Among the most recent examples of antagonism to the Evolution-Theory, the most interesting is a book by Fleischmann, professor of zoology in Erlangen, published in 1901, and entitled, “The Theory of Descent.” It consists of “popular lectures on the rise and decline of a scientific hypothesis” (namely, the Theory of Descent), and it is a complete recantation by a quondam Darwinian of the doctrine of his school, even of its fundamental proposition, the concept of evolution itself. For Fleischmann is not guilty, like Weismann, of the inaccuracy of using “Theory of Descent” as equivalent to Darwinism; he is absolutely indifferent to the theory of natural selection. His book keeps strictly to matters of fact, and rejects as speculation everything in the least beyond these; it does not express even an opinion on the question of the origin of species, but merely criticises and analyses.
It does not bring forward any new and overwhelming arguments in refutation of the Theory of Descent, but strongly emphasises difficulties that have always beset it, and discusses these in detail. The old dispute which interested Goethe, Geoffroy St. Hilaire, and Cuvier, as to the unity or the fundamental heterogeneity of the “architectural plan” in nature is revived. Modern zoology recognises not merely the four types of Cuvier, but seventeen different styles, “phyla,” or groups of forms, to derive one of which from another is hopeless. And what is true of the whole is true also of the subdivisions within each phylum; _e.g._, within the vertebrate phylum with its fishes, amphibians, reptiles, birds and mammals. No bridge leads from one to the other. This is proved particularly by the very instance which is the favourite illustration in support of the Theory of Descent—the fin of fishes and its relation to the five-fingered hand of vertebrates. The so-called transition forms (Archæopteryx, monotremes, &c.) are discredited. So with the “stalking-horse” of evolutionists—the genealogical tree of the Equidæ, which is said to be traceable palæontologically right back, without a break, from the one-toed horses of the present day to the normal five-toed ancestry; and so with another favourite instance of evolution, the history of the pond-snails (_Planorbis multiformis_), the numerous varieties of which occur with transitions between them in actual contiguity in the Steinheim beds, and thus seem to afford an obvious example of the transformation of species. Against these cases, and against using the palæontological archives as a basis for the construction of genealogical trees in general, the weighty and apparently decisive objection is urged, that nowhere are the soft parts of the earlier forms of life preserved, and that it is impossible to establish relationships with any certainty on the basis of hard parts only, such as bones, teeth and shells. Even Haeckel admits that snails of very different bodily structure may form very similar and even hardly distinguishable shells.