division of the human race during the last few hours, as it were, of its existence. On the other hand, as I have said, it is not true that animal species never display any traces of intellectual improvement from generation to generation. Were this the case, as already remarked, mental evolution could never have taken place in the brute creation, and so the phenomena of mind would have been wholly restricted to man: all animals would have required to present but a vegetative form of life. But, apart from this general consideration, we meet with many particular instances of mental improvement in successive generations of animals, taking place even within the limited periods over which human observations can extend. In my previous work numerous cases will be found (especially in the chapters on the plasticity and blended origin of instincts), showing that it is quite a usual thing for birds and mammals to change even the most strongly inherited of their instinctive habits, in order to improve the conditions of their life in relation to some change which has taken place in their environments. And if it should be said that in such a case “the animal still does not rise above the level of birdhood or of beasthood,” the answer, of course, is, that neither does a Shakespeare or a Newton rise above the level of manhood. On the whole, then, I cannot see that there is any valid distinction to be drawn between human and brute psychology with respect to improvement from generation to generation. Indeed, I should deem it almost more philosophical in any opponent of the theory of evolution, who happened to be acquainted with the facts bearing upon the subject, if he were to adopt the converse position, and argue that for the purposes of this theory there is _not a sufficient_ distinction between human and brute psychology in this respect. For when we remember the great advance which, according to the theory of evolution, the mind of palæolithic man must already have made upon that of the higher apes, and when we remember that all races of existing men have the immense advantage of some form of language whereby to transmit to progeny the results of individual experience,—when we remember these things, the difficulty appears to me to lie on the side of explaining why, with such a start and with such advantages, the human species, both when it first appears upon the pages of geological history, and as it now appears in the great majority of its constituent races, should so far resemble animal species in the prolonged stagnation of its intellectual life.