Other Instances of Dissatisfaction with the Theory of Descent.
What was with Virchow only a suggestion of the [pg 112] need for caution, or controversial matter to be subsequently allowed for or contradicted, had more serious consequences to others, and led to still greater hesitancy as regards evolutionist generalisations and speculations, and sometimes to sharp antagonism to them.
One of the best known of the earlier examples of this mood is Kerner von Marilaun's large and beautiful work on “Plant Life.”[21] He does, indeed, admit that our species are variations of antecedent forms, but only in a very limited sense. Within the stocks or grades of organisation which have always existed, variations have come about, through “hybridisation,” through the crossing of similar, but relatively different forms; these variations alter the configuration and appearance in detail, but neither affect the general character nor cause any transition from “lower” to “higher.”
Kerner disposes of the chief argument in favour of the theory of descent, the homology of individual organs, by explaining that the homology is due to the similarity of function in the different organisms. A similar argument is used in regard to “ontogeny recapitulating phylogeny.” Palæontology does not disclose in the plant-world any “synthetic types,” which might have been the common primitive stock from which many now divergent branches have sprung, nor does it disclose any “transition links” really intermediate, [pg 113] for instance, between cryptogams and gymnosperms, or between gymnosperms and angiosperms. That the higher races are apparently absent from the earlier strata is not a proof that they have never existed. The peat-bog flora must have involved the existence of a large companion-flora, without which the peat could not have been formed, but all trace of this is absent in the still persistent vestiges of these times.[22] Life, with energy and matter, has existed as a phenomenon of the universe from all eternity, and thus its chief forms and manifestations have not “arisen,” but have always been. If facts such as these contradict the Kant-Laplace theory of the universe, then the latter must be corrected in the light of them, not conversely. The extreme isolation of Kerner and his theory is probably due especially to this corollary of his views.
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 [pg 114] 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 [pg 115] 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.
Fleischmann further asserts that Haeckel's “fundamental biogenetic law” has utterly collapsed. “Recapitulation” does not occur. Selenka's figures of ovum-segmentation show that there are specific differences in the individual groups. The origin and development of the blastoderm or germinal disc has nothing to do with recapitulation of the phylogeny. It is not the case that the embryos of higher vertebrates are indistinguishable from one another. Even the egg-cell has a specific character, and is totally different from any unicellular organism at the Protistan level. The much-cited “gill-clefts” of higher vertebrates in the embryonic stage are not persistent reminiscences of [pg 116] earlier lower stages; they are rudiments or primordia shared by all vertebrates, and developing differently at the different levels; (thus in fishes they become breathing organs, and in the higher vertebrates they become in part associated with the organs of hearing, or in part disappear again).
Though Fleischmann's vigorous protest against over-hastiness in construction and over-confidence on the part of the adherents of the doctrine of descent is very interesting, and may often be justified in detail, it is difficult to resist the impression that the wheat has been rejected with the chaff.[23]
Even a layman may raise the following objections: Admitting that the great groups of forms cannot be traced back to one another, the palæontological record still proves, though it may be only in general outline, that within each phylum there has been a gradual succession and ascent of forms. How is the origin of what is new to be accounted for? Without doing violence to our thinking, without a sort of intellectual autonomy, we cannot rest content with the mere fact that new elements occur. So, in spite of all “difficulties,” the assumption of an actual descent quietly forces itself upon us as the only satisfactory clue. And the fact, which Fleischmann does not discuss, that even at present we may observe the establishment of what are at least new breeds, impels us to accept an analogous [pg 117] origin of new species. Even if the biogenetic law really “finds its chief confirmation in its exceptions,” even if we cannot speak of a strict recapitulation of earlier stages of evolution, there are indisputable facts which are most readily interpreted as reminiscences, as due to affiliation (ideal or hereditary), with ancestral forms. (Note, for instance, Weismann's “prediction,” &c.[24]) Even if Archæopteryx and other intermediate forms cannot be regarded as connecting links in the strict sense, i.e., as being stages in the actual pedigree, yet the occurrence of reptilian and avian peculiarities side by side in one organism, goes far to prove the close relationship of the two classes.