Chapter IX

THEORY OF THE PROGRESSIVE DEVELOPMENT OF ORGANIC LIFE AT SUCCESSIVE GEOLOGICAL PERIODS.

Theory of the progressive development of organic life--Evidence in
its support inconclusive--Vertebrated animals, and plants of the
most perfect organization, in strata of very high
antiquity--Differences between the organic remains of successive
formations--Comparative modern origin of the human race--The popular
doctrine of successive development not established by the admission
that man is of modern origin--Introduction of man, to what extent a
change in the system.

_Progressive development of organic life._--In the preceding chapters I have considered whether revolutions in the general climate of the globe afford any just ground of opposition to the doctrine that the former changes of the earth which are treated of in geology belong to one uninterrupted series of physical events governed by ordinary causes. Against this doctrine some popular arguments have been derived from the great vicissitudes of the organic creation in times past; I shall therefore proceed to the discussion of such objections, which have been thus formally advanced by the late Sir Humphrey Davy. "It is impossible," he affirms, "to defend the proposition, that the present order of things is the ancient and constant order of nature, only modified by existing laws: in those strata which are deepest, and which must, consequently, be supposed to be the earliest deposited, forms even of vegetable life are rare; shells and vegetable remains are found in the next order; the bones of fishes and oviparous reptiles exist in the following class; the remains of birds, with those of the same genera mentioned before, in the next order; those of quadrupeds of extinct species in a still more recent class; and it is only in the loose and slightly consolidated strata of gravel and sand, and which are usually called diluvian formations, that the remains of animals such as now people the globe are found, with others belonging to extinct species. But, in none of these formations, whether called secondary, tertiary, or diluvial, have the remains of man, or any of his works, been discovered; and whoever dwells upon this subject must be convinced, that the present order of things, and the comparatively recent existence of man as the master of the globe, is as certain as the destruction of a former and a different order, and the extinction of a number of living forms which have no types in being. In the oldest secondary strata there are no remains of such animals as now belong to the surface; and in the rocks, which may be regarded as more recently deposited, these remains occur but rarely, and with abundance of extinct species;--there seems, as it were, a gradual approach to the present system of things, and a succession of destructions and creations preparatory to the existence of man."[211]

In the above passages, the author deduces two important conclusions from geological data: first, that in the successive groups of strata, from the oldest to the most recent, there is a progressive development of organic life, from the simplest to the most complicated forms;--secondly, that man is of comparatively recent origin, and these conclusions he regards as inconsistent with the doctrine, "that the present order of things is the ancient and constant order of nature only modified by existing laws."

With respect, then, to the first of these propositions, we may ask whether the theory of the progressive development of animal and vegetable life, and their successive advancement from a simple to a more perfect state, has any secure foundation in fact? No geologists who are in possession of all the data now established respecting fossil remains, will for a moment contend for the doctrine in all its detail, as laid down by the distinguished philosopher to whose opinions we have referred: but naturalists, who are not unacquainted with recent discoveries, continue to defend it in a modified form. They say that in the first period of the world (by which they mean the earliest of which we have yet brought to light any memorials), the vegetation was characterized by a predominance of cryptogamic plants, while the animals which coexisted were almost entirely confined to zoophytes, testacea, and a few fish. Plants of a less simple structure, coniferae and cycadeae, flourished largely in the next epoch, when oviparous reptiles began also to abound. Lastly, the terrestrial flora became most diversified and most perfect when the highest orders of animals, the mammalia and birds, were called into existence.

Now in the first place, it may be observed, that many naturalists are guilty of no small inconsistency in endeavoring to connect the phenomena of the earliest vegetation with a nascent condition of organic life, and at the same time to deduce from the numerical predominance of certain forms, the greater heat or uniformity of the ancient climate. The arguments in favor of the latter conclusion are without any force, unless we can assume that the rules followed by the Author of Nature in the creation and distribution of organic beings were the same formerly as now; and that, as certain families of animals and plants are now most abundant in, or exclusively confined to regions where there is a certain temperature, a certain degree of humidity, a certain intensity of light, and other conditions, so also analogous phenomena were exhibited at every former era.

If this postulate be denied, and the prevalence of particular families be declared to depend on a certain order of precedence in the introduction of different classes into the earth, and if it be maintained that the standard of organization was raised successively, we must then ascribe the numerical preponderance, in the earlier ages, of plants of simpler structure, _not to the heat_, or other climatal conditions, but to those different laws which regulate organic life in newly created worlds.

Before we can infer a warm and uniform temperature in high latitudes, from the presence of 250 species of ferns, some of them arborescent, accompanied by lycopadiacae of large size, and araucariae, we must be permitted to assume, that at all times, past, present, and future, a heated and moist atmosphere pervading the northern hemisphere has a tendency to produce in the vegetation a predominance of analogous forms.

It should moreover be borne in mind, when we are considering the question of development from a botanical point of view, that naturalists are by no means agreed as to the existence of an ascending scale of organization in the vegetable world corresponding to that which is very generally recognized in animals. "From the sponge to man," in the language of De Blainville, there may be a progressive chain of being, although often broken and imperfect; but if we seek to classify plants according to a linear arrangement, ascending gradually from the lichen to the lily or the rose, we encounter incomparably greater difficulties. Yet the doctrine of a more highly developed organization in the plants created at successive periods presupposes the admission of such a graduated scale.

We have as yet obtained but scanty information respecting the state of the terrestrial flora at periods antecedent to the coal. In the carboniferous epoch, about 500 species of fossil plants are enumerated by Adolphe Brongniart, which we may safely regard as a mere fragment of an ancient flora; since, in Europe alone, there are now no less than 11,000 living species. I have already hinted that the plants which produced coal were not drifted from a distance, but that nearly all of them grew on the spots where they became fossil. They appear to have belonged, as before explained (p. 115), to a peculiar class of _stations_,--to low level and swampy regions, in the deltas of large rivers, slightly elevated above the level of the sea. From the study, therefore, of such a vegetation, we can derive but little insight into the nature of the contemporaneous upland flora, still less of the plants of the mountainous or Alpine country; and if so, we are enabled to account for the apparent monotony of the vegetation, although its uniform character was doubtless in part owing to a greater uniformity of climate then prevailing throughout the globe. Some of the commonest trees of this period, such as the sigillariae, which united the structure of ferns and of cycadeae, departed very widely from all known living types. The coniferae and ferns, on the contrary, were very closely allied to living genera. It is remarkable that none of the exogens of Lindley (dicotyledonous angiosperms of Brongniart), which comprise four-fifths of the living flora of the globe, and include all the forest trees of Europe except the fir-tribe, have yet been discovered in the coal measures, and a very small number--fifteen species only--of monocotyledons. If several of these last are true plants, an opinion to which Messrs. Lindley, Unger, Corda, and other botanists of note incline, the question whether any of the most highly organized plants are to be met with in ancient strata is at once answered in the affirmative. But the determination of these palms being doubtful, we have as yet in the coal no positive proofs either of the existence of the most perfect, or of the most simple forms of flowering or flowerless vegetation. We have no fungi, lichens, hepatici or mosses: yet this latter class may have been as fully represented then as now.

In the flora of the secondary eras, all botanists agree that palms existed, although in Europe plants of the family of zamia and cycas together with coniferae predominated, and must have given a peculiar aspect to the flora. As only 200 or 300 species of plants are known in all the rocks ranging from the Trias to the Oolite inclusive, our data are too scanty as yet to affirm whether the vegetation of this second epoch was or was not on the whole of a simpler organization than that of our own times.

In the Lower Cretaceous formation, near Aix-la-Chapelle, the leaves of a great many dicotyledonous trees have lately been discovered by Dr. Debey, establishing the important fact of the coexistence of a large number of angiosperms with cycadeae, and with that rich reptilian fauna comprising the ichthyosaur, plesiosaur, and pterodactyl, which some had supposed to indicate a state of the atmosphere unfavorable to a dicotyledonous vegetation.

The number of plants hitherto obtained from _tertiary_ strata of different ages is very limited, but is rapidly increasing. They are referable to a much greater variety of families and classes than an equal number of fossil species taken from secondary or primary rocks, the angiosperms bearing the same proportion to the gymnosperms and acrogens as in the present flora of the globe. This greater variety may, doubtless, be partly ascribed to the greater diversity of stations in which the plants grew, as we have in this case an opportunity, rarely enjoyed in studying the secondary fossils, of investigating inland or lacustrine deposits accumulated at different heights above the sea, and containing the memorials of plants washed down from adjoining mountains.

In regard, then, to the strata from the cretaceous to the uppermost tertiary inclusive, we may affirm that we find in them all the principal classes of living plants, and during this vast lapse of time four or five complete changes in the vegetation occurred, yet no step whatever was made in advance at any of these periods by the addition of more highly organized species.

If we next turn to the fossils of the animal kingdom, we may inquire whether, when they are arranged by the geologists in a chronological series, they imply that beings of more highly developed structure and greater intelligence entered upon the earth at successive epochs, those of the simplest organization being the first created, and those more highly organized being the last.

Our knowledge of the Silurian fauna is at present derived entirely from rocks of marine origin, no fresh-water strata of such high antiquity having yet been met with. The fossils, however, of these ancient rocks at once reduce the theory of progressive development to within very narrow limits, for already they comprise a very full representation of the radiata, mollusca, and articulata proper to the sea. Thus, in the great division of radiata, we find asteriod and helianthoid zoophytes, besides crinoid and cystidean echinoderms. In the mollusca, between 200 and 300 species of cephalopoda are enumerated. In the articulata we have the crustaceans represented by more than 200 species of trilobites, besides other genera of the same class. The remains of fish are as yet confined to the upper part of the Silurian series; but some of these belong to placoid fish, which occupy a high grade in the scale of organization. Some naturalists have assumed that the earliest fauna was exclusively marine, because we have not yet found a single Silurian helix, insect, bird, terrestrial reptile or mammifer; but when we carry back our investigation to a period so remote from the present, we ought not to be surprised if the only accessible strata should be limited to deposits formed far from land, because the ocean probably occupied then, as now, the greater part of the earth's surface. After so many entire geographical revolutions, the chances are nearly three to one in favor of our finding that such small portions of the existing continents and islands as expose Silurian strata to view, should coincide in position with the ancient ocean rather than the land. We must not, therefore, too hastily infer, from the absence of fossil bones of mammalia in the older rocks, that the highest class of vertebrated animals did not exist in remoter ages. There are regions at present, in the Indian and Pacific Oceans, coextensive in area with the continents of Europe and North America, where we might dredge the bottom and draw up thousands of shells and corals, without obtaining one bone of a land quadruped. Suppose our mariners were to report, that, on sounding in the Indian Ocean near some coral reefs, and at some distance from the land, they drew up on hooks attached to their line portions of a leopard, elephant, or tapir, should we not be skeptical as to the accuracy of their statements? and if we had no doubt of their veracity, might we not suspect them to be unskilful naturalists? or, if the fact were unquestioned, should we not be disposed to believe that some vessel had been wrecked on the spot?

The casualties must always be rare by which land quadrupeds are swept by rivers far out into the open sea, and still rarer the contingency of such a floating body not being devoured by sharks or other predaceous fish, such as were those of which we find the teeth preserved in some of the carboniferous strata. But if the carcass should escape, and should happen to sink where sediment was in the act of accumulating, and if the numerous causes of subsequent disintegration should not efface all traces of the body, included for countless ages in solid rock, is it not contrary to all calculation of chances that we should hit upon the exact spot--that mere point in the bed of an ancient ocean, where the precious relic was entombed? Can we expect for a moment, when we have only succeeded, amidst several thousand fragments of corals and shells, in finding a few bones of _aquatic_ or _amphibious_ animals, that we should meet with a single skeleton of an inhabitant of the land?

Clarence, in his dream, saw, "in the slimy bottom of the deep,"

----a thousand fearful wrecks;
A thousand men, that fishes gnaw'd upon:
Wedges of gold, great anchors, heaps of pearl.

Had he also beheld, amid "the dead bones that lay scattered by," the carcasses of lions, deer, and the other wild tenants of the forest and the plain, the fiction would have been deemed unworthy of the genius of Shakspeare. So daring a disregard of probability and violation of analogy would have been condemned as unpardonable, even where the poet was painting those incongruous images which present themselves to a disturbed imagination during the visions of the night.

Until lately it was supposed that the old red sandstone, or Devonian rocks, contained no vertebrate remains except those of fish, but in 1850 the footprints of a chelonian, and in 1851 the skeleton of a reptile, allied both to the batrachians and lizards, were found in a sandstone of that age near Elgin in Scotland.[212] Up to the year 1844 it was laid down as a received dogma in many works of high authority in geology, that reptiles were not created until after the close of the carboniferous epoch. In the course of that year, however, Hermann Von Meyer announced the discovery, in the coal measures of Rhenish Bavaria, of a reptile, called by him Apateon, related to the salamanders; and in 1847 three species of another genus, called archegosaurus by Goldfuss, were obtained from the coal of Saarbruck, between Treves and Strasburg. The footprints of a large quadruped, probably batrachian, had also been observed by Dr. King in the carboniferous rocks of Pennsylvania in 1844. The first example of the _bones_ of a reptile in the Coal of North America was detected so lately as September, 1852, by Mr. G. W. Dawson and myself in Nova Scotia. These remains, referred by Messrs. Wyman and Owen to a perennibranchiate batrachian, were met with in the interior of an erect fossil tree, apparently a sigillaria. They seem clearly to have been introduced together with sediment into the tree, during its submergence and after it had decayed and was standing as a hollow cylinder of bark, this bark being now converted into coal.

When Agassiz, in his great work on fossil fish, described 152 species of ichthyolites from the Coal, he found them to consist of 94 placoids, belonging to the families of shark and ray, and 58 ganoids. One family of the latter he called "sauroid fish," including the megalicthys and holoptychius, often of great size, and all predaceous. Although true fish, and not intermediate between that class and reptiles, they seem to have been more highly organized than any living fish, reminding us of the skeletons of saurians by the close suture of their cranial bones, their large conical teeth, striated longitudinally, and the articulation of the spinous processes with the vertebrae. Among living species they are most nearly allied to the lepidosteus, or bony pike of the North American rivers. Before the recent progress of discovery above alluded to had shown the fallacy of such ideas, it was imagined by some geologists that this ichthyic type was the more highly developed, because it took the lead at the head of nature before the class of reptiles had been created. The confident assumption indulged in till the year 1844, that reptiles were first introduced into the earth in the Permian period, shows the danger of taking for granted that the date of the creation of any family of animals or plants in past time coincides with the age of the oldest stratified rock in which the geologist has detected its remains. Nevertheless, after repeated disappointments, we find some naturalists as much disposed as ever to rely on such negative evidence, and to feel now as sure that reptiles were not introduced into the earth till after the Silurian epoch, as they were in 1844, that they appeared for the first time at an era subsequent to the carboniferous.

Scanty as is the information hitherto obtained in regard to the articulata of the coal formation, we have at least ascertained that some insects winged their way through the ancient forests. In the ironstone of Coalbrook Dale, two species of coleoptera of the Linnaean genus curculio have been met with: and a neuropterous insect resembling a corydalis, together with another of the same order related to the phasmidae. As an example of the insectivorous arachnidae, I may mention the scorpion of the Bohemian coal, figured by Count Sternberg, in which even the eyes, skin, and minute hairs were preserved.[213] We need not despair, therefore, of obtaining eventually fossil representatives of all the principal orders of hexapods and arachnidae in carboniferous strata.

Next in chronological order above the Coal comes the allied Magnesian Limestone, or Permian group, and the secondary formations from the Trias to the Chalk inclusive. These rocks comprise the monuments of a long series of ages in which reptiles of every variety of size, form, and structure peopled the earth; so that the whole period, and especially that of the Lias and Oolite, has been sometimes called "the age of reptiles." As there are now mammalia entirely confined to the land; others which, like the bat and vampire, fly in the air; others, again, of amphibious habits, frequenting rivers, like the hippopotamus, otter, and beaver; others exclusively aquatic and marine, like the seal, whale, and narwal; so in the early ages under consideration, there were terrestrial, winged, and aquatic reptiles. There were iguanodons walking on the land, pterodactyls winging their way through the air, monitors and crocodiles in the rivers, and ichthyosaurs and plesiosaurs in the ocean. It appears also that some of these ancient saurians approximated more nearly in their organization to the type of living mammalia than do any of the reptiles now existing.[214]

In the vast range of strata above alluded to, comprising the Permian, the Upper New Red Sandstone and Muschelkalk, the Lias, Oolite, Wealden, Green-sand, and Chalk, scarcely any well-authenticated instances of the occurrence of fossil birds in Europe are on record, and only two or three of fossil mammalia.

In regard to the absence of birds, they are usually wanting, for reasons afterwards to be explained (see chap. 47), in deposits of all ages, even in the tertiary periods, where we know that birds as well as land quadrupeds abounded. Some at least of the fossil remains formerly referred to this class in the Wealden (a great freshwater deposit below the chalk), have been recently shown by Mr. Owen to belong to pterodactyls.[215] But in North America still more ancient indications of the existence of the feathered tribe have been detected, the fossil foot-marks of a great variety of species, of various sizes, some larger than the ostrich, others smaller than the plover, having been observed. These bipeds have left marks of their footsteps on strata of an age decidedly intermediate between the Lias and the Coal.[216]

_Natural Size_.

Thylacotherium Prevostii (_Valenciennes_). Amphitherium (_Owen_). Lower jaw, from the slate of Stonesfield, near Oxford.[218]]

Myrmecobius fasciatus (_Waterhouse_). Recent from Swan River. Lower jaw of the natural size.[219]]

The examples of mammalia, above alluded to, are confined to the Trias and the Oolite. In the former, the evidence is as yet limited to two small molar teeth, described by Professor Plieninger in 1847, under the generic name of Microlestes. They were found near Stuttgart, and possess the double fangs so characteristic of mammalia.[217] The other fossil remains of the same class were derived from one of the inferior members of the oolitic series in Oxfordshire, and afford more full and satisfactory evidence, consisting of the lower jaws of three species of small quadrupeds about the size of a mole. Cuvier, when he saw one of them (during a visit to Oxford in 1818), referred it to the marsupial order, stating, however, that it differed from all known carnivora in having ten molar teeth in a row. Professor Owen afterwards pointed out that the jaw belonged to an extinct genus, having considerable affinity to a newly discovered Australian mammifer, the _Myrmecobius_ of Waterhouse, which has nine molar teeth in the lower jaw. (Fig. 9.) A more perfect specimen enabled Mr. Owen in 1846 to prove that the inflection of the angular process of the lower jaw was not sufficiently marked to entitle the osteologist to infer that this quadruped was marsupial, as the process is not bent inwards in a greater degree than in the mole or hedgehog. Hence the genus amphitherium, of which there are two species from Stonesfield, must be referred to the ordinary or placental type of insectivorous mammals, although it approximates in some points of structure to the myrmecobius and allied marsupials of Australia. The other contemporary genus, called phascolotherium, agrees much more nearly in osteological character and precisely in the number of the teeth with the opossums; and is believed to have been truly marsupial. (Fig. 10.)

_Natural size._

Phascolotherium Bucklandi, _Owen_. (_Syn._ Didelphis Bucklandi, _Brod._) Lower jaw, from Stonesfield.[220]

1. The jaw magnified twice in length. 2. The second molar tooth magnified six times.]

The occurrence of these most ancient memorials of the mammiferous type, in so low a member of the oolitic series, while no other representatives of the same class (if we except the microlestes) have yet been found in any other of the inferior or superior secondary strata, is a striking fact, and should serve as a warning to us against hasty generalizations, founded solely on negative evidence. So important an exception to a general rule may be perfectly consistent with the conclusion, that a small number only of mammalia inhabited European latitudes when our secondary rocks were formed; but it seems fatal to the theory of progressive development, or to the notion that the order of precedence in the creation of animals, considered chronologically, has precisely coincided with the order in which they would be ranked according to perfection or complexity of structure.

It was for many years suggested that the marsupial order to which the fossil animals of Stonesfield were supposed exclusively to belong constitutes the lowest grade in the class Mammalia, and that this order, of which the brain is of more simple form, evinces an inferior degree of intelligence. If, therefore, in the oolitic period the marsupial tribes were the only warm-blooded quadrupeds which had as yet appeared upon our planet, the fact, it was said, confirmed the theory which teaches that the creation of the more simple forms in each division of the animal kingdom preceded that of the more complex. But on how slender a support, even if the facts had continued to hold true, did such important conclusions hang! The Australian continent, so far as it has been hitherto explored, contains no indigenous quadrupeds save those of the marsupial order, with the exception of a few small rodents, while some neighboring islands to the north, and even southern Africa, in the same latitude as Australia, abound in mammalia of every tribe except the marsupial. We are entirely unable to explain on what physiological or other laws this singular diversity in the habitations of living mammalia depends; but nothing is more clear than that the causes which stamp so peculiar a character on two different provinces of wide extent are wholly independent of time, or of the age or maturity of the planet.

The strata of the Wealden, although of a later date than the oolite of Stonesfield, and although filled with the remains of large reptiles, both terrestrial and aquatic, have not yielded as yet a single marsupial bone. Were we to assume on such scanty data that no warm-blooded quadrupeds were then to be found throughout the northern hemisphere, there would still remain a curious subject of speculation, whether the entire suppression of one important class of vertebrata, such as the mammiferous, and the great development of another, such as the reptilian, implies a departure from fixed and uniform rules governing the fluctuations of the animal world; such rules, for example, as appear from one century to another to determine the growth of certain tribes of plants and animals in arctic, and of other tribes in tropical regions.

In Australia, New Zealand, and many other parts of the southern hemisphere, where the indigenous land quadrupeds are comparatively few, and of small dimensions, the reptiles do not predominate in number or size. The deposits formed at the mouth of an Australian river, within the tropics, might contain the bones of only a few small marsupial animals, which, like those of Stonesfield, might hereafter be discovered with difficulty by geologists; but there would, at the same time, be no megalosauri and other fossil remains, showing that large saurians were plentiful on the land and in the waters at a time when mammalia were scarce. This example, therefore, would afford a very imperfect parallel to the state of the animal kingdom, supposed to have prevailed during the secondary periods, when a high temperature pervaded European latitudes.

It may nevertheless be advantageous to point to some existing anomalies in the geographical development of distinct classes of vertebrata which may be comparable to former conditions of the animal creation brought to light by geology. Thus in the arctic regions, at present, reptiles are small, and sometimes wholly wanting, where birds, large land quadrupeds, and cetacea abound. We meet with bears, wolves, foxes, musk oxen, and deer, walruses, seals, whales, and narwals, in regions of ice and snow, where the smallest snakes, efts, and frogs are rarely, if ever, seen.

A still more anomalous state of things presents itself in the southern hemisphere. Even in the temperate zone, between the latitudes 52 degrees and 56 degrees S., as, for example, in Tierra del Fuego, as well as in the woody region immediately north of the Straits of Magellan, and in the Falkland Islands, no reptiles of any kind are met with, not even a snake, lizard, or frog; but in these same countries we find the guanaco (a kind of llama), a deer, the puma, a large species of fox, many small rodentia, besides the seal and otter, together with the porpoise, whale, and other cetacea.

On what grand laws in the animal physiology these remarkable phenomena depend, cannot in the present state of science be conjectured; nor could we predict whether any opposite condition of the atmosphere, in respect to heat, moisture, and other circumstances, would bring about a state of animal life which might be called the converse of that above described, namely, a state in which reptiles of every size and order might abound, and mammalia disappear.

The nearest approximation to such a fauna is found in the Galapagos Archipelago. These islands, situated under the equator, and nearly 600 miles west of the coast of Peru, have been called "the land of reptiles," so great is the number of snakes, large tortoises, and lizards, which they support. Among the lizards, the first living species proper to the ocean has been discovered. Yet, although some of these islands are from 3000 to 4000 feet high, and one of them 75 miles long, they contain, with the exception of one small mouse, no indigenous mammifer. Even here, however, it is true that in the neighboring sea there are seals, and several kinds of cetacea.[221]

It may be unreasonable to look for a nearer analogy between the fauna now existing in any part of the globe, and that which we can show to have prevailed when our secondary strata were deposited, because we must always recollect that a climate like that now experienced at the equator, coexisting with the unequal days and nights of European latitudes, was a state of things to which there is now no counterpart on the globe. Consequently, the type of animal and vegetable existence required for such a climate might be expected to deviate almost as widely from that now established, as do the flora and fauna of our tropical differ from those of our arctic regions.

_In the Tertiary strata._--The tertiary formations were deposited when the physical geography of the northern hemisphere had been entirely altered. Large inland lakes had become numerous, as in central France and other countries. There were gulfs of the sea, into which considerable rivers emptied themselves, and where strata like those of the Paris basin were accumulated. There were also formations in progress, in shallow seas not far from shore, such as are indicated by portions of the _Faluns_ of the Loire, and the English _Crag_.

The proximity, therefore, of large tracts of dry land to the seas and lakes then existing, may, in a great measure, explain why the remains of land animals, so rare in the older strata, are not uncommon in these more modern deposits. Yet even these have sometimes proved entirely destitute of mammiferous relics for years after they had become celebrated for the abundance of their fossil testacea, fish, and reptiles. Thus the calcaire grossier, a marine limestone of the district round Paris, had afforded to collectors more than 1100 species of shells, besides many zoophytes, echinodermata, and the teeth of fish, before the bones of one or two land quadrupeds were met with in the same rock. The strata called London and Plastic clay in England have been studied for more than half a century, and about 400 species of shells, 50 or more of fish, besides several kinds of chelonian and saurian reptiles, were known before a single mammifer was detected. At length, in the year 1839, there were found in this formation the remains of a monkey, an opossum, a bat,[222] and a species of the extinct genus Hyracotherium, allied to the Peccary or hog tribe.

If we examine the strata above the London clay in England, we first meet with mammiferous remains in the Isle of Wight, in beds also belonging to the Eocene epoch, such as the remains of the Palaeotherium, Anoplotherium, and other extinct quadrupeds, agreeing very closely with those first found by Cuvier, near Paris, in strata of the same age, and of similar freshwater origin.

In France we meet with another fauna, both conchological and mammalian in the Miocene "faluns" of the Loire; above which in the ascending series in Great Britain we arrive at the coralline crag of Suffolk, a marine formation which has yielded three or four hundred species of shells, very different from the Eocene testacea, and of which a large proportion, although a minority of the whole number, are recent, besides many corals, echini, foraminifera, and fish, but as yet no relic decidedly mammalian except the ear-bone of a whale.

In the shelly sand, provincially termed "Red Crag," in Suffolk, which immediately succeeds the coralline, constituting a newer member of the same tertiary group, about 250 species of shells have been recognized, of which a still larger proportion are recent. They are associated with numerous teeth of fish; but no signs of a warm-blooded quadruped had been detected until 1839, when the teeth of a leopard, a bear, a hog, and a species of ruminant, were found at Newbourn, in Suffolk, and since that time, several other genera of mammalia have been met with in the same formation, or in the Red Crag.[223]

Of a still newer date is the Norwich Crag, a fluvio-marine deposit of the Pleiocene epoch, containing a mixture of marine, fluviatile, and land shells, of which 90 per cent. or more are recent. These beds, since the time of their first investigation, have yielded a supply of mammalian bones of the genera mastodon, elephant, rhinoceros, pig, horse, deer, ox, and others, the bodies of which may have been washed down into the sea by rivers draining land, of which the contiguity is indicated by the occasional presence of terrestrial and freshwater shells.

Our acquaintance with the newer Pleiocene mammalia in Europe, South America, and Australia, is derived chiefly from cavern deposits, a fact which we ought never to forget if we desire to appreciate the superior facilities we enjoy for studying the more modern as compared to the more ancient terrestrial faunas. We know nothing of the fossil bones which must have been inclosed in the stalagmite of caverns in the older Pleiocene, or in the Miocene or Eocene epochs, much less can we derive any information respecting the inhabitants of the land from a similar source, when we carry back our inquiries to the Wealden or carboniferous epochs. We are as well assured that land and rivers then existed, as that they exist now; but it is evident that even a slight geographical revolution, accompanied by the submergence and denudation of land, would reduce to an extreme improbability the chance of our hitting on those minute points of space where caves may once have occurred in limestone rocks.

_Fossil quadrumana._--Until within a few years (1836, 1837), not a single bone of any quadrumanous animal, such as the orang, ape, baboon, and monkey, had been discovered in a fossil state, although so much progress had been made in bringing to light the extinct mammalia of successive tertiary eras, both carnivorous and herbivorous. The total absence of these anthropomorphous tribes among the records of a former world, had led some to believe that the type of organization most nearly resembling the human, came so late in the order of creation, as to be scarcely, if at all, anterior to that of man. That such generalizations were premature, I endeavored to point out in the first edition of this work,[224] in which I stated that the bones of quadrupeds hitherto met with in tertiary deposits were chiefly those which frequent marshes, rivers, or the borders of lakes, as the elephant, rhinoceros, hippopotamus, tapir, hog, deer, and ox, while species which live in trees are extremely rare in a fossil state. I also hinted, that we had as yet no data for determining how great a number of the one kind we ought to find, before we have a right to expect a single individual of the other. Lastly, I observed that the climate of the more modern (or Post-Eocene) tertiary periods in England was not tropical, and that in regard to the London clay, of which the crocodiles, turtles, and fossil fruits implied a climate hot enough for the quadrumana, we had as yet made too little progress in ascertaining what were the Eocene pachydermata of England, to entitle us to expect to have discovered any quadrumana of the same date.

Since those remarks were first written, in 1829, a great number of extinct species have been added to our collections of tertiary mammalia from Great Britain and other parts of the world. At length, between the years 1836 and 1839, a few remains of quadrumana were found in France and England, India and Brazil. Those of India, belonging to more than one extinct species of monkey, were first discovered near the Sutlej, in lat. 30 degrees N., in tertiary strata, of which the age is not yet determined; the Brazilian fossil, brought from the basin of the Rio das Velhas, about lat. 18 degrees S., is referable to a form now peculiar in America, allied to the genus Callithrix, the species being extinct. The skull and other bones met with in the South of France belong to a gibbon, or one of the tailless apes, which stand next in the scale of organization to the orang. It occurred at Sansan, about forty miles west of Toulouse, in lat. 43 degrees 40 minutes N., in freshwater strata, probably of the Miocene or middle tertiary period. Lastly, the English quadrumane first met with, occurred in a more ancient stratum than the rest, and at a point more remote from the equator. It belongs to the genus Macacus, is an extinct species, and was found in Suffolk, in lat. 52 degrees,[225] in the London clay, the fossils of which, such as crocodiles, turtles, shells of the genus Nautilus, and many curious fruits, had already led geologists to the conclusion that the climate of that era (the Eocene) was warm and nearly tropical.

Some years later (in 1846) the jaw of another British species of fossil monkey, Macacus pliocenus, was announced by Mr. Owen as having been met with in the newer Pleiocene strata, on the banks of the Thames, at Grays, in Essex, accompanying the remains of hippopotamus, elephant, and other quadrupeds, and associated with freshwater and land shells, most of which are now inhabitants of the British Isles.[226]

When we consider the small area of the earth's surface hitherto explored geologically, and the new discoveries brought to light daily, even in the environs of great European capitals, we must feel that it would be rash to assume that the Lower Eocene deposits mark the era of the first creation of quadrumana. It would, however, be still more unphilosophical to infer, as some writers have done, from a single extinct species of this family obtained in a latitude far from the tropics, that the Eocene quadrumana did not attain as high a grade of organization as they do in our own times. What would the naturalist know of the apes and orangs now contemporary with man, if our investigations were restricted to such northern latitudes as those where alone the geologist has hitherto found all the fossil quadrumana of Europe?

_Cetacea._--The absence of Cetacea from rocks older than the Eocene has been frequently adduced as lending countenance to the theory of the very late appearance of the highest class of Vertebrata on the earth. Professor Sedgwick possesses in the Cambridge Museum a mass of anchylosed cervical vertebrae of a whale, which he found in drift clay near Ely, and which he has no doubt was washed out of the Kimmeridge clay, an upper member of the Oolite. According to Professor Owen, it exhibits well-marked specific characters, distinguishing it from all other known recent or fossil cetacea. Dr. Leidy, of Philadelphia, has lately described (1851) two species of cetacea of a new genus, which he has called Priscodelphinus from the green sand of New Jersey, which corresponds in age with the English Chalk or the cretaceous strata above the gault. The specimens consist of dorsal and cervical vertebrae.[227] Even in the Eocene strata of Europe, the discovery of cetaceans has never kept pace with that of land quadrupeds. The only instance cited in Great Britain is a species of Monodon, from the London clay, of doubtful authenticity as to its geological position. On the other hand, the gigantic Zeuglodon of North America occurs abundantly in the Middle Eocene strata of Georgia and Alabama, from which as yet no bones of land quadrupeds have been obtained.

In the present imperfect state then of our information, we can scarcely say more than that the cetacea seem to have been scarce in the secondary and primary periods. It is quite conceivable that when aquatic saurians, some of them carnivorous, like the Ichthyosaurus, were swarming in the sea, and when there were large herbivorous reptiles, like the Iguanodon, on the land, the class of reptiles may, to a certain extent, have superseded the cetacea, and discharged their functions in the animal economy.

That mammalia had been created long before the epoch of the Kimmeridge clay, is shown by the Microlestes of the Trias before alluded to, and by the Stonesfield quadrupeds from the Inferior Oolite. And we are bound to remember, whenever we infer the poverty of the flora or fauna of any given period of the past, from the small number of fossils occurring in ancient rocks, that it has been evidently no part of the plan of Nature to hand down to us a complete or systematic record of the former history of the animate world. We may have failed to discover a single shell, marine or freshwater, or a single coral or bone in certain sandstones, such as that of the valley of the Connecticut, where the footprints of bipeds and quadrupeds abound; but such failure may have arisen, not because the population of the land or sea was scanty at that era, but because in general the preservation of any relics of the animals or plants of former times is the exception to a general rule. Time so enormous as that contemplated by the geologist may multiply exceptional cases till they seem to constitute the rule, and so impose on the imagination as to lead us to infer the non-existence of creatures of which no monuments happen to remain. Professor Forbes has remarked, that few geologists are aware how large a proportion of all known species of fossils are founded on single specimens, while a still greater number are founded on a few individuals discovered in one spot. This holds true not only in regard to animals and plants inhabiting the land, the lake, and the river, but even to a surprising number of the marine mollusca, articulata, and radiata. Our knowledge, therefore, of the living creation of any given period of the past may be said to depend in a great degree on what we commonly call chance, and the casual discovery of some new localities rich in peculiar fossils may modify or entirely overthrow all our previous generalizations.

Upon the whole then we derive this result from a general review of the fossils of the successive tertiary strata, namely, that since the Eocene period, there have been several great changes in the land quadrupeds inhabiting Europe, probably not less than five complete revolutions, during which there has been no step whatever made in advance, no elevation in the scale of being; so that had man been created at the commencement of the Eocene era, he would not have constituted a greater innovation on the state of the animal creation previously established than now, when we believe him to have begun to exist at the close of the Pleiocene. The views, therefore, which I proposed in the first edition of this work, January, 1830, in opposition to the theory of progressive development, do not seem to me to require material modification, notwithstanding the large additions since made to our knowledge of fossil remains.

These views may be thus briefly stated. From the earliest period at which plants and animals can be proved to have existed, there has been a continual change going on in the position of land and sea, accompanied by great fluctuations of climate. To these ever-varying geographical and climatal conditions the state of the animate world has been unceasingly adapted. No satisfactory proof has yet been discovered of the gradual passage of the earth from a chaotic to a more habitable state, nor of any law of progressive development governing the extinction and renovation of species, and causing the fauna and flora to pass from an embryonic to a more perfect condition, from a simple to a more complex organization.

The principle of adaptation to which I have alluded, appears to have been analogous to that which now peoples the arctic, temperate, and tropical regions contemporaneously with distinct assemblages of species and genera, or which, independently of mere temperature, gives rise to a predominance of the marsupial or didelphous tribe of quadrupeds in Australia, of the placental or monodelphous tribe in Asia and Europe, or which causes a profusion of reptiles without mammalia in the Galapagos Archipelago, and of mammalia without reptiles in Greenland.

_Recent origin of man._--If, then, the popular theory of the successive development of the animal and vegetable world, from the simplest to the most perfect forms, rests on a very insecure foundation; it may be asked, whether the recent origin of man lends any support to the same doctrine, or how far the influence of man may be considered as such a deviation from the analogy of the order of things previously established, as to weaken our confidence in the uniformity of the course of nature.

Antecedently to investigation, we might reasonably have anticipated that the vestiges of man would have been traced back at least as far as those modern strata in which all the testacea and a certain number of the mammalia are of existing species, for of all the mammalia the human species is the most cosmopolite, and perhaps more capable than any other of surviving considerable vicissitudes in climate, and in the physical geography of the globe.

No inhabitant of the land exposes himself to so many dangers on the waters as man, whether in a savage or a civilized state;[228] and there is no animal, therefore, whose skeleton is so liable to become imbedded in lacustrine or submarine deposits; nor can it be said that his remains are more perishable than those of other animals; for in ancient fields of battle, as Cuvier has observed, the bones of men have suffered as little decomposition as those of horses which were buried in the same grave.[229] But even if the more solid parts of our species had disappeared, the impression of their form would have remained engraven on the rocks, as have the traces of the tenderest leaves of plants, and the soft integuments of many animals. Works of art, moreover, composed of the most indestructible materials, would have outlasted almost all the organic contents of sedimentary rocks. Edifices, and even entire cities, have, within the times of history, been buried under volcanic ejections, submerged beneath the sea, or engulfed by earthquakes; and had these catastrophes been repeated throughout an indefinite lapse of ages, the high antiquity of man would have been inscribed in far more legible characters on the framework of the globe than are the forms of the ancient vegetation which once covered the islands of the northern ocean, or of those gigantic reptiles which at still later periods peopled the seas and rivers of the northern hemisphere.[230]

Dr. Prichard has argued that the human race have not always existed on the surface of the earth, because "the strata of which our continents are composed were once a part of the ocean's bed"--"mankind had a beginning, since we can look back to the period when the surface on which they lived began to exist."[231] This proof, however, is insufficient, for many thousands of human beings now dwell in various quarters of the globe where marine species lived within the times of history, and, on the other hand, the sea now prevails permanently over large districts once inhabited by thousands of human beings. Nor can this interchange of sea and land ever cease while the present causes are in existence. Terrestrial species, therefore, might be older than the continents which they inhabit, and aquatic species of higher antiquity than the lakes and seas which they now people.

But so far as our interpretation of physical movements has yet gone, we have every reason to infer that the human race is extremely modern, even when compared to the larger number of species now our contemporaries on the earth, and we may, therefore, ask whether his creation can be considered as one step in a supposed progressive system, by which the organic world has advanced slowly from a more simple to a more complex and perfect state? If we concede, for a moment, the truth of the proposition, that the sponge, the cephalopod, the fish, the reptile, the bird, and the mammifer, have followed each other in regular chronological order, the creation of each class being separated from the other by vast intervals of time, should we be able to recognize, in man's entrance upon the earth, the last term of one and the same series of progressive developments?

In reply to this question it should first be observed, that the superiority of man depends not on those faculties and attributes which he shares in common with the inferior animals, but on his reason, by which he is distinguished from them. When it is said that the human race is of far higher dignity than were any pre-existing beings on the earth, it is the intellectual and moral attributes of our race, rather than the physical, which are considered; and it is by no means clear that the organization of man is such as would confer a decided pre-eminence upon him, if, in place of his reasoning powers, he was merely provided with such instincts as are possessed by the lower animals.

If this be admitted, it would not follow, even if there were sufficient geological evidence in favor of the theory of progressive development, that the creation of man was the last link in the same chain. For the sudden passage from an irrational to a rational animal, is a phenomenon of a distinct kind from the passage from the more simple to the more perfect forms of animal organization and instinct. To pretend that such a step, or rather leap, can be part of a regular series of changes in the animal world, is to strain analogy beyond all reasonable bounds.

_Introduction of man, to what extent a change in the system._--But setting aside the question of progressive development, another and a far more difficult one may arise out of the admission that man is comparatively of modern origin. Is not the interference of the human species, it may be asked, such a deviation from the antecedent course of physical events, that the knowledge of such a fact tends to destroy all our confidence in the uniformity of the order of nature, both in regard to time past and future? If such an innovation could take place after the earth had been exclusively inhabited for thousands of ages by inferior animals, why should not other changes as extraordinary and unprecedented happen from time to time? If one new cause was permitted to supervene, differing in kind and energy from any before in operation, why may not others have come into action at different epochs? Or what security have we that they may not arise hereafter? And if such be the case, how can the experience of one period, even though we are acquainted with all the possible effects of the then existing causes, be a standard to which we can refer all natural phenomena of other periods?

Now these objections would be unanswerable, if adduced against one who was contending for the absolute uniformity throughout all time of the succession of sublunary events--if, for example, he was disposed to indulge in the philosophical reveries of some Egyptian and Greek sects, who represented all the changes both of the moral and material world as repeated at distant intervals, so as to follow each other in their former connection of place and time. For they compared the course of events on our globe to astronomical cycles; and not only did they consider all sublunary affairs to be under the influence of the celestial bodies, but they taught that on the earth, as well as in the heavens, the same identical phenomena recurred again and again in a perpetual vicissitude. The same individual men were doomed to be re-born, and to perform the same actions as before; the same arts were to be invented, and the same cities built and destroyed. The Argonautic expedition was destined to sail again with the same heroes, and Achilles with his Myrmidons to renew, the combat before the walls of Troy.

Alter erit tum Tiphys, et altera quae vehat Argo
Dilectos heroas; erunt etiam altera bella,
Atque iterum ad Trojam magnus mittetur Achilles.[232]

The geologist, however, may condemn these tenets as absurd, without running into the opposite extreme, and denying that the order of nature has, from the earliest periods, been uniform in the same sense in which we believe it to be uniform at present, and expect it to remain so in future. We have no reason to suppose, that when man first became master of a small part of the globe, a greater change took place in its physical condition than is now experienced when districts, never before inhabited, become successively occupied by new settlers. When a powerful European colony lands on the shores of Australia, and introduces at once those arts which it has required many centuries to mature; when it imports a multitude of plants and large animals from the opposite extremity of the earth, and begins rapidly to extirpate many of the indigenous species, a mightier revolution is effected in a brief period than the first entrance of a savage horde, or their continued occupation of the country for many centuries, can possibly be imagined to have produced. If there be no impropriety in assuming that the system is uniform when disturbances so unprecedented occur in certain localities, we can with much greater confidence apply the same language to those primeval ages when the aggregate number and power of the human race, or the rate of their advancement in civilization, must be supposed to have been far inferior. In reasoning on the state of the globe immediately before our species was called into existence, we must be guided by the same rules of induction as when we speculate on the state of America in the interval that elapsed between the introduction of man into Asia, the supposed cradle of our race, and the arrival of the first adventurers on the shores of the New World. In that interval, we imagine the state of things to have gone on according to the order now observed in regions unoccupied by man. Even now, the waters of lakes, seas, and the great ocean, which teem with life, may be said to have no immediate relation to the human race--to be portions of the terrestrial system of which man has never taken, nor ever can take possession; so that the greater part of the inhabited surface of the planet may still remain as insensible to our presence as before any isle or continent was appointed to be our residence.

If the barren soil around Sydney had at once become fertile upon the landing of our first settlers; if, like the happy isles whereof the poets have given such glowing descriptions, those sandy tracts had begun to yield spontaneously an annual supply of grain, we might then, indeed, have fancied alterations still more remarkable in the economy of nature to have attended the first coming of our species into the planet. Or if, when a volcanic island like Ischia was, for the first time, brought under cultivation by the enterprise and industry of a Greek colony, the internal fire had become dormant, and the earthquake had remitted its destructive violence, there would then have been some ground for speculating on the debilitation of the subterranean forces, when the earth was first placed under the dominion of man. But after a long interval of rest, the volcano bursts forth again with renewed energy, annihilates one half of the inhabitants, and compels the remainder to emigrate. The course of nature remains evidently unchanged; and, in like manner, we may suppose the general condition of the globe, immediately before and after the period when our species first began to exist, to have been the same, with the exception only of man's presence.

The modifications in the system of which man is the instrument do not, perhaps, constitute so great a deviation from previous analogy as we usually imagine; we often, for example, form an exaggerated estimate of the extent of our power in extirpating some of the inferior animals, and causing others to multiply; a power which is circumscribed within certain limits, and which, in all likelihood, is by no means exclusively exerted by our species.[233] The growth of human population cannot take place without diminishing the numbers, or causing the entire destruction, of many animals. The larger beasts of prey, in particular, give way before us; but other quadrupeds of smaller size, and innumerable birds, insects, and plants, which are inimical to our interests, increase in spite of us, some attacking our food, others our raiment and persons, and others interfering with our agricultural and horticultural labors. We behold the rich harvest which we have raised by the sweat of our brow, devoured by myriads of insects, and are often as incapable of arresting their depredations, as of staying the shock of an earthquake, or the course of a stream of lava.

A great philosopher has observed, that we can command nature only by obeying her laws; and this principle is true even in regard to the astonishing changes which are superinduced in the qualities of certain animals and plants by domestication and garden culture. I shall point out in the third book that we can only effect such surprising alterations by assisting the development of certain instincts, or by availing ourselves of that mysterious law of their organization, by which individual peculiarities are transmissible from one generation to another.[234]

It is probable from these and many other considerations, that as we enlarge our knowledge of the system, we shall become more and more convinced, that the alterations caused by the interference of man deviate far less from the analogy of those effected by other animals than is usually supposed.[235] We are often misled, when we institute such comparisons, by our knowledge of the wide distinction between the instincts of animals and the reasoning power of man; and we are apt hastily to infer, that the effects of a rational and irrational species, considered merely as _physical agents_, will differ almost as much as the faculties by which their actions are directed.

It is not, however, intended that a real departure from the antecedent course of physical events cannot be traced in the introduction of man. If that latitude of action which enables the brutes to accommodate themselves in some measure to accidental circumstances could be imagined to have been at any former period so great, that the operations of instinct were as much diversified as are those of human reason, it might, perhaps, be contended, that the agency of man did not constitute an anomalous deviation from the previously established order of things. It might then have been said, that the earth's becoming at a particular period the residence of human beings, was an era in the moral, not in the physical world--that our study and contemplation of the earth, and the laws which govern its animate productions, ought no more to be considered in the light of a disturbance or deviation from the system, than the discovery of the satellites of Jupiter should be regarded as a physical event affecting those heavenly bodies. Their influence in advancing the progress of science among men, and in aiding navigation and commerce, was accompanied by no reciprocal action of the human mind upon the economy of nature in those distant planets; and so the earth might be conceived to have become, at a certain period, a place of moral discipline and intellectual improvement to man, without the slightest derangement of a previously existing order of change in its animate and inanimate productions.

The distinctness, however, of the human from all other species, considered merely as an efficient cause in the physical world, is real; for we stand in a relation to contemporary species of animals and plants widely different from that which other irrational animals can ever be supposed to have held to each other. We modify their instincts, relative numbers, and geographical distribution, in a manner superior in degree, and in some respects very different in kind from that in which any other species can affect the rest. Besides, the progressive movement of each successive generation of men causes the human species to differ more from itself in power at two distant periods, than any one species of the higher order of animals differs from another. The establishment, therefore, by geological evidence, of the first intervention of such a peculiar and unprecedented agency, long after other parts of the animate and inanimate world existed, affords ground for concluding that the experience during thousands of ages of all the events which may happen on this globe, would not enable a philosopher to speculate with confidence concerning future contingencies.

If, then, an intelligent being, after observing the order of events for an indefinite series of ages, had witnessed at last so wonderful an innovation as this, to what extent would his belief in the regularity of the system be weakened?--would he cease to assume that there was permanency in the laws of nature?--would he no longer be guided in his speculations by the strictest rules of induction? To these questions it may be answered, that, had he previously presumed to dogmatize respecting the absolute uniformity of the order of nature, he would undoubtedly be checked by witnessing this new and unexpected event, and would form a more just estimate of the limited range of his own knowledge, and the unbounded extent of the scheme of the universe. But he would soon perceive that no one of the fixed and constant laws of the animate or inanimate world was subverted by human agency, and that the modifications now introduced for the first time were the accompaniments of new and extraordinary circumstances, and those not of a _physical_ but a _moral_ nature. The deviation permitted would also appear to be as slight as was consistent with the accomplishment of the new _moral_ ends proposed, and to be in a great degree temporary in its nature, so that, whenever the power of the new agent was withheld, even for a brief period, a relapse would take place to the ancient state of things; the domesticated animal, for example, recovering in a few generations its wild instinct, and the garden-flower and fruit-tree reverting to the likeness of the parent stock.

Now, if it would be reasonable to draw such inferences with respect to the future, we cannot but apply the same rules of induction to the past. We have no right to anticipate any modifications in the results of existing causes in time to come, which are not conformable to analogy, unless they be produced by the progressive development of human power, or perhaps by some other new relations which may hereafter spring up between the moral and material worlds. In the same manner, when we speculate on the vicissitudes of the animate and inanimate creation in former ages, we ought not to look for any anomalous results, unless where man has interfered, or unless clear indications appear of some other _moral_ source of temporary derangement.