare himself for Darwin, and to revise his whole system in accordance with the theory of evolution, so that this theory early began to find adherents among students of philosophy in all lands where English is spoken, it was not long before the newer schools of France and Germany began to follow in their wake. Now every year, and almost every month, brings with it a fresh supply of books, pamphlets, and magazine articles on "The Evolution of Morality," "L'Evolution de la Morale," "Die Evolution der Sittlichkeit," "Sittlichkeit und Darwinismus," etc. So many are the waters which now pour themselves into this common stream that the current threatens soon to become too deep and swift for any but the most expert swimmers. In a short review of Evolutional Ethics, it will be impossible to consider all the literature that has added to our knowledge on this subject; we must confine ourselves to the few books that are most prominent. The first laborer in this line, not only indirectly through general theory, but also directly through particular theory, is, as usual, Charles Darwin; and though Darwin was himself no psychologist, and moreover advances his ideas on the origin and development of morals only in the tentative manner that necessarily attaches to a first attempt when made by so conscientious a thinker, he doubtless suggested to all other writers in this field a very large part of that which was best in their work. A Review of Evolutional Ethics must, therefore, in order to start with the proper origin of the science, begin with CHARLES DARWIN In the essay on "Instinct" appended to G. J. Romanes' "Mental Evolution in Animals,"[1] Darwin says: "The social instinct is indispensable to some animals, useful to still more, and apparently only pleasant to some few animals." The social tendency being thus classed as an instinct, it belongs to our work to examine what are Darwin's theories as to the origin and nature of instinct.