Problems of Life and Mind. Second series, George Henry Lewes [e book reading free TXT] 📗

102. If any reader of these pages who, from theological or zoölogical suspicion of the Development Hypothesis, clings to the hypothesis of a creative Plan which once for all arranged the organic world in Types that could not change, will ask what rational interpretation can be given to the succession of phases each embryo is forced to pass through, it may help to give him pause. He will observe that none of these phases have any adaptation to the future state of the animal, but are in positive contradiction to it, or are simply purposeless; whereas all show stamped on them the unmistakable characters of ancestral adaptations and the progressions of Organic Evolution. What does the fact imply? There is not a single known example of a complex organism which is not developed out of simpler forms. Before it can attain the complex structure which distinguishes it, there must be an evolution of forms similar to those which distinguish the structures of organisms lower in the series. On the hypothesis of a Plan which prearranged the organic world, nothing could be more unworthy of a supreme intelligence than this inability to construct an organism at once, without previously making several tentative efforts, undoing to-day what was so carefully done yesterday, and repeating for centuries the same tentatives, and the same corrections, in the same succession. Do not let us blink this consideration. There is a traditional phrase much in vogue among the anthropomorphists, which arose naturally enough from the tendency to take human methods as an explanation of the divine—a phrase which becomes a sort of argument—“The Great Architect.” But if we are to admit the human point of view, a glance at the facts of embryology must produce very uncomfortable reflections. For what should we say to an architect who was unable, or being able was obstinately unwilling, to erect a palace except by first using his materials in the shape of a hut, then pulling it down and rebuilding them as a cottage, then adding story to story and room to room, not with any reference to the ultimate purposes of the palace, but wholly with reference to the way in which houses were constructed in ancient times? What should we say to the architect who could not form a museum out of bricks and mortar, but was forced to begin as if going to build a mansion: and after proceeding some way in this direction, altered his plan into a palace, and that again into a museum? Yet this is the sort of succession on which organisms are constructed. The fact has long been familiar; how has it been reconciled with Infinite Wisdom? Let the following passage answer for a thousand:—“The embryo is nothing like the miniature of the adult. For a long while the body in its entirety and its details presents the strangest of spectacles. Day by day and hour by hour the aspect of the scene changes, and this instability is exhibited by the most essential parts no less than by the accessory parts. One would say that Nature feels her way, and only reaches the goal after many times missing the path,—on dirait que la nature tâtonne et ne conduit son œuvre à bon fin qu’après s’être souvent trompée.”45 Writers have no compunction in speaking of Nature feeling her way and blundering; but if in lieu of Nature, which may mean anything, the Great Architect be substituted, it is probable that the repugnance to using such language of evasion may cause men to revise their conceptions altogether; they dare not attribute ignorance and incompetence to the Creator.

103. Obviously the architectural hypothesis is incompetent to explain the phenomena of organic development. Evolution is the universal process; not creation of a direct kind. Von Baer, who very properly corrected the exaggerations which had been put forth respecting the identity of the embryonic forms with adult forms lower in the scale, who showed that the mammalian embryo never was a bird, a reptile, or a fish, nevertheless emphasized the fact that the mammalian embryo passes through all the lower typical forms; so much so that, except by their size, it is impossible to distinguish the embryos of mammal, bird, lizard, or snake. “In my collection,” he says, “there are two little embryos which I have omitted to label, so that I am now quite incompetent to say to what class they belong. They may be lizards, they may be small birds, or very young mammals; so complete is the similarity in the mode of formation of the head and trunk. The extremities have not yet made their appearance. But even if they existed in the earliest stage we should learn nothing from them, for the feet of lizards, mammals, and the wings of birds, all arise from the same common form.” He sums up with his formula: “The special type is always evolved from a more general type.”46

Such reminiscences of earlier forms are intelligible on the supposition that originally the later form was a modification of the earlier form, and that this modification is repeated; or on the supposition that there was a similarity in the organic conditions, which similarity ceased at the point where the new form emerged. But on no hypothesis of creative Plan are they intelligible. They are useless structures, failing even to subserve a temporary purpose. Sometimes, as Mr. Darwin remarks, a trace of the embryonic resemblance lasts till a late age: “Thus birds of the same genus, and of closely allied genera, often resemble each other in their first and second plumage: as we see in the spotted feathers in the thrush group. In the cat tribe most of the species are striped and spotted in lines; and stripes or spots can plainly be distinguished in the whelp of the lion and the puma. We occasionally, though rarely, see something of this kind in plants.... The points of structure in which the embryos of widely different animals of the same class resemble each other often have no direct relation to their conditions of existence. We cannot, for instance, suppose that in the embryos of the vertebrata the peculiar loop-like courses of the arteries near the bronchial slits are related to similar conditions in the young mammal which is nourished in the womb of its mother, in the egg of a bird which is hatched in a nest, and in the spawn of a frog under water.”

104. It would be easy to multiply examples, but I will content myself with three. The tadpole of the Salamander has gills, and passes his existence in the water; but the Salamandra atra, which lives high up among the mountains, brings forth its young full-formed. This animal never lives in the water. Yet if we open a gravid female, we find tadpoles inside her with exquisitely feathered gills, and (as I have witnessed) these tadpoles “when from the mother’s womb untimely ripped,” if placed in water, swim about like the tadpoles of water newts. Obviously this aquatic organization has no reference to the future life of the animal, nor has it any adaptation to its embryonic condition; it has solely reference to ancestral forms, it repeats a phase in the development of its progenitors. Again, in the embryo of the naked Nudibranch, we always observe a shell, although the animal is without a shell, and there can be no purpose served by the shell in embryonic life.47 Finally, the human embryo has a tail, which is of course utterly purposeless, and which, although to be explained as a result of organic laws, is on the creative hypothesis only explained as an adherence to the general plan of structure—a specimen of pedantic trifling “worthy of no intellect above the pongo’s.”48

105. Humanly appreciated, not only is it difficult to justify the successive stages of development, the incessant building up of structures immediately to be taken down, but also to explain why development was necessary at all. Why are not plants and animals formed at once, as Eve was mythically affirmed to be taken from Adam’s rib, and Minerva from Jupiter’s head? The theory of Evolution answers this question very simply; the theory of Creation can only answer it by affirming that such was the ordained plan. But the theory of Evolution not only gives the simpler and more intelligible answer to this question, it gives an answer to the further question which leaves the theory of Creation no loophole except a sophism—namely, why the formation of organisms is constantly being frustrated or perverted? And, further, it gives an explanation of the law noticed by Milne Edwards, that Nature is as economical in her means as she is prodigal in her variation of them: “On dirait qu’avant de recourir à des ressources nouvelles elle a voulu épuiser, en quelque sorte, chacun des procédés qu’elle avait mis en jeu.”49 The applause bestowed on Nature for being economical is a curious transference to Nature of human necessities. Why, with a whole universe at her disposal, should Nature be economical? Why must she always be working in the same groove, and using but a few out of the many substances at her command? Economy is a virtue only in the poor. If Nature, in organic evolutions, is restricted to a very few substances, and a very few modes of combination, always creating new forms by modification of the old, and apparently incapable of creating an organism at once, this must imply an inherent necessity which is very unlike the free choice that can render economy a merit.

106. There may indeed be raised an objection to the Development Hypothesis on the ground that if the complex forms were all developed from the simpler forms, we ought to trace the identities through all their stages. If the fish developed into the reptile, the reptile into the bird, and the bird into the mammal (which I, for one, think questionable), we ought to find, it is urged, evidence of this passage. And at one time it was asserted that the evidence existed; but this has been disproved, and on the disproof the opponents of Evolution take their stand. Although I cannot feel much confidence in the idea of such a passage from Type to Type, and although the passage, if ever it occurred, must have occurred at so remote a period as to leave no evidence more positive than inference, I cannot but think the teaching of Embryology far more favorable to it than to our opponents. Supposing, for the sake of argument, that the passage did take place, ought we to find the embryonic stages accurately reproducing the permanent forms of lower types? Von Baer thinks we ought; and lesser men may follow him without reproach. But it seems to me that he starts from an inadmissible assumption, namely, that the development must necessarily be in a straight line rather than in a multiplicity of divergent lines. “When we find the embryonic condition,” he says, “differing from the adult, we ought to find a corresponding condition somewhere in the lower animals.”50 Not necessarily. We know that the mental development of a civilized man passes through the stages which the race passed through in the course of its long history, and the psychology of the child reproduces the psychology of the savage. But as this development takes place under conditions in many respects different, and as certain phases are hurried over, we do not expect to find a complete parallel. It is enough if we can trace general resemblances. Von Baer