The doctrine of evolution, according to Herbert Spencer, further
considered.
In the last two preceding chapters I have examined what Mr. Spencer
regards as the direct supports of the doctrine of evolution. I have now
to consider the different orders of facts which, as he claims, yield to
it indirect support. These are the facts derived from classification,
from embryology, from morphology, and from distribution. An explanation
is here needful of the sense in which he uses these respective terms,
before the reader, who is not accustomed to them, is called upon to
understand and appreciate the argument:
1. By classification is meant an arrangement of organic beings in some
systematic manner, according to attributes which they have in common,
and which may form the principle of a division into different classes
or families. Pointing out that in the early history of botanical and
zoölogical science the tendency was to make classifications according
to a single characteristic, Mr. Spencer reminds us that later
naturalists, by attending to a greater number of characteristics,
and finally to the greatest number that can be found to be common to
various classes of vegetable and animal organisms, have constructed
systems of classification which, in place of a linear or a serial
order, have exhibited the alliances of different groups, then the
sub-groups, and the sub-sub-groups, so that the divergences and
redivergences become developed, while the resemblances which obtain
are preserved throughout the whole class. But it is at once apparent
that, although classification, on whatever principle it is conducted,
may be valuable as a means of fixing in the mind the resemblances
or differences of structure that obtain in the different orders
of organized beings, as, for example, among the vertebrate or the
invertebrate animals, the flowering or the flowerless plants, the seeds
naked or the seeds inclosed in seed-vessels, yet that any other system
of classification, based upon other resemblances or differences which
actually present means of grouping or separating the different families
of organized beings, is just as valuable an aid in the investigation of
facts. How far any classification affords an argument, or the means of
constructing an argument, which will yield a support to the doctrine of
evolution superior to that which it yields to the doctrine of special
creations, is of course a question.
2. Embryology: This is the term employed to express that branch of
inquiry which is concerned in a comparison of the increase of different
organisms through the stages of their embryonic life, and in noting
at different stages of this growth the characters which they have
in common with each other; the resemblances of structure which at
corresponding phases of a later embryonic stage are displayed by a less
extensive multitude of organisms; and so on step by step, until we find
the class of resembling embryos becoming narrower and narrower, and
then we finally end in the species of which a particular embryo is a
member. This process of tracing and eliminating embryonic resemblances
is said to have "a profound significance"; because, beginning with
a great multitude of resemblances between the embryonic development
of different organisms, it reveals the divergences which they take
on, and through every successive step we find new divergences, by
means of which "we may construct an embryological tree, expressing
the developmental relations of the organisms, resembling the tree
which symbolizes their classificatory relations." We thus arrive at
"that subordination of classes, orders, genera and species, to which
naturalists have been gradually led," and which is said to be "that
subordination which results from the divergence and redivergence
of embryos, as they all unfold."[79] On this mode of comparing the
embryonic development of different organized beings Mr. Spencer builds
a scientific parallelism, which indicates, as he claims, a "primordial
kinship of all organisms," and a "progressive differentiation of them,"
which justifies a belief in an original stock from which they have all
been derived. In what way this method of investigation destroys or
tends to destroy the hypothesis of special creations, or how it affords
an important support to the doctrine of evolution, will be considered
hereafter.[80]
3. Morphology, or the science of form, involves a comparison of
the structure of different organisms in their mature state; an
ascertainment of the resemblances between their structures, and of
the community of plan that exists between them. Here, as in the aids
derived from classification and embryology, it is claimed that the
fundamental likenesses of forms of structure have a meaning which is
altogether inconsistent with the hypothesis of predetermined typical
plans pursued throughout immensely varied forms of organisms.
4. Distribution: This is the term applied to the phenomena exhibited
by the presence of different organisms in different localities of the
globe; or, as Mr. Spencer phrases it, "the phenomena of distribution
in space." These phenomena are very various. Sometimes, it is said, we
find adjacent territories, with similar conditions, occupied by quite
different faunas. In other regions, we find closely allied faunas in
areas remote from each other in latitude, and contrasted in both soil
and climate. The reasoning, as given by Mr. Darwin and adopted by Mr.
Spencer, is this: that "as like organisms are not universally or even
generally found in like habitats, nor very unlike organisms in very
unlike habitats, there is no predetermined adaptation of the organisms
to the habitats." "In other words," Mr. Spencer adds, "the facts of
distribution in space do not conform to the hypothesis of design."
The reason why they do not is claimed to be that there are impassable
barriers between the similar areas which are peopled by dissimilar
forms; whereas there are no such barriers between the dissimilar areas
which are peopled by dissimilar forms. The conclusion is, "that each
species of organism tends ever to expand its sphere of existence--to
intrude on other areas, other modes of life, other media." That is
to say, there is a constant competition among races of organisms
for possession of the fields in which they can find the means of
subsistence and expansion; and this leads to new modes of existence,
new media of life, new structures and new habitats.
The reader can now retrace his steps, and advert to the facts that are
relied upon, under the four heads of the argument:
1. With regard to the argument derived from classification: it is to
be observed that any system of classification is in a certain sense
artificial, and at all events is manifestly conventional. But, in
order that no injustice may be done to this branch of the argument for
evolution, I shall state it in its full force. The classifications
which naturalists make of the different organized beings according
to their resemblances and differences reveal the fact of unity amid
multiformity. This fact it is said points to propinquity of descent,
"which is the only known cause of the similarity of organic beings."
It is the bond, hidden indeed by various degrees of modification, but
nevertheless revealed to us by the classifications which display the
resemblances. Again, we have, it is said, in the influence of various
conditions of animated organisms, "the only known cause of divergence
of structure." Classification reveals to us these divergences. We have,
then, the bond of resemblances which indicate propinquity of descent,
and the divergences of structure produced by varying conditions of
life. Put the two together, and we have remarkable harmonies of
likenesses obscured by unlikenesses; and to this state of facts it is
claimed that no consistent interpretation can be given, without the
hypothesis that the likenesses and the unlikenesses were produced by
the evolution of organisms out of organisms by successive generation,
through a great lapse of time.
This argument contains no inconsiderable amount of assumption. While
it may be true that some naturalists do not assign any cause for the
similarity which obtains among organic beings excepting their descent
from a common ancestral stock, it is not true that the similarity
of structure is inconsistent with the hypothesis of another cause,
namely, the adoption of a general plan of structure for a large class
of organisms, and an intentional variation in those parts of structure
which mark the divisions of that class into species that are very
unlike. It is true that evolutionists treat with scorn the idea of
a pattern of structure followed throughout a class of animals, but
made by designed adaptations to coalesce with differences that mark
the peculiarities which distinguish one organism of that class from
all the others. Mr. Spencer, for example, observes that "to say that
the Creator followed a pattern throughout, merely for the purpose of
maintaining the pattern, is to assign a motive which, if avowed by a
human being, we should call whimsical."
Let us now follow this mode of disposing of the hypothesis of special
creations, by adverting to some of the facts that are adduced in its
summary condemnation; and, although the passage which I am about to
quote is found in Mr. Spencer's work under the head of morphology, the
illustration applies equally well to his argument from classification.
Speaking of fundamental likenesses of structure, he says: "Under
the immensely varied forms of insects, greatly elongated like the
dragon-fly, or contracted in shape like the lady-bird, winged like
the butterfly, or wingless like the flea, we find this character in
common--there are primarily twenty segments. These segments may be
distinctly marked, or they may be so fused as to make it difficult to
find the divisions between them. This is not all. It has been shown
that the same number of segments is possessed by all the _Crustacea_.
The highly consolidated crab, and the squilla with its long,
loosely-jointed divisions, are composed of the same number of somites.
Though, in the higher crustaceans, some of these successive indurated
rings, forming the exo-skeleton, are never more than partially marked
off from each other, yet they are identifiable as homologous with
segments, which, in other crustaceans, are definitely divided. What,
now, can be the meaning of this community of structure among these
hundreds of thousands of species filling the air, burrowing in the
earth, swimming in the water, creeping about among the sea-weed, and
having such enormous differences of size, outline, and substance, as
that no community would be suspected between them? Why, under the
down-covered body of the moth and under the hard wing-cases of the
beetle, should there be discovered the same number of divisions as in
the calcareous framework of the lobster? It can not be by _chance_ that
there exist just twenty segments in all these hundreds of thousands of
species. There is no reason to think it was _necessary_, in the sense
that no other number would have made a possible organism. And to say
that it is the result of _design_--to say that the Creator followed
this pattern throughout, merely for the purpose of maintaining the
pattern--is to assign a motive which, if avowed by a human being, we
should call whimsical. No rational interpretation of this, and hosts
of like morphological truths, can be given except by the hypothesis of
evolution; and from the hypothesis of evolution they are corollaries.
If organic forms have arisen from common stocks by perpetual
divergences and redivergences--if they have continued to inherit, more
or less clearly, the characters of ancestral races, then there will
naturally result these communities of fundamental structure among
extensive assemblages of creatures, that have severally become modified
in countless ways and degrees, in adaptation to their respective
modes of life. To this let it be added that, while the belief in an
intentional adhesion to a predetermined pattern throughout a whole
group is totally negatived by the occurrence of occasional deviations
from the pattern, such deviations are reconcilable with the belief in
evolution. As pointed out in the last chapter, there is reason to think
that remote ancestral traits will be obscured more or less according
as the superposed modifications of structure have or have not been
great or long maintained. Hence, though the occurrence of articulate
animals, such as spiders and mites, having fewer than twenty segments,
is fatal to the supposition that twenty segments was decided on for the
three groups of superior _Articulata_, it is not incongruous with the
supposition that some primitive races of articulate animals bequeathed
to these three groups this common typical character--a character which
has nevertheless, in many cases, become greatly obscured, and in some
of the most aberrant orders of these classes quite lost."[81]
Whatever may be the explanation suggested by one or another hypothesis
as to the mode in which this uniformity of structure came to exist, it
is certain that it does exist. Twenty segments are found in hundreds
of thousands of species which are immensely different from each other
in size, outline, substance and modes of existence. Here, then, is a
plan. There is a pattern, on which all these different organisms are
constructed with a common peculiarity. It is averred that this could
not have been the result of design, because this would be to impute to
the Creator a whimsical motive, namely, that he followed the pattern
throughout a vast group of different organisms merely for the purpose
of following it. On the contrary, it may be contended that this
uniformity of plan, this repeated pattern, affords the highest probable
evidence of design; and that the supposed whimsicality of motive will
entirely disappear as soon as we reach a purpose which may have had
very solid reasons for this uniformity of structure. When we reason
about the works of the Creator, we are reasoning about the methods of
a being who, we must suppose, is governed by a purpose in all that he
does. In reasoning about the methods of such a being, it is entirely
unphilosophical to suppose that he has done anything merely for the
sake of doing it, or for the sake of exercising or displaying his
powers in repetitions that had no practical value. In order to reason
consistently with the supposed attributes of the Creator, we should
endeavor to find the value of any given pattern which we discover in a
certain very large class of organisms differing widely from each other
in other respects; and in order to find that value it is by no means
essential to make out that the particular plan of construction was
necessary to the making of any organism whatever. The true question
is, not whether twenty segments were necessary to the construction
of any organism, but whether, in each of the different species, this
peculiar number of divisions was useful to each particular organism. If
naturalists of the evolution school, instead of looking at everything
through the medium of a certain theory, would in their dissection,
for example, of the framework of the lobster, the body of the moth,
and the body of the beetle, furnish us with facts which would show
that these twenty divisions are of no use either for strength, or
resistance, or suppleness, or adaptation to what is contained within
them, we should have a body of evidence that could be claimed as
tending to overthrow the hypothesis of intentional design. They might
then speak of the repetition of this pattern as whimsical, upon the
hypothesis that it was a repetition by design. But so little is done
by this class of naturalists to give due consideration to the value
of such repetitions, and so little heed is paid to the truth that
the Creator does nothing that is useless--a truth which all sound
philosophy must assume, because it is a necessary corollary from the
attributes of the Creator--that we are left without the aid which we
might expect from these specialists in natural science. Is it, then,
impossible to discover, or even to suggest, that for each of these
organisms this number of twenty divisions had a value? If they were of
no value, we may safely conclude that they would never have existed,
unless we ignore the hypothesis of infinite wisdom and skill. That
hypothesis is a postulate without which we can not reason on the
case at all. With it, we have as a starting-point the conception of
a being of infinite perfections, who does nothing idly, nothing from
whim, nothing from caprice, and nothing that is without value to the
creature in which it is found. So that, while we can not in all cases
as yet assign that value, we have the strongest reasons for believing
that there is a value; and, instead of asserting that an extensive
community of structure throughout a great branch of the animal kingdom
has no meaning excepting upon the doctrine of evolution, it is the
part of true science to assume that it may have another meaning, and
to discover if possible what that other meaning is. This is the part
of true science, because it is the part of sound philosophy. There
is another remark to be made upon Mr. Spencer's reasoning on this
particular case of a community of pattern. He says that it can not
be imputed to _chance_. It was, then, either an intentional design,
or it came about through the process of descent "from common stocks,
which process was at the same time producing perpetual divergences and
redivergences." Without turning aside for the present to ask from how
many common stocks, it may be shown as in the highest degree probable
that the occasional deviations from the pattern did not arise by the
evolution process, because that process has in itself an element
of chance which is fatal to the theory. The assertion is that "an
intentional adhesion to a predetermined plan throughout a whole group
is totally negatived by the occurrence of occasional deviations from
the pattern." Let this assertion be examined first in the light of
facts, and secondly by the absence of facts.
The hypothesis is that some primitive race of articulated animals,
possessed by some means of the twenty segments, transmitted this
ancestral trait to hundreds of thousands of species having no community
of structure in other respects. Unfortunately for the theory, no
figures can measure the chances against the preservation of a single
pattern through such a multitude of differing organisms descending
from a common stock. Infinity alone can express the chances against
such a result. While, according to the theory, the deviations from the
original type were constantly working out new organisms of the most
diversified forms, until there came to be hundreds of thousands of new
species differing from each other in all but this one peculiarity--a
diversity which is supposed to have been caused by the fundamental law
of evolution--how did it happen that the same law did not break this
uniformity of articulation? If it was potent enough to differentiate
the enormous multitude of these animals in all other traits, why did
it not vary the number of segments with which the primitive race
was endowed? Is the law of evolution limited or unlimited? If it is
limited in its effects, then there are patterns of animal structure
which it has not modified, and the presence of which in hundreds of
thousands of different species must be explained as a form of structure
designed for some end that was to be common to a great multitude
of different beings. If the law of evolution was unlimited in its
power, then the community of pattern has had to undergo chances of
destruction or discontinuance that are immeasurable; as there can be
no measure which will represent to the mind the infinitely diversified
and innumerable causes that have produced the dissimilarities
which compel a classification into the different species, upon the
hypothesis of their descent from a common stock. Grant, too, for the
purpose of the argument, that the occasional deviations from the
pattern of twenty segments, producing a few groups with a smaller
number of articulations, are reconcilable with the belief that some
later ancestral form became endowed with the smaller number which it
transmitted to its descendants. How came that later ancestral form
to be endowed with the smaller number of segments? Was there a still
more remote ancestral race, which in some way became possessed of the
smaller number, or did the spiders and the mites, in the countless
generations of evolution, branch off from ancestral races having the
full number of twenty segments? Upon either supposition, what an
infinity of chances there were, against the natural selection of the
smaller number, and against its preservation as the unvarying type of
articulation found in the spiders and the mites! The supposition that
the number of twenty segments was decided on for the three groups of
superior _Articulata_ for the mere sake of adhering to a pattern is
doubtless unphilosophical. But it is not unphilosophical to suppose
that whatever amount of articulation is found in each species was
given to it because in that species it would be useful. If in some of
the most aberrant orders of these animals the articulation is greatly
obscured, or not found at all, the conclusion that it was not needed,
or not needed in a like degree, is far more rational than the theory
which commits the particular result to an infinity of chances against
it; or which supposes it to have been worked by a process that might
have produced a very different result, since it can not be claimed that
natural selection works by methods of which any definite result can be
predicated more than another.
Thus far I have considered Mr. Spencer's argument from the _Articulata_
in the light of the facts that he adduces. Let us now test it by the
absence of facts. In a former discussion, I have asked for facts
which show, aside from the theory, that any one species of animal,
distinctly marked as a continuing type, is connected by intermediate
types or forms with any pre-existing race of another character. Take
this class of the articulated animals, said to be of hundreds of
thousands of different species having no community of form but this
of articulation, and now known as perfect organisms, each after its
kind. What naturalist has discovered the continuity of lives with
lives, which would furnish the steps of descent of any one of this
species from an antecedent and a different species? It is very easy
to construct a theory, and from it to argue that there must have been
intermediate links, which, if discovered, would show the continuity
of lives from lives which the descent of one organism from another
necessarily implies. To a certain extent, within certain limits, the
sub-groups and the sub-sub-groups of the articulated class of animals,
which classification or morphology reveals, may lay the foundation for
a theoretical belief in an ancestral stock from which the different
and now perfect forms of these distinct animals may have become
developed by successive changes of structure. But the extent to which
connected changes can be actually traced in the animal kingdom is
extremely limited; and the important practical question is whether any
one fact, or class of facts, has been discovered which will warrant
the belief that beings of totally dissimilar forms and habits of
life have, without any design, been evolved by the ordinary process
of successive generation, through the operation of causes that have
gradually modified the structure in all respects save one, and have at
the same time enabled or allowed that one peculiarity of structure to
escape from the influences which have modified both structure and modes
of life in every other respect. Why, for example, upon the hypothesis
of descent from a common stock, has that stock deviated under the
influences of natural selection into the lobster, the moth, and the
beetle, and yet the community of twenty segments of articulation
has entirely escaped the effect of those influences? No reason can
be assigned for the fact that it has escaped those influences,
excepting that it was originally designed, and was impressed upon the
proto-typical stock with such force as to place it beyond the reach
of all such causes of modification as those which are ascribed to
natural or sexual selection. Without the latter supposition, those
causes were just as potent to bring about a modification in the number
of articulations as they were to bring about all the astonishing
diversities of structure and modes of life that we see, and therefore
the most probable conclusion from the fact of this uniformity of the
twenty segments is, that there was a barrier placed in this whole
class of organisms, which has limited the modifying force of the
supposed process of evolution, for the reason of some peculiar utility
in this plan of articulation.
Perhaps it will be said that the process of evolution itself tends to
the preservation of whatever is most useful, while the modifications
are going on which develop new organs and new structures; and that
thus, in the case before us, the twenty segments have been preserved
throughout an enormous group by one of the fundamental laws of
evolution, so that, if there is any peculiar utility in the twenty
segments, that utility has been answered by the very process of gradual
descent of one organism from another. But the difficulty with this
reasoning is, that while it assumes for the modifying influences of
natural and sexual selection a range of fortuitous causes sufficient to
change the ancestral type into the acquisition of vastly diversified
organs, powers, and modes of existence, so as to constitute new
animals, it yet assumes that, by some recognition of a superior and
paramount utility in the particular number of segments, the law of
evolution has preserved that number from the influence of causes
which have changed everything else. Now, the range of causes which
was sufficiently varied, accidental, long-continued and complex to
produce the diversities of structure in all other respects, by the
infinitely modifying influences which have developed new organs and
new modes of existence, must also have been of a sufficiently varied,
accidental, long-continued, and complex character to have broken this
plan of the twenty segments, unless we suppose that in some mysterious
and inexplicable manner the different generations of these beings were
endowed with some kind of sagacity which would enable them to strive
for the preservation of this one peculiarity, or unless we suppose that
Nature was ever on the watch to guard them from its destruction or
variation, on account of its peculiar utility. The first supposition is
not in accordance with the evolution theory; for that theory rejects
all idea of conscious exertion on the part of any of the organisms.
The second supposition leads us at once to the inquiry, how came it
to be imposed upon a whole group of beings as a law of nature, that
whatever utility of structure was of paramount importance to the
whole group should be preserved against the modifying influences that
were to produce species differing absolutely from each other, through
hundreds of thousands of varieties, in every other feature of their
existence? Can we get along here without the hypothesis of design? And,
if there was such design, how does the fact of this uniformity amid
such diversity become an argument against the hypothesis of a Creator?
Or, how does it tend to displace the hypothesis of special creations,
when we find that the very process of so-called evolution has failed
to break the uniformity of a pattern that is conceded not to have been
the result of chance, although that pattern was exposed to just as
many and as powerful causes of modification as those which are assumed
to have brought about the modifications in every other feature of the
animal existence? The truth would seem to be, that the uniformity amid
so great a diversity was either the result of a design which placed it
out of the reach of all the modifying influences, or else it has, by a
most incalculable result, escaped from the effect of those influences
by a chance in which the ratio of one to infinity can alone measure the
probability of such an escape.
Let us now advert to another of Mr. Spencer's illustrations of the
futility of the "supernatural" and of the rationality of the "natural"
interpretation.[82] This illustration is derived from what are
called "homologous" organs; and the particular instance selected is
the vertebral column.[83] There are creatures, such as snakes, a low
order of the vertebrate kingdom, in which the bony axis is divided
into segments of about the same dimensions from end to end, for the
obvious advantage of flexibility throughout the whole length of the
animal. But in most of the higher vertebrata, some parts of this axis
are flexible and others are inflexible; and this is especially the case
in that part of the vertebral column called the sacrum, which is the
fulcrum that has to bear the greatest strain to which the skeleton is
exposed, and which is yet made not of one long segment or vertebra,
but of several segments "fused together." Mr. Spencer says: "In man
there are five of these confluent sacral vertebræ; and in the ostrich
tribe they number from seventeen to twenty. Why is this? Why, if the
skeleton of each species was separately contrived, was this bony mass
made by soldering together a number of vertebræ like those forming the
rest of the column, instead of being made out of one single piece? And
why, if typical uniformity was to be maintained, does the number of
sacral vertebræ vary within the same order of birds? Why, too, should
the development of the sacrum be the roundabout process of first
forming its separate constituent vertebræ, and then destroying their
separativeness? In the embryo of a mammal or bird, the substance of the
vertebral column is, at the outset, continuous. The segments that are
to become vertebræ, arise gradually in the midst of this originally
homogeneous axis. Equally in those parts of the spine which are to
remain flexible, and in those which are to grow rigid, these segments
are formed, and that part of the spine which is to compose the sacrum,
having passed out of its original unity into disunity by separating
itself into segments, passes again into unity by the coalescence of
these segments. To what end is this construction and reconstruction?
If, originally, the spine in vertebrate animals consisted from head to
tail of separate movable segments, as it does still in fishes and some
reptiles--if, in the evolution of the higher vertebrata, certain of
these movable segments were rendered less movable with respect to each
other, by the mechanical conditions to which they were exposed, and at
length became relatively immovable--it is comprehensible why the sacrum
formed out of them should continue ever after to show more or less
clearly its originally segmented structure. But on any other hypothesis
this segmented structure is inexplicable."
We here see the predominating force of a theory which refuses all
possible rationality to any hypothesis but its own. The confident tone
with which facts are arrayed and are then pronounced inexplicable
upon any other hypothesis than that which the writer asserts, without
one scintilla of proof of their tendency to exclude every other
supposition, renders the refutation of such reasoning a wearisome
task. But there is here one plain and sufficient answer to the whole
of the supposed difficulty. The evolution theory, in this particular
application of it, is that originally there were vertebrate animals
in which the spine consisted of separate movable segments from head
to tail, as it does now in fishes and reptiles; but, as the higher
vertebrata were evolved out of these lower forms, the movable segments
were rendered less movable with respect to each other, and at length
in the sacrum the segments became relatively immovable, and yet the
originally segmented structure was retained in this part of the
column, by force of the propinquity of descent from an antecedent type
which had the whole column divided into movable segments. Upon no other
hypothesis, it is asserted, is this result explicable.
Mr. Spencer's analysis of the sacrum is somewhat defective. It is, as
he says, that part of the vertebrate column which in the higher class
of vertebrate animals is, during fœtal life, composed, like all the
rest of the column, of distinct vertebræ. These vertebræ, like the
others, are flexible in the fœtal stage, but after birth they become
coalesced or united into one piece, instead of remaining in separate
pieces. Thus far, Mr. Spencer's description is, I am informed by
anatomists, correct. But the questions which he propounds as if they
were unanswerable upon the assumption that this change is inexplicable
upon any other hypothesis than that of the evolution of the higher
vertebrata out of the lower vertebrate animals, and that the sacrum,
with its continuous piece, has retained the segmented outward form by
force of the descent, demand closer consideration. Let us trace the
process of formation in the human species, and then see what is the
just conclusion to be derived from it. In the embryonic condition,
the substance which is to form the vertebral column is continuous.
As the fœtus is developed, this substance separates itself into
the segments which are called vertebræ, and these segments remain
flexible and movable throughout the column. After birth, the five
lower segments become united in what is substantially one piece,
but of course the marks of the original segments remain. This is
what occurs in the origin and growth of the individual. Now, looking
back to the period when this species of animal did not exist, and
supposing it to have been specially created in the two related forms
of male and female, endowed with the same process of procreation and
gestation that has been going on ever since there is any recorded or
traditionary knowledge of the race, why should not this very growth
of the sacrum have been designed, in order to produce, after the
birth of the individual, that relative rigidity which would in this
part of the vertebral column be useful to an animal destined to an
upright posture of the whole skeleton and to the habits and life of
a biped? And, if we extend the inquiry to other species, why should
we not expect to find, as in the case of an oviparous vertebrate like
the ostrich, a repetition of the same general plan of forming the
spinal column, for the same ultimate purpose, with such a variation in
the number of original segments that are to constitute the sacrum as
would be most useful to that bird, thus establishing for the ostrich
a sacrum that in a reptile or a fish would not only not be required,
but would be a positive incumbrance? Upon the hypothesis of special
creations of the different species of vertebrate animals, every one
of Mr. Spencer's questions, asked as if they were unanswerable, can
receive a satisfactory solution. Thus, he asks, "Why, if the skeleton
of each species was separately contrived, was this bony mass [the
sacrum] made by soldering together a number of vertebræ like those
forming the rest of the column, instead of being made [aboriginally]
in one single piece?" The answer is, that in the establishment of
the process of gestation and fœtal growth, if a human artificer and
designer could have devised the process, he would have selected the
very one that now exists, for certain obvious reasons. First, he would
have designedly made the process to consist, in the embryo, of a
division of the substance which was to form the vertebral column in a
continuous and uniform division into segments, because the whole column
is to have at first the flexibility that may be derived from such a
division. Secondly, when the time was to arrive at which the formation
of the sacrum, with its practical continuity of a single piece, was
to commence, he would select the number of the lower vertebræ that
would make a sacrum most useful to the particular species of animal,
and would weld them together so as to give them the relative rigidity
and action of a single piece. But as the whole formation is the result
of a growth of the sacrum out of a part of the slowly forming column
originally divided into vertebræ, the marks of these separate vertebræ
would remain distinguishable, while they would cease to have the
mechanical action of separate vertebræ.
Another of Mr. Spencer's questions is, "Why, if typical uniformity was
to be maintained, does the number of sacral vertebræ vary within the
same order of birds?" The answer is the same as that which assigns
a reason for all other variations in the skeleton of animals of the
same order but of different varieties, namely, the special utility
of the variations in the number of sacral vertebræ that would be
most useful in that variety. The typical uniformity maintained is a
uniformity in the process of growth and formation, down to a point
where the variations are to come in which mark one animal from another;
and I have more than once had occasion to suggest that the typical
uniformity, and its adaptation to the varying requirements of different
beings, is the highest kind of moral evidence of the existence, wisdom,
and power of a supreme artificer, and that it militates so strongly
against the doctrine of evolution that, without more proof than can
possibly be claimed for that doctrine, we ought not to yield to it our
belief.
The theory that the original condition of all vertebrate animals was
that of separate movable segments throughout the spinal column, as it
is now in fishes and some reptiles, and that in the evolution of the
higher vertebrates out of these lower forms, certain of these movable
segments were rendered less movable with respect to each other by
the mechanical conditions to which the successive generations were
exposed, until at length the sacrum was formed, is undoubtedly a theory
that excludes all design of an infinite artificer, and all intention
whatever. It is a theory which relegates the most special contrivances
and the most exact adaptations to the fortuitous operation of causes
that could not have produced the variations of structure and at the
same time have preserved the typical uniformity. It is certainly a
theory which we should not apply to the works of man, if we were
investigating products which seemed to be the result of human ingenuity
and skill, but of the origin of which we had no direct evidence. In
such a case, we should not shut our eyes to the proofs of intentional
variations and adaptation, or, if we did, our speculations would not
be likely to command the assent of cultivated and sound reasoners. We
may treat the works of Nature by a system of logic that we should not
apply to the works of man, but if we do, we shall end in no tenable
results. The principal and in fact the only essential distinction to
be observed between the works of Nature and the works of man relates
to the degree of power, intelligence, and skill in the actor. If we
assume, as we must, that in the one case there was an actor, applying
will, intelligence, and power to the properties of matter, and molding
it into certain products and uses, and that in the other case there
was no actor, but that all products and results are but the ungoverned
effects of what are called natural laws in contradistinction to all
intentional purposes, we must argue upon principles that are logically
and diametrically inconsistent in themselves, and at variance with
fundamental laws of reasoning.
I will now advert to an omission in Mr. Spencer's analysis of the
sacrum, which overlooks one of the strongest proofs of intentional
design afforded by that part of the spinal column. We have seen what
was its general purpose and growth, and the process of its formation.
We have now to note its variations in the male and the female skeleton.
In the male, the sacrum, thus formed before birth, after birth answers
to and performs its ultimate function of a comparatively rigid and
inflexible piece of bone, and it is provided with no other special
characteristic. In the female, on the contrary, there is a most
remarkable adaptation of this piece to the function of maternity. While
all the upper vertebræ of which this piece was originally composed
are welded together after birth in the female as in the male, in the
female the lowest segment of all remains for a certain time flexible
relatively to the upper part of the sacrum, in order to admit of the
necessary expansion of the pelvis during the passage of the infant
from the womb of the mother. In the normal condition of females of
all the vertebrate orders, this flexibility of the lower part of the
sacrum continues while the period of possible maternity continues. If
in any individual female it happens to be wanting during the period
of possible conception, delivery can not take place without danger
to the mother or the offspring, or both. Hence, in very bad cases,
nature has to be assisted by extraordinary means. But in the normal
condition of the female sacrum, this flexibility, so essential in the
process of safe delivery, is always found, and its special purpose is
known to every anatomist, while it has no existence in the structure
of the male. Is this distinction to be accounted for by the same
kind of reasoning that undertakes to account for all the other great
distinctions between the related forms of male and female, which
reproduce their kind by a common process of the sexual union, namely,
that this division of male and female came about by a habit that
resulted now in the production of a male and now in the production
of a female, from tendencies that were ungoverned by any special
purpose? Must we not conclude, however inscrutable are the causes that
determine the sex of a particular infant, that the sexes themselves
were specially ordained? And if they were specially ordained, how are
we to account for the special construction and function of each of
them, without the interposition of a special design? And when we find
a structure in the female obviously designed for a special purpose, and
not existing in the male, are we to conclude that some particular race
of females, in some remote period of antiquity, among the countless
generations of the vertebrata, found that this flexibility of the
sacrum would be highly convenient to them, and, having adopted it
as a habit, transmitted it, as a specially acquired peculiarity of
structure, to their female descendants? This is all very well as a
theoretical speculation, but as a speculation it is entirely defective,
because it assigns the peculiarity of structure to a cause that could
not have produced it. On the other hand, the hypothesis of its special
creation assigns it to a cause that could have produced it, and its
existence is among the highest of the multitudinous evidences of
intentional design and special formation.
Wherein consists the irrationality of the hypothesis that a plan of
construction was intentionally, and with supreme skill, framed for
very different beings, to answer in each of them a common purpose? The
asserted irrational character of this hypothesis consists in nothing
but a denial that there was a Creator. It comes down to this, if it
comes to anything: because, if we assume that there was a Supreme Being
who took any care whatever of the complex and manifold product that we
call nature--if we suppose that he ordained anything--we must suppose
that his power to construct was boundless, and that a repetition of
his plans wherever they would be useful, to answer the beneficent
and diversified ends of infinite skill and benevolence, is just as
much in accordance with the whole hypothesis of his attributes as it
is to suppose that he caused anything whatever to exist. If we deny
his existence, if we can not satisfy ourselves of it at all, if we
suppose that nothing was ordained, nothing was created, but that all
these diversified forms of animal organisms grew out of a protoplasmic
substance, and that there was never any absolute commencement of
organic life on the globe, or any absolute commencement of anything
whatever, it is of course idle to speculate upon the adoption or
preservation of patterns, as it is equally idle to pursue the theory of
evolution through stages which at last end nowhere whatever.[84]
It may be well to cite Mr. Spencer's final summary of the general
truths which he claims to be revealed by morphology, because it will
enable the reader to see just where the logical inconsequence of his
position occurs: "The general truths of morphology thus coincide
in their implications. Unity of type, maintained under extreme
dissimilarities of form and mode of life, is explicable as resulting
from descent with modification; but is otherwise inexplicable. The
likenesses disguised by unlikenesses, which the comparative anatomist
discovers between various organs in the same organisms, are worse than
meaningless if it be supposed that organisms were severally formed as
we now see them; but they fit in quite harmoniously with the belief
that each kind of organism is a product of accumulated modifications
upon modifications. And the presence, in all kinds of animals and
plants, of functionally useless parts corresponding to parts that are
functionally useful in allied animals and plants, while it is totally
incongruous with the belief in a construction of each organism by
miraculous interposition, is just what we are led to expect by the
belief that organisms have arisen by progression."[85]
Without expending much criticism upon the phrase "miraculous
interposition," as a description of what takes place in special
creation, it is sufficient to say that the act of special creation of a
distinct organism is to be first viewed by itself, as if it stood alone
in nature, and that it is like any other act of causing a new thing
to exist which did not exist before. To this idea should be added
the fact that in the creation of an animal organism there is involved
the direct formation of a peculiar type of animal, with a capacity
of producing other individuals of the same type through a process of
generation. When, after having attained this conception of the act of
special creation, and contemplated a single instance of the supposed
exercise of such a power, we extend our inquiries, we find many other
instances of the exercise of the same power; and then we observe a
certain unity of type in some peculiarity of structure, maintained
under extreme dissimilarities of form and mode of life. How, then,
is this one similarity of pattern, amid such multiformity in other
respects, "worse than meaningless," if we suppose that "organisms were
severally framed as we now see them"? The very hypothesis that they
were so severally framed carries in itself a meaning which can not be
thus summarily ignored; because that hypothesis implies a power in the
Creator to do just what we see. You may deny the power; but if you
admit the existence of the infinite creating power, you are remitted
to the inquiry into its probable methods; and you can no more say that
the special creation of distinct organisms, with a certain unity amid
a great multiformity, leaves the whole phenomena without a meaning,
than you can say that any method which you can suggest is necessarily
the only method which will afford a rational meaning in what we see.
You must go the length of denying the entire postulate of a Creator,
before you can be in a situation to deny the meaning that is involved
in the idea of creation; for that idea implies an absolute power to
apply a uniform pattern of structure to a whole class of organisms
varied in all other respects. The theory that each kind of organism
is a product of accumulated modifications upon modifications, without
any special interposition to produce the modified and distinct forms,
must be maintained on one of two suppositions: either that at some
period there was an absolute commencement of organic life in some form,
upon this globe, and that then all the other forms which we see were
left to be evolved out of that one by the ungoverned accumulation of
modifications upon modifications, or else that there was never any
absolute commencement of organic life at any time, but that matter,
by some peculiar property derived from some source that is not
suggested, took on combinations which resulted in some crude form of
animated organism, and that then the accumulations of modifications
upon modifications followed from some process of generation by which
the successive organisms became multiplied and varied. Of the former
supposition, I understand Mr. Darwin to have been a representative
naturalist. Of the latter, I understand Mr. Spencer to be an advocate.
Upon what may be called the Darwinian doctrine, the idea of a Creator,
causing to exist at some time some crude form of animal life, is
admitted. Upon the Spencerian doctrine, which will be in this respect
more closely examined hereafter, I do not see that the idea of a
creating power comes in anywhere, either at the commencement of a
series of organisms or at any point in that series. But, upon the
logical proposition asserted in the passage last above quoted, it is
obvious that, unless the idea of a Creator is absolutely denied, the
presence of a unity of type amid any amount of dissimilarities of form
and mode of life can not be pronounced to be without meaning, because
the idea of a Creator implies a power to make that very unity amid the
uniformity, which is asserted to be inexplicable without resorting
to the theory that it was not made at all, but that it grew out of
events over which no superintending or governing power was exercised.
Upon this kind of dogmatic assertion there can be no common ground of
reasoning.
The assumed incongruity between the facts and the hypothesis of a
special creation of each organism is an incongruity that arises out of
the assumption that such special creation was an impossibility. If once
the idea of an infinite creating faculty is assumed as the basis of the
reasoning, all seeming incongruity vanishes, and the probable method
of that creating power must be determined by the preponderance of
evidence. If the power is denied, we must grope our way through systems
which impute everything to the properties of substance, without any
suggestion of a source from which those properties were derived, and
without anything to guide them but the tendencies implanted in them,
we know not how or when, and of the origin of which we have not even a
suggestion. Some of the speculations of Greek philosophers adverted to
in a previous chapter may serve to show us what comes of the omission
to conceive of power as abstracted from substance or its properties.
The philosophy which first attained to this conception led the way
to that conception of an Infinite Being, without whose existence and
attributes all speculation upon the phenomena of nature leads to
nothing. A belief in his existence and attributes must undoubtedly be
attained by an examination of his works, if we set aside the teachings
of revealed religion. But if we can not attain it, we have no better
means for believing in the doctrine of evolution than we have for
believing in any other method by which the phenomena of nature have
become what they are.
The question here is, not whether descent of organisms from organisms,
with modifications upon modifications, is a supposable theory, but
whether it is so satisfactorily shown that it can be said to exclude
the hypothesis of a special creation of each organism. There may be
parts of structure in one animal which seem to have no functional use,
although we should be cautious in making the assumption that they are
of no use because we have not yet discovered that use. But let it be
assumed that these apparently useless parts in one animal correspond to
parts which in another animal are functionally useful. If there was
established for these two separately created animals a like system of
procreation and gestation, that system, affected at the same time by a
law of growth imposed by the special type of the species, might in one
species lead to the presence of parts of which we can not recognize
the use, and might in other species lead to the presence of parts of
which we can see the use. It does not help to a better explanation
to say that there has been an accumulation of modifications upon
modifications in the course of an unknown descent of one organism from
another. Why did these modifications stop short of the production of
a species or of several species in which no resemblance of parts more
or less functionally useful could be found? The supposition is that
the modifications have been going on through millions of years. Time
enough, therefore, has elapsed for the destruction of all uniformity
of structure; and the causes of modification are as immeasurable as
the period through which they are supposed to have been operating.
The imaginary ancestral stock, wherever it is placed in the line of
remote descent, had, in its first distinctive existence, a peculiar
structure, which it bequeaths to its offspring. In the countless
generations of its descendants, modifications of that structure take
place, until a new animal is evolved. What preserved any unity of
type from the modifying influences? It was not choice on the part of
the several descending species; not a conscious exertion to preserve
something; it was nothing but the propinquity of descent, which by the
law of heredity transmitted certain resemblances. But why was that
law so potent that it could preserve a certain unity of type, and at
the same time so powerless as not to prevent the modifications which
the successive organisms have undergone in all other respects? Or, to
reverse the terms of the question, why were the causes of modification
sufficiently powerful to produce distinct species, and yet not
powerful enough to eliminate the resemblances which we find obtaining
throughout the whole group of animals to which these several species
belong? It would seem that here we are not to lose sight of the fact
that, in the animal kingdom, procreation never takes place between
a male and a female of distinct species, and that we have no reason
to believe that it ever did take place. Now, although the evolution
hypothesis supposes that, starting from an ancestral stock, the
modifications of structure have been produced in offspring descended
from parents of that same stock, which have transmitted acquired
peculiarities to their immediate progeny, and so on indefinitely, yet
there must have been a time when the diverging species became distinct
and peculiar organisms, and when it became impossible for any crossing
of these organisms to take place. All the supposed modifications,
therefore, have taken place within the limits of an actual descent of
one kind of animal from another, each successive pair belonging to the
species from which they were individually generated. In this descent
of lives from lives, there came about changes which in progress of
time led to two animals as wide asunder as the man and the ostrich,
or as the man and the horse, and yet the causes which were powerful
enough to produce these widely diverging species were not powerful
enough to break up all unity of plan in some one or more respects. If
naturalists of the evolution school would explain how there has come to
be, for example, in the skeleton of the _vertebrata_, a bony structure
called the spine, in which a certain resemblance and a certain function
obtain throughout the whole class, and yet one species creeps upon its
belly, another walks on four legs, and another on two, and one flies
in the air and another never can do so, and how this could be without
any design or special interposition of a creating power, but that the
whole of this uniformity amid such diversity has arisen from acquired
habits among the different descendants from an aboriginal stock that
had no such habits in either mode of locomotion, and no organs for such
modes of life, they would at least be able to commend their theory to
a better appreciation of its claims than is now possible to those who
want "grounds more relative" than a naked hypothesis.
3. The argument from embryology requires for its appreciation a
careful statement of its abstract proposition, and a statement of
it in a concrete form. As an abstract proposition, embryology, or
the comparison of the development of different organisms under their
embryonic stages, shows that in the earliest stage of any organism
it has the greatest number of characters in common with all other
organisms in their earliest stage; that at a later stage its structure
is like the structures displayed at corresponding phases by a less
extensive number of organisms; that at each subsequent stage the
developing embryo becomes more and more distinguished from the groups
of embryos that it previously resembled; and that this divergence goes
on, until we reach the species of which the embryo is a member, in
which the class of similar forms is finally narrowed to that species.
It seems that Von Baer formulated this generalization of embryologic
development into an "embryologic law," which, according to Mr.
Spencer, becomes a support to the hypothesis of evolution in this way:
Species that had a common ancestry will exhibit a parallelism in the
embryonic development of their individual members. As the embryos of
the ancestral stock were developed in their growth, so the embryos of
the descended species would be developed at corresponding phases in a
similar way. As one species diverged from its ancestral stock, there
would come about modifications in the development of its embryos, and
thus a later ancestral stock would be formed, which would in turn
transmit to its descendants in the development of the embryo less and
less resemblances, and so on, until finally the individual animal, at
birth, would structurally resemble only the individual infants of its
own race.
Here, then, is another remarkable instance of the force of an adopted
theory. First, we have a comparison of the embryonic development of
different animals from their seminal germs which displays certain
phenomena of resemblances and departures. Next, we have the assumption
of an ancestral stock, the common origin of all the organisms in the
development of whose embryos among its descendants an embryologic law
was to work, starting from the visible resemblance of all the germs,
then exhibiting structural changes into later ancestral stocks, and so
on, until the resemblances are reduced to those which obtain only among
individuals of the same species. So that, without the hypothesis, the
assumption of an ancestral stock of all the organisms, formed somehow
in the course of descent from a germ that gave rise to an animal of
some kind, we have nothing to which to apply the embryologic law. We
are to infer the embryologic law from the parallelism of embryonic
development which prevails in the whole series of animal generation, or
from its divergences, or from both, and then we draw from _this law_
the inference that the whole series of animals came from some common
stock. The difficulty with this whole theory is, as I have more than
once suggested, that we have no means, aside from the theory itself, of
connecting lives with lives, in the generation of one distinct species
out of another. Without some proof of the fact that the human fœtus was
a diverging growth out of some ancestral stock that was the same as
that from which the fœtus of another animal was a different diverging
growth, the embryologic law is no help to us whatever. If this kinship
of the human fœtus with the fœtus of some other animal can not be
found, by tracing the intermediate links which carry them respectively
back to their common ancestor, between what animals in respect to
their embryonic development can such kinship be found, excepting upon
the theoretical assumption of a common origin of the whole vertebral
class? If there was such a common ancestral stock, where is it to
be placed, what was its character, when did the law of embryologic
development begin to operate upon its descendants? Until some facts
can be adduced which will have a satisfactory tendency to show the
kinship of one animal with another by reason of ancestral descent from
a common ancestral stock that was unlike either of them, the phenomena
of embryologic development have no tendency to displace the hypothesis
of special creations; for, on the latter hypothesis, the phenomena of
resemblances and differences in the growth from the germ into the fœtus
and from the fœtus into the newly born infant, evinced by any range of
comparison of the different species, would be the same. If man was a
special creation, and one of the higher quadrumana was also a distinct
and separate creation, the establishment for each of a like process of
procreation and gestation would produce all the resemblances of fœtal
growth that obtain between them, and the ordained differences of their
animal destinies would explain all the divergences. Let us see if this
is not a rational conclusion.
It is exceedingly difficult for the common reader of such a work
as that of Mr. Spencer, on which I am now commenting, to avoid the
influence of the perpetual assertion that facts are explicable upon
one hypothesis alone. At each step in the argument, the array of facts
terminates with the assertion that, upon the hypothesis of design, the
facts are inexplicable; and yet we are furnished with no reasoning
that has a tendency to show that the facts necessarily exclude
the hypothesis of design, or, in other words, that the facts are
inconsistent with that hypothesis. It is essential to understand what
is the true scope of the hypothesis of special creation; for, without
a definite idea of what that term implies, we have no proper means of
comparing the facts of animal resemblances or differences with the
rationality of the hypothesis that they resulted from an intentional
design. Recollecting, then, that we are now pursuing the resemblances
and divergences that are found in a comparison of the embryologic
development of different species of animals, let us endeavor to
understand the meaning of what I have suggested at the close of the
last preceding paragraph; namely, the establishment for a large class
of animals of a like general system of procreation and gestation, and
the ordination of different destinies for the different species of
animals belonging to that class. I have said that the two branches of
this hypothesis would account for the resemblances in the embryological
growth of different animals, and would explain the divergences which
obtain among their embryological developments. The first inquiry is,
whether this hypothesis presents a true philosophic idea of special
creation. The next inquiry is, whether it affords a satisfactory
explanation of the phenomena of comparative embryologic development.
We must never lose sight of the one grand postulate of an infinite
Creator. This postulate must be conceded to the believers in special
creations, because any idea of creation implies a creating power. If
we conceive of creation without a Creator, we must stop all argument.
Now, the hypothesis of creation, as I have more than once said,
implies a being of boundless faculties. There can be absolutely no
limitation to the power of such a being, either in respect to the
methods by which he will accomplish his objects, or to the number and
variety of these objects, or to the purposes for which they are to
exist. If we narrow our conception of creating power to anything less
than an infinite faculty; if we suppose it to be restricted in any
direction; if we argue about it as if there were things that it can not
do, we shall be without the means of reasoning soundly upon anything
that it is supposed to have done. It is quite otherwise when we are
reasoning about the operation and effect of secondary causes. There
is no secondary cause--no imaginable operation of a fixed quality of
substance--no action of any of the properties of substance--that is not
limited. The scope of its action may be very wide; within its sphere it
may be enormously potent; but in its very nature it is bounded.[86] It
is not so with the First Cause of all things; not so with the Infinite
Power which, upon the hypothesis of a First Cause, has established all
the physical laws of the universe and all the properties of matter.
So that, when we reason about the methods of that infinite creating
power, if we find a general system established, or a pattern repeated
through a very large class of organisms, the proper inference is, not
that the power was limited, but that it has been exercised to the whole
extent of what was useful, and in that direction has been exercised
no further; and if we find variations or additional structures
incorporated with the repetition of a general pattern, the proper
inference is that the unlimited creating power has put forth all the
additional exertion and skill needful for the formation of new beings.
What, then, does the establishment of a like system of procreation
and gestation imply, upon the supposition of the distinct creation of
species? It implies a certain parallel embryonic development, from
the germ to the fœtus and from the fœtus to the new-born infant,
throughout a large group of different animals; and this parallelism
would in certain stages of the embryonic growth display identity
or close similarity of form and structure. But as in each species
of animal the distinct creation would necessarily imply a distinct
destiny, the parallelism of embryonic form and structure would cease
at the point of development at which the characteristic structure
of the species would begin to unfold itself. The general system of
procreation and gestation common to a whole class of different animals,
and the ordained diversity of species, would present the same phenomena
of resemblances and differences in the embryonic development that
are supposed to be explicable only by the hypothesis of a descent of
all the species from a common ancestral stock through the process of
evolution.
Notwithstanding the mystery and obscurity in which the process of
animal procreation is involved--a mystery and obscurity which will
perhaps never be fully solved--we can see enough to warrant some
definite conclusions. One of these conclusions is that, in the
formation of the germ which becomes developed into the fœtus, the male
and female parent each contributes some cellular substance to the
compound which constitutes that germ. We may safely infer this, because
the individual animal becomes a union of characteristics belonging
to both the parents, although the traits that are peculiar to one of
the parents may be more or less marked in their different offspring,
so that in one of the descendants the paternal and in another the
maternal traits will predominate. But in every descendant from the
same pair there is more or less of the peculiarities of each parent
plainly discernible. The inference, therefore, may be safely drawn
that the male and the female parent each contributes to the formation
of the ante-fœtal germ some cellular substance, in which resides the
typical characteristic of animal organism which each parent possesses.
The compound germ that is thus formed is endowed with the mysterious
principle of animal life which admits of growth and development; and
whether after its formation the female parent bestows most or bestows
least upon the product, that product consists of a union of cellular
substances contributed by both the male and the female parent in
the sexual act of procreation. This compound resultant germ, in the
earliest stage of its formation, like the separate cells of which it is
a union, exhibits no visible difference when we compare the ante-fœtal
germ of one animal with that of a different animal. Perhaps we shall
never be able to detect either chemical or mechanical differences
in the cellular substances or in the earliest stage of the compound
product which has resulted from their union. But in that compound
product there resides a contributory cellular substance derived from
each of the parents; and it is a just inference from this fact, and
from what we learn when we trace the further development, that there
is a peculiar and typical structure impressed upon and inwrapped in
this compound germ, which is to grow into a fœtal development by a
law of its own. There will at the same time be a particular law of
development for each distinct species of animal, and a general law of
development for a great variety of species among whom there obtains a
common process of the sexual union and of the contribution of male and
female cellular substance. When the fœtus becomes formed, there will
still be marked resemblances in the different species, before the stage
is reached at which the characteristic structure of each species is to
begin to unfold itself. But at some time the fundamental difference of
structure originally lodged in the cellular substances of which the
compound ante-fœtal germ was composed, and impressed upon that germ as
the type which was gradually to unfold itself into a distinct being,
will begin to exert its force. The resemblances of structure will
become less and less, as the fœtus of the different animals approaches
to the time of birth. Organs, or appearances of organs, which at one
stage of the comparison have seemed to indicate descent from a common
ancestral stock, but which may have been only the result of a common
process of fœtal development, will be found to be varied by force of
the original diversity of structure and destiny that was made to reside
in the seminal substance of each distinct species of animal; and, at
length, this original and intentional peculiarity of structure and
being would become perfected at or before the period when birth is to
take place, leaving only those resemblances which must obtain in all
organisms constructed in certain respects upon a uniform plan, and
brought into being by a common process of procreation and gestation.
Let us now see whether this reasoning involves any such unphilosophical
or unscientific belief as is supposed. Passing by the often-repeated
assertion that the facts of comparative embryologic development are
reconcilable only with the belief in evolution, let us advert to some
of those facts. "The substitutions," says Mr. Spencer, "of organs and
the suppression of organs, are among those secondary embryological
phenomena which harmonize with the belief in evolution, but can not
be reconciled with any other belief. There are cases where, during
its earlier stages of development, an embryo possesses organs that
afterward dwindle away, as there arise other organs to discharge the
same functions. And there are cases where organs make their appearance,
grow to certain points, have no functions to discharge, and disappear
by absorption." The concrete illustration of this substitution and
suppression of organs is thus given by Mr. Spencer:
"We have a remarkable instance of this substitution in the successive
temporary appliances for aërating the blood which the mammalian embryo
exhibits. During the first phase of its development, the mammalian
embryo circulates its blood through a system of vessels distributed
over what is called the _area vasculosa_, a system of vessels
homologous with one which, among fishes, serves for aërating the blood
until the permanent respiratory organs come into play. After a time,
there buds out from the mammalian embryo a vascular membrane called the
allantois, homologous with one which, in birds and reptiles, replaces
the first as a breathing apparatus. But while, in the higher oviparous
vertebrates, the allantois serves the purpose of a lung during the
rest of embryonic life, it does not do so in the mammalian embryo. In
implacental mammals it aborts, having no function to discharge; and in
the higher mammals it becomes "placentiferous, and serves as the means
of intercommunication between the parent and the offspring"--becomes
an organ of nutrition more than of respiration. Now, since the first
system of external blood-vessels, not being in contact with a directly
oxygenated medium, can not be very serviceable to the mammalian embryo
as a lung; and since the second system of external blood-vessels is, to
the implacental embryo, of no greater avail than the first; and since
the communication between the embryo and the placenta among placental
mammals might as well or better have been made directly, instead
of by metamorphosis of the allantois--these substitutions appear
unaccountable as results of design. But they are quite congruous with
the supposition that the mammalian type arose out of lower vertebrate
types. For, in such case, the mammalian embryo, passing through states
representing, more or less distinctly, those which its remote ancestors
had, in common with the lower _vertebrata_, develops these subsidiary
organs in like ways with the lower vertebrata."[87]
In what way, then, are these substitutions unaccountable as results
of design, and why are they any more congruous with the supposition
that the mammalian type arose out of the lower vertebrate type? In the
first place, it is necessary to have a distinct conception of what
is meant by design. In the present case, it means that for a certain
large group of animals there was established a system of reproduction
by the sexual union of male and female, each contributing a cellular
substance peculiar to itself, in the formation of a compound cellular
substance in which the separate substances are united, and which is
to be developed into the fœtus by a law of growth; and as a further
design there is wrapped up in the compound germ of each distinct
species of animal a typical plan of ultimate form and structure.
This typical plan can not be detected in the germ itself, as it is
too subtile and obscure even for the microscope; but we have every
reason to believe that it is there in all its distinctness of original
purpose, because at a later stage of the embryonic development we
find a distinct species of animal is the result. This is a conclusion
that must be adopted by the evolutionist, as well as by the believer
in special creations, because it has nothing to do with the question
of how distinct species came to exist. Whether they were designedly
and separately created, or were evolved out of one another, the
reproductive process by which the individuals of the same species
are brought into being alike involves the conclusion that, in the
ante-fœtal germ of that species, there is somehow involved, in a form
so minute that it can not be seen, the type of animal which is to
belong to that species, and to no other. Here, then, we have the grand
and compound design which is to obtain throughout a whole group of
different animals; namely, that they shall multiply in the production
of individuals of their own types, by a sexual union, in which the
male and the female each contributes a cellular substance of its own
to the formation of a compound germ, and in that germ there is made
to reside the typical form and structure of a distinct organism, so
minute that we can not see it, but which we must conclude from the
result has been put there to be developed by a law of growth ordained
for the accomplishment of a certain distinct order of beings. But
the very obscurity of this type, in the earliest stage of embryonic
development, leads to the conclusion that while it will never be lost,
so long as its life is preserved, it will unfold itself in ways that
will be equally beyond our ken, until the point is reached where it is
no longer obscured, but where it is revealed in all its distinctness
of outline and its peculiarity of structure. What is certain and
invariable is, that the type peculiar to the species is at some time
in the growth of the individual animal perfectly developed. But in the
modes of its development through different embryonic stages, there will
be variations and substitutions of organs in the different species,
but in each distinct species these variations and substitutions will
be uniformly the same, because the law of development imposed by
the distinct type, while it may operate differently among different
species, will always operate in the same way in the same species.
Thus in one animal the development from the original type which was
implanted in its seminal ante-fœtal germ may at one stage exhibit an
organ for which at a later stage another organ will be substituted; and
in another animal a seemingly corresponding organ may serve a different
purpose, or may altogether abort. These embryologic phenomena, varying
in different species, but occurring uniformly in the same species,
are necessarily among the most obscure of all the phenomena of animal
life, on account of the fact that they take place where we can not
watch the changes or modifications as they are taking place during
actual fœtal life. But they are no more explicable upon the hypothesis
of the descent of distinct animals from a common stock, than they are
upon the hypothesis of distinct creations of species. Upon the former
hypothesis, the assumed propinquity of descent implies the preservation
of the same mode of embryonic development until it becomes varied by
the operation of causes that bring about a new habit of development,
and then a fixation in this new habit after a new species or a new
ancestral stock is formed; so that in each distinct species there comes
at length to be a uniform process of substituting and suppressing
organs, or changing the functions of organs. But how are we to account
for the operation of causes that have preserved a parallelism of
development, along with the operation of causes that have produced the
different modes of development, when all the species are supposed to be
derived from a common ancestral stock, which first began to procreate
and to develop its descendants in one and the same way? What are the
facts which will enable us to say that the mammalian type arose out
of the lower vertebrate types, when we compare the different modes
of their embryologic development? How are we to estimate the chances
for a preservation of so much resemblance as exists between the two
in their embryologic lives, and the chances for the variations that
are observable? What we can safely conclude is that there is a law
which holds each species in a constant repetition of its own fœtal
growth, according to its unvarying development in the same series of
changes, substitutions, or suppressions. But we can not safely conclude
that this species became formed in the supposed process of descent
from a remote ancestral stock, which may or may not have originally
exhibited the same series of changes, substitutions, or suppressions.
If the ancestors of the mammalian vertebrates were the kind of animal
supposed, we have to find, in order to justify the supposed descent,
those states which represent the correspondence between the mode in
which the ancestral stock developed its own embryos, when compared
with the mode in which the type of the lower vertebrata developed its
embryos, so as to make it reasonably certain that these subsidiary
organs derived their several substitutions or suppressions from the
process of descent, and not from any special mode of development
ordained for each distinct species. We may imagine these states through
which the mammalian embryo has passed, but as yet we have only a theory
which suggests their existence without facts to support it. The truth
would seem to be that this whole subject of comparative embryology,
upon the hypothesis of the kinship of all organized beings, or the
descent of many distinct species from a common stock, is involved in
very great difficulties; not the least of which is the difficulty of
explaining how the diverging descendants from that stock came to be
endowed with habits of embryologic life and growth that resulted in the
production of very different modes of development, and at the same time
preserved for each new species its own peculiar mode of development.
To say, for example, that the mammalian embryo passed through states
representing, more or less distinctly, those which its remote ancestors
had in common with the lower vertebrata, and that it developed certain
subsidiary organs in like ways with the lower vertebrata, is merely to
state a theory, which, without some evidence that the mammalian embryo
was a formation resulting from a connection of lives with lives back
to a common ancestor whose embryo was developed as those of the lower
vertebrata are, amounts to nothing. Often as this want of evidence has
been adverted to, it must be here again pointed out: for the whole
argument from embryology, like that derived from a comparison of the
forms of mature animals, lacks the support of facts that are essential
to show the connection of life with life which descent from a common
ancestral stock necessarily implies.
On the other hand, the hypothesis of the distinct creation of
different species deals with the phenomena of embryologic life in
a very different way. It supposes the creation of a pair, male and
female, and a law of procreation, designed for the multiplication of
individuals of a fixed type. It supposes many such creations, each
having in its own peculiar germ the characteristic type of organism
that will distinguish the mature animal from all the others. It
supposes finally a law of development common to all the species the
individuals of which are multiplied by the sexual union of male
and female; a law of growth under like conditions, which leads to
a parallelism of development until the typical plan of form and
structure designed for each distinct animal, and implanted in its germ,
begins to take on a mode of development peculiar to that species,
and at length the perfect individual of that species is the result.
In this hypothesis, therefore, there is no necessity for resorting
to any connection with an imaginary ancestral stock of a different
type, or for resorting to a theoretical process by which successive
generations may be supposed to have gradually arisen out of the
ancestral stock by successive changes which have at length resulted
in a totally new species. The new species is what is supposed to have
been aboriginally created, and to have been placed under its own law
for the multiplication of individuals of the same type. In point of
simplicity, of comparative certainty, of freedom from accidental
causes of variation of which we can predicate no specific result, this
hypothesis seems to have a far greater degree of probable evidence in
its favor than the theory which entirely lacks the requisite evidence
of intermediate connections between the lives of one species with the
lives of a remote and different species. For, while it may be truly
said that no man ever saw a special creation take place, and while such
an act of the infinite power is of a nature that places it beyond the
observation of our senses, it is neither inconceivable nor improbable,
nor inconsistent with the idea of the divine attributes which we
derive from the study of nature. On the other hand, it is not only
equally true that no man ever saw, or in the nature of things ever can
see, an evolution of distinct species out of other distinct species,
but the whole nature of the supposed process of transformation involves
an element of chance which forbids all calculation of the results.
How, for example, in this very matter of comparative embryological
development on the hypothesis of descent of all the species of the
vertebrate animals from a common ancestral stock of a different type,
are we to account for the fact that the embryo of any one of the
descended species has come to be developed in a mode peculiar to itself
and differing from the mode in which the embryo of the ancestral stock
was developed? The law of sexual union, under which the individuals
of the supposed ancestral stock were multiplied, must have imposed on
that species an invincible necessity of reproducing in its offspring
the same type that constituted the peculiar organism of the parents,
whether these parents were or were not the fittest survivors of their
race after the severest struggle for existence which they may have had
to undergo. If the pair, or the male of that pair, has in the course
of that struggle acquired a new organ, or more completely developed
an old one, before the act of procreation takes place, how is it that
the ovum is developed into the fœtus, and the fœtus into the newly
born infant, in an invariable mode peculiar to the species to which
the parents belonged? Why did not the same causes of variation which
are supposed to have changed the ancestral type into one of a new and
entirely distinct character, also vary the mode of fœtal development?
When and how did the new organs become fixed in the type which the
parents have transmitted to the offspring? And if they became so
fixed in the germ which was formed out of the cellular substance
contributed by each of the parents, why do we find in every known
species participating in this process of reproduction a uniform mode
of embryologic development peculiar to the species, and exhibiting its
own suppressions and substitutions of organs, irrespective of any newly
acquired peculiarities in the individual structures of the parents?
The believer in special creations has to answer no such questions as
these. His hypothesis assumes the creation of a pair of animals of a
certain distinct species; a law of procreation and gestation common
to a vast multitude of organisms; and a law of embryologic growth
peculiar to each species. Whatever peculiarities of structure may have
been possessed by the immediate parents of any individual of any one
of these different species--peculiarities which did not separate the
parents from their race, but only made them the fittest survivors of
their race--those peculiarities would or would not descend to their
immediate offspring, according to varying and very inappreciable
circumstances. But that which constituted the special type of the
race, and especially that which constituted its peculiar mode of
development during the embryonic stage, would remain unaffected by
these incidental and accidental peculiarities of the parents, because,
from all that we can discover, that special type was impressed upon
the embryo at the earliest stage of its existence, and constituted
the living model that was to be developed into the perfect animal of
that species, by a law which placed it beyond the influence of any
adventitious and non-essential advantages which the male or female
parent may have acquired over other individuals of the same race. So
that, if the postulate of a special creation of species be assumed
as the groundwork of the reasoning, we have to go through with no
speculations about a common ancestral stock of all the species, and
we have to account for no phenomena that are exposed to chances which
might have produced very different results from those which are open to
our observation, and results of which we can predicate nothing with
any degree of certainty. On the hypothesis of the special creation of
a species, and an aboriginal pair of each species, with all that this
implies, we can with a high degree of certainty predicate most of the
phenomena that we have to observe, and more especially so much of the
phenomena of embryologic growth of the different species as are open to
our investigation after the life of both mother and embryo has become
extinct.
It only remains for me to give to this reasoning a concrete
application. Take the case made use of by Mr. Spencer in the passage
above cited--that of the "allantois," a vascular membrane, which is
said to be in the mammalian embryo homologous with one which in the
higher oviparous vertebrates, such as the birds and reptiles, replaces
what was at first a breathing apparatus, and becomes for them, during
the rest of embryonic life, a sort of lung, or an organ that aërates
the blood until the permanent respiratory organs come into play. In
the mammalian embryo, the first appliance for aërating the blood is
described as a system of vessels distributed over the _area vasculosa_,
and like that which is first observable for the same purpose in
fishes. But, as the mammalian embryo continues to grow, a change
takes place. There buds out from it the vascular membrane called the
"allantois," which is substituted in the place of the first aërating
apparatus. Then a further change takes place, as between the higher
oviparous vertebrates and the mammalian vertebrates. In the former, the
"allantois" continues to perform the breathing function through the
rest of the embryonic life. In the mammalian vertebrates it undergoes
two changes: In the implacental mammals, it aborts, having no function
to discharge; in the placental mammals it becomes modified into another
organ, namely, that which serves to convey nutrition from the mother to
the offspring. After birth, it is of course ended.
Now, the reasoning, or rather the assertion, that these substitutions
are unaccountable as the results of design, appears to me to be
singularly inconclusive. It is quite illogical, according to all
philosophic meaning of design as applied to the works of the Creator,
or to the works of nature, if that term is preferred, to argue that
a particular object could have been better accomplished directly,
than by a metamorphosis of an organ from one function to another, or
by substitution. The metamorphosis, or substitution, which in such
cases we find in nature, is of itself the very highest evidence that
the indirect method was the best, if we admit the idea of a Creator,
because it was the method chosen by a being of infinite perfections
for reasons which we may not be able to discover, but which we must
presume to have existed, if we concede that hypothesis of attributes
which "design" in this case necessarily implies. But how are these
metamorphoses and substitutions any more accountable upon the
supposition that the mammalian type arose by generation out of the
lower vertebrate types which in their embryonic life exhibited the same
changes? The doctrine or theory of evolution does not account for them
at all; for, while the doctrine supposes, as matters of pure theory,
that there were certain states through which the mammalian embryo
passed, which represented more or less distinctly those which it had in
common with its assumed remote ancestors, the lower vertebrata, it does
nothing more than to suggest the theoretical idea that the mammalian
embryo came to develop these subsidiary organs in the mode in which
they were developed in the embryo of the lower vertebrata, because it
was descended from the lower vertebrata. The varying states through
which the embryo passed from the lower vertebrata to the mammalian
type, are all hypothetical, and there is, therefore, no basis of
fact on which to rest the belief in a common mode of development, as
resulting from a connection of lives with lives between the mammalian
type and the types of birds, reptiles, or fishes.
On the other hand, the hypothesis of the special creation of a species
implies the simple fact of a designed process of embryonic development
for each species, with substitutions of organs and changes of function
in certain organs peculiar to that species; a fact which may well
consist in a certain parallelism in the different metamorphoses, and
a preservation of the same unvarying changes in the development of
each separate embryo. Why these changes should exist, we can not tell;
but their existence is very strong proof that they were designed, or
made to take place, for some reason, if we admit the hypothesis of a
Creator. For that hypothesis, we must look to a wider class of facts,
and to the whole phenomena of nature.
4. We now come to the argument from distribution. This is one of the
weakest of the indirect supports of the doctrine of evolution; but,
as it is much relied upon, it must be stated with all the force that
it is supposed to have. The facts that are relied upon are these:
When we survey the whole surface of the globe, so far as it is known
to us, we find, in the first place, that the areas which have similar
conditions (of soil and climate), and sometimes, where the areas are
nearly adjacent, are occupied by quite different faunas. On the other
hand, it is said that areas remote from each other in latitude, and
contrasted in soil and climate, are occupied by closely allied faunas.
The inference drawn is, that there is no manifest predetermined
adaptation of the organisms to the areas, or habitats, in which they
are found, because we do not find that like organisms are universally
or generally found in like habitats, nor very unlike organisms in very
unlike habitats. The conclusion is, that the facts of distribution
in space do not conform to the hypothesis of design. In other words,
the different animals found in different regions were not specially
designed for those regions, but some of them have extended into regions
of a different character; and when the regions are very unlike there
are not found very unlike organisms, but there is a general similarity,
or a less extensive variety. There is said, also, to be another
important fact, namely, that "the similar areas peopled by dissimilar
forms are those between which there are impassable barriers; while the
dissimilar areas peopled by similar forms, are those between which
there are no such barriers." Hence is drawn the conclusion that "each
species of organism tends ever to expand its sphere of existence--to
intrude on other areas, other modes of life, other media."[88] A good
deal of aid is supposed to be derived for this argument respecting
animal life by analogies drawn from the vegetable kingdom; but I
can not help thinking that there is much caution to be observed in
formulating such analogies into a law of universal application, or into
one that relates to the existence of animal organisms. The origin,
the multiplication, and the spread of animals involve a principle of
life, organization and development which is very different in some
important respects from that which obtains in the vegetable world.
But, without laying any stress upon this distinction, and without
intending to deprive the argument for animal evolution of any aid which
it can derive from such supposed analogies, I pass to the specific
argument respecting animal distribution. The argument is this: Races
of organisms become distributed over different areas, and also through
different media. They are thrust by the pressure of overpopulation from
their old into new habitats, and as they diverge more widely in space
they undergo more and more modifications of structure, by reason of the
new conditions on which they enter. Thus, these powerfully incident
forces, the new conditions on which the migrating races enter in new
regions, vary the structure which they originally brought with them,
and which descended to them from the common stock of which they were
modified descendants. The widest divergences in space, under such
circumstances, will indicate the longest periods of time during which
these various descendants from a common stock have been subject to
modifying conditions. There will, therefore, come to be, it is said,
among organisms of the same group, smaller contrasts of structure in
the smaller areas; and, where the varying incident forces vary greatly
within given areas, the alterations will become more numerous than in
equal areas which are less variously conditioned: that is to say, in
the most uniform regions there will be the fewest species, and in the
most multiform regions there will be the most numerous species. These
hypotheses are said to be in accordance with the facts of distribution
in space.[89]
But there are also facts of distribution through different media. The
meaning of this is, that, whereas all forms of organisms have descended
from some primordial simplest form, which inhabited some one medium,
such as the water, its descendants, by migration into some other
medium or other media, underwent adaptations to media quite unlike
the original medium. In other words, the earth and the air have been
colonized from the water. Numerous facts are adduced in support of this
conclusion, which are thus summarized:
There are particular habitats in which animals are subject to changes
of media. In such habitats exist animals having, in various degrees,
the power to live in both media, consequent on various phases of
transitional organization. Near akin to these animals, there are some
that, after passing their early lives in the water, acquire more
completely the structures fitting them to live on land, to which
they then migrate. Lastly, we have closely-allied creatures like
the Surinam toad and the terrestrial salamander, which, though they
belong by their structures to the class Amphibia, are not amphibious
in their habits--creatures the larvæ of which do not pass their early
lives in the water, and yet go through these same metamorphoses!
Must we, then, think that the distribution of kindred organisms
through different media presents an insurmountable difficulty? On the
contrary, with facts like these before us, the evolution-hypothesis
supplies possible interpretations of many phenomena that are else
unaccountable. Realizing the way in which such changes of media are
in some cases gradually imposed by physical conditions, and in other
cases voluntarily commenced and slowly increased in the search after
food, we shall begin to understand how, in the course of evolution,
there have arisen those strange obscurations of one type by the
externals of another type. When we see land-birds occasionally feeding
by the water-side, and then learn that one of them, the water-ouzel,
an "anomalous member of the strictly terrestrial thrush family, wholly
subsists by diving--grasping the stones with its feet and using its
wings under water"--we are enabled to comprehend how, under pressure
of population, aquatic habits may be acquired by creatures organized
for aërial life; and how there may eventually arise an ornithic type,
in which the traits of the bird are very much disguised.
Finding among mammals some that, in search of prey or shelter, have
taken to the water in various degrees, we shall cease to be perplexed
on discovering the mammalian structure hidden under a fish-like form,
as it is in the Cetacea. Grant that there has even been going on that
redistribution of organisms which we see still resulting from their
intrusions on one another's areas, media, and modes of life, and we
have an explanation of those multitudinous cases in which homologies
of structure are complicated with analogies. And while it accounts for
the occurrence, in one medium of organic types fundamentally organized
for another medium, the doctrine of evolution accounts also for the
accompanying unfitness. Either the seal has descended from some mammal
which, little by little, became aquatic in its habits, in which
case the structure of its hind-limbs has a meaning; or else it was
specially framed for its present habitat, in which case the structure
of its hind-limbs is incomprehensible.[90]
Along with these phenomena of distribution in space and in medium of
life, we have the further element of distribution in time; the facts
of which are admitted, however, to be too fragmentary to be conclusive
either for or against the doctrine of evolution. Still it is claimed
that there is one general truth respecting distribution in time,
which is "profoundly significant, namely, that the relations between
the extinct forms of life, found by geological exploration, and the
present forms of life, especially in each great geographical region,
show in the aggregate a close kinship, and a connection which is in
perfect harmony with the belief in evolution, but quite irreconcilable
with any other belief. As Mr. Darwin has expressed it, there is 'a
wonderful relationship in the same continent between the living and the
dead.'"[91]
The argument from distribution is thus summed up by Mr. Spencer:
Given, then, that pressure which species exercise on one another,
in consequence of the universal overfilling of their respective
habitats--given the resulting tendency to thrust themselves into one
another's areas, and media, and modes of life, along such lines of
least resistance as from time to time are found--given, besides the
changes in modes of life hence arising, those other changes which
physical alterations of habitats necessitate--given the structural
modifications directly or indirectly produced in organisms by modified
conditions--and the facts of distribution in space and time are
accounted for. That divergence and redivergence of organic forms,
which we saw to be shadowed forth by the truths of classification
and the truths of embryology, we see to be also shadowed forth by
the truths of distribution. If that aptitude to multiply, to spread,
to separate, and to differentiate, which the human races have in
all times shown, be a tendency common to races in general, as we
have ample reason to assume, then there will result that kind of
relation among the species, and genera, and orders, peopling the
earth's surface, which we find exists. Those remarkable identities
of type discovered between organisms inhabiting one medium, and
strangely-modified organisms inhabiting another medium, are at
the same time rendered comprehensible. And the appearances and
disappearances of species which the geological record shows us, as
well as the connections between successive groups of species from
early eras down to our own, cease to be inexplicable.[92]
Passing by what is here said of the aptitude of the human race to
multiply, to spread, to separate, and to differentiate--an aptitude
which has never resulted in the production of an essentially different
animal, or in anything but incidental variations within the limits
of the same species--I propose now to apply to this argument from
distribution a test which seems to me to be a perfectly fair one,
and one which it ought to be able to encounter. If the theory that
the different species of animals now known to us have been evolved
successively by descent from some primordial simplest form through
modifications induced by change of habitation, of medium of life, and
accumulation of new structures occurring through an immense period of
time, be a sound hypothesis, the process which has evolved superior out
of inferior organizations ought, in consistency with itself and with
all its supposed conditions, to be capable of being reversed, so as
to lead to the evolution of inferior out of superior organisms. For,
although the doctrine of evolution has thus far been applied only to
facts which are supposed to show an ascent in the scale of being, the
argument ought to be equally good for a descent in the scale of being,
provided we take care to include all the elements and causes of a
change of structure, mode and medium of life, and the necessary element
of time, in the operation of the process. The imaginary case that is
about to be put shall include all the elements of the evolutionary
hypothesis, and will serve to test at least the rationality of that
theory.
Let it be supposed, then, that there was a period in the history of
this earth when the whole human race, however it originated, was
confined to an island, thousands of miles from any other land. This
race of men adapted to a life in one medium, the air, may be supposed
to have so far advanced in the ruder arts of hunting and fishing,
and in the higher art of tillage, as to be able for many generations
to support life by what the sea and the land would put within their
reach, and by the product which their rude agriculture could extract
from the soil, or which the soil would spontaneously yield. But as the
centuries flow on, the population begins to press upon the resources
of the territory, and the struggle for life becomes very great. At
length a point is reached where the supply of food from the land
becomes inadequate to sustain the population, and what can be made
up from the sea will not supply the deficiency. The population will
then slowly decrease, but, while this decrease goes on, there comes
in a disturbing cause which will prevent any adjustment of the supply
of food to the diminished number of the consumers. The sea begins by
almost imperceptible but steadily progressing encroachments to diminish
the area of dry land; a change of climate reduces the number of other
animals available for human food, and reduces the productive capacity
of the earth. Then ensues that struggle for existence which is supposed
to entail changes of medium of life, and to induce transformations of
structure. The conditions of existence have become wholly changed.
The wretched descendants of a once comparatively thriving race are
dwelling on a territory which has become a marsh. They have no means
of migrating to another territory; they can only migrate to another
medium. They begin by feeding exclusively on what the water will
afford. They pass their lives in the pursuit of a prey which lives
only in the water, and in this change of life they acquire or develop
organs adapted to the new condition, organs which, in such miserable
reproduction of their own species as can go on, they transmit to their
offspring. Modifications upon modifications accumulate in this way
through untold periods of time, until at last a new aquatic or a new
amphibious creature is formed, and the difference between that creature
and his remote ancestral human stock is as great as that between man
and the seal, or between man and any fish that swims. Still, there will
be peculiarities of structure retained, which might lead any inhabitant
of another world, alighting on this globe and undertaking to trace the
origin of this new creature, to the supposition that he was akin to a
race of men whose fossil remains he might find buried in some stratum
beneath the marsh which was the last habitat of this unfortunate race,
when it had all the characteristics of its original type.
Is it conceivable that this transformation could take place? Could such
a condition and situation result in anything but the utter extinction
of the human race, or, in other words, in an absolute break? Could
there be any modifications exhibited by the last survivors of that race
other than those which are familiar to us among the varieties of the
human species which have never separated themselves from their race,
and between whom and their ancestral stock, wherever it was originally
placed on this globe, we recognize no fundamental difference of
structure, whatever may have been the changes of habitat or conditions
of life? Yet the conditions and elements of this imaginary case,
which is simply the process of evolution reversed, are just what the
evolution theory assumes as the causes of that modification which
proceeds from a lower to a higher organism; and whatever may be said of
the tendency, through "the survival of the fittest," to evolve higher
out of lower forms of animal life, if we allow time enough for the
process, there is no reason, in the nature of things, why corresponding
conditions should not lead to a degradation as well as to an elevation
in the scale of beings. There is, however, one reason why no such
potency should be ascribed to the conditions, either in respect to
the one result or the other. That reason is that all such causes of
modification, either in the ascending or the descending scale, are so
limited in their effects that distinct beings can not be rationally
predicated as their product, whereas the power of the Infinite
Artificer to give existence to distinct beings is absolutely without
limit. If naturalists would turn their attention to the limitations
upon the power of all such causes as those which are supposed to work
in the process of evolution, and would give us the explanations to
which those limitations point, in those cases of local variation which
are exhibited by animals that can clearly be traced to a parent form,
they would not be compelled to resort to a sweeping theory that refuses
all force to any hypothesis but its own.
But now let us go a step further in this imaginary case. Let us suppose
that after this new creature, fish or amphibian, descended from the
human race, has inhabited the water surrounding the ill-fated island
for a million of years, another great change takes place. The water
begins to recede from the land by gradations as slow as those by which
in the former period it encroached. The land rises from the low level
to which it had sunk, by volcanic action. Forests spring up upon the
sides of mountains. The soil becomes firm; verdure overspreads the
fields; the climate grows genial; the wilderness blossoms as the rose.
Allow another million years for this restoration of the territory
to an inhabitable condition. Slowly and in an unbroken series of
generations the aquatic creatures, descended from the ancient human
inhabitants of the island, emerge from the sea and betake themselves
to the land. Modifications upon modifications accumulate, new organs
are acquired; the survival of the fittest perpetuates them; the animals
ascend in the scale of being, until the human type is again evolved
out of the degraded descendants of the population which two millions
of years previously dwelt as men upon the island, and carried on in
some primitive fashion the simpler arts of human life. Is not this just
as supposable as the evolution of the human race out of some lower
form of organism? Are not all the elements--time, migration from one
medium to another, change of conditions, and what is supposed to lead
to the production of different organisms--just as powerful to produce
the inferior out of the superior as to produce the superior out of the
inferior, and so on interchangeably? The answer in each case is, that
all such causes of modification in the animal kingdom are limited; that
when once a distinct species is in existence, we have no evidence that
it loses its distinct type or merges itself in another, although the
earth may be full of evidence that types which formerly existed are no
longer among the living organisms.
FOOTNOTES:
[79] "Biology," i, p. 366.
[80] "In the presence of the various genealogical trees of animal
descent which have been put forward so frequently of late, a judicious
skepticism seems the attitude best warranted by the evidence yet
obtained. If so many similar forms have arisen in mutual independence,
then the affinities of the animal kingdom can never be represented by
the symbol of a tree. Rather, we should conceive of the existence of
a grove of trees, closely approximated, greatly differing in age and
size, with their branches interlaced in a most complex entanglement.
The great group of apes is composed of two such branches; but their
relations one to another, to the other branches which represent
mammalian groups, and to the trunks from which such branches diverge,
are problems still awaiting solution."--_"Encyclopædia Britannica,"
article "Apes."_
[81] "Biology," i, pp. 380-382.
[82] I use these terms with quotation-marks, because I do not admit
any philosophical antagonism such as they are intended to imply.
[83] "Homology" is defined by lexicographers as "the doctrine of
similar parts." "Homologous organs" is a term used by scientific
writers to describe organs having a relation of some proportion to
each other. In this particular case of the vertebral column, the
different parts of the column are treated as if they were different
organs, and they are said to be homologous organs in the same animal,
because they bear a certain relation or ratio of proportion to each
other.
[84] See the discussion of how evolution works, _post_.
[85] "Biology," i, p. 387.
[86] The Greek philosophers, as we have seen, before Plato and
Aristotle, found that their systems of causes, which did not involve
the idea of power as abstracted from substance, would not account for
the phenomena of nature. With all their subtilty and ingenuity, they
did not reach the truth that secondary causes are necessarily limited
in their action, and that there must be an unlimited cause.
[87] "Biology," i, pp. 369, 370.
[88] "Biology," i, p. 388.
[89] "Biology," i, pp. 390, 391.
[90] "Biology," i, p. 396.
[91] "Biology," i, p. 399. It is to be noted that the relationship
here referred to is supposed or apparent kinship between the
_aggregate_ of the surviving and the _aggregate_ of the extinct forms
which have died out in recent geologic times. But this does not supply
the steps of descent by which any one surviving form can be traced
back to any one extinct form.
[92] "Biology," i, p. 401.