CHAPTER V.
Talking in beetles—Identity of Egyptian animals with those now existing: does this prove fixity of species?—Examination of the celebrated argument of species not having altered in four thousand years—Impossibility of distinguishing species from varieties—The affinities of animals—New facts proving the fertility of Hybrids—The hare and the rabbit contrasted—Doubts respecting the development hypothesis—On hypothesis in Natural History—Pliny, and his notion on the formation of pearls—Are pearls owing to a disease of the oyster?—Formation of the shell; origin of pearls—How the Chinese manufacture pearls.
A witty friend of mine expressed her sense of the remoteness of the ancient Egyptians, and her difficulty in sympathizing with them, by declaring that “they talked in beetles, you know.” She referred, of course, to the hieroglyphics in which that curious people now speak to us from ancient tombs. Whether those swarthy sages were eloquent and wise, or obscure and otherwise, in their beetle-speech, it is certain that entomologists of our day recognize their beetles as belonging to the same species that are now gathered into collections. Such as the Egyptians knew them, such we know them now. Nay, the sacred cats found in those ancient tombs, are cats of the same kind as our own familiar mousers; they purred before Pharaoh as they purr on our hearthrugs; and the descendants of the very dogs which irreligiously worried those cats, are to this day worrying the descendants of those sacred cats. The grains of wheat, which the savans found in the tombs, were planted in the soil of France, and grew into waving corn in no respect distinguishable from the corn grown from the grain of the previous year.
Have these familiar facts any important significance? Are we entitled to draw any conclusion from the testimony of paintings and sculptures, at least four thousand years old, which show that several of our well-known Species of animals, and several of the well-marked Races of men, existed then, and have not changed since then? Nimrod hunted with dogs and horses, which would be claimed as ancestors by the dogs and horses at Melton Mowbray. The Negroes who attended Semiramis and Rhamses are in every respect similar to the Negroes now toiling amid the sugar-canes of Alabama. If, during four thousand years Species and Races have not changed, why should we suppose that they ever will change? Why should we not take our stand on that testimony, and assert that Species are unchangeable?
Such has been the argument of Cuvier and his followers; an argument on which they have laid great stress, and which they have further strengthened by a challenge to adversaries to produce one single case where a transmutation of species has taken place:—“Here we show you evidence that Species have persisted unaltered during four thousand years, and you cannot show us a single case of Species having changed—you cannot show us one case of a wolf becoming a dog, an ass becoming a horse, a hare becoming a rabbit. Yet you must admit that if there were any inherent tendency to change, four thousand years is a long enough period for that tendency to display itself in; and we ought to see a very marked difference between the Species which lived under Semiramis, and those which are living under Victoria. Instead of this, we see that there has been no change: the dog has remained a dog, the horse has remained a horse; every Species retains its well-marked characters.”
No one will say that I have not done justice to this argument. I have stated it as clearly and forcibly as possible, not with any design to captivate your assent, but to make the answer complete. This argument is the cheval de bataille of the Cuvier school; but like many other argumentative war-horses, it proves, on close inspection, to be spavined and brokenwinded. The first criticism we must pass on it is, that it implies the existence of Species as a thing, which can be spoken of as fixed or variable; whereas, as we saw last month, Species is an abstraction, like Whiteness or Strength. No one supposes that there exists any whiteness apart from white things, or strength apart from strong things; yet the naturalists who maintain the fixity of Species, constantly talk as if Species existed independently of the individual animals. Instead of saying that by the word Species is indicated a certain group of characters, and that whenever we meet with this group we say, here is an animal of the same Species; they explicitly declare, or tacitly imply, that although an individual dog may vary, there is something above all individuals—the Species—and that cannot vary. As it is possible some readers may protest that no respectable authority in modern times ever held the opinion here imputed to a school, I will quote the very explicit language of one of Cuvier’s disciples—the last editor of Buffon—who, no later than 1856, could declare that “Species are the primitive forms of Nature. Individuals are nothing but the representatives—the copies of these forms: Les espèces sont les formes primitives de la Nature. Les individus n’en sont que des représentations, des copies.”[12] According to this very explicit, but very extravagant, statement, an individual dog is nothing but a copy of the primitive form—the typical dog—the idea of a dog, as Plato would say; and of course, if this be true, it matters little how widely individual dogs may vary, the type, or species, of which it is the representative, remains unaltered. Indeed it is on this ground that many physiologists explain the fact of hereditary transmission: the individual may vary, it is said, but the species is preserved; and if a dog, without its fore paws, has offspring, every one of which possesses the fore paws, the reason is, that l’idée de l’espèce se reproduit dans le fruit, et lui donne des organes qui manquaient au père ou à la mère.[13] It is not easy to understand how the idea of species can reproduce itself, and give the offspring of a dog the organs which were wanting in the parents; but to those who believe that Species exist independently of individuals, and form the only real existences, the conception may be easier.
I have too much respect for the reader to drag him through a refutation of such philosophy as this; the statement of the opinion is enough. And yet, unless some such opinion be maintained, the doctrine of Fixity of Species is without a basis; for if it be said that the group of characters which constitute the dog are incapable of change, and in this sense Species are fixed, we have to ask what evidence there can be for such an assertion? since it is notorious that individual dogs do show a change in some of the characters of the group. We shall be referred to the Egyptian tombs for evidence. M. Flourens assures us that not only are these tombs evidence that Species have not changed in four thousand years, but that no species has changed—aucune espèce n’a changé—which is surely stepping a long way beyond the precincts of the tombs?
It may be paradoxical, but it is strictly true, that the fact of particular species having remained unaltered during four thousand years, does not add the slightest weight to the evidence in favour of the fixity of Species. “What!” some may exclaim, “do you pretend that four thousand years is not a period long enough to prove the fixity of animal forms?” Yes; I affirm that four thousand, or forty thousand, prove no more than four. It is only by a fallacy that the opposite opinion could gain acceptance. You would not suppose that I had strengthened my case if, instead of contenting myself with stating reasons once, I repeated these same reasons during forty successive pages; you would remind me that this iteration was not cumulation, and that no force was given to my fortieth assertion which the first wanted. Why, then, do you ask me to accept the repetition of the same fact four thousand times over, as an increase of evidence? It is a familiar fact that like produces like, that dogs resemble dogs, and do not resemble buffaloes; this fact is, of course, deepened in our conviction by the unvarying evidence we see around us, and is guaranteed by the philosophical axiom that like causes produce like effects; but when once such a conception is formed, it can gain no fresh strength from any particular instance. If we believe that crows are black, we do not hold that belief more firmly when we are shown that crows were black four thousand years ago. In like manner, if it is an admitted fact that individuals always reproduce individuals closely resembling themselves, it is not a whit more surprising that the dogs of Victoria should resemble the dogs of Semiramis, than that they should resemble their parents: the chain of four thousand years is made up of many links, each link being a repetition of the other. So long as a single pair of dogs resembling each other unite, so long will there be specimens of that species; simply because the children inherit the characteristics of the parents. So long as Negroes marry with Negroes, and Jews with Jews, so long must there be a perpetuation of the Negro and Jewish types; but the tenth generation adds nothing to the evidence of the first, nor the ten-thousandth to the tenth.
I believe that this fallacy, which destroys the whole value of the Cuvierian argument, has not before been pointed out; and even now, you may, perhaps, ask if the fixity of Species is not proved by the fact that like produces like? So far from this, that it is only by the aid of such a fact in organic nature that we can imagine new species to have arisen: in other words, those who believe in the variability of Species, and the introduction of new forms by means of modification from the old, always invoke the law of hereditary transmission as the means of establishing accidental variations. Thus, let us suppose the Egyptian king to have had one hundred dogs, all of them staghounds, and no other form of dog to have existed at that time in that country; the dog species would be represented by the staghound. These staghounds would transmit to their offspring all their specific characters. But, as every one knows, however much dogs may resemble each other, they always present individual differences in size, colour, strength, intelligence, &c. Now, if any one of these differences should happen to become marked, and to increase by the intermarriage of two dogs similarly distinguished by the marked peculiarity, this peculiarity would in time become established by hereditary transmission, and would form the starting-point of a new race of dogs—say the greyhound—unless it were obliterated by intermarriage with dogs of the old type. In the former case, we should have two races of dogs among the descendants of those figured on the Egyptian tombs; but as one of these races would still preserve the original staghound type, Cuvier would refer to it as a proof that species had not varied. We, on the other hand, should point to the greyhound as proof that animal forms are variable, and that a new form had arisen from modification of the old.
An objection will at once be raised to this illustration, to the effect that all zoologists admit the possibility of new Varieties, or Races, being formed; but they deny that new Species can be formed. It is here that the equivoque of the word Species prevents a clear understanding of each other’s argument. Whiteness may justly be said to be unalterable; but white things may vary—they may become gray, or yellow. In like manner Species must be invariable, because Species is a word indicating a particular group of characters; but animals may vary in these characters: they may present some of the characters less, or more, developed; and they may even want some of them. Now as there is no absolute standard of what constitutes Species, what Sub-species, and what Varieties, it becomes impossible to say whether any individual variation in an animal form shall constitute a new Variety, or a new Species. With regard to dogs the differences between the various races are so numerous, and so marked, as would suffice to constitute species and even genera, in other groups of animals.
We must relinquish the idea of proving anything by the paintings and sculptures of the ancients. When we find an Egyptian plough closely resembling the plough still in use in some places, we may identify it as of the same “Species” as our own; but this does not disprove the fact that steam-ploughs, and ploughs of various construction, have been since invented, all of them being modifications of the original type. Formerly, and for many years, the stage-coach was our approved mode of conveyance—and it is still kept up in some districts; nevertheless, modifications of coach-road into tramroad, and tramroad into railroad, have gradually resulted in a mode of conveyance utterly unlike the stage-coach. It is the same with animals.
Let us never forget that Species have no existence. Only individuals exist, and these all vary more or less from each other. When the variations are slight, they have no name; when they are more marked, and are transmitted from one generation to another, they constitute particular Faces, or Varieties; when the differences are still more marked they constitute Sub-species; but, as Mr. Darwin says, “Certainly no clear line of demarcation has yet been drawn between Species and Sub-species; that is, the forms which in the opinion of some naturalists come very near to, but do not quite arrive at the rank of Species; or again, between Sub-species and well-marked Varieties, or between lesser Varieties and individual differences. These differences blend into each other in an insensible series; and a series impresses the mind with the idea of an actual passage.” But the same process of divergence which establishes Varieties out of individual differences, and Species out of Varieties, also serves to establish Genera out of Species, Orders out of Genera, and Classes out of Orders. It is, doubtless, difficult to conceive by what process of modification, two animals of distinct Genera, say a dog and a cat, were produced from a common stock; but organic analogies in abundance render it easy of belief. If we knew as much of zoology as we do of embryology, in respect of the affinities of divergent forms, it would be far less surprising that two different Genera should arise from a common stock, than that all the various parts of the skeleton should arise from a common osseous element. We know that the jaws are identical with arms and legs—both being divergent modifications of a common osseous structure. We know that the arm of a man is identical with the fin of a whale, or the wing of a bird. The differences here in form, size, and function are much greater than the differences which establish orders and classes in the animal series. Unless animal forms were modifications of some common type, it would be difficult to explain their remarkable affinities. As Mr. Darwin says, “It is a truly wonderful fact—the wonder of which we are apt to overlook from familiarity—that all animals and all plants throughout all time and space should be related to each other in group, subordinate to group, in the manner which we everywhere behold, namely, varieties of the same species most closely related together, species of the same genus less closely and unequally related together, forming sections and sub-genera, species of distinct genera much less closely related, and genera related in different degrees, forming sub-families, families, orders, sub-classes, and classes. The several subordinate groups in any class cannot be ranked in a single file, but seem rather to be clustered round points, and these round other points, and so on in almost endless circles. On the view that each species has been independently created, I can see no explanation of this great fact in the classification of all organic beings; but to the best of my judgment it is explained through inheritance, and the complex action of natural selection, entailing extinction and divergence of character. The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth. The green and budding twigs may represent existing species; and those produced during each former year may represent the long succession of extinct species. At each period of growth all the growing twigs have tried to branch out on all sides, and to overtop and kill the surrounding twigs and branches, in the same manner as species and groups of species have tried to overmaster other species in the great struggle for life. The limbs divided into great branches, and these into lesser branches, were themselves once, when the tree was small, budding twigs; and this connection of the former and present buds by ramifying branches, may well represent the classification of all extinct and living species in groups subordinate to groups. Of the many twigs which flourished when the tree was a mere bush, only two or three, now grown into great branches, yet survive and bear all the other branches. So with the species which lived during long-past geological periods, very few now have living and modified descendants.... As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch: so by generation, I believe, it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever-branching and beautiful ramifications.”[14]
It will not be expected that in these brief and desultory remarks I should touch on all, or nearly all, the important points in the discussion respecting the Fixity of Species. Mr. Darwin’s book is in everybody’s hands, and my object has been to facilitate, if possible, the comprehension of his book, and the adoption of a more philosophical hypothesis, by pointing out the weakness of the chief argument on the other side. There is one more argument which may be noticed—the more so as it is constantly adduced with triumph by the one school, and admitted as a difficulty by the other. Its force is so great that it prevents many from accepting the development hypothesis. It is the argument founded on the alleged impossibility of Hybrids continuing the race. More than two or three generations of Hybrids, it is said, can never be maintained; after that, the new form perishes: thus clearly showing how Nature repudiates such amalgamations, and keeps her species jealously distinct and invariable. This argument is held to be the touchstone of the doctrine of species. I wish it were so; because, in that case, the question would no longer be one of hypothesis, since we have now the indubitable proof that some Hybrids are fertile unto the thirteenth generation and onwards.
A history of the various attempts which have been made to prove and disprove the fertility of Hybrids, would lead us beyond our limits; the curious reader is referred to the works cited below.[15] One decisive case alone shall be given here, and no one will dispute that it is decisive.
The hare (lepus timidus) is assuredly of a distinct species from the rabbit (lepus cuniculus). So distinct are these species, that any classification which should range them as one, would violate every accepted principle. The hare is solitary, the rabbit gregarious; the hare lives on the surface of the earth, the rabbit burrows under the surface; the hare makes her home among the bushes, the rabbit makes a sort of nest for her young in her burrow—keeping them there till they are weaned; the hare has reddish-brown flesh, the rabbit white flesh; while the odour exhaled by each, and the flavour of each, are unmistakeably different. The hare has many anatomical characters differing from those of the rabbit: such as greater length and strength of the hind legs, larger body, shorter intestine, thicker skin, firmer hair, and different colour. The hare breeds only twice or thrice a year, and at each litter has only two or four; the rabbit will breed eight times a year, and each time has four, six, seven, and even eight young ones. Finally, the two are violent foes: the rabbits always destroy the hares, and all sportsmen are aware that if the rabbits be suffered to multiply on an estate, there will be small chance of hares.
Nevertheless, between species so distinct as these, a new hybrid race has been reared by M. Rouy, of Angoulême, who each year sends to market upwards of a thousand of his Leporides, as he calls them. His object was primarily commercial, not scientific. His experiments, extending from 1847 to the present time, have not only been of great commercial value—introducing a new and valuable breed—but have excited the attention of scientific men, who are now availing themselves of his skill and experience to help them in the solution of minor problems. It is enough to note here, that these hybrids of the hare and the rabbit are fertile, not only with either hares or rabbits, but with each other. Thirteen generations have already been enumerated, and the last remains so vigorous that no cessation whatever is to be anticipated.
In presence of this case (and others, though less striking, might be named) there is but one alternative; either we must declare that rabbits and hares form one and the same species—which is absurd—or we must admit that new types may be formed by the union of two existing types; and consequently that species are variable. If the doctrine of Fixity of Species acknowledges the touchstone of hybridity, the fate of the doctrine is settled for ever.
Although I conceive the doctrine of Fixity of Species to be altogether wrong, I cannot say that the arguments adduced in favour of the development hypothesis rise higher than a high degree of probability, still very far from demonstration; they will leave even the most willing disciple beset with difficulties and doubts. When stated in general terms, that hypothesis has a fascinating symmetry and simplicity, but no sooner do we apply it to particular cases, than a thick veil of mystery descends, and our pathway becomes a mere blind groping towards the light. There is nothing but what is perfectly conceivable, and in harmony with all analogies, in the idea of all animal forms having arisen from successive modifications of one original form; but there are many things perfectly conceivable, which have nevertheless no existence; there are many explanations perfectly probable, which are not true; and when we come to seek for the evidence of the development hypothesis, that evidence fails us. It may be true, but we cannot say that it is true. Ten years ago, I espoused the hypothesis, and believed that it must be the truth; but ten years of study, instead of deepening, have loosened that conviction: they have strengthened my opposition to the hypothesis of fixity of species, but they have given greater force to the difficulties which beset the development hypothesis, and have made me feel that at present the requisite evidence is wanting. I conclude with reminding the reader that the question of the origin of species is at present incapable of a positive answer; of the two hypotheses, that of development seems the more harmonious with our knowledge; but it is no more than an hypothesis, and will probably for ever remain one. Now, an hypothesis, although indispensable as a provisional mode of grouping together facts, and giving them some sort of explanation, is after all only a guess, and it may be absurdly wide of the truth. In Natural History, as in all other departments of speculative ingenuity, there have been a goodly number of outrageously extravagant hypotheses, gravely propounded, and credulously accepted. Men prefer an absurd guess to a blank; they would rather have a false opinion than no opinion; and one of the last developments of philosophic culture, is the power of abstaining from forming an opinion, where the necessary data are absent.
If you wish to see how easily hypotheses are formed and accepted, you need only turn over the history of any science. If you want a laugh at credulity, read a chapter of Pliny’s Natural History. Pliny is a classic, and was for centuries an authority; but looked at with impartial eyes, he appears the veriest “old woman” that ever wrote in a beautiful style. He was a mere bookworm, without a particle of scientific insight. His was not an age when men had much regard to evidence; but to him the suspicion never seems to have occurred that Gossip Report could be given to romancing, or that travellers could “see strange things.” No fable is too monstrous for his credulity.
One of the pretty fables Pliny repeats, is, that pearls are formed by drops of dew falling into the gaping valves of the oyster. It never occurred to him to ask whether oysters were ever exposed to the dew? whether the drops could fall into their valves? whether oysters kept their valves open, except when under water? or, finally, whether, if the dew did fall in, it would remain a rounded drop? The drop of dew had a certain superficial resemblance to the pearl, and that was enough. Ælian’s hypothesis was somewhat better: he supposed that the pearls were produced by lightning flashing into the open shells.
Turning from these ancient sages, you will ask how pearls are formed? And almost any ingenious modern, not a zoologist, will tell you (and tell you falsely), that the pearl is a disease of the oyster. One is somewhat fatigued with the merciless frequency with which this notion has been dragged in, as an illustration of genius issuing out of sorrow and adversity; and it is time to stop that “damnable iteration” by discrediting the notion. Know then, that if
“Most wretched men
Are cradled into poetry by wrong:
They learn in suffering what they teach in song”—
it is not true that oysters secrete in suffering what women wear as necklaces. Disease would be the very worst cradle for pearls. The idea of disease originated in a fanciful supposition of pearls being to the oyster and mussel what gall-stones and urinary calculi are to higher and more suffering animals. Réaumur, to whom we owe so many good observations and suggestive ideas, came near the truth when, in 1717, he showed that the structure of pearls was identical with the structure of the shells in which they grow. He attributed their formation to the morbid effusion of coagulating shell-material.
I presume you know that shells are formed by a secretion from the mantle? The mantle is that delicate semi-transparent membrane which you observe, on opening a mussel, lining the whole interior of the shells, and having at its free margins a sort of fringe of delicate tentacles, which are sensitive and retractile. A microscopic examination of these fringes shows them to be glandular in structure—that is, they are secreting organs. The whole mantle, indeed, is a secreting organ, and its secretion is the shell-material: the fringes secrete the colouring matters of the shell, and enlarge its circumference; the rest of the mantle secretes the nacre, or mother-of-pearl, and increases the thickness of the shell. Now it is obvious that the formation of pearl nacre, and of pearls, depends on the healthy condition of the mantle, not on its diseases. If the mantle be injured the nacre is not secreted at all, or in less quantities.
But, although pearls depend upon the healthy, not the diseased activity of the mantle, it is clear that there must be some unusual condition present for their formation; since the secretion of nacre does not spontaneously assume the form of pearls. What is the unusual condition? Naturalists are at present divided into two camps, fighting vigorously for victory. The one side maintains that the origin of a pearl is this—an egg of the oyster has escaped and strayed under the mantle; or the egg of a parasite has been deposited there; this egg forms the nucleus, round which the nacre forms, and thus we have the pearl. The other side maintains with great positiveness that anything will form a nucleus, a grain of sand, no less than the egg of a parasite. ’Tis a pretty quarrel, which we may leave them to settle. Some aver that grains of sand are more numerous than anything else; but Möbius says that of forty-four sea pearls, and fifteen fresh-water pearls, examined by him, not one contained a grain of sand; and Filippi, who has extensively investigated this subject, denies that a grain of sand ever forms the nucleus of a true pearl. Both Filippi and Küchenmeister[16] declare that a parasite gets into the mussel or oyster, and its presence there stimulates an active secretion of nacre.
There are pearls, according to Möbius, which consist of three different systems of layers, like the shells in which they are formed; with this difference, that these layers are reversed: in the shell the nacre forms the innermost layer, in the pearl it forms the outermost. Hence the qualities of the pearl depend on the shell, and on the different proportions of nacre and carbonate of lime.
Since we know how pearls are made, may it not be expected that we should learn to make them? Ever since the days of Linnæus the hope has been entertained, and it is now becoming every day more likely to be realized. Imperfect pearls have been made in abundance. The Chinese have long practised the art. They simply remove the large fresh-water mussel from the water, insert a foreign substance under the mantle, and in two or three years (if I remember rightly) they take the mussels up again, and find the pearls formed. In this way they make little mother-of-pearl Josses, which are sold for a penny each; and I remember seeing a couple of large shells in the Anatomical Museum at Munich, the whole length of which was occupied by rows of little squab Josses, very comical to behold. I was informed that a copper chain of these deities had been inserted under the mollusc’s mantle, and this was the result.