Thomas Henry Huxley - Lay Sermons, Addresses and Reviews

T >> Thomas Henry Huxley >> Lay Sermons, Addresses and Reviews

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The Crinoidea, in the abundance of stalked forms in the ancient
formations as compared with their present rarity, seem to present us
with a fair case of modification from a more embryonic towards a less
embryonic condition. But then, on careful consideration of the facts,
the objection arises that the stalk, calyx, and arms of the palaeozoic
Crinoid are exceedingly different from the corresponding organs of a
larval _Comatula_; and it might with perfect justice be argued that
_Actinocrinus_ and _Eucalyptocrinus_, for example, depart to the full as
widely, in one direction, from the stalked embryo of _Comatula_, as
_Comatula_ itself does in the other.

The Echinidea, again, are frequently quoted as exhibiting a gradual
passage from a more generalized to a more specialized type, seeing that
the elongated, or oval, Spatangoids appear after the spheroidal
Echinoids. But here it might be argued, on the other hand, that the
spheroidal Echinoids, in reality, depart further from the general plan
and from the embryonic form than the elongated Spatangoids do; and that
the peculiar dental apparatus and the pedicellariae of the former are
marks of at least as great differentiation as the petaloid ambulacra and
semitae of the latter.

Once more, the prevalence of Macrurous before Brachyurous Podophthalmia
is, apparently, a fair piece of evidence in favour of progressive
modification in the same order of Crustacea; and yet the case will not
stand much sifting, seeing that the Macrurous Podophthalmia depart as
far in one direction from the common type of Podophthalmia, or from any
embryonic condition of the Brachyura, as the Brachyura do in the other;
and that the middle terms between Macrura and Brachyura--the
Anomura--are little better represented in the older Mesozoic rocks than
the Brachyura are.

None of the cases of progressive modification which are cited from among
the Invertebrata appear to me to have a foundation less open to
criticism than these; and if this be so, no careful reasoner would, I
think, be inclined to lay very great stress upon them. Among the
Vertebrata, however, there are a few examples which appear to be far
less open to objection.

It is, in fact, true of several groups of Vertebrata which have lived
through a considerable range of time, that the endoskeleton (more
particularly the spinal column) of the older genera presents a less
ossified, and, so far, less differentiated, condition than that of the
younger genera. Thus the Devonian Ganoids, though almost all members of
the same sub-order as _Polypterus,_ and presenting numerous important
resemblances to the existing genus, which possesses biconcave vertebrae,
are, for the most part, wholly devoid of ossified vertebral centra. The
Mesozoic Lepidosteidae, again, have, at most, biconcave vertebrae, while
the existing _Lepidosteus_ has Salamandroid, opisthocoelous, vertebrae.
So, none of the Palaeozoic Sharks have shown themselves to be possessed
of ossified vertebrae, while the majority of modern Sharks possess such
vertebrae. Again, the more ancient Crocodilia and Lacertilia have
vertebrae with the articular facets of their centra flattened or
biconcave, while the modern members of the same group have them
procoelous. But the most remarkable examples of progressive
modification of the vertebral column, in correspondence with geological
age, are those afforded by the Pycnodonts among fish, and the
Labyrinthodonts among Amphibia.

The late able ichthyologist Heckel pointed out the fact, that, while the
Pycnodonts never possess true vertebral centra, they differ in the
degree of expansion and extension of the ends of the bony arches of the
vertebrae upon the sheath of the notochord; the Carboniferous forms
exhibiting hardly any such expansion, while the Mesozoic genera present
a greater and greater development, until, in the Tertiary forms, the
expanded ends become suturally united so as to form a sort of false
vertebra. Hermann von Meyer, again, to whose luminous researches we are
indebted for our present large knowledge of the organization of the
older Labyrinthodonts, has proved that the Carboniferous _Archegosaurus_
had very imperfectly developed vertebral centra, while the Triassic
_Mastodonsaurus_ had the same parts completely ossified.[38]

The regularity and evenness of the dentition of the _Anoplotherium_, as
contrasted with that of existing Artiodactyles, and the assumed nearer
approach of the dentition of certain ancient Carnivores to the typical
arrangement, have also been cited as exemplifications of a law of
progressive development, but I know of no other cases based on positive
evidence which are worthy of particular notice.

What then does an impartial survey of the positively ascertained truths
of palaeontology testify in relation to the common doctrines of
progressive modification, which suppose that modification to have taken
place by a necessary progress from more to less embryonic forms, or from
more to less generalized types, within the limits of the period
represented by the fossiliferous rocks?

It negatives those doctrines; for it either shows us no evidence of any
such modification, or demonstrates it to have been very slight; and as
to the nature of that modification, it yields no evidence whatsoever
that the earlier members of any long-continued group were more
generalized in structure than the later ones. To a certain extent,
indeed, it may be said that imperfect ossification of the vertebral
column is an embryonic character; but, on the other hand, it would be
extremely incorrect to suppose that the vertebral columns of the older
Vertebrata are in any sense embryonic in their whole structure.

Obviously, if the earliest fossiliferous rocks now known are coeval with
the commencement of life, and if their contents give us any just
conception of the nature and the extent of the earliest fauna and flora,
the insignificant amount of modification which can be demonstrated to
have taken place in any one group of animals, or plants, is quite
incompatible with the hypothesis that all living forms are the results
of a necessary process of progressive development, entirely comprised
within the time represented by the fossiliferous rocks.

Contrariwise, any admissible hypothesis of progressive modification
must be compatible with persistence without progression, through
indefinite periods. And should such an hypothesis eventually be proved
to be true, in the only way in which it can be demonstrated, viz. by
observation and experiment upon the existing forms of life, the
conclusion will inevitably present itself, that the Palaeozoic, Mesozoic,
and Cainozoic faunae and florae, taken together, bear somewhat the same
proportion to the whole series of living beings which have occupied this
globe, as the existing fauna and flora do to them.

Such are the results of palaeontology as they appear, and have for some
years appeared, to the mind of an inquirer who regards that study simply
as one of the applications of the great biological sciences, and who
desires to see it placed upon the same sound basis as other branches of
physical inquiry. If the arguments which have been brought forward are
valid, probably no one, in view of the present state of opinion, will be
inclined to think the time wasted which has been spent upon their
elaboration.

FOOTNOTES:

[33] "Le plus grand service qu'on puisse rendre a la science est d'y
faire place nette avant d'y rien construire."--CUVIER.

[34] Anniversary Address for 1851, Quart. Journ. Geol. Soc. vol. vii.

[35] See Hooker's "Introductory Essay to the Flora of Tasmania," p.
xxiii.

[36] See the abstract of a Lecture "On the Persistent Types of Animal
Life" in the "Notices of the Meetings of the Royal Institution of Great
Britain," June 3, 1859, vol. iii. p. 151.

[37] "Memoirs of the Geological Survey of the United Kingdom.--Decade x.
Preliminary Essay upon the Systematic Arrangement of the Fishes of the
Devonian Epoch."

[38] As this Address is passing through the press (March 7, 1862),
evidence lies before me of the existence of a new Labyrinthodont
(_Pholidogaster_), from the Edinburgh coal-field, with well-ossified
vertebral centra.

XI.

GEOLOGICAL REFORM.

"A great reform in geological speculation seems now to have become
necessary."

"It is quite certain that a great mistake has been made,--that
British popular geology at the present time is in direct opposition
to the principles of Natural Philosophy."[39]

In reviewing the course of geological thought during the past year, for
the purpose of discovering those matters to which I might most fitly
direct your attention in the Address which it now becomes my duty to
deliver from the Presidential Chair, the two somewhat alarming sentences
which I have just read, and which occur in an able and interesting essay
by an eminent natural philosopher, rose into such prominence before my
mind that they eclipsed everything else.

It surely is a matter of paramount importance for the British geologists
(some of them very popular geologists too) here in solemn annual session
assembled, to inquire whether the severe judgment thus passed upon them,
by so high an authority as Sir William Thomson is one to which they
must plead guilty _sans phrase_, or whether they are prepared to say
"not guilty," and appeal for a reversal of the sentence to that higher
court of educated scientific opinion to which we are all amenable.

As your attorney-general for the time being, I thought I could not do
better than get up the case with a view of advising you. It is true that
the charges brought forward by the other side involve the consideration
of matters quite foreign to the pursuits with which I am ordinarily
occupied; but, in that respect, I am only in the position which is, nine
times out of ten, occupied by counsel, who nevertheless contrive to gain
their causes, mainly by force of mother-wit and common sense, aided by
some training in other intellectual exercises.

Nerved by such precedents, I proceed to put my pleading before you.

And the first question with which I propose to deal is, What is it to
which Sir W. Thomson refers when he speaks of "geological speculation"
and "British popular geology"?

I find three, more or less contradictory, systems of geological thought,
each of which might fairly enough claim these appellations, standing
side by side in Britain. I shall call one of them CATASTROPHISM, another
UNIFORMITARIANISM, the third EVOLUTIONISM; and I shall try briefly to
sketch the characters of each, that you may say whether the
classification is, or is not, exhaustive.

By CATASTROPHISM, I mean any form of geological speculation
which, in order to account for the phaenomena of geology, supposes the
operation of forces different in their nature, or immeasurably different
in power, from those which we at present see in action in the universe.

The Mosaic cosmogony is, in this sense, catastrophic, because it
assumes the operation of extra-natural power. The doctrine of violent
upheavals, _debacles_, and cataclysms in general, is catastrophic, so
far as it assumes that these were brought about by causes which have now
no parallel. There was a time when catastrophism might, pre-eminently,
have claimed the title of "British popular geology;" and assuredly it
has yet many adherents, and reckons among its supporters some of the
most honoured members of this Society.

By UNIFORMITARIANISM, I mean especially, the teaching of Hutton
and of Lyell.

That great, though incomplete work, "The Theory of the Earth," seems to
me to be one of the most remarkable contributions to geology which is
recorded in the annals of the science. So far as the not-living world is
concerned, uniformitarianism lies there, not only in germ, but in
blossom and fruit.

If one asks how it is that Hutton was led to entertain views so far in
advance of those prevalent in his time, in some respects; while, in
others, they seem almost curiously limited, the answer appears to me to
be plain.

Hutton was in advance of the geological speculation of his time,
because, in the first place, he had amassed a vast store of knowledge of
the facts of geology, gathered by personal observation in travels of
considerable extent; and because, in the second place, he was thoroughly
trained in the physical and chemical science of his day, and thus
possessed, as much as any one in his time could possess it, the
knowledge which is requisite for the just interpretation of geological
phaenomena, and the habit of thought which fits a man for scientific
inquiry.

It is to this thorough scientific training, that I ascribe Hutton's
steady and persistent refusal to look to other causes than those now in
operation, for the explanation of geological phaenomena.

Thus he writes:--"I do not pretend, as he [M. de Luc] does in his
theory, to describe the beginning of things. I take things such as I
find them at present; and from these I reason with regard to that which
must have been."[40]

And again:--"A theory of the earth, which has for object truth, can have
no retrospect to that which had preceded the present order of the world;
for this order alone is what we have to reason upon; and to reason
without data is nothing but delusion. A theory, therefore, which is
limited to the actual constitution of this earth cannot be allowed to
proceed one step beyond the present order of things."[41]

And so clear is he, that no causes beside such as are now in operation
are needed to account for the character and disposition of the
components of the crust of the earth, that he says, broadly and
boldly:-- "... There is no part of the earth which has not had the same
origin, so far as this consists in that earth being collected at the
bottom of the sea, and afterwards produced, as land, along with masses
of melted substances, by the operation of mineral causes."[42]

But other influences were at work upon Hutton beside those of a mind
logical by Nature, and scientific by sound training; and the peculiar
turn which his speculations took seems to me to be unintelligible,
unless these be taken into account. The arguments of the French
astronomers and mathematicians, which, at the end of the last century,
were held to demonstrate the existence of a compensating arrangement
among the celestial bodies, whereby all perturbations eventually reduced
themselves to oscillations on each side of a mean position, and the
stability of the solar system was secured, had evidently taken strong
hold of Hutton's mind.

In those oddly constructed periods which seem to have prejudiced many
persons against reading his works, but which are full of that peculiar,
if unattractive, eloquence which flows from mastery of the subject,
Hutton says:--

"We have now got to the end of our reasoning; we have no data further to
conclude immediately from that which actually is. But we have got
enough; we have the satisfaction to find, that in Nature there is
wisdom, system, and consistency. For having, in the natural history of
this earth, seen a succession of worlds, we may from this conclude that
there is a system in Nature; in like manner as, from seeing revolutions
of the planets, it is concluded, that there is a system by which they
are intended to continue those revolutions. But if the succession of
worlds is established in the system of Nature, it is in vain to look for
anything higher in the origin of the earth. The result, therefore, of
this physical inquiry is, that we find no vestige of a beginning,--no
prospect of an end."[43]

Yet another influence worked strongly upon Hutton. Like most
philosophers of his age, he coquetted with those final causes which have
been named barren virgins, but which might be more fitly termed the
_hetairae_ of philosophy, so constantly have they led men astray. The
final cause of the existence of the world is, for Hutton, the production
of life and intelligence.

"We have now considered the globe of this earth as a machine,
constructed upon chemical as well as mechanical principles, by which its
different parts are all adapted, in form, in quality, and in quantity,
to a certain end; an end attained with certainty or success; and an end
from which we may perceive wisdom, in contemplating the means employed.

"But is this world to be considered thus merely as a machine, to last no
longer than its parts retain their present position, their proper forms
and qualities? Or may it not be also considered as an organized body?
such as has a constitution in which the necessary decay of the machine
is naturally repaired, in the exertion of those productive powers by
which it had been formed.

"This is the view in which we are now to examine the globe; to see if
there be, in the constitution of this world, a reproductive operation,
by which a ruined constitution may be again repaired, and a duration or
stability thus procured to the machine, considered as a world sustaining
plants and animals."[44]

Kirwan, and the other Philistines of the day, accused Hutton of
declaring that his theory implied that the world never had a beginning,
and never differed in condition from its present state. Nothing could be
more grossly unjust, as he expressly guards himself against any such
conclusion in the following terms:--

"But in thus tracing back the natural operations which have succeeded
each other, and mark to us the course of time past, we come to a period
in which we cannot see any farther. This, however, is not the beginning
of the operations which proceed in time and according to the wise
economy of this world; nor is it the establishing of that which, in the
course of time, had no beginning; it is only the limit of our
retrospective view of those operations which have come to pass in time,
and have been conducted by supreme intelligence."[45]

I have spoken of Uniformitarianism as the doctrine of Hutton and of
Lyell. If I have quoted the older writer rather than the newer, it is
because his works are little known, and his claims on our veneration too
frequently forgotten, not because I desire to dim the fame of his
eminent successor. Few of the present generation of geologists have read
Playfair's "Illustrations," fewer still the original "Theory of the
Earth;" the more is the pity; but which of us has not thumbed every page
of the "Principles of Geology?" I think that he who writes fairly the
history of his own progress in geological thought, will not be able to
separate his debt to Hutton from his obligations to Lyell; and the
history of the progress of individual geologists is the history of
geology.

No one can doubt that the influence of uniformitarian views has been
enormous, and, in the main, most beneficial and favourable to the
progress of sound geology.

Nor can it be questioned that Uniformitarianism has even a stronger
title than Catastrophism to call itself the geological speculation of
Britain, or, if you will, British popular geology. For it is eminently a
British doctrine, and has even now made comparatively little progress
on the continent of Europe. Nevertheless it seems to me to be open to
serious criticism upon one of its aspects.

I have shown how unjust was the insinuation that Hutton denied a
beginning to the world. But it would not be unjust to say that he
persistently, in practice, shut his eyes to the existence of that prior
and different state of things which, in theory, he admitted; and, in
this aversion to look beyond the veil of stratified rocks, Lyell follows
him.

Hutton and Lyell alike agree in their indisposition to carry their
speculations a step beyond the period recorded in the most ancient
strata now open to observation in the crust of the earth. This is, for
Hutton, "the point in which we cannot see any farther;" while Lyell
tells us,--

"The astronomer may find good reasons for ascribing the earth's form to
the original fluidity of the mass, in times long antecedent to the first
introduction of living beings into the planet; but the geologist must be
content to regard the earliest monuments which it is his task to
interpret, as belonging to a period when the crust had already acquired
great solidity and thickness, probably as great as it now possesses, and
when volcanic rocks, not essentially differing from those now produced,
were formed from time to time, the intensity of volcanic heat being
neither greater nor less than it is now."[46]

And again, "As geologists, we learn that it is not only the present
condition of the globe which has been suited to the accommodation of
myriads of living creatures, but that many former states also have been
adapted to the organization and habits of prior races of beings. The
disposition of the seas, continents and islands, and the climates, have
varied; the species likewise have been changed; and yet they have all
been so modelled, on types analogous to those of existing plants and
animals, as to indicate, throughout, a perfect harmony of design and
unity of purpose. To assume that the evidence of the beginning, or end,
of so vast a scheme lies within the reach of our philosophical
inquiries, or even of our speculations, appears to be inconsistent with
a just estimate of the relations which subsist between the finite powers
of man and the attributes of an infinite and eternal Being."[47]

The limitations implied in these passages appear to me to constitute the
weakness and the logical defect of uniformitarianism. No one will impute
blame to Hutton that, in face of the imperfect condition, in his day, of
those physical sciences which furnish the keys to the riddles of
geology, he should have thought it practical wisdom to limit his theory
to an attempt to account for "the present order of things;" but I am at
a loss to comprehend why, for all time, the geologist must be content to
regard the oldest fossiliferous rocks as the _ultima Thule_ of his
science; or what there is inconsistent with the relations between the
finite and the infinite mind, in the assumption, that we may discern
somewhat of the beginning, or of the end, of this speck in space we call
our earth. The finite mind is certainly competent to trace out the
development of the fowl within the egg; and I know not on what ground it
should find more difficulty in unravelling the complexities of the
development of the earth. In fact, as Kant has well remarked,[48] the
cosmical process is really simpler than the biological.

This attempt to limit, at a particular point, the progress of inductive
and deductive reasoning from the things which are, to those which
were--this faithlessness to its own logic, seems to me to have cost
Uniformitarianism the place, as the permanent form of geological
speculation, which it might otherwise have held.

It remains that I should put before you what I understand to be the
third phase of geological speculation--namely, EVOLUTIONISM.

I shall not make what I have to say on this head clear, unless I
diverge, or seem to diverge, for a while, from the direct path of my
discourse, so far as to explain what I take to be the scope of geology
itself. I conceive geology to be the history of the earth, in precisely
the same sense as biology is the history of living beings; and I trust
you will not think that I am overpowered by the influence of a dominant
pursuit if I say that I trace a close analogy between these two
histories.

If I study a living being, under what heads does the knowledge I obtain
fall? I can learn its structure, or what we call its ANATOMY;
and its DEVELOPMENT, or the series of changes which it passes
through to acquire its complete structure. Then I find that the living
being has certain powers resulting from its own activities, and the
interaction of these with the activities of other things--the knowledge
of which is PHYSIOLOGY. Beyond this the living being has a
position in space and time, which is its DISTRIBUTION. All
these form the body of ascertainable facts which constitute the _status
quo_ of the living creature. But these facts have their causes; and the
ascertainment of these causes is the doctrine of AETIOLOGY.

If we consider what is knowable about the earth, we shall find that such
earth-knowledge--if I may so translate the word geology--falls into the
same categories.

What is termed stratigraphical geology is neither more nor less than the
anatomy of the earth; and the history of the succession of the
formations is the history of a succession of such anatomies, or
corresponds with development, as distinct from generation.

The internal heat of the earth, the elevation and depression of its
crust, its belchings forth of vapours, ashes, and lava, are its
activities, in as strict a sense, as are warmth and the movements and
products of respiration the activities of an animal. The phaenomena of
the seasons, of the trade winds, of the Gulf-stream, are as much the
results of the reaction between these inner activities and outward
forces, as are the budding of the leaves in spring and their falling in
autumn the effects of the interaction between the organization of a
plant and the solar light and heat. And, as the study of the activities
of the living being is called its physiology, so are these phaenomena the
subject-matter of an analogous telluric physiology, to which we
sometimes give the name of meteorology, sometimes that of physical
geography, sometimes that of geology. Again, the earth has a place in
space and in time, and relations to other bodies in both these
respects, which constitute its distribution. This subject is usually
left to the astronomer; but a knowledge of its broad outlines seems to
me to be an essential constituent of the stock of geological ideas.

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