DEVELOPMENT.
‘Are God and Nature then at strife,
That Nature lends such evil dreams?
So careful of the type she seems,
So careless of the single life;
* * * * *
‘“So careful of the type”? but no,
From scarped cliff and quarried stone
She cries, “A thousand types are gone:
I care for nothing, all shall go.”’—TENNYSON.
‘_All nature is but art_, unknown to thee;
_All chance, direction_, which thou canst not see,
All discord, harmony not understood;
All partial evil, universal good;
And spite of pride, in erring reason’s spite,
One truth is clear, whatever is, is right.’—POPE.
154. In the two preceding Chapters we have dwelt upon the laws of
energy and the ultimate constitution of matter; in other words,
we have discussed the laws according to which the machine called
the visible universe works, as well as the probable nature of the
material of which it is composed. We have in this process (Arts.
86, 151) come to the conclusion that the visible universe has been
developed out of the invisible. Once developed, it has its own laws
of action which we may discover,—laws which at present appear to
be invariably followed, as far at least as our strictly scientific
experience can inform us.
In fine, the visible universe is that which we are in a position to
observe; gaining an insight into its present method of working, and
trying also to reply to the very interesting question, Has it always
worked in its present manner, or has there ever been any apparent
break?
Let us therefore consider this visible universe immediately after its
production, and endeavour to become acquainted with the course of its
development. What did it do? Was it, or was it not, entirely left to
itself, and to what may be termed the natural laws impressed upon
it when it was produced? Or, if the results of our inquiry seem to
show that it was not entirely left to itself, when, to what extent,
and for what purposes, has there been and is there interference
proceeding from the unseen?
In replying to these questions, let us, for the sake of convenience,
consider development under the three following heads, viz., (α)
Chemical or Stuff Development, (β) Globe Development, (γ) Life
Development.
155. Beginning with chemical or stuff development, we come at once to
a very interesting and important question. Assuming that the atoms
of the present universe were developed from the invisible, were
different kinds of atoms thus developed, or were they all of one kind?
To this question the chemist of last century would have replied, that
undoubtedly there were many kinds of primeval atoms, and then would
follow a formidable list of all these various substances which he
was unable to decompose.
The chemist of thirty or forty years later would still have replied
to the question in the same way, but he would probably have furnished
a different list of primeval elements less formidable in number.
If the chemist of forty years ago had been asked, he would have
furnished a list of perhaps fifty simple substances; but then,
probably, the minimum would have been reached; for ask the chemist of
to-day, and he will furnish a list of sixty-four so-called elements.
156. But while the number of as yet undecomposed bodies is slowly
increasing by fresh discoveries, chemists are beginning to speculate
as to the possibility that these so-called elements may be in reality
nothing more than combinations differing in numbers and in tactical
arrangement, of some one kind of primordial atoms.
This idea was first entertained by Dr. Prout, the well-known
physician and chemist. He pointed out that the atomic weights of the
various so-called elements are very nearly all multiples of the half
of that of hydrogen, so that the various elements may possibly be
looked upon as formed by a grouping together of certain atoms of half
the mass of the hydrogen atom.
M. Stas, the distinguished Belgian chemist, instituted a laborious
series of experiments with the view of testing this doctrine. He came
to the conclusion that the atomic weights of the various elements
were not precisely multiples of the half of that of hydrogen, there
being greater differences than could possibly be accounted for by
errors of experiment. His researches, however, seemed to show that
in many cases there was a very near approach to Prout’s imagined
law. But in no case does the discrepance appear to us greatly to
exceed what may easily be attributed to unavoidable impurities in the
substances operated on; say only those due to the condensation of
gases in the pores of solids, which (in certain cases at least) is
known to amount to a very considerable quantity.
157. From another point of view there appears to be evidence in
favour of the so-called elementary bodies being built up, as more or
less complex arrangements of one, or at most a few, simpler kinds of
matter.
There are certain groups or families amongst these elements of such a
nature that the various members of one family appear to be related to
each other, in the same way as the corresponding members of another
family.
This clearly points to some sort of community of origin, and
thus favours the idea that the elements are in reality composite
structures. But the great difficulty felt by those who have favoured
this idea has been the apparent impossibility of decomposing such
family groups. Thus fluorine, chlorine, bromine, and iodine, while
they appear to be related to one another in some peculiar manner,
have yet apparently resisted all attempts at decomposition, and there
are other similar instances which might easily be named.
158. It has, however, at the same time, come to be recognised, that
heat of high temperature is a very powerful decomposing agent, and
that its office is by no means limited to causing the separation
from one another of the molecules of a substance, as, for instance,
when it separates the molecules of water-substance or H_{2}O from
one another, as in forming water from ice, or steam from water. It
is now understood that high-temperature heat has also the power of
separating the atomic constituents of a single molecule from each
other, so that at an extremely high temperature not only would water
be driven into steam, but steam driven into oxygen and hydrogen. We
are already familiar with many instances of this power possessed by
high-temperature heat; thus we see carbonate of lime decomposed by
the heat of the kiln into lime and carbonic-acid gas. We see also
that at the high temperatures which accompany the electric spark
almost all compounds are momentarily decomposed, if we may judge
by the spectrum of the light which is given out. Carrying on this
line of thought, we are led to imagine that, could we obtain higher
temperatures than those now at our disposal, we might decompose some
of those substances which at present seem to be elements.
159. Lockyer, in his astronomical researches, has recently started
this question. He argues that in the sun and stars, and more
especially in the whiter stars, there are temperatures very much
higher than any which have been here produced. He assumes too
that simplicity of constitution accompanies a simple spectrum, an
hypothesis which is consistent with the fact that compounds as a rule
give spectra much more complicated than those of simple substances.
Now it is a curious circumstance that the atmospheres of some of
the whiter stars, such as Sirius, do not appear to contain anything
but hydrogen; at least we have no indication that they do; other
stars, again, of less whiteness, in addition to hydrogen, have such
substances as iron, sodium, etc., while yellow, orange, and blood-red
stars and variable stars, appear to contain in their atmospheres
substances which are compounds. If then it be true that as a rule the
atmospheres of the whiter stars contain the fewer elements and those
of smallest atomic weight, and that as stars diminish in whiteness
their atmospheres rise in complexity of structure, in fine, if we
have reason to associate together whiteness and simplicity, this
undoubtedly tells in favour of the power of high-temperature heat to
split up the so-called elements.
We conclude the whiter stars to be the hotter stars, from the
fact that their spectra contain a greater proportion of the more
refrangible rays than do those of yellow or red stars.
In fine, a speculation of this nature is not to be summarily
dismissed, but ought to be retained as a working hypothesis which
may in time throw great light on the ultimate constitution of the
chemical elements. Is it fanciful to suppose that the passage
prefixed to Chapter III. may refer to this, since (literally
translated) it stands—‘... the elements, intensely heated, shall be
broken up....’?
160. Let us now turn to globe development. We have alluded to this
already while discussing the energy of the universe. In doing so
we came to the conclusion that the original state of the visible
universe was a diffused or chaotic state, in which the various
particles were widely separated from one another, but exerting on
one another gravitating force, and therefore possessed of potential
energy. As these particles came together, impinged on one another, or
gathered into groups, this potential energy was gradually transformed
into the energy of heat and into that of visible motion. We may
thus imagine the cooling and (except under very strict conditions
of original distribution) _necessarily_ revolving matter in course
of time to have thrown off certain parts of itself which would
thereafter form satellites or planetary attendants, while the central
mass would form the sun. We have here, in fact, the development
hypothesis of Kant and Laplace, and it is greatly in favour of the
truth of this hypothesis that all the planetary motions of the solar
system are nearly in one plane, and also that, looking down on the
system from above that plane, all these motions are seen to be in one
and the same direction.
161. Assuming, therefore, that the solar system and, _pari passu_,
the other sidereal systems have been formed in this way, it is very
easy to see why the central mass should be so much hotter than its
attendants. Two causes would conduce to this. In the first place,
assuming that the heat of a mass is due to the rushing together
of its particles under the force of gravitation, the velocities
would be much greater for the central mass, and hence the amount of
heat (per unit of mass, _i.e._ the temperature) developed would be
greater also. In the next place, the body being a large one would
cool less rapidly than its attendant planets. These two causes thus
combine to render the largest bodies of the universe ever since their
aggregation (and still more now) the hottest, so that the same
body which forms the gravitating centre of the system becomes, when
required, also the dispenser of light and heat.
162. Now, without speculating about the nature or extent of the
ethereal medium, we may be sure of two things. In the first place,
all but an exceedingly small fraction of the light and heat of
the sun and stars goes out into space and does not return to them
again, or in other words, the sun and stars are slowly cooling. To
restore to the sun every instant its losses by radiation, the whole
celestial vault would have to radiate as powerfully as the sun
does—in which case the earth and planets would very soon acquire (at
their surfaces) the sun’s temperature. In the next place, the visible
motion of the large bodies of the universe is gradually being stopped
by something which may be denominated ethereal friction. It follows
from this that our own sun will gradually lose his brilliancy, and
that our earth will gradually lose its orbital energy and approach
the sun in a path of slowly contracting spiral convolutions. At last
it will become entangled with the sun, and the result will be the
conversion of the remaining orbital energy into heat, after which the
two bodies will remain one.
Thus the tendency is that the sun shall ultimately absorb the
various planets of the system, his heat and energy being recruited
by the process. Now, let us imagine that the same processes are
simultaneously going on in one of the nearer fixed stars, say for
instance in Sirius.
After unimaginable ages these two stars, the Sun and Sirius, having
each long since swallowed up his attendants, but being nevertheless
exhausted in heat-energy on account of radiation into space, may be
imagined to be travelling towards one another, slowly at first, but
afterwards with an accelerated motion.
They will at last approach each other with a great velocity, and
finally form one system. Ultimately the two will rush together and
form one mass, the orbital energy of each (or rather that portion of
this energy which remains after ethereal friction) being converted
into heat, and the matter being, in consequence, probably partly
smashed into mere dust, and partly evaporated and transformed into
a gaseous, nebulous condition. Ages pass away, and the large double
mass ultimately shares the same fate that long since overtook the
single masses which composed it; that is to say, it shrinks and
throws off planets, but gives out the greater part of its light
and heat into space and gradually becomes cold and dark, until at
length it comes to form one of the constituents of a still more
stupendous collision, and has its temperature raised once again by
the conversion of visible energy into heat.
163. Our readers will remark how, by a process of this kind, the
primordial potential energy of the visible universe is gradually
converted into light and heat, and how this light and heat are
ultimately dissipated into space. They will also remark that, as the
process goes on, the masses of the universe become larger and larger.
In fine, the dissipation of the energy of the visible universe
proceeds, _pari passu_, with the aggregation of mass.
The very fact, therefore, that the large masses of the visible
universe are of finite size, is sufficient to assure us that the
process cannot have been going on for ever; or, in other words, that
the visible universe must have had its origin in time, and we may
conclude that if the visible universe be finite in mass the process
will ultimately come to an end. All this is what would take place,
provided we allow the indestructibility of ordinary matter; but we
may perhaps suppose (Art. 153) that the very material of the visible
universe will ultimately vanish into the invisible.
164. There is one peculiarity of the process of development just
described, which we beg our readers to note. We have supposed the
visible universe, after its production, to have been left to its
own laws; that is to say, to certain so-called inorganic agencies,
which for want of better knowledge we for the present call forces,
in virtue of which its development took place.[51] At the very first
there may have been only one kind of primordial atom, or, to use
another expression, absolute simplicity of material. As, however, the
various atoms approached each other, in virtue of the forces with
which they were endowed, other and more complicated structures took
the place of the perfectly simple primordial stuff. Various kinds of
molecules were produced at various temperatures, and these ultimately
came together to produce globes or worlds, some of them comparatively
small, others very large. Thus the progress is from the regular to
the irregular. And we find a similar progress when we consider the
inorganic development of our own world. The action of water rounds
pebbles, but it rounds them irregularly; it produces soil, but
the soil is irregular in the size of its grains, and variable in
constitution. Wherever what may be termed the brute forces of nature
are left to themselves, this is always the result: not so, however,
when organisms are concerned in the development. Two living things
of the same family are more like each other than two grains of sand
or than two particles of soil. The eggs of birds of the same family,
the corresponding feathers of similar birds, the ants from the same
ant-hill, all form groups whose members have a very strong likeness
to each other.
We find this likeness still more marked when we regard certain
products of human industry. Let us take, for instance, coins from the
same die, or bullets from the same mould, or impressions from the
same engraved plate, and we at once perceive the striking difference
between products developed through inorganic means and those
developed through an intelligent agent designing uniformity.
165. Let us now proceed to consider life development. Let us imagine
that the primeval atoms have long since come together, various
chemical substances being the result. And let us further imagine
that these various substances have long since gathered themselves
into worlds, of various sizes at first; but that these worlds have
gradually cooled down, until one of them, the Earth, let us say, has
at length reached conditions under which life (such as we know it)
becomes possible. Accordingly life makes its appearance; not the life
that now is, but something much ruder and simpler. But in process of
time we find quite a different order of organised beings; a higher
and more complete type has appeared, and the type continues to rise
until it culminates in the production of man, a being endowed with
intelligence, and capable of reasoning upon the phenomena around him.
Now, if man reviews these organised forms which exist on the earth
side by side with himself, he perceives at once that a number of
individuals possess certain characteristics in common, and he gives
expression to this experience by saying that these individuals are
all of one species. ‘When we call a group of animals or of plants a
species,’ says Professor Huxley,[52] ‘we may imply thereby, either
that all these animals or plants have some common peculiarity of form
or structure; or we may mean that they possess some common functional
character. That part of biological science which deals with form
and structure is called Morphology; that which concerns itself with
function, Physiology. So that we may conveniently speak of these
two senses, or aspects, of “species”—the one as morphological, the
other as physiological.... Thus horses form a species, because the
group of animals to which that name is applied is distinguished
from all others in the world by the following constantly associated
characters:—They have, 1. a vertebral column; 2. mammae; 3. a
placental embryo; 4. four legs; 5. a single well-developed toe in
each foot, provided with a hoof; 6. a bushy tail; and 7. callosities
on the inner sides of both the fore and the hind legs. The asses,
again, form a distinct species, because, with the same characters, as
far as the fifth in the above list, all asses have tufted tails, and
have callosities only on the inner side of the fore legs.’
But very often the morphological peculiarities of a species are
more easily recognised than expressed. No one, for instance, would
fail to rank the horse as one species and the ass as another, even
while ignorant of some of those specific peculiarities which the
naturalist selects as conveying the best scientific account of their
difference.
166. Let us now regard the question of species from its physiological
point of view. Suppose that two individuals, A and B, of different
sexes, breed freely together, producing offspring, and that two
individuals, C and D, do the like.
Now, if the offspring of A and B is capable of breeding freely with
that of C and D, producing offspring, generation after generation,
then A, B, C, and D may be said to belong to the same physiological
species.
To take an illustration borrowed from Professor Huxley: let us
imagine that A is an Arab, and B a dray-horse; also that C is a
dray-horse, and D an Arab. Now the progeny of these two pairs will
all be mongrels, holding a position intermediate between that of the
Arab and the dray-horse; but they will be perfectly fertile amongst
themselves when matched together. We therefore conclude that the
dray-horse and the Arab are not distinct physiological species, but
only varieties of the same species. Again, let A be a horse and B an
ass, also let C be an ass and D a horse. The pairs will still have
offspring, and these will be mules, having a character intermediate
between that of the horse and that of the ass; but, on the other
hand, these mules will not be able to breed together amongst
themselves so as to produce offspring. We are therefore justified
in asserting that a horse and an ass are of different physiological
species.
If we should ever attempt to pair together animals much more unlike
each other than the horse and the ass, we should simply fail. They
will not come together, and we cannot tell whether, if they did, they
would be capable of producing progeny. We may therefore conclude
that, as matter of fact, there are certain well-marked physiological
species that will not breed with each other at all, while there are
other species also physiologically distinct, but not so markedly
separated from each other, that may be brought to breed together,
their offspring being infertile.
167. The most apparent conclusion to be deduced from these
facts would be that of the invariability of species, and of the
impossibility of its transmutation—the infertility of hybrids being
the law which prevents any such transmutation from taking place. And
as the physiological species cannot be made different the apparent
conclusion is that in times past they have been always the same as
they are now. If this be allowed, it follows that inasmuch as they
took their origin in time, they must have originally been produced
very much as they are at the present moment,—a separate act of
production being required for each species, or rather two separate
acts for each species. This position has always been regarded as
a stronghold by a certain class of theological thinkers, and they
have resented the attempts of men of science to obtain any other
explanation of the origin of species.
Men of science have, on the other hand, asserted their right to
discuss this question with the same freedom as any other. Our
point of view is somewhat different from that of either of these
two parties. We think it is not so much the right or privilege as
the bounden duty of the man of science to put back the direct
interference of the Great First Cause—the unconditioned—as far as he
possibly can in time. This is the intellectual or rather theoretical
work which he is called upon to do—the post that has been assigned to
him in the economy of the universe.
If, then, two possible theories of the production of any phenomenon
are presented to the man of science, one of these implying the
immediate operation of the unconditioned, and the other the operation
of some cause existing in the universe, we conceive that he is called
upon by the most profound obligations of his nature and work to
choose the second in preference to the first. But we have already
sufficiently discussed this question in a previous part of this book
(Art. 85).
168. When we examine closely into the phenomena of life we find that
side by side with the general law, that like produces like, there is
a tendency to minor variations.
Thus we have already agreed to consider dray-horses and Arabs as
varieties of the species horse; and in like manner pouters, carriers,
fan-tails, and tumblers are all varieties of the species rock-pigeon.
We are therefore led to ask how such varieties were originally
produced, and how they become perpetuated after their production.
Now it is well known that there occurs occasionally an accountable
variation, so marked in its nature as to be worthy of historical
record. Two very interesting and instructive instances of this are
given by Professor Huxley, and we take the liberty of quoting these
in the Professor’s own words:—
‘The first of them is that of the “Ancon,” or “Otter” sheep,
of which a careful account is given by Colonel David Humphreys,
F.R.S., in a letter to Sir Joseph Banks, published in the
_Philosophical Transactions_ for 1813. It appears that one Seth
Wright, the proprietor of a farm on the banks of the Charles
River in Massachusetts, possessed a flock of fifteen ewes and
a ram of the ordinary kind. In the year 1791, one of the ewes
presented her owner with a male lamb differing, for no assignable
reason, from its parents by a proportionally long body and
short bandy legs, whence it was unable to emulate its relatives
in those sportive leaps over the neighbours’ fences, in which
they were in the habit of indulging, much to the good farmer’s
vexation.
* * * * *
‘With the ’cuteness characteristic of their nation, the
neighbours of the Massachusetts farmer imagined it would be
an excellent thing if all his sheep were imbued with the
stay-at-home tendencies enforced by nature upon the newly
arrived ram, and they advised Wright to kill the old patriarch
of his fold, and install the Ancon ram in his place. The result
justified their sagacious anticipations.... The young lambs were
almost always either pure Ancons or pure ordinary sheep. But
when sufficient Ancon sheep were obtained to interbreed with one
another it was found that the offspring was always pure Ancon.’
‘The second case is that detailed by a no less unexceptionable
authority than Réaumur, in his _Art de faire éclore les Poulets_.
A Maltese couple named Kelleia, whose hands and feet were
constructed upon the ordinary human model, had born to them
a son, Gratio, who possessed six perfectly moveable fingers
on each hand, and six toes, not quite so well formed, on each
foot. No cause could be assigned for the appearance of this
unusual variety of the human species. But however they may have
arisen, what especially interests us is to remark that, once in
existence, varieties obey the fundamental law of reproduction,
that like tends to produce like, and their offspring exemplify
it by tending to exhibit the same deviation from the parental
stock as themselves. Indeed, there seems to be in many instances
a prepotent influence about a newly arisen variety which
gives it what we may call an unfair advantage over the normal
descendants from the same stock. This is strikingly exemplified
by the case of Gratio Kelleia, who married a woman with the
ordinary pentadactyle extremities and had by her four children,
Salvator, George, André, and Marie. Of these children Salvator,
the eldest boy, had six fingers and six toes, like his father;
the second and third, also boys, had five fingers and five toes,
like their mother, though the hands and feet of George were
slightly deformed; the last, a girl, had five fingers and five
toes, but the thumbs were slightly deformed. The variety thus
reproduced itself purely in the eldest, while the normal type
reproduced itself purely in the third, and almost purely in the
second and last; so that it would seem, at first, as if the
normal type were more powerful than the variety. But all these
children grew up and intermarried with normal wives and husbands,
and then note what took place—Salvator had four children, three
of whom exhibited the hexadactyle members of their grandfather
and father, while the youngest had the pentadactyle limbs of the
mother and grandmother; so that here, notwithstanding a double
pentadactyle dilution of the blood the hexadactyle variety had
the best of it. The same prepotency of the variety was still more
markedly exemplified in the progeny of two of the other children,
Marie and George. Marie (whose thumbs only were deformed) gave
birth to a boy with six toes, and three other normally formed
children; but George, who was not quite so pure a pentadactyle,
begot, first, two girls, each of whom had six fingers and toes;
then a girl with six fingers on each hand, and six toes on
the right foot, but only five toes on the left; and lastly,
a boy with only five fingers and toes. In these instances,
therefore, the variety, as it were, leaped over one generation to
reproduce itself in full force in the next. Finally, the purely
pentadactyle André was the father of many children, not one of
whom departed from the normal parental type.’
169. The instances now quoted illustrate two things. Both tell us
how varieties arise, we may say spontaneously, or in other words
we cannot tell how; and the former instance, that of the Ancon
breed, shows us moreover that such varieties when they do occur
may be rendered permanent by means of artificial selection. If
the six-fingered descendants of Gratio Kelleia had been forced to
intermarry amongst themselves it is highly probable that we should
have had a permanent hexadactyle variety of the human race. It has
likewise been shown by Charles Darwin that the pouter, the fan-tail,
the carrier, and the tumbler are all varieties of the common
rock-pigeon.
170. It thus appears that permanent varieties may be produced by
artificial selection. Now Darwin and Wallace have brought before us
the very great fact that similar changes can also be produced by
natural selection.
To illustrate this, let us imagine a slight variety to arise
spontaneously, we do not know how. Having arisen there is a
‘prepotent influence’ about it which enables it to secure a
considerable proportion of offspring having its own characteristics.
Now, suppose that the characteristics are such as to adapt the
individuals possessing them more perfectly to the conditions of
nature which surround them. When, by breeding amongst themselves,
the new variety is rendered permanent, the members of this variety
will, therefore, have an advantage over their elder brethren so far
as certain conditions of nature are concerned, will in fact succeed
better in the struggle for existence, and will ultimately displace
the elder branches. Thus the struggle for existence bears to natural
selection the same relation as man bears to artificial selection.
171. We now come to the real point of difficulty, or at least the
unproved point, in the Darwinian hypothesis. We may cross one
race with another, but we do not obtain, so far as we know, those
phenomena of infertility which are exhibited when we cross distinct
species with each other. The Ancon sheep were perfectly fertile when
matched with their elder brethren, and the dray-horse and the Arab,
or the pouter and the tumbler, breed together as easily as if they
were of the same race. But if we cannot produce infertility, how
can we apply the results of artificial selection to account for the
origin of species?
This difficulty is met by Darwin and his followers in this way:—‘It
is not as yet proved,’ says Professor Huxley, ‘that a race ever
exhibits, when crossed with another race of the same species, those
phenomena of hybridisation which are exhibited by many species when
crossed with other species. On the other hand, not only is it not
proved that all species give rise to hybrids infertile _inter se_,
but there is much reason to believe that, in crossing, species
exhibit every gradation from perfect sterility to perfect fertility.’
This appears to carry weight; the old theory went with a leap from
perfect fertility to perfect sterility, and did not contemplate the
possibility of a continuous gradation from the one extreme to the
other; at least its argument was founded upon the neglect of such
a gradation. But if there be a gradation of this kind, it follows
that infertility will merely represent the results of crossing two
species whose functional characteristics are very different from each
other; and, on the other hand, the reason why artificially produced
varieties are not infertile when crossed with one another may only
be that the experiment has not been continued long enough.
Time, in fact, is the essential requisite in all such attempts to
imitate nature.
172. In connection with this subject, Mr. Darwin has remarked that
certain plants are more fertile with the pollen of another species
than with their own; and Professor Huxley tells us that there are
certain _fuci_ whose male element will fertilise the ovule of a
plant of distinct species, while the males of the latter species are
ineffective with the females of the first. So obscure in some of its
branches is the working of the reproductive system.
Again, the following remark by Mr. Darwin is very suggestive:—
‘First crosses between forms known to be varieties, or sufficiently
alike to be considered as varieties, and their mongrel offspring,
are very generally, but not quite universally, fertile. Nor is this
nearly general and perfect fertility surprising, when we remember
how liable we are to argue in a circle with respect to varieties in
a state of nature; and when we remember that the greater number of
varieties have been produced under domestication, by the selection of
mere external differences, and not of differences in the reproductive
system. In all other respects, excluding fertility, there is a close
general resemblance between hybrids and mongrels.’
173. The result of all these speculations is to render it probable
that there may be in nature, give it time enough, a process which
leads to the transmutation of species.
The accumulation of successive differences, each representing some
element of success in the struggle for life, may easily be imagined
to be capable of producing, in the course of ages, a very great
change.
Reasoning out this hypothesis, the more advanced followers of Mr.
Darwin do not hesitate to describe all the varieties of living
things, including man, as the results of development from some
primordial germ taking place throughout the course of immeasurable
ages. And Mr. Darwin himself, in his work on the Descent of Man,
lays great stress on the occurrence of homologous structures in
man and the lower animals, as well as on the development in man
of rudimentary structures, which are either absolutely useless to
their possessor, or of very slight service indeed, but which appear
to serve as an index of the various stages through which the human
species has passed in its progress upwards from lower forms of life.
174. Mr. Wallace, however, sees in the production of man the
intervention of an external will.
He remarks that the lowest types of savages are in possession of a
brain, and of capacities far beyond any use to which they could apply
them in their present condition, and that therefore they could not
have been evolved from the mere necessities of their environments.
175. Finally, Professor Huxley imagines the possibility of the
Darwinian hypothesis requiring modification. Alluding to the assumed
circularity of the planetary orbits which followed the establishment
of the Copernican hypothesis (Art. 69), he remarks:—
‘But the planetary orbits turned out to be not quite circular after
all, and, grand as was the service Copernicus rendered to science,
Kepler and Newton had to come after him. What if the orbit of
Darwinism should be a little too circular? What if species should
offer residual phenomena, here and there, not explicable by natural
selection? Twenty years hence naturalists may be in a position to
say whether this is, or is not, the case; but in either event they
will owe the author of “The Origin of Species” an immense debt of
gratitude.’
176. We will defer to our last chapter some further remarks on Mr.
Darwin’s hypothesis. Meanwhile, before concluding, let us briefly
allude to the original production of living things on our globe.
It may, perhaps, eventually be possible by means of a hypothesis
of evolution, to account for the great variety of living forms on
the supposition of a single primordial germ to begin with; but the
difficulty still remains how to account for this germ.
It is against all true scientific experience that life can appear
without the intervention of a living antecedent. How then are we to
explain the production of the primordial germ?
The difficulty of doing so from our point of view would appear to
be unusually great, for we have come to the conclusion that, as a
matter of scientific principle, we cannot admit any such breach of
continuity as a pure act of creation in time would imply.
If, then, a pure act of creation in time be an inadmissible
hypothesis, and if the hypothesis of Abiogenesis be equally
inadmissible, our readers may well ask how are we to surmount the
difficulty. For our reply to this question, we must once more beg to
refer them to our concluding chapter.