Part 2 (1/2)

Now the great question arises--whence, by what power, or by what law, were these reiterated transitions brought about? Were the organized species of one geological epoch, by some long-continued agency of natural causes, trans.m.u.ted into other and succeeding species? or were there an extinction of species, and a replacement of them by others, through special and miraculous acts of creation? or, lastly, did species gradually degenerate and die out from the influence of the altered and unfavourable physical conditions in which they were placed, and be supplanted by immigrants of different species, and to which the new conditions were more congenial?

The last, we confess, is the view to which we are most inclined--first, because we think a trans.m.u.tation of species, from a lower to a higher type, has not been satisfactorily proved; and second, because of the strong impression we entertain, that the universe, subject to certain cyclical and determinate mutations, was made complete at first, with self-subsisting provisions for its perpetual renewal and conservation.

We shall advert to this matter hereafter; but at present it is the conclusions of the author of the _Vestiges_ that claim consideration. He adopts the first interpretation of animal phenomena, namely, that there has been a trans.m.u.tation of species, that the scale of creation has been gradually advancing in virtue of an inherent and organic law of development. Nature, he contends, began humbly; her first works were of simple form, which were gradually meliorated by circ.u.mstances favourable to improvement, and that everywhere animals and plants exhibit traces of a parallel advance of the physical conditions and the organic structure.

The general principle, he inculcates, is, that each animal of a higher kind, in the progress of its embryo state, pa.s.ses through states which are the final condition of the lower kind; that the higher kinds of animals came later, and were developed from the lower kinds, which came earlier in the series of rock formations, by new peculiar conditions operating upon the embryo, and carrying it to a higher stage. These conclusions the author maintains geology has established, and of the results thence derived he gives the subjoined recapitulation:--

”In pursuing the progress of the development of both plants and animals upon the globe, we have seen an advance in both cases, from simple to higher forms of organization. In the botanical department we have first sea, afterwards land plants; and amongst these the simpler (cellular and cryptogamic) before the more complex. In the department of zoology, we see, first, traces all but certain of infusoria [sh.e.l.led animalculae]; then polypiaria, crinoidea, and some humble forms of the articulata and mollusca; afterwards higher forms of the mollusca; and it appears that these existed for ages before there were any higher types of being. The first step forward gives fishes, the humblest cla.s.s of the vertebrata; and, moreover, the earliest fishes partake of the character of the lower sub-kingdom, the articulata. Afterwards come land animals, of which the first are reptiles, universally allowed to be the type next in advance from fishes, and to be connected with these by the links of an insensible gradation. From reptiles we advance to birds, and thence to mammalia, which are commenced by marsupialia, acknowledgedly low forms in their cla.s.s. That there is thus a progress of some kind, the most superficial glance at the geological history is sufficient to convince us.”

Now this appears plausible and conclusive, but the correctness of the recapitulation here made, and its conformity to actual nature, have been sharply disputed. It may be true that sea plants came first, but of this there is no proof; and of land plants there is not a shadow of evidence that the simpler forms came into being before the more complex: the simple and complex forms are found together in the more ancient _flora_.

It is true that we first see polypiaria, crinoidea, articulata, and mollusca, but not exactly in the order stated by the author. It is true that the next step gives us fishes, but it is not true that the earliest fishes link on to the lower sub-kingdom, the articulata. It is true that we afterwards find reptiles, but those which first appear belong to the highest order of the cla.s.s, and show no links of an insensible gradation into fishes. In the tertiary deposit of the London clay the evidence of concatenation entirely fails. Among the millions of organic forms, from corals up to mammalia of the London and Paris basins, hardly a single secondary species is found. In the south of France it is said that two or three secondary species struggle into the tertiary strata; but they form a rare and evanescent exception to the general rule. Organic nature at this stage seems formed on a new pattern--plants as well as animals are changed. It might seem as if we had been transported to a new planet; for neither in the arrangement of the genera and the species, nor in their affinities with the types of a pre-existing world, is there any approach to a connected chain of organic development.

For some discrepancies the author endeavours to account, and it is fair to give his explanation:--

”Fossil history has no doubt still some obscure pa.s.sages; and these have been partially adverted to. Fuci, the earliest vegetable fossils as yet detected, are not, it has been remarked, the lowest forms of aquatic vegetation; neither are the plants of the coal-measures the very lowest, though they are a low form, of land vegetation. There is here in reality no difficulty of the least importance. The humblest forms of marine and land vegetation are of a consistence to forbid all expectation of their being preserved in rocks. Had we possessed, contemporaneously with the fuci of the Silurians, or the ferns of the carboniferous formation, fossils of higher forms respectively, _equally unsubstantial_, but which had survived all contingencies, then the absence of mean forms of similar consistency might have been a stumbling-block in our course; but no such phenomena are presented. The blanks in the series are therefore no more than blanks; and when a candid mind further considers that the botanical fossils actually present are all in the order of their organic development, the whole phenomena appear exactly what might have been antic.i.p.ated. It is also remarked, in objection, that the mollusca and articulata appear in the same group of rocks (the slate system) with polypiaria, crinoidea, and other specimens of the humblest sub-kingdom; some of the mollusca, moreover, being cephalopods, which are the highest of their division in point of organization. Perhaps, in strict fact, the cephalopoda do not appear till a later time, that of the Silurian rocks. But even though the cephalopoda could be shewn as pervading all the lowest fossiliferous strata, what more would the fact denote than that, in the first seas capable of sustaining any kind of animal life, the creative energy advanced it, in the s.p.a.ce of one formation, (no one can say how long a time this might be,) to the highest forms possible in that element, excepting such as were of vertebrate structure. It may here be inquired if geologists are ent.i.tled to set so high a value as they do upon the point in the scale of organic life which is marked by the upper forms of the mollusca. It will afterwards be seen that this is a low point compared with the whole scale, if we are to take as a criterion that parity of development which has been observed in the embryo of one of the higher animals. _The human embryo pa.s.ses through the whole s.p.a.ce representing the invertebrate animals in the first month, a mere fraction of its course._ There is indeed a remarkably rapid change of forms in such an embryo at first: the rapidity, says Professor Owen, is 'in proportion to the proximity of the ovum to the commencement of its development;' and, conformable to this fact, we find the same zoologist stating that, in the lowest division of the animal kingdom, (the Acrita of his arrangement,) there is a much quicker advance of forms towards the next above it, than is to be seen in subsequent departments. There is, indeed, to the most ordinary observation, a rapidity and force in the productive powers of the lowest animals, which might well suggest an explanation of that rush of life which seems to be indicated in the slate and Silurian rocks. With regard to the so-called early occurrence of fishes partaking of the saurian character, I would say that their occurrence a full formation after the earliest and simplest fishes, is, considering how little we know of the s.p.a.ce of time represented by a formation, not early: their being later in any degree is the fact mainly important. The subsequent rise of new orders of fishes, fully piscine in character, may be explained by the supposition of their having been developed, as is most likely, from a different portion of the inferior sub-kingdom. In short, all the objections which have been made to the great fact of a general progress of organic development throughout the geological ages, will be found, on close examination, to refer merely to doubtful appearances of small moment, which vanish into nothing when rightly understood.”

Upon some of the chief points here involved, it may be remarked that the most eminent physiologists are not agreed; they are not agreed that animals can be arranged in a series, pa.s.sing from lower to higher; nor that animals of a higher kind in the embryo state pa.s.s through the successive stages of the lower kinds; the character of these stages, in the a.s.serted doctrine, being taken from the brain and heart, and man being the highest point of the series. There are physiologists too who deny that the brain of the human embryo at any period, however early, resembles the brain of any mollusk or of any articulata. It never, they a.s.sert, pa.s.ses through a stage comparable or a.n.a.logous to a permanent condition of the same organ in any invertebrate animal; and in like manner the spinal cord in the human vertebrae at no period agrees with the corresponding part of the lower kind of animals. The moment it becomes visible in the human embryo, it is entirely dorsal in position; while in mollusks and articulatas a great part, or nearly the whole, is ventral. The same is true of the heart, or centre of the vascular system, which has always a different relative position in the great nervous centre in the human embryo from what it has in any articulate animal, and in most mollusks.

A second position in the _Vestiges_ appears not to have been established--namely, as to the uniform geological arrangement of different organic structures. It is not true that _only_ the lowest forms of animal life are found in the lowest fossiliferous rocks, and that the more complicated structures are gradually and exclusively developed among the higher bands in what might be called a natural ascending scale. On the contrary, the predaceous cephalopods and the highly organized crustaceous are among the oldest fossils. Such appears to be the order of nature as evidenced by facts, and it must be admitted, however repugnant to preconceived notions or mere mortal conjectural amendments.

In the third place the evidence seems to preponderate in favour of _permanency of species_. There can be no doubt that both plants and animals may, by the influence of breeding, and of external agents operating upon their const.i.tution, be greatly modified, so as to give rise to varieties and races different from what before existed. But there are limits to such modifications, as in the different kind and breed of dogs; and no organized beings can, by the mere working of natural causes, be made to pa.s.s from the type of one species to that of another. A wolf by domestication, for example, can never become a dog, nor the ourang-outang by the force of external circ.u.mstances be brought within the circle of the human species.

In this opinion Mr. LYELL, Dr. PRICHARD, and Mr. LAWRENCE, concur. The general conclusion at which they have arrived is, that there is a capacity in all species to accommodate themselves to a certain extent to a change of external circ.u.mstances; this extent varying greatly according to the species. There may thus be changes of appearance or structure, and some of these changes are transmissible to the offspring; but the mutations thus superinduced are governed by certain laws, and confined within certain limits. Indefinite divergence from the original type is not possible, and the extreme limit of possible variation may usually be reached in a short period of time; in short, Professor WHEWELL concludes (_Indications of Creation_, p. 56), _that every species has a real existence in nature_, and a trans.m.u.tation from one to another does not exist. Thus for example, CUVIER remarks that, notwithstanding all the differences of age, appearance and habits, which we find in the dogs of various races and countries, and though we have (in the Egyptian mummies) skeletons of this animal as it existed 3,000 years ago, the relation of the bones to each other remains essentially the same; and with all the varieties of their shape and size, there are characters which resist all the influences, both of external nature, of human intercourse, and of time.

What varieties, again, in the forms of the different breeds of horses and horned cattle; racers, hunters, coach horses, dray horses, and ponies; short-horns and long-horns, Devons and Herefords, polled galloways and Shetlands; how unlike are the unimproved breeds of cattle as they existed a century ago before the march of agricultural improvement began, and how different were most of these as then existing in what may be called the normal state from the wild cattle produced in Chillington Park. It has been found, however, when external and artificial conditions are removed, and these different breeds are allowed to run wild, as in the Pampas and Australia, no matter what the diversity of size, shape, and colour of the domestic breeds, they reverted in their wild state, in these respects, to their primitive types.

So again with regard to cultivated vegetables and flowers. How different are the species of the red cabbage and the cauliflower; who would have expected them to be varieties of the wild _bra.s.sica oleracea_? Yet from that they have been derived by cultivation. They have, however, a tendency like animals to revert to the original type, or, in the gardener's phrase, to degenerate, which it requires the utmost care on his part to counteract. When left to a state of nature, they speedily lose their acquired forms, properties and character, and regain those of the original species.

If species be permanent--if no education or training can educe new kinds--if the higher cla.s.ses of animals are not the results of meliorations of the lower--whence did they come? This question we are not bound to answer. It might be as reasonably asked, whence did the lower cla.s.ses come? Geology, like other sciences, does not conduct us to the _beginning_, it only takes up creation at certain ulterior stages of development. The changes and construction of the globe may have been different in different parts; it has not been proved that geological revolutions have been either universal or contemporary. There may have been climates and regions adapted to the existence of the higher cla.s.s of land animals, while contemporarily therewith other portions of the globe might be undergoing changes beneath the ocean. It is not improbable that the human species dwelt nearly stationary for ages on the old continents of Africa and Asia, while Europe and America were covered with water. Supposing these new continents formed, either by the gradual subsidence of the sea or the rising of its bed, successive inhabitants would follow in the order presented by existing organic remains. While covered by the sea, what now form Europe and America could only be peopled by marine animals; but as the land rose or the waters subsided into their ocean channels, and dry land appeared, reptiles and amphibiae might become the occupants; next, as the earth became drier and more salubrious, the new continent would be resorted to by terrestrial animals; in a still more advanced stage of purification and salubrity, man himself, as the lord of all the preceding cla.s.ses of immigrants, would take possession, and as he still continues the living occupant it is premature to look for his petrifaction.

ORIGIN OF THE ANIMATED TRIBES.

Science has mastered many perplexities, but is almost powerless as ever in generation. All that lives, and still more all that moves, must have a pre-existing germ formed independently of the created being, but which is essential to its existence, and fixes the type of organization. The old adage--_omne animal ab ovo_--may be taken as generally true. But though every animal has its primordial egg or germ, all germs are not identical. In the beginning of life there are other organic elements besides the ovum. Partly on direct proof and partly on good a.n.a.logy, it may be inferred that these differ in different species--that each in the first stages of existence is bound by a different and immutable mode of development--and, if so, there can be no embryotic ident.i.ty. ”By no change of conditions,” says Dr. CLARKE, ”can two ova of animals of the same species be developed into different animal species; neither by any provision of identical conditions can two ova of different species be developed into animals of the same kind.” If these views be right, and we believe them to be so, there cannot be a trans.m.u.tation of species under the influence of external circ.u.mstances.

Baffled in the effort either to create species or organically to change them, attempts have been made to approach nearer to the source of vitality, and explain the chemical, electric, or mechanical laws by which the vital principle is influenced. For this purpose various hypotheses have been put forth; one is the noted conjecture of Lord MONBODDO, that man is only an advanced development of the chimpanzee or ourang-outang. A second explanation is that given by LAMARCK, who surmised, and with much ingenuity attempted to prove, that one being advanced in the course of generations into another, in consequence merely of the experience of wants calling for the exercise of faculties in a particular direction, by which exercise new developments of organs took place, ending in variations sufficient to const.i.tute new species.

In this way the swiftness of the antelope, the claws and teeth of the lion, the trunk of the elephant, the long neck of the giraffe have been produced, it is supposed, by a certain plastic character in the construction of animals, operated upon for a long course of ages by the attempts which these animals make to attain objects which their previous organization did not place within their reach. This is what is meant by the hypothesis of _progressive tendencies_, and which requires for its validity not only the a.s.sumption of a mere capacity for change, but of active principles conducive to improvement and the attainment of higher powers and faculties. More recently ST. HILAIRE has published a paper in which he speaks of the immutability of species as a conviction that is on the decline, and that the age of CUVIER is on the close. Carried away by what Professor PHILLIPS has called a poetical conjecture that cannot be proved, this writer propounded the speculation that the present crocodiles are really the offspring of crocodilian reptiles, the difference being merely the effect of physical conditions, especially operating during long geological periods upon one original race. The human species, he contends, are but an advanced development of the higher order of the monkey tribe, and that the negroes are degenerating towards that type again. According to him the sivatherium--a fossil animal that had been found in the Himalaya mountains--was the primeval type that time had fined down into the giraffe from long-continued feeding on the branches of trees. Dr. FALCONER and Capt. CAUTLEY, however, have shown that anatomical proofs are all against this inference, but if any doubt remained it must yield to the fact, that among the _fauna_ of the Sewalik hills the sivatherium and the giraffe were contemporaries.

The author of the _Vestiges of Creation_ has put forth an hypothesis founded on the preceding conjectures, but more compact and conclusive.

He is, as we have seen, in favour of the progressive change of species, adopting the notion that men once had tails, and that the rudiments of this condal appendage are found in an undeveloped state in the _os coccygis_ (p. 199.) His leading idea of the progress of organic life is that the ”_simplest and most primitive type under a law to which that of like production is subordinate, gave birth to the type next above it; that this again produced the next higher, and so on to the very highest_, the stages of advance being in all cases very small--namely, from one species only to another; so that the phenomenon has always been of a modest and simple character.” (p. 231.) The arguments by which the author endeavours to prove his hypothesis may be thus compressed.

According to him foetal development is a science, ill.u.s.trated by HUNTER'S great collection of the Royal College of Surgeons, and established by the conclusions of ST. HILAIRE and TIEDMANN. Its primary positions are--1. That the embryos of all animals are not distinguishably different from each other; and, 2. That those of all animals pa.s.s through a series of phases of development, each of which is the type or a.n.a.logue of the permanent configuration of tribes inferior to it in the scale. Higher the order of animals, the more numerous its stages of progress. Man himself is not exempt from this law. His first foetal form is that which is permanent in the animalcule; it next pa.s.ses through ulterior stages, resembling successively a fish, a reptile, a bird, and the lower mammalia before it attains its specific maturity.

The period of gestation determines the species; protract it, and the species is advanced to a higher cla.s.s. This might be done by the force of certain conditions operating upon the system of the mother. Give good conditions and the young she produces will improve in development; give bad conditions and it will recede. Cases of monstrous birth in the human species are appealed to, in which the most important organs are left imperfectly developed; the heart, for instance, having sometimes advanced no further than the three-chambered or reptile form, while there are instances of that organ being left in the two-chambered or fish-like form. These defects arise from a failure of the power of development in the mother, occasioned by misery or bad health, and they are but the converse of those conditions that carry on species to species. The _differences of s.e.xes_ is the result of foetal progress only one degree less marked than that of a change of species. s.e.x is fully ascertained to be a matter of development. All beings are at one stage of the embryotic progress _female_. A certain number of them are afterwards advanced to the more powerful s.e.x. For proof of this, the economy of bees is cited; when they wish to raise a queen-bee, or true female, they prepare for the larva a more commodious cell, and feed it with delicate food. But we shall here stop to remark on the author's argument up to this point.

It is manifest, according to his hypothesis, that neither s.e.x nor species depend on the ancestral germ, but simply on physical conditions and mechanical development. But eminent physiologists deny that the facts are such as he has stated; they deny, as we have stated in a former section, that the foetal progress is such as the _Vestiges_ represent them to be; they deny that the human embryo, for example, exhibits in successive stages the form of fish, lizard, bird, beast: on the contrary, they contend that it is only in the earliest period of the organic germ, when the manifestations are almost too obscure for microscopic sense, that any resemblance exists; that immediately the organic germ becomes sensible to observation, s.e.x and species are found to be fixed. Take, for example, the vertebrata; in these, by some mysterious bond of union, the organic globules are seen to arrange themselves into two nearly parallel rows. We may then say that the keel of the animal is laid down, and in it we have the first rudiments of a backbone and a continuous spinal chord. But during the progress and completion of this first organic process no changes have been observed a.s.similating the nascent embryo to any of the inferior animals. The next series of changes in the germinal membrane are of two kinds--in one the nervous system, the organs of motion, the intestinal ca.n.a.l, the heart and blood-vessels are manifested; the other set of changes, which are subsequent, produce the perfection of the animal and determine its s.e.x.

All these manifestations result from germinal appendages that cannot be severed or changed without ruin to the embryo, and the conditions essential to life as the structure advances are due temperature, due nutriment of the nervous organs, and due access to the atmospheric air.

Without, therefore, pursuing further this part of the inquiry, we shall remark that the question at issue between the _Vestiges_ and its opponents is one of facts--of conflicting evidence--to be tried by the jury of the public, or rather by those who, from science or professional pursuits, are competent to form an authoritative opinion. Our own conclusion is, that in face of the testimony adduced against it, the author's hypothesis is not yet established.

For proof that species do change, and that even new species have been actually and recently produced, the author has adduced statements certainly as questionable and little satisfactory as his representation of foetal phenomena. We can only briefly enumerate them. First we are told that oats sown at midsummer, if kept cropped down, so as to be prevented shooting into ear, and then allowed to remain in the ground over winter, will spring up next year in the form of rye (p. 226). This need not be disputed about; the experiment can be easily tried; but if rye were the result, it would be no conclusive proof of a translation of species. Perhaps the oat-plants perished under the operation of repeated cuttings, and the rye seed was dormant in the earth and sprung up in its place; or, if not so, oats and rye may not be different species, only varieties of the same species. They are scarcely more dissimilar than the primrose, the cowslip, and the oxlip, which have all been raised from the seed of the same plant, and are now regarded by botanists as varieties instead of species.