SPECIES AND TIME.
Two relations of species to time.--No evidence of past existence of
minutely intermediate forms when such might be expected _a
priori_.--Bats, Pterodactyles, Dinosauria, and Birds.--Ichthyosauria,
Chelonia, and Anoura.--Horse ancestry.--Labyrinthodonts and
Trilobites.--Two subdivisions of the second relation of species to
time.--Sir William Thomson's views.---Probable period required for
ultimate specific evolution from primitive ancestral
forms.--Geometrical increase of time required for rapidly multiplying
increase of structural differences.--Proboscis monkey.--Time required
for deposition of strata necessary for Darwinian evolution.--High
organization of Silurian forms of life.--Absence of fossils in oldest
rocks.--Summary and conclusion.
Two considerations present themselves with regard to the necessary relation
of species to time if the theory of "Natural Selection" is valid and
sufficient.
The first is with regard to the evidences of the past existence of
intermediate form, their duration and succession.
The second is with regard to the total amount of time required for the
evolution of all organic forms from a few original ones, and the bearing of
other sciences on this question of time.
As to the first consideration, evidence is as yet against the modification
of species by "Natural Selection" alone, because not only are minutely
transitional forms generally absent, but they are absent in cases where we
might certainly _a priori_ have expected them to be present. [Page 129]
Now it has been said:[125] "If Mr. Darwin's theory be true, the number of
varieties differing one from another a very little must have been
indefinitely great, so great indeed as probably far to exceed the number of
individuals which have existed of any one variety. If this be true, it
would be more probable that no two specimens preserved as fossils should be
of one variety than that we should find a great many specimens collected
from a very few varieties, provided, of course, the chances of preservation
are equal for all individuals." "It is really strange that vast numbers of
perfectly similar specimens should be found, the chances against their
perpetuation as fossils are so great; but it is also very strange that the
specimens should be so exactly alike as they are, if, in fact, they came
and vanished by a gradual change."
Mr. Darwin attempts[126] to show cause why we should believe _a priori_
that intermediate varieties would exist in lesser numbers than the more
extreme forms; but though they would doubtless do so sometimes, it seems
too much to assert that they would do so generally, still less universally.
Now little less than universal and very marked inferiority in numbers would
account for the absence of certain series of minutely intermediate fossil
specimens. The mass of palæontological evidence is indeed overwhelmingly
against minute and gradual modification. It is true that when once an
animal has obtained powers of flight its means of diffusion are
indefinitely increased, and we might expect to find many relics of an
aërial form and few of its antecedent state--with nascent wings just
commencing their suspensory power. Yet had such a slow mode of origin, as
Darwinians contend for, operated exclusively in all cases, it is absolutely
incredible that birds, bats, and pterodactyles should have left the remains
they have, and yet not a single relic be preserved in any one instance{130}
of any of these different forms of wing in their incipient and relatively
imperfect functional condition!
[Illustration: WING-BONES OF PTERODACTYLE, BAT, AND BIRD.]
Whenever the remains of bats have been found they have presented the exact
type of existing forms, and there is as yet no indication of the conditions
of an incipient elevation from the ground.
The pterodactyles, again, though a numerous group, are all true and perfect
pterodactyles, though surely _some_ of the many incipient forms, which on
the Darwinian theory have existed, must have had a good chance of
preservation.
As to birds, the only notable instance in which discoveries recently made
appear to fill up an important hiatus, is the interpretation given by
Professor Huxley[127] to the remains of Dinosaurian reptiles, and which
were noticed in the third chapter of this work. The learned Professor has
(as also has Professor Cope in America) shown that in very important {131}
and significant points the skeletons of the Iguanodon and of its allies
approach very closely to that existing in the ostrich, emeu, rhea, &c. He
has given weighty reasons for thinking that the line of affinity between
birds and reptiles passes to the birds last named from the Dinosauria
rather than from the Pterodactyles, through Archeopteryx-like forms to the
ordinary birds. Finally, he has thrown out the suggestion that the
celebrated footsteps left by some extinct three-toed creatures on the very
ancient sandstone of Connecticut were made, not, as hitherto supposed, by
true birds, but by more or less ornithic reptiles. But even supposing all
that is asserted or inferred on this subject to be fully proved, it would
not approach to a demonstration of specific origin by _minute_
modification. And though it harmonizes well with "Natural Selection," it is
equally consistent with the rapid and sudden development of new specific
forms of life. Indeed, Professor Huxley, with a laudable caution and
moderation too little observed by some Teutonic Darwinians, guarded himself
carefully from any imputation of asserting dogmatically the theory of
"Natural Selection," while upholding fully the doctrine of evolution.
But, after all, it is by no means certain, though very probable, that the
Connecticut footsteps were made by very ornithic reptiles, or extremely
sauroid birds. And it must not be forgotten that a completely carinate[128]
bird (the Archeopteryx) existed at a time, when, as yet, we have no
evidence of some of the Dinosauria having come into being. Moreover, if the
remarkable and minute similarity of the coracoid of a pterodactyle to that
of a bird be merely the result of function and no sign of genetic affinity,
it is not inconceivable that pelvic and leg resemblances of Dinosauria to
birds may be functional likewise, though such an explanation is, of {132}
course, by no means necessary to support the view maintained in this book.
[Illustration: THE ARCHEOPTERYX (OF THE OOLITE STRATA).]
[Illustration: SKELETON OF AN ICHTHYOSAURUS.]
But the number of forms represented by many individuals, yet by _no
transitional ones_, is so great that only two or three can be selected as
examples. Thus those remarkable fossil reptiles, the Ichthyosauria and
Plesiosauria, extended, through the secondary period, probably over the
greater part of the globe. Yet no single transitional form has yet been met
with in spite of the multitudinous individuals preserved. Again, with their
modern representatives the Cetacea, one or two aberrant forms alone {133}
have been found, but no series of transitional ones indicating minutely the
line of descent. This group, the whales, is a very marked one, and it is
curious, on Darwinian principles, that so few instances tending to indicate
its mode of origin should have presented themselves. Here, as in the bats,
we might surely expect that some relics of unquestionably incipient stages
of its development would have been left.
[Illustration: SKELETON OF A PLESIOSAURUS.]
The singular order Chelonia, including the tortoises, turtles, and
terrapins (or fresh-water tortoises), is another instance of an extreme
form without any, as yet known, transitional stages. Another group may be
finally mentioned, viz. the frogs and toads, anourous Batrachians, of which
we have at present no relic of any kind linking them on to the Eft group on
the one hand, or to reptiles on the other.
The only instance in which an approach towards a series of nearly related
forms has been obtained is the existing horse, its predecessor Hipparion
and other extinct forms. But even here there is no proof whatever of
modification by minute and infinitesimal steps; _a fortiori_ no approach to
a proof of modification by "Natural Selection," acting upon indefinite
fortuitous variations. On the contrary, the series is an admirable example
of successive modification in one special direction along one beneficial
line, and the teleologist must here be allowed to consider that one {134}
motive of this modification (among probably an indefinite number of motives
inconceivable to us) was the relationship in which the horse was to stand
to the human inhabitants of this planet. These extinct forms, as Professor
Owen, remarks,[129] "differ from each other in a greater degree than do the
horse, zebra, and ass," which are not only good _zoological_ species as to
form, but are species _physiologically_, _i.e._ they cannot produce a race
of hybrids fertile _inter se_.
As to the mere action of surrounding conditions, the same Professor
remarks:[130] "Any modification affecting the density of the soil might so
far relate to the changes of limb-structure, as that a foot with a pair of
small hoofs dangling by the sides of the large one, like those behind the
cloven hoof of the ox, would cause the foot of Hipparion, _e.g._, and _a
fortiori_ the broader based three-hoofed foot of the Palæothere, to sink
less deeply into swampy soil, and be more easily withdrawn than the more
concentratively simplified and specialized foot of the horse. Rhinoceroses
and zebras, however, tread together the arid plains of Africa in the
present day; and the horse has multiplied in that half of America where two
or more kinds of tapir still exist. That the continents of the Eocene or
Miocene periods were less diversified in respect of swamp and sward, pampas
or desert, than those of the Pliocene period, has no support from
observation or analogy."
Not only, however, do we fail to find any traces of the incipient stages of
numerous very peculiar groups of animals, but it is undeniable that there
are instances which appeared at first to indicate a _gradual transition_,
yet which instances have been shown by further investigation and discovery
not to indicate truly anything of the kind. Thus at one time the remains of
Labyrinthodonts, which up till then had been discovered, seemed to justify
the opinion that as time went on, forms had successively appeared with{135}
more and more complete segmentation and ossification of the backbone, which
in the earliest forms was (as it is in the lowest fishes now) a soft
continuous rod or notochord. Now, however, it is considered probable that
the soft back-boned Labyrinthodont Archegosaurus, was an immature or larval
form,[131] while Labyrinthodonts with completely developed vertebræ have
been found to exist amongst the very earliest forms yet discovered. The
same may be said regarding the eyes of the trilobites, some of the oldest
forms having been found as well furnished in that respect as the very last
of the group which has left its remains accessible to observation.
[Illustration: TRILOBITE.]
Such instances, however, as well as the way in which marked and special
forms (as the Pterodactyles, &c., before referred to) appear at once in and
similarly disappear from the geological record, are of course explicable on
the Darwinian theory, provided a sufficiently enormous amount of past time
be allowed. The alleged extreme, and probably great, imperfection of that
record may indeed be pleaded in excuse. But it _is_ an excuse.[132] {136}
Nor is it possible to deny the _a priori_ probability of the preservation
of at least a few _minutely transitional_ forms in some instances if
_every_ species without exception has arisen exclusively by such minute and
gradual transitions.
It remains, then, to turn to the other considerations with regard to the
relation of species to time: namely (1) as to the total amount of time
allowable by other sciences for organic evolution; and (2) the proportion
existing, on Darwinian principles, between the time anterior to the earlier
fossils, and the time since; as evidenced by the proportion between the
amount of evolutionary change during the latter epoch and that which must
have occurred anteriorly.
Sir William Thomson has lately[133] advanced arguments from three distinct
lines of inquiry, and agreeing in one approximate result. The three lines
of inquiry were--1. The action of the tides upon the earth's rotation. 2.
The probable length of time during which the sun has illuminated this
planet; and 3. The temperature of the interior of the earth. The result
arrived at by these investigations is a conclusion that the existing state
of things on the earth, life on the earth, all geological history showing
continuity of life, must be limited within some such period of past time as
one hundred million years. The first question which suggests itself,
supposing Sir W. Thomson's views to be correct, is, Is this period anything
like enough for the evolution of all organic forms by "Natural Selection"?
The second is, Is this period anything like enough for the deposition of
the strata which must have been deposited if all organic forms have been
evolved by _minute_ steps, according to the Darwinian theory?
In the first place, as to Sir William Thomson's views, the Author of this
book cannot presume to advance any opinion; but the fact that they have not
been refuted, pleads strongly in their favour when we consider how {137}
much they tell against the theory of Mr. Darwin. The last-named author only
remarks that "many of the elements in the calculation are more or less
doubtful,"[134] and Professor Huxley[135] does not attempt to _refute_ Sir
W. Thomson's arguments, but only to show cause for suspense of judgment,
inasmuch as the facts _may be_ capable of other explanations.
Mr. Wallace, on the other hand,[136] seems more disposed to accept them,
and, after considering Sir William's objections and those of Mr. Croll,
puts the probable date of the beginning of the Cambrian deposits[137] at
only twenty-four million years ago. On the other hand, he seems to consider
that specific change has been more rapid than generally supposed, and
exceptionally stable during the last score or so of thousand years.
Now, first, with regard to the time required for the evolution of all
organic forms by merely accidental, minute, and fortuitous variations, the
useful ones of which have been preserved:
Mr. Murphy[138] is distinctly of opinion that there has not been time
enough. He says, "I am inclined to think that geological time is too short
for the evolution of the higher forms of life out of the lower by that
accumulation of imperceptibly slow variations, to which alone Darwin
ascribes the whole process."
"Darwin justly mentions the greyhound as being equal to any natural species
in the perfect co-ordination of its parts, 'all adapted for extreme
fleetness and for running down weak prey.'" "Yet it is an artificial
species (and not _physiologically_ a species _at all_), formed by
long-continued selection under domestication; and there is no reason to
suppose that any of the variations which have been selected to form it have
been other than gradual and almost imperceptible. Suppose that it has {138}
taken five hundred years to form the greyhound out of his wolf-like
ancestor. This is a mere guess, but it gives the order of the magnitude."
Now, if so, "how long would it take to obtain an elephant from a protozoon,
or even from a tadpole-like fish? Ought it not to take much more than a
million times as long?"[139]
Mr. Darwin[140] would compare with the natural origin of a species
"unconscious selection, that is, the preservation of the most useful or
beautiful animals, with no intention of modifying the breed." He adds: "But
by this process of unconscious selection, various breeds have been sensibly
changed in the course of two or three centuries."
"Sensibly changed!" but not formed into "new species." Mr. Darwin, of
course, could not mean that species _generally_ change so rapidly, which
would be strangely at variance with the abundant evidence we have of the
stability of animal forms as represented on Egyptian monuments and as shown
by recent deposits. Indeed, he goes on to say,--"Species, however, probably
change much more slowly, and within the same country only a few change at
the same time. This slowness follows from all the inhabitants of the same
country being already so well adapted to each other, that places in the
polity of nature do not occur until after long intervals, when changes of
some kind in the physical conditions, or through immigration, have
occurred, and individual differences and variations of the right nature, by
which some of the inhabitants might be better fitted to their new places
under altered circumstances, might not at once occur." This is true, and
not only will these changes occur at distant intervals, but it must be
borne in mind that in tracing back an animal to a remote ancestry, we pass
through modifications of such rapidly increasing number and importance that
a geometrical progression can alone indicate the increase of periods {139}
which such profound alterations would require for their evolution through
"Natural Selection" only.
Thus let us take for an example the proboscis monkey of Borneo
(_Semnopithecus nasalis_). According to Mr. Darwin's own opinion, this form
might have been "sensibly changed" in the course of two or three centuries.
According to this, to evolve it as a true and perfect species one thousand
years would be a very moderate period. Let ten thousand years be taken to
represent approximately the period of substantially constant conditions
during which no considerable change would be brought about. Now, if one
thousand years may represent the period required for the evolution of the
species _S. nasalis_, and of the other species of the genus Semnopithecus;
ten times that period should, I think, be allowed for the differentiation
of that genus, the African Cercopithecus and the other genera of the family
Simiidæ--the differences between the genera being certainly more than
tenfold greater than those between the species of the same genus. Again we
may perhaps interpose a period of ten thousand years' comparative repose.
For the differentiation of the families Simiidæ and Cebidæ--so very much
more distinct and different than any two genera of either family--a period
ten times greater should, I believe, be allowed than that required for the
evolution of the subordinate groups. A similarly increasing ratio should be
granted for the successive developments of the difference between the
Lemuroid and the higher forms of primates; for those between the original
primate and other root-forms of placental mammals; for those between
primary placental and implacental mammals, and perhaps also for the
divergence of the most ancient stock of these and of the monotremes, for in
all these cases modifications of structure appear to increase in complexity
in at least that ratio. Finally, a vast period must be granted for the
development of the lowest mammalian type from the primitive stock of the
whole vertebrate sub-kingdom. Supposing this primitive stock to have {140}
arisen directly from a very lowly organized animal indeed (such as a
nematoid worm, or an ascidian, or a jelly-fish), yet it is not easy to
believe that less than two thousand million years would be required for the
totality of animal development by no other means than minute, fortuitous,
occasional, and intermitting variations in all conceivable directions. If
this be even an approximation to the truth, then there seem to be strong
reasons for believing that geological time is not sufficient for such a
process.
The second question is, whether there has been time enough for the
deposition of the strata which must have been deposited, if all organic
forms have been evolved according to the Darwinian theory?
Now this may at first seem a question for geologists only, but, in fact, in
this matter geology must in some respects rather take its time from zoology
than the reverse; for if Mr. Darwin's theory be true, past time down to the
deposition of the Upper Silurian strata can have been but a very small
fraction of that during which strata have been deposited. For when those
Upper Silurian strata were formed, organic evolution had already run a
great part of its course, perhaps the longest, slowest, and most difficult
part of that course.
At that ancient epoch not only were the vertebrate, molluscous, and
arthropod types distinctly and clearly differentiated, but highly developed
forms had been produced in each of these sub-kingdoms. Thus in the
Vertebrata there were fishes not belonging to the lowest but to the very
highest groups which are known to have ever been developed, namely, the
Elasmobranchs (the highly organized sharks and rays) and the Ganoids, a
group now poorly represented, but for which the sturgeon may stand as a
type, and which in many important respects more nearly resemble higher
Vertebrata than do the ordinary or osseous fishes. Fishes in which the
ventral fins are placed in front of the pectoral ones (_i.e._ jugular
fishes) have been generally considered to be comparatively modern forms.
But Professor Huxley has kindly informed me that he has discovered a {141}
jugular fish in the Permian deposits.
Amongst the molluscous animals we have members of the very highest known
class, namely, the Cephalopods, or cuttle-fish class; and amongst
articulated animals we find Trilobites and Eurypterida, which do not belong
to any incipient worm-like group, but are distinctly differentiated
Crustacea of no low form.
[Illustration: CUTTLE-FISH.
A. Ventral aspect. B. Dorsal aspect.]
We have in all these animal types nervous systems differentiated on
distinctly different patterns, fully formed organs of circulation,
digestion, excretion, and generation, complexly constructed eyes and other
sense organs; in fact, all the most elaborate and complete animal
structures built up, and not only once, for in the fishes and mollusca we
have (as described in the third chapter of this work) the coincidence of
the independently developed organs of sense attaining a nearly similar
complexity in two quite distinct forms. If, then, so small an advance {142}
has been made in fishes, molluscs, and arthropods since the Upper Silurian
deposits, it will probably be within the mark to consider that the period
before those deposits (during which all these organs would, on the
Darwinian theory, have slowly built up their different perfections and
complexities) occupied time at least a hundredfold greater.
Now it will be a moderate computation to allow 25,000,000 years for the
deposition of the strata down to and including the Upper Silurian. If,
then, the evolutionary work done during this deposition, only represents a
hundredth part of the sum total, we shall require 2,500,000,000 (two
thousand five hundred million) years for the complete development of the
whole animal kingdom to its present state. Even one quarter of this,
however, would far exceed the time which physics and astronomy seem able to
allow for the completion of the process.
Finally, a difficulty exists as to the reason of the absence of rich
fossiliferous deposits in the oldest strata--if life was then as abundant
and varied as, on the Darwinian theory, it must have been. Mr. Darwin
himself admits[141] "the case at present must remain inexplicable; and may
be truly urged as a valid argument against the views" entertained in his
book.
Thus, then, we find a wonderful (and on Darwinian principles an all but
inexplicable) absence of minutely transitional forms. All the most marked
groups, bats, pterodactyles, chelonians, ichthyosauria, anoura, &c., appear
at once upon the scene. Even the horse, the animal whose pedigree has been
probably best preserved, affords no conclusive evidence of specific origin
by infinitesimal, fortuitous variations; while some forms, as the
labyrinthodonts and trilobites, which seemed to exhibit gradual change, are
shown by further investigation to do nothing of the sort. As regards the
time required for evolution (whether estimated by the probably minimum{143}
period required for organic change or for the deposition of strata which
accompanied that change), reasons have been suggested why it is likely that
the past history of the earth does not supply us with enough. First,
because of the prodigious increase in the importance and number of
differences and modifications which we meet with as we traverse
successively greater and more primary zoological groups; and, secondly,
because of the vast series of strata necessarily deposited if the period
since the Lower Silurian marks but a small fraction of the period of
organic evolution. Finally, the absence or rarity of fossils in the oldest
rocks is a point at present inexplicable, and not to be forgotten or
neglected.
Now all these difficulties are avoided if we admit that new forms of animal
life of all degrees of complexity appear from time to time with comparative
suddenness, being evolved according to laws in part depending on
surrounding conditions, in part internal--similar to the way in which
crystals (and, perhaps from recent researches, the lowest forms of life)
build themselves up according to the internal laws of their component
substance, and in harmony and correspondence with all environing influences
and conditions. [Page 144]
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