Evolution and Ethics and Other Essays
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Thomas H. Huxley >> Evolution and Ethics and Other Essays
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This is the kernel of the new theory, the Darwinian creed, as recited
at the close of the introduction to the remarkable book under
consideration. The questions, "What will he do with it?" and "How far
will he carry it?" the author answers at the close of the volume:
"I cannot doubt that the theory of descent with modification embraces
all the members of the same class." Furthermore, "I believe that all
animals have descended from at most only four or five progenitors, and
plants from an equal or lesser number."
Seeing that analogy as strongly suggests a further step in the same
direction, while he protests that "analogy may be a deceitful guide,"
yet he follows its inexorable leading to the inference that--
"Probably all the organic beings which have ever lived on this ear have
descended from some one primordial form, into which life was first
breathed."[III-4]
In the first extract we have the thin end of the wedge driven a little
way; in the last, the wedge driven home.
We have already sketched some of the reasons suggestive of such a
theory of derivation of species, reasons which gave it plausibility,
and even no small probability, as applied to our actual world and to
changes occurring since the latest tertiary period. We are well pleased
at this moment to find that the conclusions we were arriving at in this
respect are sustained by the very high authority and impartial judgment
of Pictet, the Swiss paleontologist. In his review of Darwins
book[III-5] -- the fairest and most admirable opposing one that has
appeared--he freely accepts that ensemble of natural operations which
Darwin impersonates under the now familiar name of Natural Selection,
allows that the exposition throughout the first chapters seems "a la
fois prudent et fort," and is disposed to accept the whole argument in
its foundations, that is, so far as it relates to what is now going on,
or has taken place in the present geological period--which period he
carries back through the diluvial epoch to the borders of the
tertiary.[III-6] Pictet accordingly admits that the theory will very
well account for the origination by divergence of nearly-related
species, whether within the present period or in remoter geological
times; a very natural view for him to take, since he appears to have
reached and published, several years ago, the pregnant conclusion that
there most probably was some material connection between the
closely-related species of two successive faunas, and that the numerous
close species, whose limits are so difficult to determine, were not all
created distinct and independent. But while thus accepting, or ready
to accept, the basis of Darwins theory, and all its legitimate direct
inferences, he rejects the ultimate conclusions, brings some weighty
arguments to bear against them, and is evidently convinced that he can
draw a clear line between the sound inferences, which he favors, and
the unsound or unwarranted theoretical deductions, which he rejects. We
hope he can.
This raises the question, Why does Darwin press his theory to these
extreme conclusions? Why do all hypotheses of derivation converge so
inevitably to one ultimate point? Having already considered some of the
reasons which suggest or support the theory at its outset--which may
carry it as far as such sound and experienced naturalists as Pictet
allow that it may be true--perhaps as far as Darwin himself unfolds it
in the introductory proposition cited at the beginning of this
article--we may now inquire after the motives which impel the theorist
so much farther. Here proofs, in the proper sense of the word, are not
to be had. We are beyond the region of demonstration, and have only
probabilities to consider. What are these probabilities? What work will
this hypothesis do to establish a claim to be adopted in its
completeness? Why should a theory which may plausibly enough account
for the diversification of the species of each special type or genus be
expanded into a general system for the origination or successive
diversification of all species, and all special types or forms, from
four or five remote primordial forms, or perhaps from one? We accept
the theory of gravitation because it explains all the facts we know,
and bears all the tests that we can put it to. We incline to accept the
nebular hypothesis, for similar reasons; not because it is proved--thus
far it is incapable of proof--but because it is a natural theoretical
deduction from accepted physical laws, is thoroughly congruous with the
facts, and because its assumption serves to connect and harmonize these
into one probable and consistent whole. Can the derivative hypothesis
be maintained and carried out into a system on similar grounds? If so,
however unproved, it would appear to be a tenable hypothesis, which is
all that its author ought now to claim. Such hypotheses as, from the
conditions of the case, can neither be proved nor disproved by direct
evidence or experiment, are to be tested only indirectly, and therefore
imperfectly, by trying their power to harmonize the known facts, and to
account for what is otherwise unaccountable. So the question comes to
this: What will an hypothesis of the derivation of species explain
which the opposing view leaves unexplained?
Questions these which ought to be entertained before we take up the
arguments which have been advanced against this theory. We can barely
glance at some of the considerations which Darwin adduces, or will be
sure to adduce in the future and fuller exposition which is promised.
To display them in such wise as to indoctrinate the unscientific reader
would require a volume. Merely to refer to them in the most general
terms would suffice for those familiar with scientific matters, but
would scarcely enlighten those who are not. Wherefore let these trust
the impartial Pictet, who freely admits that, "in the absence of
sufficient direct proofs to justify the possibility of his hypothesis,
Mr. Darwin relies upon indirect proofs, the bearing of which is real
and incontestable;" who concedes that "his theory accords very well
with the great facts of comparative anatomy and zoology--comes in
admirably to explain unity of composition of organisms, also to explain
rudimentary and representative organs, and the natural series of genera
and species--equally corresponds with many paleontological data--agrees
well with the specific resemblances which exist between two successive
faunas, with the parallelism which is sometimes observed between the
series of paleontological succession and of embryonal development,"
etc.; and finally, although he does not accept the theory in these
results, he allows that "it appears to offer the best means of
explaining the manner in which organized beings were produced in epochs
anterior to our own."
What more than this could be said for such an hypothesis? Here,
probably, is its charm, and its strong hold upon the speculative mind.
Unproven though it be, and cumbered prima facie with cumulative
improbabilities as it proceeds, yet it singularly accords with great
classes of facts otherwise insulated and enigmatic, and explains many
things which are thus far utterly inexplicable upon any other
scientific assumption.
We have said that Darwins hypothesis is the natural complement to
Lyells uniformitarian theory in physical geology. It is for the organic
world what that is for the inorganic; and the accepters of the latter
stand in a position from which to regard the former in the most
favorable light. Wherefore the rumor that the cautious Lyell himself
has adopted the Darwinian hypothesis need not surprise us. The two
views are made for each other, and, like the two counterpart pictures
for the stereoscope, when brought together, combine into one apparently
solid whole.
If we allow, with Pictet, that Darwins theory will very well serve for
all that concerns the present epoch of the worlds history--an epoch in
which this renowned paleontologist includes the diluvial or quaternary
period--then Darwins first and foremost need in his onward course is a
practicable road from this into and through the tertiary period, the
intervening region between the comparatively near and the far remote
past. Here Lyells doctrine paves the way, by showing that in the
physical geology there is no general or absolute break between the two,
probably no greater between the latest tertiary and the quaternary
period than between the latter and the present time. So far, the
Lyellian view is, we suppose, generally concurred in. It is largely
admitted that numerous tertiary species have continued down into the
quaternary, and many of them to the present time. A goodly percentage
of the earlier and nearly half of the later tertiary mollusca,
according to Des Hayes, Lye!!, and, if we mistake not, Bronn, still
live. This identification, however, is now questioned by a naturalist
of the very highest authority. But, in its bearings on the new theory,
the point here turns not upon absolute identity so much as upon close
resemblance. For those who, with Agassiz, doubt the specific identity
in any of these cases, and those who say, with Pictet, that "the later
tertiary deposits contain in general the debris of species very nearly
related to those which still exist, belonging to the same genera, but
specifically different," may also agree with Pictet, that the
nearly-related species of successive faunas must or may have had "a
material connection." But the only material connection that we have an
idea of in such a case is a genealogical one. And the supposition of a
genealogical connection is surely not unnatural in such cases--is
demonstrably the natural one as respects all those tertiary species
which experienced naturalists have pronounced to be identical with
existing ones, but which others now deem distinct For to identify the
two is the same thing as to conclude the one to be the ancestor of the
other No doubt there are differences between the tertiary and the
present individuals, differences equally noticed by both classes of
naturalists, but differently estimated By the one these are deemed
quite compatible, by the other incompatible, with community of origin
But who can tell us what amount of difference is compatible with
community of origin? This is the very question at issue, and one to be
settled by observation alone Who would have thought that the peach and
the nectarine came from one stock? But, this being proved is it now
very improbable that both were derived from the almond, or from some
common amygdaline progenitor? Who would have thought that the cabbage,
cauliflower, broccoli kale, and kohlrabi are derivatives of one
species, and rape or colza, turnip, and probably ruta-baga, of another
species? And who that is convinced of this can long undoubtingly hold
the original distinctness of turnips from cabbages as an article of
faith? On scientific grounds may not a primordial cabbage or rape be
assumed as the ancestor of all the cabbage races, on much the same
ground that we assume a common ancestry for the diversified human
races? If all Our breeds of cattle came from one stock why not this
stock from the auroch, which has had all the time between the diluvial
and the historic periods in which to set off a variation perhaps no
greater than the difference between some sorts of domestic cattle?
That considerable differences are often discernible between tertiary
individuals and their supposed descendants of the present day affords
no argument against Darwins 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 Darwins
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? And is
it at all likely that these several gradations came to be established
in two totally different ways--some of them (though naturalists cant
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
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[III-7]--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, hippopotamus; South
America, its armadillos, sloths, and anteaters; 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 subtropical
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.
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
hypothesis. 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 zoologist, "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 Cetacea, are other examples of such prophetic
types."--(Agassiz, "Contributions, Essay on Classification," p. 117.)
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 Agassizs book will read
their fulfillment in Darwins.
Note also, in this 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 afterward reappears. Why is this, but that
the link of generation has been sundered? Why, on the hypothesis of
independent originations, were not failing species recreated, 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--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 they 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 there 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 page 98) 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, since 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. Wallaces
inference is really true. Certainly it is not yet generally accepted;
but a strong current is setting toward 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
DOrbigny, 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 afterward--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 Wallaces 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.
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