Book: Atlantic Monthly Volume 6, No. 34, August, 1860

V >> Various >> Atlantic Monthly Volume 6, No. 34, August, 1860




That considerable differences are often discernible between tertiary
individuals and their supposed descendants of the present day affords
no argument against Darwin's theory, as has been rashly thought, but is
decidedly in its favor. If the identification were so perfect that no
more differences were observable between the tertiary and the recent
shells than between various individuals of either, then Darwin's
opponents, who argue the immutability of species from the ibises and
cats preserved by the ancient Egyptians being just like those of the
present day, could triumphantly add a few hundred thousand years more to
the length of the experiment and to the force of their argument. As the
facts stand, it appears, that, while some tertiary forms are essentially
undistinguishable from existing ones, others are the same with a
difference, which is judged not to be specific or aboriginal, and yet
others show somewhat greater differences, such as are scientifically
expressed by calling them marked varieties, or else doubtful species;
while others, differing a little more, are confidently termed distinct,
but nearly related species. Now is not all this a question of degree,
of mere gradation of difference? Is it at all likely that these several
gradations came to be established in two totally different ways,--some
of them (though naturalists can't agree which) through natural
variation, or other secondary cause, and some by original creation,
without secondary cause? We have seen that the judicious Pictet answers
such questions as Darwin would have him do, in affirming, that, in all
probability, the nearly related species of two successive faunas were
materially connected, and that contemporaneous species, similarly
resembling each other, were not all created so, but have become so. This
is equivalent to saying that species (using the term as all naturalists
do and must continue to employ the word) have only a relative, not an
absolute fixity; that differences fully equivalent to what are held to
be specific may arise in the course of time, so that one species may at
length be naturally replaced by another species a good deal like it, or
may be diversified through variation or otherwise into two, three, or
more species, or forms as different as species. This concedes all that
Darwin has a right to ask, all that he can directly infer from evidence.
We must add that it affords a _locus standi_, more or less tenable, for
inferring more.

Here another geological consideration comes in to help on this
inference. The species of the later tertiary period for the most part
not only resembled those of our days, many of them so closely as to
suggest an absolute continuity, but, also occupied in general the same
regions that their relatives occupy now. The same may be said, though
less specially, of the earlier tertiary and of the later secondary; but
there is less and less localization of forms as we recede, yet some
localization even in palaeozoic times. While in the secondary period one
is struck with the similarity of forms and the identity of many of the
species which flourished apparently at the same time in all or in the
most widely separated parts of the world, in the tertiary epoch, on the
contrary, along with the increasing specialization of climates and
their approximation to the present state, we find abundant evidence
of increasing localization of orders, genera, and species; and
this localization strikingly accords with the present geographical
distribution of the same groups of species. Where the imputed
forefathers lived, their relatives and supposed descendants now
flourish. All the actual classes of the animal and vegetable kingdoms
were represented in the tertiary faunas and floras, and in nearly the
same proportions and the same diversities as at present. The faunas of
what is now Europe, Asia, America, and Australia differed from
each other much as they now differ: in fact,--according to Adolphe
Brongniart, whose statements we here condense,[a]--the inhabitants of
these different regions appear for the most part to have acquired,
before the close of the tertiary period, the characters which
essentially distinguish their existing faunas. The eastern continent
had then, as now, its great pachyderms, elephants, rhinoceros, and
hippopotamus; South America its armadillos, sloths, and ant-eaters;
Australia a crowd of marsupials; and the very strange birds of New
Zealand had predecessors of similar strangeness. Everywhere the same
geographical distribution as now, with a difference in the particular
area, as respects the northern portion of the continents, answering to a
warmer climate then than ours, such as allowed species of hippopotamus,
rhinoceros, and elephant to range even to the regions now inhabited
by the reindeer and the musk-ox, and with the serious disturbing
intervention of the glacial period within a comparatively recent time.
Let it be noted, also, that those tertiary species which have continued
with little change down to our days are the marine animals of the
lower grades, especially mollusca. Their low organization, moderate
sensibility, and the simple conditions of an existence in a medium
like the ocean, not subject to great variation and incapable of sudden
change, may well account for their continuance; while, on the other
hand, the more intense, however gradual, climatic vicissitudes on land,
which have driven all tropical and sub-tropical forms out of the higher
latitudes and assigned to them their actual limits, would be almost sure
to extinguish such huge and unwieldy animals as mastodons, mammoths, and
the like, whose power of enduring altered circumstances must have been
small.

[Footnote a: In _Comptes Rendus, Acad. des Sciences_, Fevr. 2, 1857.]

This general replacement of the tertiary species of a country by
others so much like them is a noteworthy fact. The hypothesis of the
independent creation of all species, irrespective of their antecedents,
leaves this fact just as mysterious as is creation itself; that of
derivation undertakes to account for it. Whether it satisfactorily does
so or not, it must be allowed that the facts well accord with that
assumption.

The same may be said of another conclusion, namely, that the geological
succession of animals and plants appears to correspond in a general
way with their relative standing or rank in a natural system of
classification. It seems clear, that, though no one of the _grand types_
of the animal kingdom can be traced back farther than the rest, yet the
lower _classes_ long preceded the higher; that there has been on the
whole a steady progression within each class and order; and that the
highest plants and animals have appeared only in relatively modern
times. It is only, however, in a broad sense that this generalization
is now thought to hold good. It encounters many apparent exceptions and
sundry real ones. So far as the rule holds, all is as it should be upon
an hypothesis of derivation.

The rule has its exceptions. But, curiously enough, the most striking
class of exceptions, if such they be, seems to us even more favorable to
the doctrine of derivation than is the general rule of a pure and simple
ascending gradation. We refer to what Agassiz calls prophetic and
synthetic types; for which the former name may suffice, as the
difference between the two is evanescent.

"It has been noticed," writes our great zooelogist, "that certain types,
which are frequently prominent among the representatives of past ages,
combine in their structure peculiarities which at later periods are only
observed separately in different, distinct types. Sauroid fishes before
reptiles, Pterodactyles before birds, Ichthyosauri before dolphins, etc.
There are entire families, of nearly every class of animals, which
in the state of their perfect development exemplify such prophetic
relations.... The sauroid fishes of the past geological ages are an
example of this kind. These fishes, which preceded the appearance of
reptiles, present a combination of ichthyic and reptilian characters not
to be found in the true members of this class, which form its bulk at
present. The Pterodactyles, which preceded the class of birds, and the
Ichthyosauri, which preceded the Cetaeca, are other examples of such
prophetic types."[a]

[Footnote a: Agassiz, _Contributions: Essay on Classification_, p.
117, where, we may be permitted to note, the word "Crustacea" is by a
typographical error printed in place of _Cetacea_.]

Now these reptile-like fishes, of which gar-pikes are the living
representatives, though of earlier appearance, are admittedly of higher
rank than common fishes. They dominated until reptiles appeared, when
they mostly gave place to--or, as the derivationists will insist, were
resolved by divergent variation and natural selection into--common
fishes, destitute of reptilian characters, and saurian reptiles, the
intermediate grades, which, according to a familiar piscine saying,
are "neither fish, flesh, nor good red-herring," being eliminated and
extinguished by natural consequence of the struggle for existence which
Darwin so aptly portrays. And so, perhaps, of the other prophetic types.
Here type and antitype correspond. If these are true prophecies, we need
not wonder that some who read them in Agassiz's book will read their
fulfilment in Darwin's.

Note also, in tins connection, that, along with a wonderful persistence
of type, with change of species, genera, orders, etc., from formation to
formation, no species and no higher group which has once unequivocally
died out ever afterwards reappears. Why is this, but that the link of
generation has been sundered? Why, on the hypothesis of independent
originations, were not failing species re-created, either identically or
with a difference, in regions eminently adapted to their well-being? To
take a striking case. That no part of the world now offers more suitable
conditions for wild horses and cattle than the Pampas and other plains
of South America is shown by the facility with which they have there run
wild and enormously multiplied, since introduced from the Old World not
long ago. There was no wild American stock. Yet in the times of the
Mastodon and Megatherium, at the dawn of the present period, wild
horses and cattle--the former certainly very much like the existing
horse--roamed over those plains in abundance. On the principle of
original and direct created adaptation of species to climate and other
conditions, why were these types not reproduced, when, after the colder
intervening era, those regions became again eminently adapted to such
animals? Why, but because, by their complete extinction in South
America, the line of descent was here utterly broken? Upon the ordinary
hypothesis, there is no scientific explanation possible of this series
of facts, and of many others like them. Upon the new hypothesis, "the
succession of the same types of structure within the same areas during
the later geological periods ceases to be mysterious, and is simply
explained by inheritance." Their cessation is failure of issue.

Along with these considerations the fact (alluded to on p. 114) should
be remembered, that, as a general thing, related species of the present
age are geographically associated. The larger part of the plants, and
still more of the animals, of each separate country are peculiar to
it; and, as most species now flourish over the graves of their by-gone
relatives of former ages, so they now dwell among or accessibly near
their kindred species.

Here also comes in that general "parallelism between the order of
succession of animals and plants in geological times, and the gradation
among their living representatives" from low to highly organized,
from simple and general to complex and specialized forms; also "the
parallelism between the order of succession of animals in geological
times--and the changes their living representatives undergo during their
embryological growth,"--as if the world were one prolonged gestation.
Modern science has much insisted on this parallelism, and to a certain
extent is allowed to have made it out. All these things, which conspire
to prove that the ancient and the recent forms of life "are somehow
intimately connected together in one grand system," equally conspire to
suggest that the connection is one similar or analogous to generation.
Surely no naturalist can be blamed for entering somewhat confidently
upon a field of speculative inquiry which here opens so invitingly; nor
need former premature endeavors and failures utterly dishearten him.

All these things, it may naturally be said, go to explain the order, not
the mode, of the incoming of species. But they all do tend to bring out
the generalization expressed by Mr. Wallace in the formula, that "every
species has come into existence coincident both in time and space with
preexisting closely allied species." Not, however, that this is proved
even of existing species as a matter of general fact. It is obviously
impossible to _prove_ anything of the kind. But we must concede that the
known facts strongly suggest such an inference. And since species are
only congeries of individuals, and every individual came into existence
in consequence of preexisting individuals of the same sort, so leading
up to the individuals with which the species began, and since the only
material sequence we know of among plants and animals is that from
parent to progeny, the presumption becomes exceedingly strong that
the connection of the incoming with the preexisting species is a
genealogical one.

Here, however, all depends upon the probability that Mr. Wallace's
inference is really true. Certainly it is not yet generally accepted;
but a strong current is setting towards its acceptance.

So long as universal cataclysms were in vogue, and all life upon the
earth was thought to have been suddenly destroyed and renewed many times
in succession, such a view could not be thought of. So the equivalent
view maintained by Agassiz, and formerly, we believe, by D'Orbigny,
that, irrespectively of general and sudden catastrophes, or any known
adequate physical cause, there has been a total depopulation at the
close of each geological period or formation, say forty or fifty times,
or more, followed by as many independent great acts of creation, at
which alone have species been originated, and at each of which a
vegetable and an animal kingdom were produced entire and complete,
full-fledged, as flourishing, as wide-spread and populous, as varied and
mutually adapted from the beginning as ever afterwards,--such a view, of
course, supersedes all material connection between successive species,
and removes even the association and geographical range of species
entirely out of the domain of physical causes and of natural science.
This is the extreme opposite of Wallace's and Darwin's view, and is
quite as hypothetical. The nearly universal opinion, if we rightly
gather it, manifestly is, that the replacement of the species of
successive formations was not complete and simultaneous, but partial
and successive; and that along the course of each epoch some species
probably were introduced, and some, doubtless, became extinct. If all
since the tertiary belongs to our present epoch, this is certainly true
of it: if to two or more epochs, then the hypothesis of a total change
is not true of them.

Geology makes huge demands upon time; and we regret to find that it has
exhausted ours,--that what we meant for the briefest and most general
sketch of some geological considerations in favor of Darwin's hypothesis
has so extended as to leave no room for considering "the great facts of
comparative anatomy and zooelogy" with which Darwin's theory "very well
accords," nor for indicating how "it admirably serves for explaining the
unity of composition of all organisms, the existence of representative
and rudimentary organs, and the natural series which genera and species
compose." Suffice it to say that these are the real strongholds of the
new system on its theoretical side; that it goes far towards explaining
both the physiological and the structural gradations and relations
between the two kingdoms, and the arrangement of all their forms in
groups subordinate to groups, all within a few great types; that it
reads the riddle of abortive organs and of morphological conformity, of
which no other theory has ever offered a scientific explanation, and
supplies a ground for harmonizing the two fundamental ideas which
naturalists and philosophers conceive to have ruled the organic world,
though they could not reconcile them, namely: Adaptation to Purpose and
the Conditions of Existence, and Unity of Type. To reconcile these two
undeniable principles is a capital problem in the philosophy of natural
history; and the hypothesis which consistently does so thereby secures a
great advantage.

We all know that the arm and hand of a monkey, the foreleg and foot of
a dog and of a horse, the wing of a bat, and the fin of a porpoise are
fundamentally identical; that the long neck of the giraffe has the same
and no more bones than the short one of the elephant; that the eggs of
Surinam frogs hatch into tadpoles with as good tails for swimming as any
of their kindred, although as tadpoles they never enter the water; that
the Guinea-pig is furnished with incisor teeth which it never uses,
as it sheds them before birth; that embryos of mammals and birds
have branchial slits and arteries running in loops, in imitation or
reminiscence of the arrangement which is permanent in fishes; and that
thousands of animals and plants have rudimentary organs which, at least
in numerous cases, are wholly useless to their possessors, etc., etc.
Upon a derivative theory this morphological conformity is explained by
community of descent; and it has not been explained in any other way.

Naturalists are constantly speaking of "related species," of
the "affinity" of a genus or other group, and of "family
resemblance,"--vaguely conscious that these terms of kinship are
something more than mere metaphors, but unaware of the grounds of their
aptness. Mr. Darwin assures them that they have been talking derivative
doctrine all their lives without knowing it.

If it is difficult and in some cases practically impossible to fix the
limits of species, it is still more so to fix those of genera; and those
of tribes and families are still less susceptible of exact natural
circumscription. Intermediate forms occur, connecting one group with
another in a manner sadly perplexing to systematists, except to those
who have ceased to expect absolute limitations in Nature. All this
blending could hardly fail to suggest a former material connection among
allied forms, such as that which an hypothesis of derivation demands.

Here it would not be amiss to consider the general principle of
gradation throughout organic Nature,--a principle which answers in a
general way to the law of continuity in the inorganic world, or
rather is so analogous to it that both may fairly be expressed by
the Leibnitzian axiom, _Natura non agit saltatim_. As an axiom or
philosophical principle, used to test modal laws or hypotheses, this in
strictness belongs only to physics. In the investigation of Nature at
large, at least in the organic world, nobody would undertake to apply
this principle as a test of the validity of any theory or supposed law.
But naturalists of enlarged views will not fail to infer the principle
from the phenomena they investigate,--to perceive that the rule holds,
under due qualifications and altered forms, throughout the realm of
Nature; although we do not suppose that Nature in the organic world
makes no distinct steps, but only short and serial steps,--not
infinitely fine gradations, but no long leaps, or few of them.

To glance at a few illustrations out of many that present themselves. It
would be thought that the distinction between the two organic kingdoms
was broad and absolute. Plants and animals belong to two very different
categories, fulfil opposite offices, and, as to the mass of them, are
so unlike that the difficulty of the ordinary observer would be to find
points of comparison. Without entering into details, which would fill an
article, we may safely say that the difficulty with the naturalist is
all the other way,--that all these broad differences vanish one by one
as we approach the lower confines of the two kingdoms, and that no
_absolute_ distinction whatever is now known between them. It is quite
possible that the same organism may be both vegetable and animal, or may
be first the one and then the other. If some organisms may be said to be
at first vegetables and then animals, others, like the spores and other
reproductive bodies of many of the lower Algae, may equally claim to
have first a characteristically animal, and then an unequivocally
vegetable existence. Nor is the gradation purely restricted to these
simple organisms. It appears in general functions, as in that of
reproduction, which is reducible to the same formula in both kingdoms,
while it exhibits close approximations in the lower forms; also in a
common or similar ground of sensibility in the lowest forms of both,
a common faculty of effecting movements tending to a determinate end,
traces of which pervade the vegetable kingdom,--while on the other hand,
this indefinable principle, this vegetable _animula vagula, blandula_,
graduates into the higher sensitiveness of the lower class of animals.
Nor need we hesitate to recognize the fine gradations from simple
sensitiveness and volition to the higher instinctive and other psychical
manifestations of the higher brute animals. The gradation is undoubted,
however we may explain it. Again, propagation is of one mode in the
higher animals, of two in all plants; but vegetative propagation, by
budding or offshoots, extends through the lower grades of animals. In
both kingdoms there may be separation of the offshoots, or indifference
in this respect, or continued and organic union with the parent stock;
and this either with essential independence of the offshoots, or with
a subordination of these to a common whole, or finally with such
subordination and amalgamation, along with specialization of function,
that the same parts, which in other cases can be regarded only as
progeny, in these become only members of an individual.

This leads to the question of individuality, a subject quite too large
and too recondite for present discussion. The conclusion of the whole
matter, however, is, that individuality--that very ground of _being_ as
distinguished from _thing_--is not attained in Nature at one leap. If
anywhere truly exemplified in plants, it is only in the lowest and
simplest, where the being is a structural unit, a single cell,
memberless and organless, though organic,--the same thing as those cells
of which all the more complex plants are built up, and with which every
plant and (structurally) every animal began its development. In the
ascending gradation of the vegetable kingdom individuality is, so to
say, striven after, but never attained; in the lower animals it is
striven after with greater, though incomplete success; it is realized
only in animals of so high a rank that vegetative multiplication or
offshoots are out of the question, where all parts are strictly
members and nothing else, and all subordinated to a common nervous
centre,--fully realized, perhaps, only in a conscious person.

So, also, the broad distinction between reproduction by seeds or ova and
propagation by buds, though perfect in some of the lowest forms of life,
becomes evanescent in others; and even the most absolute law we know in
the physiology of genuine reproduction, that of sexual co-operation,
has its exceptions in both kingdoms in parthenogenesis, to which in the
vegetable kingdom a most curious series of gradations leads. In plants,
likewise, a long and most finely graduated series of transitions leads
from bisexual to unisexual blossoms; and so in various other respects.
Everywhere we may perceive that Nature secures her ends, and makes her
distinctions on the whole manifest and real, but everywhere without
abrupt breaks. We need not wonder, therefore, that gradations between
species and varieties should occur; the more so, since genera, tribes,
and other groups into which the naturalist collocates species are
far from being always absolutely limited in Nature, though they are
necessarily represented to be so in systems. From the necessity of the
case, the classifications of the naturalist abruptly define where Nature
more or less blends. Our systems are nothing, if not definite. They
are intended to express differences, and perhaps some of the coarser
gradations. But this evinces, not their perfection, but their
imperfection. Even the best of them are to the system of Nature what
consecutive patches of the seven colors are to the rainbow.

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