an excerpt from his famous: DISCOURSE ON THE REVOLUTIONARY UPHEAVALS ON THE SURFACE OF THE GLOBE AND ON THE CHANGES WHICH THEY HAVE PRODUCED IN THE ANIMAL KINGDOM (Paris, 1825)
Relationships between Species and the Strata
What is more important, indeed what constitutes the
most essential object of all my work and
establishes its true relationship with the theory of the earth, is to know in which strata we find each species, and whether there are any universal laws relative to the zoological subdivisions or to the greater or lesser similarity between those species and today's. The recognized laws in this respect are excellent and very clear.
First, it is certain that the oviparous quadrupeds appear much earlier than the viviparous quadrupeds [those which give birth to live offspring], that they are even more abundant, stronger, and more varied in the ancient strata than on the present surface of the earth.
The ichthyosaurs, the plesiosaurus, several turtles, and several crocodiles are under the chalk in the lands commonly called the Jura. The monitors [a species of lizard] of Thuringia would be even older, if, as the Werner school maintains, the copper schists which contain them in the middle of so many varieties of fish believed to be fresh water creatures are among the most ancient beds of the secondary formation. The immense saurians [species of reptile] and the huge turtles of Maestricht are in the chalk formation itself. But these are marine animals.
This first appearance of bony fossils seems therefore already to announce that there existed dry lands and fresh waters before the formation of the chalk. But neither at this period nor during the time when the chalk was formed, nor even long after that, is there any encrustation of fossilized bones of terrestrial mammals or at least the small number of them which people claim forms only an almost inconsequential exception.
We begin to find the bones of marine mammals, that is to say, of lamantins [manatees] and seals, in the rough limestone with shells which covers the chalk in our regions. At that level, however, there is still no bone of a terrestrial mammal.
In spite of the most through research, I have not be able to discover any distinct trace of this class of animals [terrestrial mammals] before the formations deposited on top of the rough limestone. To be sure, some lignites and molasse [soft greenish sandstone] contain them, but I doubt very much whether these formations are all, as is believed, earlier than this limestone. The places where they have furnished bones are too limited, too few in number, so that one is obliged to assume some irregularity or some change in their formation. By contrast, as soon as we reach the formations above the rough limestone, the bones of land animals show up in large numbers.
Thus, since it is reasonable to believe that the shell fish and fish did not exist at the time when the primordial formations were established, we must also believe that the oviparous quadrupeds began at the same time as the fish, as early as the first ages which produced the secondary formations, but that the terrestrial quadrupeds did not come, at least in considerable numbers, until a long time later, when the rough limestones which contain most of our species of shell creatures, although in species different from ours, had already been laid down.
We should note that these rough limestones, the ones which supply Paris with construction materials, are the last layers which indicate a long and tranquil period of the sea above our continents. After them we certainly find again formations full of shells and other products of the sea, but these are loose formations, sands, marls, sandstones, clays, which reveal a more or less disturbed means of transport rather than a calm precipitation. If there are there some small regular rocky layers below or above these transported formations, they generally show indications of having been deposited in fresh water.
Thus, almost all the known bones of viviparous quadrupeds are either in formations made from fresh water or in these formations of transported material. Consequently there is every reason to believe that these quadrupeds began to live or at least to leave their remains in the layers which we can excavate only since the penultimate retreat of the sea, during the conditions which preceded its last irruption.
But there is also an order in the disposition of these bones among themselves, and this order reveals once more a very remarkable succession among the species. In the deposits we are quite sure of, at first all the genera unknown today, the palaeotheriums, the anoplotheriums, and so on, belong in the most ancient of formations of those under consideration here, those which rest immediately on top of the rough limestone. These are principally the ones which fill the regular layers deposited by fresh waters or the beds of transported material, formed a very long time ago, composed in general of sands and round pebbles. These were perhaps the first alluvial deposits of this ancient world. We also find with them some lost species of known genera, but in small numbers, and some oviparous quadrupeds and fish, all apparently fresh water creatures. The beds which contain them are always covered to a greater or lesser extent by layers of transported material filled with shells and other marine products.
The fossil mastodons, the most famous of these unknown species which belong to known genera or to genera very closely related to those that we do know about, like the elephants, rhinoceroses, and hippopotamuses, are not found with these older genera. We find them only in the formations of transported material, sometimes with sea shells, sometimes with shells from fresh water, but never in the regular rocky layers. Everything found with these species is either unknown, like them, or at least doubtful.
Finally, the bones of species which appear the same as ours are buried only in the last alluvial deposits formed on the edges of rivers or on the bottoms of ancient ponds or dried up swamps, or in the depths of peat layers, or in the cracks and caverns of some escarpments, or finally a little distance below ground in those places where they could have been buried by rock slides or by human beings. Their shallow position has also made these bones, the most recent of all, almost always the least well preserved.
We must not believe, however, that this classification of the various deposits is as clear as the
classification of the species nor that it displays a similarly demonstrable character. There are numerous reasons why this is not the case.
Firstly, all my determinations of species were made on the bones themselves or on good diagrams. However, I have not often myself observed all the places where these bones were discovered. Very frequently I was obliged to rely on vague or ambiguous details, provided by people who did not clearly realize themselves what it was necessary to observe. Even more frequently I have not found any of that information at all.
Secondly, in this matter it is possible to have infinitely more ambiguity than with the bones themselves. The same ground can appear recent in those places where it is shallow and old in those places where it is covered by the layers which have succeeded it. Some ancient formations could have been transported by partial floods and have covered recent bones. They could have collapsed on them, buried them, and mixed them up with old marine material which they had previously hidden. Some ancient bones could have been washed away by water and later caught again in recent alluvial deposits. Finally, some recent bones could have fallen in fissures or caverns in ancient rocks and there have been enveloped by stalactites or other encrustations. It would be necessary in each case to analyze and take into account all of these circumstances, which could hide the true origin of the fossils. And rarely have the people who collected these bones suspected this need. Thus, the result has been that the true features of their deposit have almost always been neglected or unappreciated.
Thirdly, there are some doubtful species which have affected to a greater or lesser extent the reliability of results for such a long time that we will not reach clear distinctions concerning them. Thus the horses and buffalo, which are found with the elephants, do not yet have any specific and particular characteristics. And for many years to come geologists unwilling to adopt my chronological sequence for the bony fossils will be able to derive from these doubtful species an argument, and do so all the more conveniently because they will take it from my book.
But while admitting that these time lines are susceptible to some objections from people who will consider some particular case casually, I am no less persuaded that those who take into account the totality of the phenomena will be stopped by these small partial difficulties. They will recognize with me that there has been at least one and very probably two stages in the class of quadrupeds before the one which today lives on the earth's land surface.
Here I expect one more objection; indeed, people have already made it to me.
The Lost Species Are Not Varieties of the Living Species
Someone will say to me, Why would the present races
not be modifications of these ancient ones
which we find among the fossils, modifications produced by local circumstances and climatic
changes, carried to this extreme difference by the long succession of years?
This objection must appear especially strong to those who believe in the indefinite possibility of
changes in the structure of forms in organic bodies and who think that through habit over centuries all species could change themselves from one species into another or result from a single one of their species.
However, we can reply to them following their own logic that if the species have changed by degrees, we ought to have found traces of these gradual modifications, that we ought to have discovered certain intermediate structures between the palaeotherium and today's species and that up to the present time this has not happened at all. Why have the depths of the earth not preserved monuments of such a curious genealogy, unless it is because the earlier species were as unchanging as our own, or at least because the catastrophe which destroyed them did not leave them time to develop their variations?
As for the naturalists who recognize that the varieties keep within certain limits fixed by nature, in order to respond to them, we must examine just how far these limits extend, a curious study, extremely interesting in itself in all its ramifications, a subject which, however, people have concerned themselves with very little up to now.
My research assumes the definition of species which serves as the basic use made of the term,
understanding that the word species means the individuals who descend from one another or from common parents and those who resemble them as much as they resemble each other. Thus, we call varieties of a species only those races more or less different which can arise from it by reproduction. Our observations on the differences among the ancestors and the descendants are therefore for us the only reasonable rule, because all others would take us back to hypotheses without proofs.
Now, by taking the word variety in this way, we observe that the differences which constitute it
depend on fixed circumstances and that their extent increases according to the intensity of these
Thus the most superficial characteristics are the most variable. Colour is closely related to sunlight; the thickness of the hair to heat; size to the abundance of nourishment. But in a wild animal even these varieties are strongly limited by what is natural for this animal, which does not willingly stray from the places where it conveniently finds everything necessary to maintain the species and which spreads out to a distant place only when it finds there the same combination of these conditions. Thus, although the wolf and the fox live from the torrid zone right up to the glacial zone, they hardly give evidence, in this immense space, of another variety except for a little more or a less beauty in their fur. I have compared the fox skulls from the north and from Egypt with those from France, and I have found only individual differences. Those wild animals who are hemmed in by more limited spaces vary much less again, above all the carnivores. A more abundant mane is the only difference between the Persian and the Moroccan hyenas.
The herbivorous wild animals demonstrate a little more significantly the influence of the climate, because it is linked to the influence of food, which is going to differ in amount and quality. Thus, elephants will be larger in one forest than in another. They will have slightly longer tusks in the places where their food is better for the formation of the ivory material. It will be the same for reindeer and stags in relation to their forests. But let someone take two elephants, as different as can be, and let him see if there is the least difference in the number or the articulations of the bones, in the structure of their teeth, and so on. Moreover, the herbivorous species in the wild appear less widely dispersed than the carnivores, because the type of food and the temperature restrict them.
Nature takes care also to prevent the alteration of species which could result from interbreeding, by the mutual aversion which she has created in them. It takes every trick, all the power of man to bring about a union, even with species which resemble each other the most. And when the offspring are fertile, something which happens very rarely, their fertility does not go on beyond a few generations and would probably not take place without the continuation of the care which aroused it. We do not see in our woods individuals intermediate between the hare and the rabbit, between the red deer and the fallow deer, between the marten and the stone marten.
But the empire of man alters this order. It develops all the variations to which the type of each species is susceptible and derives from them products which the species, left to themselves, would never have produced. Here the degree of variations is still proportional to the intensity of their cause, which is slavery.
The degree of variation is not very high in the semi-domesticated species, like the cat. Softer hair, more vibrant colours, a stronger or weaker build, that is all that this shows. But there is no constant difference between the skeleton of an Angora cat and the skeleton of a feral cat.
In the domestic herbivores, which we transport to all sorts of climates and subject to all sorts of diets, to which we apportion different forms of work and food, we do obtain larger variations, but still entirely superficial. Some variation in size, longer or shorter horns, sometimes missing entirely, a stronger or weaker hump of fat on the shoulders--these constitute the differences among bulls. And these differences remain for a long time, even in races transported out of the country where they were formed, when one takes care to prevent crossbreeding. The innumerable varieties of sheep are like this as well, whose differences are a matter chiefly of the wool, because that is what man has given the most attention to. The varieties are a little fewer in the horse, although they are still very noticeable. In general, the forms of the bones vary little; their connections, articulations, and the structure of the large molar teeth never vary. The little development in the tusks of the domestic pig and the fusion of its cloven hooves in a few of its types are the extreme of the differences which we have produced in the domestic herbivores.
The most marked effects of the influence of man are revealed in the animal of which he has made the most complete conquest, the dog, that species so devoted to ours, that individual animals have apparently sacrificed for us even their identity, their interests, their own feeling. Carried by human beings throughout the entire universe, subjected to all causes capable of influencing their development, matched in their unions at the will of their masters, dogs vary by colour; by the abundance of their hair, which they even lose entirely sometimes; in their nature; in their height, which can differ by a factor of five in linear dimensions (equivalent to more than a factor of one hundred in weight); in the shape of the ears, nose, and tail; in height relative to the legs; in the progressive development of the skull in domestic varieties, from which the very form of their head develops, sometimes skinny with a tapering muzzle and a flat forehead, sometimes a short muzzle and a bulging forehead; to the point where these apparent differences between a mastiff and a water spaniel or a greyhound and a pug are stronger than those of any wild species of a similar natural genus. Finally, and this is the greatest amount of variation known up to this point in the animal kingdom, there are types of dogs who have one digit more on the rear foot along with the corresponding tarsal bones, as there are in the human
species some families with six digits.
But in all these variations, the relationships of the bones remain the same, and the structure of the teeth never changes to an appreciable degree. At the very most there are some individuals in which an additional false molar develops, whether on one side or on the other (77). There are thus characteristics in the animals which resist all influences, whether natural or human, and nothing indicates that the passage of time has, so far as they are concerned, more effect than the climate and domestication.
I know that some naturalists rely a great deal on the thousands of centuries which they add up with the stroke of a pen. But in such matters we can hardly judge what a lengthy time would produce, except by multiplying mentally what a lesser time produces. I have therefore sought to collect the oldest documents on the structures of animals. There are none at all still extant as old or as abundant as those Egypt has provided us. That country offers us, not only the pictures, but the very bodies of the animals embalmed in its catacombs.
In ancient Rome I have examined with the greatest care the pictures of animals and birds engraved on the numerous obelisques which have come from Egypt. In their overall shapes, the only thing which could have concerned the artists, all these figures bear a perfect resemblance to the species as we see them today.
Anyone can examine the copies of them which Kirker and Zoega produced. Without retaining the purity of outline in the originals, they still offer very recognizable figures. We can easily distinguish there the ibis, vulture, owl, falcon, Egyptian goose, peewit, the corn crake [a common bird], the Haje viper or asp, the ceraste [horned viper], the Egyptian hare with its long ears, even the hippopotamus. In the numerous monuments engraved in the important book on Egypt, we see sometimes the rarest animals, the algazel [species of gazelle], for example, which has not been seen in Europe for some years (78)
My knowledgeable colleague, Geoffroy Saint-Hilaire, impressed with the importance of this research, has taken care to collect in the tombs and temples of Higher and Lower Egypt as many animal mummies as he could. He brought back embalmed cats, ibises, birds of prey, dogs, monkeys, crocodiles, and the head of a bull. We certainly do not observe more differences between these creatures and those which we see today than between human mummies and today's human skeletons. We could find differences between the mummies of the ibis and the ibis as naturalists have described it right up to the present time. However, I have resolved all doubts in a report on this bird, a document which is found in a supplement to this discourse, where I have shown that the ibis is now still as it was at the time of the pharaohs. I am very aware that I refer there only to individual specimens two or three thousand years old. But it is always a matter of going back as far one can.
Thus, in the known facts, there is nothing which can in the least support the public opinion that the new genera which I have discovered or established among the fossils, any more than those which other naturalists have established, the palaeotheriums, anoplotheriums, megalonyx, mastodons, pterodactyls, ichtyosaurus, and so on, could have been the ancestors of some animals today, those differentiated from them only by the influence of time or climate. And even if it were true (something I am still far from believing) that elephants, rhinoceroses, elks, and fossil bears do not differ from present animals more than dogs differ among themselves, we would not be able to conclude from that the identity of species, because the dogs types have been subjected to the influence of domesticity which the other animals have neither been subjected to nor could endure.
Moreover, when I maintain that the rock strata contain the bones of several genera and the loose strata contain the fossil bones of several species which no longer exist, I do not claim that a new creation must have produced those species existing today. I say only that they did not exist in the places where we see them at present and that they must have come there from somewhere else.
Let us suppose, for example, that a huge irruption of the sea covers the continent of New Holland with a mountain of sand or other debris. The sea will bury there the bodies of kangaroos, phascolomes [wombats], dasyures [small carnivorous marsupials], perameles [bandicoots], flying phalangers [species of Australian marsupial], echidna [species ant eater] and ornithorhynchus [duck-billed platypus], and will destroy entirely the species of all these genera, because none of them exists now in other countries.
Suppose this same revolution changes into dry land the numerous small straits which separate New Holland from the continent of Asia. It will open the way for elephants, rhinoceroses, buffaloes, horses, camels, tigers, and all the other Asian quadrupeds. These will come to populate the land where they have been previously unknown.
Suppose then that a naturalist, having diligently studied all this living nature, decides to search through the soil on which it dwells. He will find there the remains of totally different creatures.