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The Rise and Progress of Palaeontology This is Essay #2 from "Science and Hebrew Tradition" by Thomas Henry Huxley

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by Thomas Henry Huxley
This is Essay #2 from "Science and Hebrew Tradition"

That application of the sciences of biology and geology, which
is commonly known as palaeontology, took its origin in the mind
of the first person who, finding something like a shell, or a
bone, naturally imbedded in gravel or rock, indulged in
speculations upon the nature of this thing which he had dug out
--this "fossil"--and upon the causes which had brought it into
such a position. In this rudimentary form, a high antiquity may
safely be ascribed to palaeontology, inasmuch as we know that,
500 years before the Christian era, the philosophic doctrines of
Xenophanes were influenced by his observations upon the fossil
remains exposed in the quarries of Syracuse. From this time
forth not only the philosophers, but the poets, the historians,
the geographers of antiquity occasionally refer to fossils;
and, after the revival of learning, lively controversies arose
respecting their real nature. But hardly more than two centuries
have elapsed since this fundamental problem was first
exhaustively treated; it was only in the last century that the
archaeological value of fossils--their importance, I mean, as
records of the history of the earth--was fully recognised;
the first adequate investigation of the fossil remains of any
large group of vertebrated animals is to be found in Cuvier's
"Recherches sur les Ossemens Fossiles," completed in 1822;
and, so modern is stratigraphical palaeontology, that its
founder, William Smith, lived to receive the just recognition of
his services by the award of the first Wollaston Medal in 1831.

But, although palaeontology is a comparatively youthful
scientific speciality, the mass of materials with which it has
to deal is already prodigious. In the last fifty years the
number of known fossil remains of invertebrated animals has been
trebled or quadrupled. The work of interpretation of vertebrate
fossils, the foundations of which were so solidly laid by
Cuvier, was carried on, with wonderful vigour and success, by
Agassiz in Switzerland, by Von Meyer in Germany, and last, but
not least, by Owen in this country, while, in later years, a
multitude of workers have laboured in the same field. In many
groups of the animal kingdom the number of fossil forms already
known is as great as that of the existing species. In some cases
it is much greater; and there are entire orders of animals of
the existence of which we should know nothing except for the
evidence afforded by fossil remains. With all this it may be
safely assumed that, at the present moment, we are not
acquainted with a tittle of the fossils which will sooner or
later be discovered. If we may judge by the profusion yielded
within the last few years by the Tertiary formations of North
America, there seems to be no limit to the multitude of
mammalian remains to be expected from that continent;
and analogy leads us to expect similar riches in Eastern Asia,
whenever the Tertiary formations of that region are as carefully
explored. Again, we have, as yet, almost everything to learn
respecting the terrestrial population of the Mesozoic epoch;
and it seems as if the Western territories of the United States
were about to prove as instructive in regard to this point as
they have in respect of tertiary life. My friend Professor Marsh
informs me that, within two years, remains of more than 160
distinct individuals of mammals, belonging to twenty species and
nine genera, have been found in a space not larger than the
floor of a good-sized room; while beds of the same age have
yielded 300 reptiles, varying in size from a length of 60 feet
or 80 feet to the dimensions of a rabbit.

The task which I have set myself to-night is to endeavour to lay
before you, as briefly as possible, a sketch of the successive
steps by which our present knowledge of the facts of
palaeontology and of those conclusions from them which are
indisputable, has been attained; and I beg leave to remind you,
at the outset, that in attempting to sketch the progress of a
branch of knowledge to which innumerable labours have
contributed, my business is rather with generalisations than
with details. It is my object to mark the epochs of
palaeontology, not to recount all the events of its history.

That which I just now called the fundamental problem of
palaeontology, the question which has to be settled before any
other can be profitably discussed, is this, What is the nature
of fossils? Are they, as the healthy common sense of the ancient
Greeks appears to have led them to assume without hesitation,
the remains of animals and plants? Or are they, as was so
generally maintained in the fifteenth, sixteenth, and
seventeenth centuries, mere figured stones, portions of mineral
matter which have assumed the forms of leaves and shells and
bones, just as those portions of mineral matter which we call
crystals take on the form of regular geometrical solids?
Or, again, are they, as others thought, the products of the
germs of animals and of the seeds of plants which have lost
their way, as it were, in the bowels of the earth, and have
achieved only an imperfect and abortive development? It is easy
to sneer at our ancestors for being disposed to reject the first
in favour of one or other of the last two hypotheses; but it is
much more profitable to try to discover why they, who were
really not one whit less sensible persons than our excellent
selves, should have been led to entertain views which strike us
as absurd, The belief in what is erroneously called spontaneous
generation, that is to say, in the development of living matter
out of mineral matter, apart from the agency of pre-existing
living matter, as an ordinary occurrence at the present day--
which is still held by some of us, was universally accepted as
an obvious truth by them. They could point to the arborescent
forms assumed by hoar-frost and by sundry metallic minerals as
evidence of the existence in nature of a "plastic force"
competent to enable inorganic matter to assume the form of
organised bodies. Then, as every one who is familiar with
fossils knows, they present innumerable gradations, from shells
and bones which exactly resemble the recent objects, to masses
of mere stone which, however accurately they repeat the outward
form of the organic body, have nothing else in common with it;
and, thence, to mere traces and faint impressions in the
continuous substance of the rock. What we now know to be the
results of the chemical changes which take place in the course
of fossilisation, by which mineral is substituted for organic
substance, might, in the absence of such knowledge, be fairly
interpreted as the expression of a process of development in the
opposite direction--from the mineral to the organic. Moreover,
in an age when it would have seemed the most absurd of paradoxes
to suggest that the general level of the sea is constant, while
that of the solid land fluctuates up and down through thousands
of feet in a secular ground swell, it may well have appeared far
less hazardous to conceive that fossils are sports of nature
than to accept the necessary alternative, that all the inland
regions and highlands, in the rocks of which marine shells had
been found, had once been covered by the ocean. It is not so
surprising, therefore, as it may at first seem, that although
such men as Leonardo da Vinci and Bernard Palissy took just
views of the nature of fossils, the opinion of the majority of
their contemporaries set strongly the other way; nor even that
error maintained itself long after the scientific grounds of the
true interpretation of fossils had been stated, in a manner that
left nothing to be desired, in the latter half of the
seventeenth century. The person who rendered this good service
to palaeontology was Nicolas Steno, professor of anatomy in
Florence, though a Dane by birth. Collectors of fossils at that
day were familiar with certain bodies termed "glossopetrae," and
speculation was rife as to their nature. In the first half of
the seventeenth century, Fabio Colonna had tried to convince his
colleagues of the famous Accademia dei Lincei that the
glossopetrae were merely fossil sharks' teeth, but his arguments
made no impression. Fifty years later, Steno re-opened the
question, and, by dissecting the head of a shark and pointing
out the very exact correspondence of its teeth with the
glossopetrae, left no rational doubt as to the origin of the
latter. Thus far, the work of Steno went little further than
that of Colonna, but it fortunately occurred to him to think out
the whole subject of the interpretation of fossils, and the
result of his meditations was the publication, in 1669, of a
little treatise with the very quaint title of "De Solido intra
Solidum naturaliter contento." The general course of Steno's
argument may be stated in a few words. Fossils are solid bodies
which, by some natural process, have come to be contained within
other solid bodies, namely, the rocks in which they are
embedded; and the fundamental problem of palaeontology, stated
generally, is this: "Given a body endowed with a certain shape
and produced in accordance with natural laws, to find in that
body itself the evidence of the place and manner of its
production."<1> The only way of solving this problem is by the
application of the axiom that "like effects imply like causes,"
or as Steno puts it, in reference to this particular case, that
"bodies which are altogether similar have been produced in the
same way."<2> Hence, since the glossopetrae are altogether
similar to sharks' teeth, they must have been produced by
sharklike fishes; and since many fossil shells correspond, down
to the minutest details of structure, with the shells of
existing marine or freshwater animals, they must have been
produced by similar animals; and the like reasoning is applied
by Steno to the fossil bones of vertebrated animals, whether
aquatic or terrestrial. To the obvious objection that many
fossils are not altogether similar to their living analogues,
differing in substance while agreeing in form, or being mere
hollows or impressions, the surfaces of which are figured in the
same way as those of animal or vegetable organisms, Steno
replies by pointing out the changes which take place in organic
remains embedded in the earth, and how their solid substance may
be dissolved away entirely, or replaced by mineral matter, until
nothing is left of the original but a cast, an impression, or a
mere trace of its contours. The principles of investigation thus
excellently stated and illustrated by Steno in 1669, are those
which have, consciously or unconsciously, guided the researches
of palaeontologists ever since. Even that feat of palaeontology
which has so powerfully impressed the popular imagination, the
reconstruction of an extinct animal from a tooth or a bone, is
based upon the simplest imaginable application of the logic of
Steno. A moment's consideration will show, in fact, that Steno's
conclusion that the glossopetrae are sharks' teeth implies the
reconstruction of an animal from its tooth. It is equivalent to
the assertion that the animal of which the glossopetrae are
relics had the form and organisation of a shark; that it had a
skull, a vertebral column, and limbs similar to those which are
characteristic of this group of fishes; that its heart, gills,
and intestines presented the peculiarities which those of all
sharks exhibit; nay, even that any hard parts which its
integument contained were of a totally different character from
the scales of ordinary fishes. These conclusions are as certain
as any based upon probable reasonings can be. And they are so,
simply because a very large experience justifies us in believing
that teeth of this particular form and structure are invariably
associated with the peculiar organisation of sharks, and are
never found in connection with other organisms. Why this should
be we are not at present in a position even to imagine; we must
take the fact as an empirical law of animal morphology, the
reason of which may possibly be one day found in the history of
the evolution of the shark tribe, but for which it is hopeless
to seek for an explanation in ordinary physiological reasonings.
Every one practically acquainted with palaeontology is aware
that it is not every tooth, nor every bone, which enables us to
form a judgment of the character of the animal to which it
belonged; and that it is possible to possess many teeth, and
even a large portion of the skeleton of an extinct animal, and
yet be unable to reconstruct its skull or its limbs. It is only
when the tooth or bone presents peculiarities, which we know by
previous experience to be characteristic of a certain group,
that we can safely predict that the fossil belonged to an animal
of the same group. Any one who finds a cow's grinder may be
perfectly sure that it belonged to an animal which had two
complete toes on each foot and ruminated; any one who finds a
horse's grinder may be as sure that it had one complete toe on
each foot and did not ruminate; but if ruminants and horses were
extinct animals of which nothing but the grinders had ever been
discovered, no amount of physiological reasoning could have
enabled us to reconstruct either animal, still less to have
divined the wide differences between the two. Cuvier, in the
"Discours sur les Revolutions de la Surface du Globe," strangely
credits himself, and has ever since been credited by others,
with the invention of a new method of palaeontological research.
But if you will turn to the "Recherches sur les Ossemens
Fossiles" and watch Cuvier, not speculating, but working, you
will find that his method is neither more nor less than that of
Steno. If he was able to make his famous prophecy from the jaw
which lay upon the surface of a block of stone to the pelvis of
the same animal which lay hidden in it, it was not because
either he, or any one else, knew, or knows, why a certain form
of jaw is, as a rule, constantly accompanied by the presence of
marsupial bones, but simply because experience has shown that
these two structures are co-ordinated.

The settlement of the nature of fossils led at once to the next
advance of palaeontology, viz. its application to the
deciphering of the history of the earth. When it was admitted
that fossils are remains of animals and plants, it followed
that, in so far as they resemble terrestrial, or freshwater,
animals and plants, they are evidences of the existence of land,
or fresh water; and, in so far as they resemble marine
organisms, they are evidences of the existence of the sea at the
time at which they were parts of actually living animals and
plants. Moreover, in the absence of evidence to the contrary, it
must be admitted that the terrestrial or the marine organisms
implied the existence of land or sea at the place in which they
were found while they were yet living. In fact, such conclusions
were immediately drawn by everybody, from the time of Xenophanes
downwards, who believed that fossils were really organic
remains. Steno discusses their value as evidence of repeated
alteration of marine and terrestrial conditions upon the soil of
Tuscany in a manner worthy of a modern geologist.
The speculations of De Maillet in the beginning of the
eighteenth century turn upon fossils; and Buffon follows him
very closely in those two remarkable works, the "Theorie de la
Terre" and the "Epoques de la Nature" with which he commenced
and ended his career as a naturalist.

The opening sentences of the "Epoques de la Nature" show us how
fully Buffon recognised the analogy of geological with
archaeological inquiries. "As in civil history we consult deeds,
seek for coins, or decipher antique inscriptions in order to
determine the epochs of human revolutions and fix the date of
moral events; so, in natural history, we must search the
archives of the world, recover old monuments from the bowels of
the earth, collect their fragmentary remains, and gather into
one body of evidence all the signs of physical change which may
enable us to look back upon the different ages of nature. It is
our only means of fixing some points in the immensity of space,
and of setting a certain number of waymarks along the eternal
path of time."

Buffon enumerates five classes of these monuments of the past
history of the earth, and they are all facts of palaeontology.
In the first place, he says, shells and other marine productions
are found all over the surface and in the interior of the dry
land; and all calcareous rocks are made up of their remains.
Secondly, a great many of these shells which are found in Europe
are not now to be met with in the adjacent seas; and, in the
slates and other deep-seated deposits, there are remains of
fishes and of plants of which no species now exist in our
latitudes, and which are either extinct, or exist only in more
northern climates. Thirdly, in Siberia and in other northern
regions of Europe and of Asia, bones and teeth of elephants,
rhinoceroses, and hippopotamuses occur in such numbers that
these animals must once have lived and multiplied in those
regions, although at the present day they are confined to
southern climates. The deposits in which these remains are found
are superficial, while those which contain shells and other
marine remains lie much deeper. Fourthly, tusks and bones of
elephants and hippopotamuses are found not only in the northern
regions of the old world, but also in those of the new world,
although, at present, neither elephants nor hippopotamuses occur
in America. Fifthly, in the middle of the continents, in regions
most remote from the sea, we find an infinite number of shells,
of which the most part belong to animals of those kinds which
still exist in southern seas, but of which many others have no
living analogues; so that these species appear to be lost,
destroyed by some unknown cause. It is needless to inquire how
far these statements are strictly accurate; they are
sufficiently so to justify Buffon's conclusions that the dry
land was once beneath the sea; that the formation of the
fossiliferous rocks must have occupied a vastly greater lapse of
time than that traditionally ascribed to the age of the earth;
that fossil remains indicate different climatal conditions to
have obtained in former times, and especially that the polar
regions were once warmer; that many species of animals and
plants have become extinct; and that geological change has had
something to do with geographical distribution.

But these propositions almost constitute the frame-work of
palaeontology. In order to complete it but one addition was
needed, and that was made, in the last years of the eighteenth
century, by William Smith, whose work comes so near our own
times that many living men may have been personally acquainted
with him. This modest land-surveyor, whose business took him
into many parts of England, profited by the peculiarly
favourable conditions offered by the arrangement of our
secondary strata to make a careful examination and comparison of
their fossil contents at different points of the large area over
which they extend. The result of his accurate and widely-
extended observations was to establish the important truth that
each stratum contains certain fossils which are peculiar to it;
and that the order in which the strata, characterised by these
fossils, are super-imposed one upon the other is always the
same. This most important generalisation was rapidly verified
and extended to all parts of the world accessible to geologists;
and now it rests upon such an immense mass of observations as to
be one of the best established truths of natural science. To the
geologist the discovery was of infinite importance as it enabled
him to identify rocks of the same relative age, however their
continuity might be interrupted or their composition altered.
But to the biologist it had a still deeper meaning, for it
demonstrated that, throughout the prodigious duration of time
registered by the fossiliferous rocks, the living population of
the earth had undergone continual changes, not merely by the
extinction of a certain number of the species which had at first
existed, but by the continual generation of new species, and the
no less constant extinction of old ones.

Thus the broad outlines of palaeontology, in so far as it is the
common property of both the geologist and the biologist, were
marked out at the close of the last century. In tracing its
subsequent progress I must confine myself to the province of
biology, and, indeed, to the influence of palaeontology upon
zoological morphology. And I accept this limitation the more
willingly as the no less important topic of the bearing of
geology and of palaeontology upon distribution has been
luminously treated in the address of the President of the
Geographical Section.<3>

The succession of the species of animals and plants in time
being established, the first question which the zoologist or the
botanist had to ask himself was, What is the relation of these
successive species one to another? And it is a curious
circumstance that the most important event in the history of
palaeontology which immediately succeeded William Smith's
generalisation was a discovery which, could it have been rightly
appreciated at the time, would have gone far towards suggesting
the answer, which was in fact delayed for more than half a
century. I refer to Cuvier's investigation of the mammalian
fossils yielded by the quarries in the older tertiary rocks of
Montmartre, among the chief results of which was the bringing to
light of two genera of extinct hoofed quadrupeds, the
Anoplotherium and the Palaeotherium. The rich
materials at Cuvier's disposition enabled him to obtain a full
knowledge of the osteology and of the dentition of these two
forms, and consequently to compare their structure critically
with that of existing hoofed animals. The effect of this
comparison was to prove that the Anoplotherium, though it
presented many points of resemblance with the pigs on the one
hand and with the ruminants on the other, differed from both to
such an extent that it could find a place in neither group.
In fact, it held, in some respects, an intermediate position,
tending to bridge over the interval between these two groups,
which in the existing fauna are so distinct. In the same way,
the Palaeotherium tended to connect forms so different as
the tapir, the rhinoceros, and the horse. Subsequent
investigations have brought to light a variety of facts of the
same order, the most curious and striking of which are those
which prove the existence, in the mesozoic epoch, of a series of
forms intermediate between birds and reptiles--two classes of
vertebrate animals which at present appear to be more widely
separated than any others. Yet the interval between them is
completely filled, in the mesozoic fauna, by birds which have
reptilian characters, on the one side, and reptiles which have
ornithic characters, on the other. So again, while the group of
fishes, termed ganoids, is, at the present time, so distinct
from that of the dipnoi, or mudfishes, that they have been
reckoned as distinct orders, the Devonian strata present us with
forms of which it is impossible to say with certainty whether
they are dipnoi or whether they are ganoids.

Agassiz's long and elaborate researches upon fossil fishes,
published between 1833 and 1842, led him to suggest the
existence of another kind of relation between ancient and modern
forms of life. He observed that the oldest fishes present
many characters which recall the embryonic conditions of
existing fishes; and that, not only among fishes, but in several
groups of the invertebrata which have a long palaeontological
history, the latest forms are more modified, more specialised,
than the earlier. The fact that the dentition of the older
tertiary ungulate and carnivorous mammals is always complete,
noticed by Professor Owen, illustrated the same generalisation.

Another no less suggestive observation was made by Mr. Darwin,
whose personal investigations during the voyage of the
Beagle led him to remark upon the singular fact, that the
fauna, which immediately precedes that at present existing in
any geographical province of distribution, presents the same
peculiarities as its successor. Thus, in South America and in
Australia, the later tertiary or quaternary fossils show that
the fauna which immediately preceded that of the present day
was, in the one case, as much characterised by edentates and, in
the other, by marsupials as it is now, although the species of
the older are largely different from those of the newer fauna.

However clearly these indications might point in one direction,
the question of the exact relation of the successive forms of
animal and vegetable life could be satisfactorily settled only
in one way; namely, by comparing, stage by stage, the series of
forms presented by one and the same type throughout a long
space of time. Within the last few years this has been done
fully in the case of the horse, less completely in the case of
the other principal types of the ungulata and of the carnivora;
and all these investigations tend to one general result, namely,
that, in any given series, the successive members of that series
present a gradually increasing specialisation of structure.
That is to say, if any such mammal at present existing has
specially modified and reduced limbs or dentition and
complicated brain, its predecessors in time show less and less
modification and reduction in limbs and teeth and a less highly
developed brain. The labours of Gaudry, Marsh, and Cope furnish
abundant illustrations of this law from the marvellous fossil
wealth of Pikermi and the vast uninterrupted series of tertiary
rocks in the territories of North America.

I will now sum up the results of this sketch of the rise and
progress of palaeontology. The whole fabric of palaeontology is
based upon two propositions: the first is, that fossils are the
remains of animals and plants; and the second is, that the
stratified rocks in which they are found are sedimentary
deposits; and each of these propositions is founded upon the
same axiom, that like effects imply like causes. If there is any
cause competent to produce a fossil stem, or shell, or bone,
except a living being, then palaeontology has no foundation;
if the stratification of the rocks is not the effect of such
causes as at present produce stratification, we have no means of
judging of the duration of past time, or of the order in which
the forms of life have succeeded one another. But if these two
propositions are granted, there is no escape, as it appears to
me, from three very important conclusions. The first is that
living matter has existed upon the earth for a vast length of
time, certainly for millions of years. The second is that,
during this lapse of time, the forms of living matter have
undergone repeated changes, the effect of which has been that
the animal and vegetable population, at any period of the
earth's history, contains certain species which did not exist at
some antecedent period, and others which ceased to exist at some
subsequent period. The third is that, in the case of many groups
of mammals and some of reptiles, in which one type can be
followed through a considerable extent of geological time, the
series of different forms by which the type is represented, at
successive intervals of this time, is exactly such as it would
be, if they had been produced by the gradual modification of the
earliest forms of the series. These are facts of the history of
the earth guaranteed by as good evidence as any facts in
civil history.

Hitherto I have kept carefully clear of all the hypotheses to
which men have at various times endeavoured to fit the facts of
palaeontology, or by which they have endeavoured to connect
as many of these facts as they happened to be acquainted with.
I do not think it would be a profitable employment of our time
to discuss conceptions which doubtless have had their
justification and even their use, but which are now obviously
incompatible with the well-ascertained truths of palaeontology.
At present these truths leave room for only two hypotheses.
The first is that, in the course of the history of the earth,
innumerable species of animals and plants have come into
existence, independently of one another, innumerable times.
This, of course, implies either that spontaneous generation on
the most astounding scale, and of animals such as horses and
elephants, has been going on, as a natural process, through all
the time recorded by the fossiliferous rocks; or it necessitates
the belief in innumerable acts of creation repeated innumerable
times. The other hypothesis is, that the successive species of
animals and plants have arisen, the later by the gradual
modification of the earlier. This is the hypothesis of
evolution; and the palaeontological discoveries of the last
decade are so completely in accordance with the requirements of
this hypothesis that, if it had not existed, the palaeontologist
would have had to invent it.

I have always had a certain horror of presuming to set a limit
upon the possibilities of things. Therefore I will not venture
to say that it is impossible that the multitudinous species of
animals and plants may have been produced, one separately
from the other, by spontaneous generation; nor that it is
impossible that they should have been independently originated
by an endless succession of miraculous creative acts. But I must
confess that both these hypotheses strike me as so astoundingly
improbable, so devoid of a shred of either scientific or
traditional support, that even if there were no other evidence
than that of palaeontology in its favour, I should feel
compelled to adopt the hypothesis of evolution. Happily, the
future of palaeontology is independent of all hypothetical
considerations. Fifty years hence, whoever undertakes to record
the progress of palaeontology will note the present time as the
epoch in which the law of succession of the forms of the higher
animals was determined by the observation of palaeontological
facts. He will point out that, just as Steno and as Cuvier were
enabled from their knowledge of the empirical laws of co-
existence of the parts of animals to conclude from a part to the
whole, so the knowledge of the law of succession of forms
empowered their successors to conclude, from one or two terms of
such a succession, to the whole series; and thus to divine the
existence of forms of life, of which, perhaps, no trace remains,
at epochs of inconceivable remoteness in the past.


(1) De Solidoiintra Solidum, p.5--"Dato corpore certa
figura praedito et juxta leges naturae producto, in ipso corpore
argumenta invenire locum et modum productionis detegentia."
(2) "Corpora sibi invicem omnino similia simili etiam modo
producta sunt."
(3) Sir J. D. Hooker.

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