Part 4 (2/2)
In all candor we must at least concede that such considerations suggest a genetic descent from the drift period down to the present, and allow time enough--if time is of any account-- for variation and natural selection to work out some appreciable results in the way of divergence into races, or even into so-called species. Whatever might have been thought, when geological time was supposed to be separated from the present era by a clear line, it is now certain that a gradual replacement of old forms by new ones is strongly suggestive of some mode of origination which may still be operative. When species, like individuals, were found to die out one by one, and apparently to come in one by one, a theory for what Owen sonorously calls ”the continuous operation of the ordained becoming of living things” could not be far off.
That all such theories should take the form of a derivation of the new from the old seems to be inevitable, perhaps from our inability to conceive of any other line of secondary causes in this connection. Owen himself is apparently in travail with some trans.m.u.tation theory of his own conceiving, which may yet see the light, although Darwin's came first to the birth.
Different as the two theories will probably be, they cannot fail to exhibit that fundamental resemblance in this respect which betokens a community of origin, a common foundation on the general facts and the obvious suggestions of modern science. Indeed--to turn the point of a pungent simile directed against Darwin--the difference between the Darwinian and the Owenian hypotheses may, after all, be only that between h.o.m.oeopathic and heroic doses of the same drug.
If theories of derivation could only stop here, content with explaining the diversification and succession of species between the teritiary period and the present time, through natural agencies or secondary causes still in operation, we fancy they would not be generally or violently objected to by the savants of the present day. But it is hard, if not impossible, to find a stopping-place. Some of the facts or accepted conclusions already referred to, and several others, of a more general character, which must be taken into the account, impel the theory onward with acc.u.mulated force.
Vires (not to say virus) acquirit eundo. The theory hitches on wonderfully well to Lyell's uniformitarian theory in geology--that the thing that has been is the thing that is and shall be--that the natural operations now going on will account for all geological changes in a quiet and easy way, only give them time enough, so connecting the present and the proximate with the farthest past by almost imperceptible gradations--a view which finds large and increasing, if not general, acceptance in physical geology, and of which Darwin's theory is the natural complement.
So the Darwinian theory, once getting a foothold, marches; boldly on, follows the supposed near ancestors of our present species farther and yet farther back into the dim past, and ends with an a.n.a.logical inference which ”makes the whole world kin.” As we said at the beginning, this upshot discomposes us. Several features of the theory have an uncanny look. They may prove to be innocent: but their first aspect is suspicious, and high authorities p.r.o.nounce the whole thing to be positively mischievous. In this dilemma we are going to take advice. Following the bent of our prejudices, and hoping to fortify these by new and strong arguments, we are going now to read the princ.i.p.al reviews which undertake to demolish the theory--with what result our readers shall be duly informed.
II
”I can entertain no doubt, after the most deliberate study and dispa.s.sionate judgment of which I am capable, that the view which most naturalists entertain, and which I formerly entertained, namely, that each species has been independently created, is erroneous. I am fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species, in the same manner as the acknowledged varieties of any one species are the descendants of that species. Furthermore, I am convinced that Natural Selection has been the main, but not exclusive, means of modification.”
This is the kernel of the new theory, the Darwinian creed, as recited at the close of the introduction to the remarkable book under consideration.
The questions, ”What will he do with it?” and ”How far will he carry it?”
the author answers at the close of the volume:
”I cannot doubt that the theory of descent with modification embraces all the members of the same cla.s.s.” Furthermore, ”I believe that all animals have descended from at most only four or five progenitors, and plants from an equal or lesser number.”
Seeing that a.n.a.logy as strongly suggests a further step in the same direction, while he protests that ”a.n.a.logy may be a deceitful guide,” yet he follows its inexorable leading to the inference that--
”Probably all the organic beings which have ever lived on this ear have descended from some one primordial form, into which life was first breathed.”[III-4]
In the first extract we have the thin end of the wedge driven a little way; in the last, the wedge driven home.
We have already sketched some of the reasons suggestive of such a theory of derivation of species, reasons which gave it plausibility, and even no small probability, as applied to our actual world and to changes occurring since the latest tertiary period. We are well pleased at this moment to find that the conclusions we were arriving at in this respect are sustained by the very high authority and impartial judgment of Pictet, the Swiss paleontologist. In his review of Darwin's book[III-5] -- the fairest and most admirable opposing one that has appeared--he freely accepts that ensemble of natural operations which Darwin impersonates under the now familiar name of Natural Selection, allows that the exposition throughout the first chapters seems ”a la fois prudent et fort,” and is disposed to accept the whole argument in its foundations, that is, so far as it relates to what is now going on, or has taken place in the present geological period--which period he carries back through the diluvial epoch to the borders of the tertiary.[III-6] Pictet accordingly admits that the theory will very well account for the origination by divergence of nearly-related species, whether within the present period or in remoter geological times; a very natural view for him to take, since he appears to have reached and published, several years ago, the pregnant conclusion that there most probably was some material connection between the closely-related species of two successive faunas, and that the numerous close species, whose limits are so difficult to determine, were not all created distinct and independent.
But while thus accepting, or ready to accept, the basis of Darwin's theory, and all its legitimate direct inferences, he rejects the ultimate conclusions, brings some weighty arguments to bear against them, and is evidently convinced that he can draw a clear line between the sound inferences, which he favors, and the unsound or unwarranted theoretical deductions, which he rejects. We hope he can.
This raises the question, Why does Darwin press his theory to these extreme conclusions? Why do all hypotheses of derivation converge so inevitably to one ultimate point? Having already considered some of the reasons which suggest or support the theory at its outset--which may carry it as far as such sound and experienced naturalists as Pictet allow that it may be true--perhaps as far as Darwin himself unfolds it in the introductory proposition cited at the beginning of this article--we may now inquire after the motives which impel the theorist so much farther. Here proofs, in the proper sense of the word, are not to be had. We are beyond the region of demonstration, and have only probabilities to consider. What are these probabilities? What work will this hypothesis do to establish a claim to be adopted in its completeness? Why should a theory which may plausibly enough account for the diversification of the species of each special type or genus be expanded into a general system for the origination or successive diversification of all species, and all special types or forms, from four or five remote primordial forms, or perhaps from one? We accept the theory of gravitation because it explains all the facts we know, and bears all the tests that we can put it to. We incline to accept the nebular hypothesis, for similar reasons; not because it is proved--thus far it is incapable of proof--but because it is a natural theoretical deduction from accepted physical laws, is thoroughly congruous with the facts, and because its a.s.sumption serves to connect and harmonize these into one probable and consistent whole. Can the derivative hypothesis be maintained and carried out into a system on similar grounds? If so, however unproved, it would appear to be a tenable hypothesis, which is all that its author ought now to claim. Such hypotheses as, from the conditions of the case, can neither be proved nor disproved by direct evidence or experiment, are to be tested only indirectly, and therefore imperfectly, by trying their power to harmonize the known facts, and to account for what is otherwise unaccountable. So the question comes to this: What will an hypothesis of the derivation of species explain which the opposing view leaves unexplained?
Questions these which ought to be entertained before we take up the arguments which have been advanced against this theory. We can barely glance at some of the considerations which Darwin adduces, or will be sure to adduce in the future and fuller exposition which is promised. To display them in such wise as to indoctrinate the unscientific reader would require a volume. Merely to refer to them in the most general terms would suffice for those familiar with scientific matters, but would scarcely enlighten those who are not. Wherefore let these trust the impartial Pictet, who freely admits that, ”in the absence of sufficient direct proofs to justify the possibility of his hypothesis, Mr. Darwin relies upon indirect proofs, the bearing of which is real and incontestable;” who concedes that ”his theory accords very well with the great facts of comparative anatomy and zoology--comes in admirably to explain unity of composition of organisms, also to explain rudimentary and representative organs, and the natural series of genera and species--equally corresponds with many paleontological data--agrees well with the specific resemblances which exist between two successive faunas, with the parallelism which is sometimes observed between the series of paleontological succession and of embryonal development,”
etc.; and finally, although he does not accept the theory in these results, he allows that ”it appears to offer the best means of explaining the manner in which organized beings were produced in epochs anterior to our own.”
What more than this could be said for such an hypothesis? Here, probably, is its charm, and its strong hold upon the speculative mind. Unproven though it be, and c.u.mbered prima facie with c.u.mulative improbabilities as it proceeds, yet it singularly accords with great cla.s.ses of facts otherwise insulated and enigmatic, and explains many things which are thus far utterly inexplicable upon any other scientific a.s.sumption.
We have said that Darwin's hypothesis is the natural complement to Lyell's uniformitarian theory in physical geology. It is for the organic world what that is for the inorganic; and the accepters of the latter stand in a position from which to regard the former in the most favorable light.
Wherefore the rumor that the cautious Lyell himself has adopted the Darwinian hypothesis need not surprise us. The two views are made for each other, and, like the two counterpart pictures for the stereoscope, when brought together, combine into one apparently solid whole.
If we allow, with Pictet, that Darwin's theory will very well serve for all that concerns the present epoch of the world's history--an epoch in which this renowned paleontologist includes the diluvial or quaternary period--then Darwin's first and foremost need in his onward course is a practicable road from this into and through the tertiary period, the intervening region between the comparatively near and the far remote past.
Here Lyell's doctrine paves the way, by showing that in the physical geology there is no general or absolute break between the two, probably no greater between the latest tertiary and the quaternary period than between the latter and the present time. So far, the Lyellian view is, we suppose, generally concurred in. It is largely admitted that numerous tertiary species have continued down into the quaternary, and many of them to the present time. A goodly percentage of the earlier and nearly half of the later tertiary mollusca, according to Des Hayes, Lye!!, and, if we mistake not, Bronn, still live. This identification, however, is now questioned by a naturalist of the very highest authority. But, in its bearings on the new theory, the point here turns not upon absolute ident.i.ty so much as upon close resemblance. For those who, with Aga.s.siz, doubt the specific ident.i.ty in any of these cases, and those who say, with Pictet, that ”the later tertiary deposits contain in general the debris of species very nearly related to those which still exist, belonging to the same genera, but specifically different,” may also agree with Pictet, that the nearly-related species of successive faunas must or may have had ”a material connection.” But the only material connection that we have an idea of in such a case is a genealogical one. And the supposition of a genealogical connection is surely not unnatural in such cases--is demonstrably the natural one as respects all those tertiary species which experienced naturalists have p.r.o.nounced to be identical with existing ones, but which others now deem distinct For to identify the two is the same thing as to conclude the one to be the ancestor of the other No doubt there are differences between the tertiary and the present individuals, differences equally noticed by both cla.s.ses of naturalists, but differently estimated By the one these are deemed quite compatible, by the other incompatible, with community of origin But who can tell us what amount of difference is compatible with community of origin? This is the very question at issue, and one to be settled by observation alone Who would have thought that the peach and the nectarine came from one stock? But, this being proved is it now very improbable that both were derived from the almond, or from some common amygdaline progenitor? Who would have thought that the cabbage, cauliflower, broccoli kale, and kohlrabi are derivatives of one species, and rape or colza, turnip, and probably ruta-baga, of another species? And who that is convinced of this can long undoubtingly hold the original distinctness of turnips from cabbages as an article of faith? On scientific grounds may not a primordial cabbage or rape be a.s.sumed as the ancestor of all the cabbage races, on much the same ground that we a.s.sume a common ancestry for the diversified human races? If all Our breeds of cattle came from one stock why not this stock from the auroch, which has had all the time between the diluvial and the historic periods in which to set off a variation perhaps no greater than the difference between some sorts of domestic cattle?
That considerable differences are often discernible between tertiary individuals and their supposed descendants of the present day affords no argument against Darwin's theory, as has been rashly thought, but is decidedly in its favor. If the identification were so perfect that no more differences were observable between the tertiary and the recent sh.e.l.ls than between various individuals of either, then Darwin's opponents, who argue the immutability of species from the ibises and cats preserved by the ancient Egyptians being just like those of the present day, could triumphantly add a few hundred thousand years more to the length of the experiment and to the force of their argument.
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