display we behold! That our collections are imperfect is admitted by
every one. The remark of that admirable paleontologist, Edward Forbes,
should never be forgotten, namely, that very many fossil species are
known and named from single and often broken specimens, or from a few
specimens collected on some one spot. Only a small portion of the
surface of the earth has been geologically explored, and no part with
sufficient care, as the important discoveries made every year in Europe
prove. No organism wholly soft can be preserved. Shells and bones decay
and disappear when left on the bottom of the sea, where sediment is not
accumulating. We probably take a quite erroneous view, when we assume
that sediment is being deposited over nearly the whole bed of the sea,
at a rate sufficiently quick to imbed and preserve fossil remains.
Throughout an enormously large proportion of the ocean, the bright blue
tint of the water bespeaks its purity. The many cases on record of a
formation conformably covered, after an immense interval of time, by
another and later formation, without the underlying bed having suffered
in the interval any wear and tear, seem explicable only on the view
of the bottom of the sea not rarely lying for ages in an unaltered
condition. The remains which do become imbedded, if in sand or gravel,
will, when the beds are upraised, generally be dissolved by the
percolation of rain-water charged with carbonic acid. Some of the many
kinds of animals which live on the beach between high and low water
mark seem to be rarely preserved. For instance, the several species of
the _Chthamalinæ_ (a sub-family of sessile cirripeds) coat the rocks
all over the world in infinite numbers: they are all strictly littoral,
with the exception of a single Mediterranean species, which inhabits
deep water, and this has been found fossil in Sicily, whereas not
one other species has hitherto been found in any tertiary formation;
yet it is known that the genus _Chthamalus_ existed during the Chalk
period. Lastly, many great deposits, requiring a vast length of time
for their accumulation, are entirely destitute of organic remains,
without our being able to assign any reason; one of the most striking
instances is that of the Flysch formation, which consists of shale and
sandstone, several thousand, occasionally even six thousand, feet in
thickness, and extending for at least three hundred miles from Vienna
to Switzerland; and, although this great mass has been most carefully
searched, no fossils, except a few vegetable remains, have been found.
WIDE INTERVALS OF TIME BETWEEN THE GEOLOGICAL FORMATIONS.
[Page 271.]
But the imperfection in the geological record largely results from
another and more important cause than any of the foregoing; namely,
from the several formations being separated from each other by wide
intervals of time. This doctrine has been emphatically admitted by
many geologists and paleontologists, who, like E. Forbes, entirely
disbelieve in the change of species. When we see the formations
tabulated in written works, or when we follow them in nature, it is
difficult to avoid believing that they are closely consecutive. But
we know, for instance, from Sir R. Murchison’s great work on Russia,
what wide gaps there are in that country between the superimposed
formations; so it is in North America, and in many other parts of
the world. The most skillful geologist, if his attention had been
confined exclusively to these large territories, would never have
suspected that, during the periods which were blank and barren in his
own country, great piles of sediment, charged with new and peculiar
forms of life, had elsewhere been accumulated. And if, in each separate
territory, hardly any idea can be formed of the length of time which
has elapsed between the consecutive formations, we may infer that this
could nowhere be ascertained. The frequent and great changes in the
mineralogical composition of consecutive formations, generally implying
great changes in the geography of the surrounding lands, whence the
sediment was derived, accord with the belief of vast intervals of time
having elapsed between each formation.
* * * * *
[Page 278.]
It is all-important to remember that naturalists have no golden rule
by which to distinguish species and varieties; they grant some little
variability to each species, but, when they meet with a somewhat
greater amount of difference between any two forms, they rank both
as species, unless they are enabled to connect them together by the
closest intermediate gradations; and this, from the reasons just
assigned, we can seldom hope to effect in any one geological section.
Supposing B and C to be two species, and a third, A, to be found in an
older and underlying bed; even if A were strictly intermediate between
B and C, it would simply be ranked as a third and distinct species,
unless at the same time it could be closely connected by intermediate
varieties with either one or both forms. Nor should it be forgotten,
as before explained, that A might be the actual progenitor of B and C,
and yet would not necessarily be strictly intermediate between them
in all respects. So that we might obtain the parent-species and its
several modified descendants from the lower and upper beds of the same
formation, and, unless we obtained numerous transitional gradations, we
should not recognize their blood-relationship, and should consequently
rank them as distinct species.
SUDDEN APPEARANCE OF GROUPS OF ALLIED SPECIES.
[Origin of
Species,
page 282.]
The abrupt manner in which whole groups of species suddenly appear
in certain formations has been urged by several paleontologists--for
instance, by Agassiz, Pictet, and Sedgwick--as a fatal objection to the
belief in the transmutation of species. If numerous species, belonging
to the same genera or families, have really started into life at once,
the fact would be fatal to the theory of evolution through natural
selection. For the development by this means of a group of forms, all
of which are descended from some one progenitor, must have been an
extremely slow process; and the progenitors must have lived long before
their modified descendants. But we continually overrate the perfection
of the geological record, and falsely infer, because certain genera or
families have not been found beneath a certain stage, that they did
not exist before that stage. In all cases positive paleontological
evidence may be implicitly trusted; negative evidence is worthless,
as experience has so often shown. We continually forget how large the
world is, compared with the area over which our geological formations
have been carefully examined; we forget that groups of species may
elsewhere have long existed, and have slowly multiplied, before they
invaded the ancient archipelagoes of Europe and the United States. We
do not make due allowance for the intervals of time which have elapsed
between our consecutive formations--longer, perhaps, in many cases
than the time required for the accumulation of each formation. These
intervals will have given time for the multiplication of species from
some one parent-form; and, in the succeeding formation, such groups or
species will appear as if suddenly created.
HOW LITTLE WE KNOW OF FORMER INHABITANTS OF THE WORLD.
[Page 283.]
Even in so short an interval as that between the first and second
edition of Pictet’s great work on Paleontology, published in 1844–’46
and in 1853–’57, the conclusions on the first appearance and
disappearance of several groups of animals have been considerably
modified; and a third edition would require still further changes. I
may recall the well-known fact that in geological treatises, published
not many years ago, mammals were always spoken of as having abruptly
come in at the commencement of the tertiary[B] series. And now one
of the richest known accumulations of fossil mammals belongs to the
middle of the secondary series; and true mammals have been discovered
in the new red sandstone at nearly the commencement of this great
series. Cuvier used to urge that no monkey occurred in any tertiary
stratum; but now extinct species have been discovered in India, South
America, and in Europe, as far back as the Miocene stage. Had it not
been for the rare accident of the preservation of footsteps in the
new red sandstone of the United States, who would have ventured to
suppose that no less than at least thirty different bird-like animals,
some of gigantic size, existed during that period? Not a fragment of
bone has been discovered in these beds. Not long ago, paleontologists
maintained that the whole class of birds came suddenly into existence
during the Eocene period; but now we know, on the authority of
Professor Owen, that a bird certainly lived during the deposition
of the upper greensand; and still more recently, that strange bird,
the archeopteryx, with a long, lizard-like tail, bearing a pair of
feathers on each joint, and with its wings furnished with two free
claws, has been discovered in the oölitic slates of Solenhofen. Hardly
any recent discovery shows more forcibly than this, how little we as
yet know of the former inhabitants of the world.
[B] TERTIARY.--The latest geological epoch, immediately
preceding the establishment of the present order of things.
THE EXTINCTION OF SPECIES INVOLVED IN MYSTERY.
[Origin of
Species,
page 294.]
The extinction of species has been involved in the most gratuitous
mystery. Some authors have even supposed that as the individual has
a definite length of life, so have species a definite duration. No
one can have marveled more than I have done at the extinction of
species. When I found in La Plata the tooth of a horse imbedded with
the remains of mastodon, megatherium, toxodon, and other extinct
monsters, which all co-existed with still living shells at a very late
geological period, I was filled with astonishment; for, seeing that
the horse, since its introduction by the Spaniards into South America,
has run wild over the whole country and has increased in numbers at
an unparalleled rate, I asked myself what could so recently have
exterminated the former horse under conditions of life apparently so
favorable. But my astonishment was groundless. Professor Owen soon
perceived that the tooth, though so like that of the existing horse,
belonged to an extinct species. Had this horse been still living, but
in some degree rare, no naturalist would have felt the least surprise
at its rarity; for rarity is the attribute of a vast number of species
of all classes, in all countries. If we ask ourselves why this or
that species is rare, we answer that something is unfavorable in its
conditions of life; but what that something is we can hardly ever
tell. On the supposition of the fossil horse still existing as a rare
species, we might have felt certain, from the analogy of all other
mammals, even of the slow-breeding elephant, and from the history of
the naturalization of the domestic horse in South America, that under
more favorable conditions it would in a very few years have stocked
the whole continent. But we could not have told what the unfavorable
conditions were which checked its increase, whether some one or several
contingencies, and at what period of the horse’s life, and in what
degree, they severally acted. If the conditions had gone on, however
slowly, becoming less and less favorable, we assuredly should not have
perceived the fact, yet the fossil horse would certainly have become
rarer and rarer, and finally extinct;--its place being seized on by
some more successful competitor.
It is most difficult always to remember that the increase of every
creature is constantly being checked by unperceived hostile agencies;
and that these same unperceived agencies are amply sufficient to cause
rarity, and finally extinction. So little is this subject understood
that I have heard surprise repeatedly expressed at such great monsters
as the mastodon and the more ancient dinosaurians having become
extinct; as if mere bodily strength gave victory in the battle of life.
Mere size, on the contrary, would in some cases determine, as has
been remarked by Owen, quicker extermination from the greater amount
of requisite food. Before man inhabited India or Africa, some cause
must have checked the continued increase of the existing elephant. A
highly capable judge, Dr. Falconer, believes that it is chiefly insects
which, from incessantly harassing and weakening the elephant in India,
check its increase; and this was Bruce’s conclusion with respect to
the African elephant in Abyssinia. It is certain that insects and
blood-sucking bats determine the existence of the larger naturalized
quadrupeds in several parts of South America.
* * * * *
[Page 295.]
I may repeat what I published in 1845, namely, that to admit that
species generally become rare before they become extinct--to feel no
surprise at the rarity of a species, and yet to marvel greatly when the
species ceases to exist, is much the same as to admit that sickness
in the individual is the forerunner of death--to feel no surprise at
sickness, but, when the sick man dies, to wonder and to suspect that he
died by some deed of violence.
DEAD LINKS BETWEEN LIVING SPECIES.
[Page 302.]
No one will deny that the Hipparion is intermediate between the
existing horse and certain older ungulate forms. What a wonderful
connecting link in the chain of mammals is the Typotherium from South
America, as the name given to it by Professor Gervais expresses, and
which can not be placed in any existing order! The Sirenia form a very
distinct group of mammals, and one of the most remarkable peculiarities
in the existing dugong and lamentin is the entire absence of hind
limbs, without even a rudiment being left; but the extinct Halitherium
had, according to Professor Flower, an ossified thigh-bone “articulated
to a well-defined acetabulum in the pelvis,” and it thus makes some
approach to ordinary hoofed quadrupeds, to which the Sirenia are in
other respects allied. The cetaceans or whales are widely different
from all other mammals, but the tertiary Zeuglodon and Squalodon, which
have been placed by some naturalists in an order by themselves, are
considered by Professor Huxley to be undoubtedly cetaceans, “and to
constitute connecting links with the aquatic carnivora.”
Even the wide interval between birds and reptiles has been shown
by the naturalist just quoted to be partially bridged over in the
most unexpected manner, on the one hand, by the ostrich and extinct
Archeopteryx, and on the other hand, by the Compsognathus, one of
the dinosaurians--that group which includes the most gigantic of all
terrestrial reptiles. Turning to the Invertebrata, Barrande asserts,
and a higher authority could not be named, that he is every day taught
that, although palæozoic animals can certainly be classed under
existing groups, yet that at this ancient period the groups were not so
distinctly separated from each other as they now are.
Some writers have objected to any extinct species, or group of species,
being considered as intermediate between any two living species or
groups of species. If by this term it is meant that an extinct form
is directly intermediate in all its characters between two living
forms or groups, the objection is probably valid. But in a natural
classification many fossil species certainly stand between living
species, and some extinct genera between living genera, even between
genera belonging to distinct families. The most common case, especially
with respect to very distinct groups, such as fish and reptiles, seems
to be that, supposing them to be distinguished at the present day by a
score of characters, the ancient members are separated by a somewhat
lesser number of characters; so that the two groups formerly made a
somewhat nearer approach to each other than they now do.
LIVING DESCENDANTS OF FOSSIL SPECIES.
[Page 311.]
It may be asked in ridicule, whether I suppose that the megatherium
and other allied huge monsters, which formerly lived in South America,
have left behind them the sloth, armadillo, and ant-eater, as their
degenerate descendants. This can not for an instant be admitted. These
huge animals have become wholly extinct, and have left no progeny. But
in the caves of Brazil there are many extinct species which are closely
allied in size and in all other characters to the species still living
in South America; and some of these fossils may have been the actual
progenitors of the living species. It must not be forgotten that, on
our theory, all the species of the same genus are the descendants of
some one species; so that, if six genera, each having eight species,
be found in one geological formation, and in a succeeding formation
there be six other allied or representative genera each with the
same number of species, then we may conclude that generally only one
species of each of the older genera has left modified descendants,
which constitute the new genera containing the several species;
the other seven species of each old genus having died out and left
no progeny. Or, and this will be a far commoner case, two or three
species in two or three alone of the six older genera will be the
parents of the new genera: the other species and the other whole genera
having become utterly extinct. In failing orders, with the genera
and species decreasing in numbers as is the case with the Edentata
of South America, still fewer genera and species will leave modified
blood-descendants.
UNNECESSARY TO EXPLAIN THE CAUSE OF EACH INDIVIDUAL DIFFERENCE.
[Animals and
Plants, vol.
ii, page 425.]
In accordance with the views maintained by me in this work and
elsewhere, not only various domestic races, but the most distinct
genera and orders within the same great class--for instance, mammals,
birds, reptiles, and fishes--are all the descendants of one common
progenitor, and we must admit that the whole vast amount of difference
between these forms has primarily arisen from simple variability. To
consider the subject under this point of view is enough to strike
one dumb with amazement. But our amazement ought to be lessened when
we reflect that beings almost infinite in number, during an almost
infinite lapse of time, have often had their whole organization
rendered in some degree plastic, and that each slight modification of
structure which was in any way beneficial under excessively complex
conditions of life has been preserved, while each which was in any
way injurious has been rigorously destroyed. And the long-continued
accumulation of beneficial variations will infallibly have led to
structures as diversified, as beautifully adapted for various purposes
and as excellently co-ordinated, as we see in the animals and plants
around us. Hence I have spoken of selection as the paramount power,
whether applied by man to the formation of domestic breeds, or by
nature to the production of species.
If an architect were to rear a noble and commodious edifice, without
the use of cut stone, by selecting from the fragments at the base of a
precipice wedge-formed stones for his arches, elongated stones for his
lintels, and flat stones for his roof, we should admire his skill and
regard him as the paramount power. Now, the fragments of stone, though
indispensable to the architect, bear to the edifice built by him the
same relation which the fluctuating variations of organic beings bear
to the varied and admirable structures ultimately acquired by their
modified descendants.
Some authors have declared that natural selection explains nothing,
unless the precise cause of each slight individual difference be made
clear. If it were explained to a savage utterly ignorant of the art of
building, how the edifice had been raised stone upon stone, and why
wedge-formed fragments were used for the arches, flat stones for the
roof, etc., and if the use of each part and of the whole building were
pointed out, it would be unreasonable if he declared that nothing had
been made clear to him, because the precise cause of the shape of each
fragment could not be told. But this is a nearly parallel case with
the objection that selection explains nothing, because we know not the
cause of each individual difference in the structure of each being.
The shape of the fragments of stone at the base of our precipice may be
called accidental, but this is not strictly correct; for the shape of
each depends on a long sequence of events, all obeying natural laws;
on the nature of the rock, on the lines of deposition or cleavage, on
the form of the mountain, which depends on its upheaval and subsequent
denudation, and lastly on the storm or earthquake which throws down the
fragments. But in regard to the use to which the fragments may be put,
their shape may be strictly said to be accidental.
“FACE TO FACE WITH AN INSOLUBLE DIFFICULTY.”
[Page 427.]
And here we are led to face a great difficulty, in alluding to which I
am aware that I am traveling beyond my proper province. An omniscient
Creator must have foreseen every consequence which results from the
laws imposed by him. But can it be reasonably maintained that the
Creator intentionally ordered, if we use the words in any ordinary
sense, that certain fragments of rock should assume certain shapes so
that the builder might erect his edifice? If the various laws which
have determined the shape of each fragment were not predetermined for
the builder’s sake, can it be maintained with any greater probability
that he specially ordained for the sake of the breeder each of the
innumerable variations in our domestic animals and plants--many of
these variations being of no service to man, and not beneficial, far
more often injurious, to the creatures themselves? Did he ordain that
the crop and tail-feathers of the pigeon should vary in order that the
fancier might make his grotesque pouter and fantail breeds? Did he
cause the frame and mental qualities of the dog to vary in order that a
breed might be formed of indomitable ferocity, with jaws fitted to pin
down the bull for man’s brutal sport? But if we give up the principle
in one case--if we do not admit that the variations of the primeval dog
were intentionally guided in order that the greyhound, for instance,
that perfect image of symmetry and vigor, might be formed--no shadow of
reason can be assigned for the belief that variations, alike in nature
and the result of the same general laws, which have been the groundwork
through natural selection of the formation of the most perfectly
adapted animals in the world, man included, were intentionally and
specially guided. However much we may wish it, we can hardly follow
Professor Asa Gray in his belief “that variation has been led along
certain beneficial lines,” like a stream “along definite and useful
lines of irrigation.” If we assume that each particular variation was
from the beginning of all time preordained, then that plasticity of
organization, which leads to many injurious deviations of structure,
as well as the redundant power of reproduction which inevitably leads
to a struggle for existence, and, as a consequence, to the natural
selection or survival of the fittest, must appear to us superfluous
laws of nature. On the other hand, an omnipotent and omniscient Creator
ordains everything and foresees everything. Thus we are brought face
to face with a difficulty as insoluble as is that of free-will and
predestination.
WHY DISTASTEFUL?
[Descent of
Man, page 618.]