Georges Cuvier
(1769-1832)
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
circumstances.
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.
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