engine is greater by unity than the preceding number_, which law the
observer had deduced from an induction of a hundred million instances,
_was not the true law that regulated its action_, and that the occurrence
of the number 100,010,002 at the 100,000,002nd term was _as necessary a
consequence of the original adjustment_, _and might have been as fully
foreknown at the commencement_, _as was the regular succession of any one
of the intermediate numbers to its immediate antecedent_. The same
remark applies to the next apparent deviation from the new law, which was
founded on an induction of 2761 terms, and also to the succeeding law,
with this limitation only—that, whilst their consecutive introduction at
various definite intervals, is a necessary consequence of the mechanical
structure of the engine, our knowledge of analysis does not enable us to
predict the periods themselves at which the more distant laws will be
introduced.”
It is not difficult to apply the philosophy of this passage to the
question under consideration. It must be borne in mind that the
gestation of a single organism is the work of but a few days, weeks, or
months; but the gestation (so to speak) of a whole creation is a matter
probably involving enormous spaces of time. Suppose that an ephemeron,
hovering over a pool for its one April day of life, were capable of
observing the fry of the frog in the water below. In its aged afternoon,
having seen no change upon them for such a long time, it would be little
qualified to conceive that the external branchiæ of these creatures were
to decay, and be replaced by internal lungs, that feet were to be
developed, the tail erased, and the animal then to become a denizen of
the land. Precisely such may be our difficulty in conceiving that any of
the species which people our earth is capable of advancing by generation
to a higher type of being. During the whole time which we call the
historical era, the limits of species have been, to ordinary observation,
rigidly adhered to. But the historical era is, we know, only a small
portion of the entire age of our globe. We do not know what may have
happened during the ages which preceded its commencement, as we do not
know what may happen in ages yet in the distant future. All, therefore,
that we can properly infer from the apparently invariable production of
like by like is, that such is the ordinary procedure of nature in the
time immediately passing before our eyes. Mr. Babbage’s illustration
powerfully suggests that this ordinary procedure may be subordinate to a
higher law which only _permits_ it for a time, and in proper season
interrupts and changes it. We shall soon see some philosophical evidence
for this very conclusion.
It has been seen that, in the reproduction of the higher animals, the new
being passes through stages in which it is successively fish-like and
reptile-like. But the resemblance is not to the adult fish or the adult
reptile, but to the fish and reptile at a certain point in their fœtal
progress; this holds true with regard to the vascular, nervous, and other
systems alike. It may be illustrated by a simple diagram. The fœtus of
all the four classes may be supposed to advance in an identical condition
to the point A. [Picture: Diagram] The fish there diverges and passes
along a line apart, and peculiar to A itself, to its mature state at F.
The reptile, bird, and mammal, go on together to C, where the reptile
diverges in like manner, and advances by itself to R. The bird diverges
at D, and goes on to B. The mammal then goes forward in a straight line
to the highest point of organization at M. This diagram shews only the
main ramifications; but the reader must suppose minor ones, representing
the subordinate differences of orders, tribes, families, genera, &c., if
he wishes to extend his views to the whole varieties of being in the
animal kingdom. Limiting ourselves at present to the outline afforded by
this diagram, it is apparent that the only thing required for an advance
from one type to another in the generative process is that, for example,
the fish embryo should not diverge at A, but go on to C before it
diverges, in which case the progeny will be, not a fish, but a reptile.
To protract the _straightforward part of the gestation over a small
space_—and from species to species the space would be small indeed—is all
that is necessary.
This might be done by the force of certain external conditions operating
upon the parturient system. The nature of these conditions we can only
conjecture, for their operation, which in the geological eras was so
powerful, has in its main strength been long interrupted, and is now
perhaps only allowed to work in some of the lowest departments of the
organic world, or under extraordinary casualties in some of the higher,
and to these points the attention of science has as yet been little
directed. But though this knowledge were never to be clearly attained,
it need not much affect the present argument, provided it be
satisfactorily shewn that there must be some such influence within the
range of natural things.
To this conclusion it must be greatly conducive that the law of organic
development is still daily seen at work to certain effects, only somewhat
short of a transition from species to species. Sex we have seen to be a
matter of development. There is an instance, in a humble department of
the animal world, of arrangements being made by the animals themselves
for adjusting this law to the production of a particular sex. Amongst
bees, as amongst several other insect tribes, there is in each community
but one true female, the queen bee, the workers being false females or
neuters; that is to say, sex is carried on in them to a point where it is
attended by sterility. The preparatory states of the queen bee occupy
sixteen days; those of the neuters, twenty; and those of males,
twenty-four. Now it is a fact, settled by innumerable observations and
experiments, that the bees can so modify a worker in the larva state,
that, when it emerges from the pupa, it is found to be a queen or true
female. For this purpose they enlarge its cell, make a pyramidal hollow
to allow of its assuming a vertical instead of a horizontal position,
keep it warmer than other larvæ are kept, and feed it with a peculiar
kind of food. From these simple circumstances, leading to a shortening
of the embryotic condition, results a creature different in form, and
also in dispositions, from what would have otherwise been produced. Some
of the organs possessed by the worker are here altogether wanting. We
have a creature “destined to enjoy love, to burn with jealousy and anger,
to be incited to vengeance, and to pass her time without labour,” instead
of one “zealous for the good of the community, a defender of the public
rights, enjoying an immunity from the stimulus of sexual appetite and the
pains of parturition; laborious, industrious, patient, ingenious,
skilful; incessantly engaged in the nurture of the young, in collecting
honey and pollen, in elaborating wax, in constructing cells and the
like!—paying the most respectful and assiduous attention to objects
which, had its ovaries been developed, it would have hated and pursued
with the most vindictive fury till it had destroyed them!” {215} All
these changes may be produced by a mere modification of the embryotic
progress, which it is within the power of the adult animals to effect.
But it is important to observe that this modification is different from
working a direct change upon the embryo. It is not the different food
which effects a metamorphosis. All that is done is merely to accelerate
the period of the insect’s perfection. By the arrangements made and the
food given, the embryo becomes sooner fit for being ushered forth in its
imago or perfect state. Development may be said to be thus arrested at a
particular stage—that early one at which the female sex is complete. In
the other circumstances, it is allowed to go on four days longer, and a
stage is then reached between the two sexes, which in this species is
designed to be the perfect condition of a large portion of the community.
Four days more make it a perfect male. It is at the same time to be
observed that there is, from the period of oviposition, a destined
distinction between the sexes of the young bees. The queen lays the
whole of the eggs which are designed to become workers, before she begins
to lay those which become males. But probably the condition of her
reproductive system governs the matter of sex, for it is remarked that
when her impregnation is delayed beyond the twenty-eighth day of her
entire existence, she lays only eggs which become males.
We have here, it will be admitted, a most remarkable illustration of the
principle of development, although in an operation limited to the
production of sex only. Let it not be said that the phenomena concerned
in the generation of bees may be very different from those concerned in
the reproduction of the higher animals. There is a unity throughout
nature which makes the one case an instructive reflection of the other.
We shall now see an instance of development operating within the
production of what approaches to the character of variety of species. It
is fully established that a human family, tribe, or nation, is liable, in
the course of generations, to be either advanced from a mean form to a
higher one, or degraded from a higher to a lower, by the influence of the
physical conditions in which it lives. The coarse features, and other
structural peculiarities of the negro race only continue while these
people live amidst the circumstances usually associated with barbarism.
In a more temperate clime, and higher social state, the face and figure
become greatly refined. The few African nations which possess any
civilization also exhibit forms approaching the European; and when the
same people in the United States of America have enjoyed a within-door
life for several generations, they assimilate to the whites amongst whom
they live. On the other hand, there are authentic instances of a people
originally well-formed and good-looking, being brought, by imperfect diet
and a variety of physical hardships, to a meaner form. It is remarkable
that prominence of the jaws, a recession and diminution of the cranium,
and an elongation and attenuation of the limbs, are peculiarities always
produced by these miserable conditions, for they indicate an unequivocal
retrogression towards the type of the lower animals. Thus we see nature
alike willing to go back and to go forward. Both effects are simply the
result of the operation of the law of development in the generative
system. Give good conditions, it advances; bad ones, it recedes. Now,
perhaps, it is only because there is no longer a possibility, in the
higher types of being, of giving sufficiently favourable conditions to
carry on species to species, that we see the operation of the law so far
limited.
Let us trace this law also in the production of certain classes of
monstrosities. A human fœtus is often left with one of the most
important parts of its frame imperfectly developed: the heart, for
instance, goes no farther than the three-chambered form, so that it is
the heart of a reptile. There are even instances of this organ being
left in the two-chambered or fish form. Such defects are the result of
nothing more than a failure of the power of development in the system of
the mother, occasioned by weak health or misery. Here we have apparently
a realization of the converse of those conditions which carry on species
to species, so far, at least, as one organ is concerned. Seeing a
complete specific retrogression in this one point, how easy it is to
imagine an access of favourable conditions sufficient to reverse the
phenomenon, and make a fish mother develop a reptile heart, or a reptile
mother develop a mammal one. It is no great boldness to surmise that a
super-adequacy in the measure of this under-adequacy (and the one thing
seems as natural an occurrence as the other) would suffice in a goose to
give its progeny the body of a rat, and produce the ornithorynchus, or
might give the progeny of an ornithorynchus the mouth and feet of a true
rodent, and thus complete at two stages the passage from the aves to the
mammalia.
Perhaps even the transition from species to species does still take place
in some of the obscurer fields of creation, or under extraordinary
casualties, though science professes to have no such facts on record. It
is here to be remarked, that such facts might often happen, and yet no
record be taken of them, for so strong is the prepossession for the
doctrine of invariable like-production, that such circumstances, on
occurring, would be almost sure to be explained away on some other
supposition, or, if presented, would be disbelieved and neglected.
Science, therefore, has no such facts, for the very same reason that some
small sects are said to have no discreditable members—namely, that they
do not receive such persons, and extrude all who begin to verge upon the
character. There are, nevertheless, some facts which have chanced to be
reported without any reference to this hypothesis, and which it seems
extremely difficult to explain satisfactorily upon any other. One of
these has already been mentioned—a progression in the forms of the
animalcules in a vegetable infusion from the simpler to the more
complicated, a sort of microcosm, representing the whole history of the
progress of animal creation as displayed by geology. Another is given in
the history of the Acarus Crossii, which may be only the ultimate stage
of a series of similar transformations effected by electric agency in the
solution subjected to it. There is, however, one direct case of a
translation of species, which has been presented with a respectable
amount of authority. {221} It appears that, whenever oats sown at the
usual time are kept cropped down during summer and autumn, and allowed to
remain over the winter, a thin crop of rye is the harvest presented at
the close of the ensuing summer. This experiment has been tried
repeatedly, with but one result; invariably the _secale cereale_ is the
crop reaped where the _avena sativa_, a recognised different species, was
sown. Now it will not satisfy a strict inquirer to be told that the
seeds of the rye were latent in the ground and only superseded the dead
product of the oats; for if any such fact were in the case, why should
the usurping grain be always rye? Perhaps those curious facts which have
been stated with regard to forests of one kind of trees, when burnt down,
being succeeded (without planting) by other kinds, may yet be found most
explicable, as this is, upon the hypothesis of a progression of species
which takes place under certain favouring conditions, now apparently of
comparatively rare occurrence. The case of the oats is the more
valuable, as bearing upon the suggestion as to a protraction of the
gestation at a particular part of its course. Here, the generative
process is, by the simple mode of cropping down, kept up for a whole year
beyond its usual term. The type is thus allowed to advance, and what was
oats becomes rye.
The idea, then, which I form of the progress of organic life upon the
globe—and the hypothesis is applicable to all similar theatres of vital
being—is, _that the simplest and most primitive type_, _under a law to
which that of like-production is subordinate_, _gave birth to the type
next above it_, _that this again produced the next higher_, _and so on to
the very highest_, the stages of advance being in all cases very
small—namely, from one species only to another; so that the phenomenon
has always been of a simple and modest character. Whether the whole of
any species was at once translated forward, or only a few parents were
employed to give birth to the new type, must remain undetermined; but,
supposing that the former was the case, we must presume that the moves
along the line or lines were simultaneous, so that the place vacated by
one species was immediately taken by the next in succession, and so on
back to the first, for the supply of which the formation of a new
germinal vesicle out of inorganic matter was alone necessary. Thus, the
production of new forms, as shewn in the pages of the geological record,
has never been anything more than a new stage of progress in gestation,
an event as simply natural, and attended as little by any circumstances
of a wonderful or startling kind, as the silent advance of an ordinary
mother from one week to another of her pregnancy. Yet, be it remembered,
the whole phenomena are, in another point of view, wonders of the highest
kind, for in each of them we have to trace the effect of an Almighty Will
which had arranged the whole in such harmony with external physical
circumstances, that both were developed in parallel steps—and probably
this development upon our planet is but a sample of what has taken place,
through the same cause, in all the other countless theatres of being
which are suspended in space.
This may be the proper place at which to introduce the preceding
illustrations in a form calculated to bring them more forcibly before the
mind of the reader. The following table was suggested to me, in
consequence of seeing the scale of animated nature presented in Dr.
Fletcher’s Rudiments of Physiology. Taking that scale as its basis, it
shews the wonderful parity observed in the progress of creation, as
presented to our observation in the succession of fossils, and also in
the fœtal progress of one of the principal human organs. {224} This
scale, it may be remarked, was not made up with a view to support such an
hypothesis as the present, nor with any apparent regard to the history of
fossils, but merely to express the appearance of advancement in the
orders of the Cuvierian system, assuming, as the criterion of that
advancement, “an increase in the number and extent of the manifestations
of life, or of the relations which an organized being bears to the
external world.” Excepting in the relative situation of the annelida and
a few of the mammal orders, the parity is perfect; nor may even these
small discrepancies appear when the order of fossils shall have been
further investigated, or a more correct scale shall have been formed.
Meanwhile, it is a wonderful evidence in favour of our hypothesis, that a
scale formed so arbitrarily should coincide to such a nearness with our
present knowledge of the succession of animal forms upon earth, and also
that both of these series should harmonize so well with the view given by
modern physiologists of the embryotic progress of one of the organs of
the highest order of animals.
[Picture: Complex table of animal kingdom] {226}
The reader has seen physical conditions several times referred to, as to
be presumed to have in some way governed the progress of the development
of the zoological circle. This language may seem vague, and, it may be
asked,—can any particular physical condition be adduced as likely to have
affected development? To this it may be answered, that air and light are
probably amongst the principal agencies of this kind which operated in
educing the various forms of being. Light is found to be essential to
the development of the individual embryo. When tadpoles were placed in a
perforated box, and that box sunk in the Seine, light being the only
condition thus abstracted, they grew to a great size in their original
form, but did not pass through the usual metamorphose which brings them
to their mature state as frogs. The proteus, an animal of the frog kind,
inhabiting the subterraneous waters of Carniola, and which never acquires
perfect lungs so as to become a land animal, is presumed to be an example
of arrested development, from the same cause. When, in connexion with
these facts, we learn that human mothers living in dark and close cells
under ground,—that is to say, with an inadequate provision of air and
light,—are found to produce an unusual proportion of defective children,
{229} we can appreciate the important effects of both these physical
conditions in ordinary reproduction. Now there is nothing to forbid the
supposition that the earth has been at different stages of its career
under different conditions, as to both air and light. On the contrary,
we have seen reason for supposing that the proportion of carbonic acid
gas (the element fatal to animal life) was larger at the time of the
carboniferous formation than it afterwards became. We have also seen
that astronomers regard the zodiacal light as a residuum of matter
enveloping the sun, and which was probably at one time denser than it is
now. Here we have the indications of causes for a progress in the
purification of the atmosphere and in the diffusion of light during the
earlier ages of the earth’s history, with which the progress of organic
life may have been conformable. An accession to the proportion of
oxygen, and the effulgence of the central luminary, may have been the
immediate prompting cause of all those advances from species to species
which we have seen, upon other grounds, to be necessarily supposed as
having taken place. And causes of the like nature may well be supposed
to operate on other spheres of being, as well as on this. I do not
indeed present these ideas as furnishing the true explanation of the
progress of organic creation; they are merely thrown out as hints towards
the formation of a just hypothesis, the completion of which is only to be
looked for when some considerable advances shall have been made in the
amount and character of our stock of knowledge.