Others beside Haeckel have held this kind of view at one time or another; but, unlike him, most of them have recanted and seen the error of their ways. He is, indeed, aware that several of his great German contemporaries have been through this phase of thought and come out on the other side, notably the physiologist-philosopher Wundt, and he refers to them fairly and instructively thus:— "What seems to me of special importance and value in Wundt's work is that he 'extends the law of the persistence of force for the first time to the psychic world.' "Thirty years afterwards, in a second edition, Wundt emancipated himself from the fundamental errors of the first, and says that he 'learned many years ago to consider the work a sin of his youth'; it 'weighed on him as a kind of crime, from which he longed to free himself as soon as possible.' In the first, psychology is treated as a _physical_ science, on the same laws as the whole of physiology, of which it is only a part; thirty years afterwards he finds psychology to be a _spiritual_ science, with principles and objects entirely different from those of physical science. "I myself," says Haeckel, "naturally consider the 'youthful sin' of the young physiologist Wundt to be a correct knowledge of nature, and energetically defend it against the antagonistic view of the old philosopher Wundt. This entire change of philosophical principles, which we find in Wundt, as we found it in Kant, Virchow, du Bois-Reymond, Carl Ernst Baer, and others, is very interesting" (p. 36). So it is: very interesting! Professor Haeckel is so imbued with biological science that he loses his sense of proportion; and his enthusiasm for the work of Darwin leads him to attribute to it an exaggerated scope, and enables him to eliminate the third of the Kantian trilogy:— "Darwin's theory of the natural origin of species at once gave us the solution of the mystic 'problem of creation,' the great 'question of all questions'—the problem of the true character and origin of man himself" (p. 28) [_cf._ p. 19 above]. It is a great deal more than that patient observer and deep thinker Charles Darwin ever claimed, nor have his wiser disciples claimed it for him. It is familiar that he explained how variations once arisen would be clinched, if favourable in the struggle, by the action of heredity and survival; but the source or origin of the variations themselves he did not explain. Do they arise by guidance or by chance? Is natural selection akin to the verified and practical processes of artificial selection? or is it wholly alien to them and influenced by chance alone? The latter view can hardly be considered a complete explanation, though it is verbally the one adopted by Professor Haeckel, and it is of interest to see what he means by chance:—