"From scarpéd cliff and quarried stone
She cries, 'A thousand types are gone.'"
"No biological generalization rests on a wider series of
observations, or has been subjected to a more critical
scrutiny, than that every living organism has come into
existence from a living portion or portions of a pre-existing
organism."[3]
"Was there anything so absurd as to believe that a number of
atoms, by falling together of their own accord, could make a
sprig of moss, a microbe, a living animal? ... It is utterly
absurd.... Here scientific thought is compelled to accept the
idea of creative power. Forty years ago I asked Liebig ... if
he believed that the grass and flowers, which we saw around us,
grew by mere mechanical force. He answered, 'No more than I
could believe that a book of botany describing them could grow
by mere chemical force.'"[4]
"Let them not imagine that any hocus-pocus of electricity or
viscous fluids would make a living cell.... Nothing approaching
to a cell of living creature has ever yet been made.... No
artificial process whatever could make living matter out of dead."[5]
I
Ever since René Descartes, in his Holland laboratory,
dissected the heads of great numbers of animals in order to
discover the processes of imagination and memory, men have been
seeking a physical or materialistic answer to such questions
as, What is life? What is it to be alive? How shall we
distinguish the living from the not-living?
No one of to-day, in the light of the correlation of vital
processes with the general law of the conservation of energy,
believes that life in plants and animals is a separate entity
which may exist outside of and apart from matter. In a
scientific sense, we only know life by its association with
living matter, which in its simplest form is known as
protoplasm. The latter has been termed the physical
basis of life, and so far as we know every material living
thing is composed wholly of protoplasm and of the structures
which it has built up.
This grayish, viscid, slimy, semi-transparent, semi-fluid
substance, similar to the white of an egg, is the most
puzzling, the most wonderful material with which science has to
deal. Chemically it is composed of various proteids, fats,
carbohydrates, etc., and these in turn of but very few
elements, all of which are common, and none of which are
peculiar to protoplasm itself. And yet its essential
properties, its mechanical as well as its chemical make-up,
have baffled the resources of our wisest men with all their
retorts and microscopes and other instruments of precision.
Protoplasm is essentially uniform and similar in appearance
and properties wherever found, whether in the tissues of the
human body, in a blade of grass, or in the green slime of a
stagnant pool. And yet probably no two samples of protoplasm
are ever exactly similar in all respects, though we may never
be able to detect their precise differences. These differences
are due to the fact that the stuff is alive, and within
it are constantly going on those changes accompanying
metabolism, or the building up and tearing down processes that
always accompany life. All separate masses of protoplasm, such
as the one-celled amoeba or the individual cells of our own
bodies, are constantly taking in food and as constantly
throwing off wastes. Hence, in the very nature of things, it is
impossible to find any mass of protoplasm absolutely pure. And
a further and impassable barrier to chemical analysis, or
indeed to any adequate scientific examination, lies in the fact
that we can never deal with protoplasm exactly as it is, since
no analysis can be performed upon it without destroying its
life. And yet even dead protoplasm, and especially its most
characteristic constituent, proteid, has been found the
most difficult material in the world to analyze, and nobody as
yet pretends to know its exact chemical make-up.
The constant effort of natural science to press back the
boundaries of the unknown is very liable to obscure some of the
things most essential to any system of clear thinking regarding
these matters. We are so prone to think that if only our
microscopes were a little stronger, if only we could devise
more effective methods of staining or of chemical analysis or
chemical synthesis, we might really find out what life is, or
what matter itself is; in short, that we might be able to solve
in a scientific way the old, old riddle of existence. But
already we have about reached the limits of the powers of the
microscope; and even if we could devise a way of seeing the
ultimate structures of which protoplasm is composed, how would
we be any better off? Would we not have to attribute to each
constituent of this living substance the properties which we
now attribute to the whole?--that is, the properties which we
attribute to masses of protoplasmic units, such as plants, or
birds, or human beings?
We look at ourselves and we feel sure that we have a separate
and real existence, that we are rationally conscious and are
endowed with choice and free will. We can say almost as much
for an intelligent bird or dog. But we hesitate to say how many
of these powers or characteristics of free and independent
personality can be assigned to the unicellular organisms, such
as the amoeba or the corpuscles of our blood. These one-celled
creatures are also alive, are just as truly alive as are those
composed of many cells. Even the corpuscles of which our bodies
are composed move, and eat, and grow, and seem really endowed
with intelligence like the higher forms of life. Suppose we
could go further than is now possible and could lay bare the
ultimate make-up of the chromatin of these one-celled
creatures, would we even then be able to prove that life with
all its properties is inherent in these material components of
the cells? In other words, would we really solve anything after
all? Or would we not rather be compelled to acknowledge that
the simplest, the most truly rational view of the question is
that in living matter we have merely a special manifestation of
the presence and the direct action of the God of nature which
we cannot so readily recognize in not-living matter? This, it
seems to me, is all that we really know, and all that we are
likely ever to know.
When we examine carefully the differences between the living
and the not-living, we see that the chief difference between
them is in their origin. The matter of growth is not a
real distinction; for crystals grow on the outside, while
inorganic liquids grow by intussusception, as when a soluble
substance is added to them, in very much the same way as an
animal grows by the ingestion of food. Even movement is hardly
an absolute distinction between the living and the not-living;
for no movement can be detected in quiescent seeds, which may
lie dormant for thousands of years; and on the other hand
inorganic foams when brought into contact with liquids of
different composition display movements that very closely
simulate those of the living matter. Lastly, irritability,
though so notably characteristic of living matter, is scarcely
peculiar to it, for many inorganic substances seem almost as
definitely responsive to external stimulation. But in the
matter of their origin there is a real and a most
fundamental difference. All living substance arises only from
other substance already living. It cannot arise from the
not-living; or at least it never has done so since the
beginning of scientific observation, though on this point have
been concentrated the learning and the laboratory technique of
thousands of chemists and microscopists.
It may not be out of place to quote here from one of the
classics dealing with this subject,--words that are just as
true to-day as when first written nearly half a century
ago:
"Let us place vividly in our imagination the picture of the
two great kingdoms of nature,--the inorganic and the
organic,--as these now stand in the light of the Law of
Biogenesis. What essentially is involved in saying that there
is no spontaneous generation of life? It is meant that the
passage from the mineral world to the plant or animal world is
hermetically sealed on the mineral side. This inorganic world
is staked off from the living world by barriers that have never
yet been crossed from within. No change of substance, no
modification of environment, no chemistry, no electricity, nor
any form of energy, nor any evolution, can endow a single atom
of the mineral world with the attribute of life. Only by the
bending down into this dead world of some living form can these
dead atoms be gifted with the properties of vitality; without
this preliminary contact with life they remain fixed in the
inorganic sphere forever.
"It is a very mysterious law which guards in this way the
portals of the living world. And if there is one thing in
nature more worth pondering for its strangeness, it is the
spectacle of this vast helpless world of the dead cut off from
the living by the Law of Biogenesis, and denied forever the
possibility of resurrection within itself. The physical laws
may explain the inorganic world; the biological laws may
account for the development of the organic. But of the point
where they meet,--of that strange border-land between the dead
and the living,--science is silent. It is as if God had placed
everything in earth and heaven in the hands of nature, but had
reserved a point at the genesis of life for His direct appearing."[6]
It would be superfluous to emphasize further this great
outstanding fact that the not-living cannot become the living
by any of the processes which we call natural; and it would be
presumptuous to attempt to emulate these eloquent words by
seeking to emphasize the completeness with which this great Law
of Biogenesis confirms the truth of a real Creation; for the
supreme grandeur and importance of this law could be only
obscured by so doing.
II
Perhaps some of the most impressive lessons on this subject
will be found in connection with the history of the discovery
of this great Law of Biogenesis, which says that life can come
only from life. For by studying the history of the way in which
this great Law has been established, we cannot fail to be
impressed with the thought that back of all the complex array
of living forms in our modern world which go on perpetuating
themselves in orderly ways according to natural law, they could
have originated only by a direct and real Creation, essentially
and radically different from any processes now going on.
The wisest of the ancients in Greece and Rome knew nothing of
this great law as we now know it. Aristotle, the embodiment of
all that the ancient world knew of natural science, expressly
taught that the lower forms of animals, such as fleas and
worms, even mice and frogs, sprang up spontaneously from the
moist earth. "All dry bodies," he declared, "which become damp,
and all damp bodies which are dried, engender animal life."
According to Vergil, bees are produced from the putrifying
entrails of a young bull. Such were the teachings of all the
Greeks and Romans, even of the scientists of the
post-Reformation period, some of whom had accumulated a very
considerable stock of knowledge concerning plants and
animals.
And similar absurdities continued to be taught until
comparatively modern times. Van Helmont, a celebrated alchemist
physician who flourished during the brilliant reign of Louis
XIV, wrote: "The smells which arise from the bottom of morasses
produce frogs, slugs, leeches, grasses, and other things." As a
recipe for producing a pot of mice offhand, he says that the
only thing necessary is partly to fill a vessel with corn and
plug up the mouth of the vessel with an old dirty shirt. In
about twenty-one days, the ferment arising from the dirty shirt
reacting with the odor from the corn will effect the
transmutation of the wheat into mice. The doctor solemnly
assures us that he himself had witnessed this wonderful fact,
and continues, "The mice are born full-grown; there are both
males and females. To reproduce the species it suffices to pair
them."
"Scoop out a hole in a brick," he says further, "put into it
some sweet basil, crushed, lay a second brick upon the first so
that the hole may be completely covered. Expose the two bricks
to the sun, and at the end of a few days the smell of the sweet
basil, acting as a ferment, will change the herb into real scorpions."[7]
Sir Thomas Browne, the famous author of "Religio Medici," had
expressed a doubt as to whether mice may be bred by
putrifaction; but another scientist, Alexander Ross, disposed
of this suggestion by the following line of argument which was
supposed to be conclusive as a reductio ad absurdum:
"So may he (Sir Thomas Browne) doubt whether in cheese and
timber worms are generated; or if beetles and wasps in cows'
dung; or if butterflies, locusts, grasshoppers, shell-fish,
snails, eels, and such like, be procreated of putrid matter,
which is apt to receive the form of that creature to which it
is by formative power disposed. To question this is to question
reason, sense and experience. If he doubts this let him go to
Egypt, and there he will find the fields swarming with mice,
begot of the mud of Nylus, to the great calamity of the in-habitants."[8]
When we remember that such nonsense constituted the wisdom of
the scientific world only about two centuries ago, we begin to
realize the fact that the doctrine of Biogenesis is indeed a
very modern doctrine. But it may be well to ask in passing, How
could the people of former ages understand or appreciate the
great truth of Creation as we moderns are able to do?
The first important step toward the refutation of this old
pagan doctrine of spontaneous generation was made by the
Italian, Redi, in 1668. He noticed that flies are always
present around decomposing meat before the appearance of
maggots, and he devised an experiment to keep the flies away
from actual contact with the meat. The meat putrified as usual,
but did not breed maggots; while the same kind of meat exposed
in open jars swarmed with them. He next placed some meat in a
jar with some wire gauze over the top. The flies were attracted
by the smell of the meat as usual, but could not reach the
meat. Instead they laid their eggs upon the gauze, where they
hatched in due time, while no maggots were generated in the
meat. Thus from this time onward it became gradually understood
that, at least in the case of all the larger and higher forms
of life, Harvey's dictum, as announced some years previously,
was true, and that life comes only from life.
But the invention of the microscope opened the way for a
renewal of the controversy regarding the origin of life.
Bacteria were discovered in 1683; and it was soon observed that
no precautions with screens or other stoppers could prevent
bacteria and other low organisms from breeding in myriads in
every kind of organic matter. Here apparently was an entirely
new foundation for the doctrine of spontaneous generation. It
was freely admitted that all the higher forms of life arise
only by process of natural generation from others of their own
kind; but did not these microscopic organisms prove that there
was "a perpetual abiogenetic fount by which the first steps in
the evolution of living organisms continued to arise, under
suitable conditions, from inorganic matter"?[9]
The famous "barnacle-geese" ought not to be omitted from any
sketch of the vicissitudes of this doctrine of Biogenesis. An
elaborate illustrated account covering their alleged natural
history was printed in one of the early volumes of the Royal
Society of London. Buds of a particular tree growing near the
sea were described as producing barnacles, and these falling
into the water were alleged to be transmuted into geese. Nor
should we omit mention of Huxley's Bathybius Haeckelii,
a slimy substance supposed to exist in great masses in the
depths of the ocean and to consist of undifferentiated
protoplasm, the exhaustless fountain from which all other forms
of life had been derived. Not long after Huxley had given it a
formal scientific name in 1868, it was discovered to be merely
a precipitate of gypsum thrown down from sea water by alcohol,
and thus a product of clumsy manipulation in the laboratory,
instead of a natural product of the deep sea. The
disappointment of those opposing biogenesis was severe; but the
lesson is still of value to the world to-day.
The masterly work of Tyndall and Louis Pasteur in doing for
the bacteria and protozoa what Redi had done for the larger
organisms, is too much a matter of modern contemporary history
to need recital here. Upon this great truth of life only from
life is based all the recent advances in the treatment and
prevention of germ diseases and all the triumphs of modern
surgery. The housewife puts up canned fruit with the utmost
confidence because she believes in this great Law of
Biogenesis. It is because we all believe in it that we use
antiseptics and fumigators and fly screens.
III
But what are the lessons to be learned from this great fact,
and what bearing has this fact on the old Bible doctrine of a
literal Creation?
Life comes now only from preëxisting life. But at some
time there was no life on the globe. It does not take any great
exercise of "philosophic faith," as Huxley suggested, "to look
beyond the abyss of geologically recorded time" and recognize
that at this beginning of things there must have taken place a
most wonderful event, essentially and radically different from
anything now going on, namely, the beginning of organic life.
But would not this be a real Creation in the old-fashioned
sense of this term? We cannot avoid this conclusion; nor is
there anything in either science or philosophy to indicate that
this creation of the living from the not-living was confined to
one mere speck of protoplasm. It is absolutely certain
that it required a real Creation to produce life from the
not-living at all; and it is just as reasonable that this
exercise of creative power may have taken place in all parts
of the earth at the same general time, as the Bible
teaches. For if a Being saw fit to create life at all, why
should He stop with one or two bits of protoplasmic units? An
architect who can make his own bricks and other building
material, can surely build what he desires out of these
materials. Common sense tells us that, if the Creator really
created life in the beginning, He did not stop with a few
specks of protoplasm here and there over the earth. The ability
to create life from the not-living implies the ability to make
full-grown trees or birds or beasts in twenty-four hours,
instead of waiting for months or years, as is usual at the
present time.
As we have already found regarding matter and energy, so of
life. The record in Genesis is confirmed, for modern science
compels us to believe in Creation as the only possible origin
of life,--a Creation entirely different from anything now going
on, and one that can never be made to fit into any scheme of
uniformitarian evolution.
____________________
[3]P.C. Mitchell, in Encyclopædia Britannica, Vol. III,
p. 952.
[4]Lord Kelvin in the London Times, May 4, 1903.
[5]Lord Kelvin, to a class of Medical Students, October 28,
1904.
[6]Henry Drummond, "Natural Law in the Spiritual World,"
Chapter I.
[7]"Louis Pasteur, His Life and Labors," p. 89.
[8]Encyclopædia Britannica, Vol. I, p. 64.
[9]Encyclopædia Britannica, Vol. I, p. 64.
I
With his usual vigor and expressiveness Henry Drummond has
given us a picture of the remarkable fact that the cells of all
plants and animals are strikingly alike, especially the single
cells from which all originate. It is easy for any one to
distinguish between an oak, a palm tree, and a lichen, while a
botanist will have elaborate scientific distinctions which he
can discern between them. "But if the first young germs of
these three plants are placed before him," says Drummond, and
the botanist is called upon to define the difference, "he finds
it impossible. He cannot even say which is which. Examined
under the highest powers of the microscope, they yield no clue.
Analyzed by the chemist, with all the appliances of his
laboratory, they keep their secret.
"The same experiment can be tried with the embryos of animals.
Take the ovule of the worm, the eagle, the elephant, and of man
himself. Let the most skilled observer apply the most searching
tests to distinguish the one from the other, and he will
fail.
"But there is something more surprising still. Compare next
the two sets of germs, the vegetable and the animal, and there
is no shade of difference. Oak and palm, worm and man, all
start in life together. No matter into what strangely different
forms they may afterwards develop, no matter whether they are
to live on sea or land, creep or fly, swim or walk, think or
vegetate,--in the embryo, as it first meets the eye of science,
they are indistinguishable. The apple which fell in Newton's
garden, Newton's dog Diamond, and Newton himself, began life at
the same point."[10]
In these remarks, of course, Drummond is dealing with the
unicellular primal form, "as it first meets the eye of
science"; and while certain slight peculiarities (such as the
constant number of chromosomes) have been detected as
characteristic of the cells of certain forms, yet for all
practical purposes these words of Drummond are just as true
to-day as when first written. Possibly it is because of a
failure in our technique or from a lack of power in our
microscopes that these wonderful protoplasmic units from which
all living things originate seem identical. But it is equally
possible that they are really identical in structure and
in chemical composition, and that only the ever present
watchcare of the great Author of nature directs the one to
develop in a certain manner, "after its kind," and another in
still another manner, "after its kind." At any rate, the
protoplasm of which they are all alike composed
is identical wherever found, so far as any scientific
tests have yet been able to determine.
II
There are many varieties of single cells known to science
which maintain an independent individual existence. Among the
unicellular plants are the bacteria, while the unicellular
animals are known as the protozoa. And although perhaps I ought
to apologize to the reader for seeming to anticipate here a
part of the discussion of the problem of "species," yet it
seems necessary to say a few words here regarding the
"persistence" of these unicellular forms.
Among the diseases which have been proved to be due to
protozoa are malaria, amoebic dysentery, and syphilis; while
among the much larger number which are due to bacteria,
bacilli, or other vegetable parasites, are cholera, typhoid
fever, the plague, pneumonia, diphtheria, tuberculosis, and
leprosy.
One of the difficulties attending the study of "species" among
the higher forms of plants and animals has always been the
length of time required to obtain any large number of
generations on which to make observations. In the case of such
plants as peas, wheat, corn, or indeed almost any form of plant
life, it is only with difficulty that more than one generation
a year can be obtained; and when two or more generations a year
are produced, they are produced under more or less unnatural
conditions. So that it takes almost a lifetime carefully to
test and record in a thoroughly scientific way the results of
any extensive experiments regarding variation and heredity.
In the case of mice or rats or rabbits or guinea pigs, many
more generations can be obtained in a few years; but in the
case of the larger kinds of animals the time taken for
development to maturity and for gestation is often much
prolonged; and scientific observation of an exact character has
been in vogue for so short a time that there has always been
the chance for advocates of evolution to take refuge under the
plea that, if we only had longer and more carefully conducted
observations, we could really see species in the making, one
form becoming transformed into a distinct form, or perhaps
giving rise to another and distinct form as an offshoot.
But in the case of the bacteria and protozoa, we can have a
new generation every hour or so, sometimes every half hour.
True, these forms of minute life have been under observation
for only a few years; but their effects have in many
cases been observed for almost the entire length of human
history. No physician would tolerate the suggestion that the
bacillus of cholera can produce the symptoms of diphtheria, or
the tubercle bacillus produce the symptoms of leprosy. Nor will
any scientist deny that such diseases as the plague,
tuberculosis, or diphtheria are identical with diseases which
ravaged Rome or Greece or Egypt thousands of years ago. And as
the symptoms of these modern diseases are similar to those
recorded by acute observers in Greece or Egypt two thousand
years or more ago, we must conclude that the organisms causing
these symptoms are doubtless identical. Similar remarks might
be made regarding fermentation and other forms of decay.
In the case of a form of bacteria which reaches maturity and
redivides in half an hour, the number of individual forms
existing at the end of two days would need about twenty-eight
figures to represent it. Doubtless these forms never multiply
at this rate uninterruptedly for any great length of time, or
else they would occupy the whole world to the exclusion of
every other form of life. And doubtless instances arise where
the period of growth to maturity and division is prolonged to
several times the half-hour period mentioned above. But in any
case, as we contemplate the length of time during which such
well marked diseases as diphtheria, leprosy, or the plague have
been known, we must acknowledge that these unicellular forms
seem to breed true during a most astonishingly long
period. How can we deny that this "persistence" of these
unicellular forms constitutes a very strong argument in favor
of the "fixity" of these forms?
III
But we must proceed to examine the behavior of the various
kinds of cells of which the various multicellular organisms are
composed.
Plants were known to be composed of cells, and their cells
were studied and described some years before it was understood
that animals also are composed of cells as units. Even then,
however, the first propounders of the cell theory (Schleiden
and Schwann) had no clear or accurate idea of the origin of
cells, or of their essential characters and structure. As to
origin, they supposed that cells arose by a sort of
crystallization from a mother liquor; and as to structure, they
looked upon the cell-wall as the really important part, the
fluid contents being quite subordinate. Hugo von Mohl (1846)
applied to the fluid contents of the cell the term
"protoplasm," and Max Schultze (1861) showed that this
protoplasm is really identical in all organisms, plants and
animals, also that the cell-wall is frequently absent in many
animal tissues and in many unicellular forms, indicating that
the protoplasm is the really important substance. By this time
also it had become known that cells never arise de novo,
as had been supposed by the earlier investigators, but that
cells arise only by division of preexisting cells; or as Rudolf
Virchow (1858) expressed it, "omnis cellula e cellulā."
It was, however, many years before the details of the growth
and reproduction of the cells (cell-division) became well
understood. Not until the last quarter of the nineteenth
century was it settled that the nucleus of the cell is also a
supremely important part; but finally in 1882 Flemming was able
to extend Virchow's aphorism to the nucleus also: omnis
nucleus e nucleo.
Since these discoveries our knowledge of the methods of
cell-division has much increased; and in the light of our
modern knowledge of these matters there is nothing in all
nature more marvellous than the regular orderly way in which
cells reproduce themselves according to fixed laws. Certain
cells in the developing embryo, for example, are early set
apart for a particular function or for building certain
structures, and thereafter are never diverted from this duty so
as to do a different work or produce a different kind of
structure. In the young embryo certain structures arise at
certain predestined times in particular places, and only there
and out of these cells alone. As to why it should be so,
we cannot tell, save as the result of deliberate design and as
an expression of the order-loving mind of the God of nature. In
the words of one of the greatest of modern authorities, "We
still do not know why a certain cell becomes a gland-cell,
another a gangleon-cell; why one cell gives rise to smooth
muscle-fiber, while a neighbor forms voluntary muscle.... It is
daily becoming more apparent that epigenesis with the three
layers of the germ furnishes no explanation of developmental
phenomena."[11]
In accordance with the general principle of a division of
labor, certain cells become early set apart to particular
functions, and in accordance with the varying demands of these
functions the developing cells may become greatly changed in
form and in vital characteristics. That is, one cell
specializes, let us say, in secretion, another in
contractility, another in receiving and carrying stimuli, etc.
In this way we will have the gland-cell, the muscle-cell, and
the nerve-cell, each cell destined to produce one of these
organs developing others "after its kind," the result being
that it is soon surrounded with numerous companions doing a
similar work, making up in this way a particular tissue or
organ--gland, muscle, or nerve--which in the aggregate has for
its function the work of the particular cells composing it.
But the important thing for us to remember in this connection
is that when cells once become thus differentiated off and
dedicated to any particular function, they can never grow or
develop into any distinctly different type of cell with other
and different functions. It is true that through pathologic
degeneration the form and even the function of cells may become
greatly changed; but never does it amount to a complete
metamorphosis or complete transformation into another
distinctly different type.
This is a very important principle, and it contains so many
lessons for us bearing on the philosophy of life in general
that it may be allowable to establish this fact by several
somewhat lengthy quotations from standard authorities.
The first will be from one of the highest authorities on
embryology, Charles Sedgwick Minot, of Harvard:
"In accordance with this law [of differentiation] we encounter
no instances, either in normal or pathological
development, of the transformation of a cell of one kind of
tissue into a cell of another kind of tissue; and further we
encounter no instances of a differentiated cell being
transformed back into an undifferentiated cell of the embryonic
type with varied potentialities."[12]
Again, we have the following from one of the foremost
pathologists, as to the strict and rather narrow limits of even
pathologic change:
"Epithelium and gland cells ... never become converted into
bone or cartilage, or vice versa; while, again, it may be laid
down that among epiblastic and hypoblastic tissues, on the one
hand, and mesoblastic tissues on the other, there is no new
development or metaplasia of the most highly specialized
tissues from less specialized tissues; a simple epithelium
cannot in the vertebrate give rise to more complex glandular
tissue, or to nerve cells; in regeneration of epithelium there
is no new formation of hair roots or cutaneous glands. The
cells of white fibrous connective tissue have not been seen to
form striated or even non-striated muscle."[13]
As implied by these quotations, a constant and progressive
differentiation of cells prevails in the developing embryo; and
when complete, certain groups of cells act as specialists in
doing only certain kinds of work for the body. These cells
maintain their specific characters in a very remarkable degree
under normal conditions. Under various abnormal conditions,
however, these cells may become modified as to functions, so
that cells or tissues of one type may assume more or less
completely the characters of another type. "But," as a very
high authority declares, "the limitations in this change in
type are strictly drawn, so that one type can assume only the
characters of another which is closely related to it. This
change of one form of closely related tissue into another is
called metaplasia....
"When differentiation has advanced so that such distinct types
of tissue have been formed as connective tissue, epithelium,
muscle, nerve, these do not again merge through metaplasia.
There is no evidence that mesoblastic tissues can be converted
into those of the epiblastic or hypoblastic type, or vice
versa."[14]
This modification of function among the cells which sometimes
goes on in the developing embryo, or under pathologic
conditions, is very closely analogous to the variation which
goes on among species of animals and plants. But, as we shall
see later, there is a well marked limit to this variation among
species, just as we see there is in the variations among the
cells. Practically the same general laws hold good in each
case.
If cells did not maintain their ancestral characters in a very
remarkable way, what would be the use of grafting a good kind
of fruit onto a stock of poorer quality? The very permanency of
the grafts thus produced is proof of the persistency with which
cells reproduce only "after their kind."
IV
How can we fail to see the bearings of these facts on the
doctrine of the transformation of species among ordinary plants
and animals, which are merely isolated and self-contained
groups of cells? Do not these facts constitute strong
presumptive evidence that among animals and plants, though
there may be variation in plenty within certain limits, perhaps
within even much wider limits than used to be thought possible,
yet among these distinct organisms, little and big, new forms
develop only after their ancestral type, in full accord with
the record given in the first chapter of the Bible?
But we are now prepared to examine in more detail the facts as
now known to modern science regarding "species" of plants and
animals.
____________________
[10]"Natural Law," Chapter X.
[11]Nature, May 23, 1901.
[12]Science, March 29, 1901, p. 490.
[13]J.G. Adami, "Principles of Pathology," pp. 641-642.
[14]Delafield and Prudden, "Text-Book of Pathology," pp. 62,
63.
I
We have seen that there is no way to account for the origin of
matter, of energy, or of life, except by postulating a real
Creation.
We have seen that cells continue to maintain their identity,
and reproduce only "after their kind."
We must now deal with the higher forms of cell aggregates,
which we call plants and animals. It has long been held that
these at least are mutable, that one kind of plant or of animal
may in the course of ages be transformed into a distinctly
different type; and of late years there has accumulated a very
voluminous literature dealing with the various intricacies of
this problem of the origin of species. How can we deal with
such a large subject in a brief way? It seems best to confine
our attention in this chapter to an attempt to answer the
question, What is a species? and are "species" natural groups
clearly delimited by nature?
II
The term "species" was at first used very loosely by
scientific writers. It meant very little more than our vague
word kind does at the present time. Not until the time
of Linnæus (1707-1778) did the term acquire a definite
and precise meaning. The aphorism of the great botanist,
"species tot sunt diversæ quot diversæ
formæ ab initio sunt creatæ"--"just so many
species are to be reckoned as there were forms created in the
beginning,"--was at least an attempt to use the term in a
well-defined sense. Of course, this definition assumed the
"fixity" of species; but with the wide prevalence of the views
of Darwin and his followers the term "species" has fallen into
disrepute, and is now regarded by many as only an artificial
rank in classification corresponding to no objective reality in
the natural world. Some writers, as Lankester, have found so
much fault with the term as to urge its complete abandonment in
scientific literature. This is logical enough from the
standpoint of Darwinism; for if the latter be true there ought
indeed to be such a swamping of every incipient "species" as to
make one kind blend with others all around it in the
classification series.
But since the term has by no means been discarded, we must
endeavor to determine the sense in which it continues to be
used in good scientific literature.
"A species," says Huxley, "is the smallest group to which
distinct and invariable characters can be assigned." The
Standard Dictionary says that the term is used for "a
classificatory group of animals or plants subordinate to a
genus, and having members that differ among themselves only in
minor details of proportion and color, and are capable of
fertile interbreeding indefinitely."
The latter authority also adds:
"In the kingdoms of organic nature species is founded on
identity of form and structure, and specifically characterized
by the power of the individuals to produce beings like
themselves, who are in turn productive."
To put the matter still more definitely before the reader, we
quote the following from a well-known scientist whose writings
on the subject of evolution have had a wide circulation:
"There are two bases on which species may be founded. Species
may be based on form, morphological species; or they may
be based on reproductive functions, physiological
species. By the one method a certain amount of difference of
form, structure, and habit, constitutes species; according to
the other, if the two kinds breed freely with each other and
the offspring is indefinitely fertile, the kinds are called
varieties, but if they do not they are called species."[15]
This author adds that this physiological test, as to whether
or not the kinds are cross fertile, "is regarded as a most
important test of true species, as contrasted with varieties or
races."
III
When we look at the matter in this light, it is very evident
that there are multitudes of long recognized specific
distinctions that ought to be discarded. For instance, there
are some twenty odd "species" of wild pigs scattered over the
Old World, which Flower and Lydekker assure us would probably
"breed freely together."[16] The yak and the zebu of India, and
the bison of America, would on this basis have to be
surrendered, for it is well known that they will all breed
freely with the common domestic cattle, as well as with one
another. Perhaps all or nearly all of the dozen or more
"species" of the genus Bos would thus be included
together. All of the dogs, wolves, and others of the
Canidæ might thus be considered as fundamentally a
unit. The cats (Felidæ) are well known to breed
freely together, Karl Hagënbeck of Hamburg having crossed
lions and tigers as well as others of the family. Practically
all of the bears have been crossed repeatedly, and the progeny
of these and other crosses are quite familiar sights at the
London Zoölogical Gardens. Among the lower forms of life
even more surprising results have been attained by Thomas Hunt
Morgan and others.
It would, however, be a very hasty conclusion to say on the
basis of these facts that there are no natural limitations to
groups of animals and plants. But we are entirely warranted in
concluding from these facts that in very many cases, perhaps in
most, our system of taxonomic classification of animals and
plants has gone altogether too far, and that scientists have
erected specific distinctions which are wholly uncalled for and
which confuse and obscure the main issues of the species
problem. Among the workers in botany and in every department of
zoölogy there have always been the "splitters" and the
"lumpers," as they are familiarly called; the former insisting
on the most minute distinctions between their "species," thus
multiplying them; the latter being more liberal and tending to
diminish the number of species in any given group. For a
generation or more in the recent past the "splitters" had
things pretty much their own way; but of late there is a
growing tendency to frown down the mania for creating new
names. Even yet it is with the utmost reluctance that long
established specific distinctions are surrendered, as is
illustrated in the case of the mammoth, which is acknowledged
by some of the very best authorities to be really
indistinguishable from the modern Asiatic elephant. Several
fossil bears were long listed in scientific books; but they are
all acknowledged now to be identical with the modern grizzly,
and as we have already intimated all the modern ones ought to
be put together. These modern rationalizing methods have made
but a slight impression on the vast complex of the fossil
plants and animals, affecting the names of only a few of the
larger and better known forms. In the realm of invertebrate
palæontology, however, the "splitters" are still holding
high carnival, in spite of the efforts of some very prominent
scientists in the opposite direction. For palæontologists
still follow the irrational course of inventing a new name,
specific or even generic, for a form that happens to be found
in a kind of rock widely separated as to "age" from the other
beds where similar forms are accustomed to be found. As Angelo
Heilprin expresses it, "It is practically certain that numerous
forms of life, exhibiting no distinctive characters of their
own, are constituted into distinct species for no other
reason than that they occur in formations widely separated from
those holding their nearest kin."[17]
As a result of these methods this same author declares: "It is
by no means improbable that many of the older genera,
now recognized as distinct by reason of our imperfect knowledge
concerning their true relationships, have in reality
representatives living in the modern seas."[18]
But the situation is very little better when we come to deal
with plants and animals of our modern world. Because, with the
many thousands of students of natural science all over the
world, each anxious to get into print as the discoverer of some
new form, the systematists have a dead weight of names on their
hands that by a rational and enlightened revision could
doubtless be reduced to but a fraction of their present
disheartening array. For as the result of the extensive
breeding experiments now being carried on under the study of
what is called Mendelism (a term that will be explained in the
next chapter), it has been found that great numbers of the
"species" of the systematists or classificationists will not
stand the physiological test of breeding, that is, they are
found to breed freely together according to the Mendelian Law.
As William Bateson remarks:
"We may even be certain that numbers of excellent species
recognized by entomologists or ornithologists, for example,
would, if subjected to breeding tests, be immediately proved to
be analytical varieties, differing from each other
merely in the presence or absence of definite factors."[19]
The following from David Starr Jordan, the leading American
authority on fishes, will serve to show how numerous have been
the new names invented in recent years, all tending further to
confuse and complicate the problem of what is a species:
"In our fresh-water fishes, each species on an average has
been described as new from three to four times, on
account of minor variations, real or supposed. In Europe, where
the fishes have been studied longer and by more different men,
upwards of six or eight nominal species have been described for
each one that is now considered distinct."[20]
And again:
"Thus the common Channel Catfish of our rivers has been
described as a new species not less than twenty-five
times, on account of differences real or imaginary, but
comparatively trifling in value."[21]
Perhaps the reader will tolerate another somewhat long
quotation because of the light which it sheds on this whole
problem.
"Some years ago we had a parasite of a very destructive aphid
down in our books as Lysiphlebus tritici. In carrying
out our investigations it became necessary to find out whether
this parasite had more than a single host insect, and whether
it could develop in more than one species of aphid. To this
end, recently emerged males and females were allowed to pair,
after which the female oviposited in several species of aphids.
Both parents were then killed and preserved and all of their
progeny not used in further experiments were also preserved,
and thus entire broods or families were kept together. In this
way females were reared out of one host species and allowed to
oviposit in others, until, often after several hosts had been
employed, it would be bred back into the species whence it
first originated. In all cases the host was reared from the
moment of birth, while with the parasite both parents and
offspring were kept together.
"The result of this little fragment of work was to send two
genera and fourteen species to the cemetery--you may call
it Mt. Synonym Cemetery, if you choose--while the insect
involved is now Aphidius testaceipes. The systematist
who studies only dried corpses will soon be out of date."[22]
IV
Now all this is not given to intimate that there is no
scientific justification for the term "species," but to make
plain to my non-professional readers what every well-informed
biologist already knows, namely, that at the present time the
"species question" is still in a very unsatisfactory state. The
facts given above would strongly suggest that there probably is
indeed such a thing as a species, in the sense assigned by
Linnæus, who as we have seen wished to make it a
designation covering all the descendants of each distinct kind
originally created. But this original aim of Linnæus is
to-day not merely ignored but treated with lofty contempt; for
according to the prevailing theories of evolution, all the
manifold diversities of life in our modern world have come
about gradually as the result of a slow development by natural
process, and hence it would be vain beyond measure to attempt
to determine the limits of a "species" in the sense understood
by Linnæus.
But we may conclude, from the facts presented above, that if
there is such a naturally delimited group as a "species" in the
Linnæan sense of the word, it by no means coincides with
what now passes under this name, but might include many
so-called species, often a whole genus, or even several.
With this in mind, we must pass on to consider the next step
in our study, as to whether new "species" are now coming into
being in our modern world under scientific observation, either
natural or artificial.
____________________
[15]Joseph Le Conte, "Evolution and Religious Thought," p.
233.
[16]"Mammals Living and Extinct," pp. 284-285.
[17]"Geographical and Geological Distribution of Animals," pp.
183, 184.
[18]Id., pp. 207, 208.
[19]"Mendel's Principles of Heredity," p. 284, 1909.
[20]"Science Sketches," p. 99.
[21]"Science Sketches," p. 96.
[22]F.M. Webster, of the U.S. Dept. of Agriculture, in
Science, April 12, 1912, p. 565.