CHAPTER I
THE ASCENT OF THE BODY
THE earliest home of Primitive Man was a cave
in the rocks--the simplest and most unevolved form of human habitation. One
day, perhaps driven by the want within his hunting-grounds of the natural cave,
he made himself a hut--an artificial cave. This simple dwelling-place was a
one-roomed hut or tent of skin and boughs, and so completely does it satisfy
the rude man's needs that down to the present hour no ordinary savage improves
upon the idea. But as the hut surrounds itself with other huts and grows into a
village, a new departure must take place. The village must have its chief, and
the chief, in virtue of his larger life, requires a more spacious home. Each
village, therefore, adds to its one-roomed huts, a hut with two rooms. From the
two-roomed hut we pass, among certain tribes, to three- and four-roomed huts,
and finally to the many-chambered lodge of the Head-Chief or King.
This passage from the simple cave to the
many-chambered lodge is an Evolution, and a similar development may be traced
in the domestic architecture of all civilized societies. The labourer's cottage
of modern England and the shieling of the Highland crofter are the survivals of
the one-roomed hut of Primitive Man, scarcely changed in any essential with the
lapse of years. In the squire's mansion also, and the nobleman's castle, we
have the representatives, but now in an immensely developed form, of the
many-roomed home of the chief. The steps by which the cottage became the castle
are the same as those by which the cave in the rocks became the lodge of the
chief. Both processes wear the hall-mark of all true development--they arise in
response to growing necessities, and they are carried out by the most simple
and natural steps.
In this evolution of a human habitation we have
an almost perfect type of the evolution of that more august habitation, the
complex tenement of clay in which Man's mysterious being has its home. The Body
of Man is a structure of a million, or a million million cells. And the history
of the unborn babe is, in the first instance, a history of additions, of room
being added to room, of organ to organ, of faculty to faculty. The general
process, also, by which this takes place is almost as clear to modern science
as in the case of material buildings. A special class of observers has
carefully watched these secret and amazing metamorphoses, and so wonderful has
been their success with mind and microscope that they can almost claim to have
seen Man's Body made. The Science of Embryology undertakes to trace the
development of Man from a stage in which he lived in a one-roomed house--a
physiological cell. Whatever the multitude of rooms, the millions and millions
of cells, in which to-day each adult carries on the varied work of life, it is
certain that when he first began to be he was the simple tenant of a single
cell. Observe, it is not some animal-ancestor or some human progenitor of Man
that lived in this single cell--that may or may not have been--but the
individual Man, the present occupant himself. We are dealing now not with
phylogeny--the history of the race--but with ontogeny--the problem of Man's
Ascent from his own earlier self. And the point at the moment is not that the
race ascends; it is that each individual man has once, in his own life-time,
occupied a single cell, and starting from that humble cradle, has passed
through stage after stage of differentiation, increase, and development, until
the myriad-roomed adult-form was attained. Whence that first cradle came is at
present no matter. Whether its remote progenitor rocked among the waves of
primeval seas or swung from the boughs of forests long since metamorphosed into
coal does not affect the question of the individual ascent of Man. The answers
to these questions are hypotheses. The fact that now arrests our wonder
is that when the earliest trace of an infant's organization meets the eye of
science it is nothing but a one-celled animal. And so closely does its
development from that distant point follow the lines of the evolution just
described in the case of the primitive savage hut, that we have but to make a
few changes in phraseology to make the one process describe the other. Instead
of rooms and chambers we shall now read cells and tissues; instead of the
builder's device of adding room to room, we shall use the physiologist's term
segmentation; the employments carried on in the various rooms will
become the functions discharged by the organs of the human frame, and line for
line the history of the evolution will be found to be the same.
The embryo of the future man begins life. Like
the primitive savage, in a one-roomed hut, a single simple cell. This cell is
round and almost microscopic in size. When fully formed it measures only
one-tenth of a line in diameter, and with the naked eye can be barely discerned
as a very fine point. An outer covering, transparent as glass, surrounds this
little sphere, and in the interior, embedded in protoplasm, lies a bright
globular spot. In form, in size, in composition there is no apparent difference
between this human cell and that of any other mammal. The dog, the elephant,
the lion, the ape, and a thousand others begin their widely different lives in
a house the same as Man's. At an earlier stage indeed, before it has taken on
its pellucid covering, this cell has affinities still more astonishing. For at
that remoter period the earlier forms of all living things, both plant and
animal, are one. It is one of the most astounding facts of modern science that
the first embryonic abodes of moss and fern and pine, of shark and crab and
coral polyp, of lizard, leopard, monkey, and Man are so exactly similar that
the highest powers of mind and microscope fail to trace the smallest
distinction between them.
But let us watch the development of this
one-celled human embryo. Increase of rooms in architecture can be effected in
either of two ways by building entirely new rooms, or by partitioning old ones.
Both of these methods are employed in Nature. The first, gemmation, or budding,
is common among the lower forms of life. The second, differentiation by
partition, or segmentation, is the approved method among higher animals, and is
that adopted in the case of Man. It proceeds, after the fertilized ovum has
completed the complex preliminaries of karyokinesis, by the division of the
interior-contents into two equal parts, so that the original cell is now
occupied by two nucleated cells with the old cell-wall surrounding them
outside. The two-roomed house is, in the next development, and by a similar
process of segmentation, developed into a structure of four rooms, and this
into one of eight, and so on.[31] In a short
time the number of chambers is so great that count is lost, and the activity
becomes so vigorous in every direction that one ceases to notice individual
cells at all. The tenement in fact consists now of innumerable groups of cells
congregated together, suites of apartments as it were, which have quickly
arranged themselves in symmetrical, definite, and withal different forms. Were
these forms not different as well as definite we should hardly call it an
evolution, nor should we characterize the resulting aggregation as a higher
organism. A hundred cottages placed in a row would never form a castle. What
makes the castle superior to the hundred cottages is not the number of its
rooms, for they are possibly fewer; nor their difference in shape, for that is
immaterial. It lies in the number and nature and variety of useful purposes to
which the rooms are put, the perfection with which each is adapted to its end,
and the harmonious co-operation among them with reference to some common work.
This also is the distinction between a higher animal and a humble organism such
as the centipede or the worm. These creatures are a monotony of similar rings,
like a string of beads. Each bead is the counterpart of the other; and with
such an organization any high or varied life becomes an impossibility. The fact
that any growing embryo is passing through a real development is decided by the
new complexity of structure, by the more perfect division of labour, and of
better kinds of labour, and by the increase in range and efficiency of the
correlated functions discharged by the whole. In the development of the human
embryo the differentiating and integrating forces are steadily acting and
co-operating from the first, so that the result is not a mere aggregation of
similar cells, but an organism with different parts and many varied functions.
When all is complete we find that one suite of cells has been specially set
apart to provide the commissariat, others have devoted themselves exclusively
to assimilation. The ventilation of the house--respiration--has been attended
to by others, and a central force-pump has been set up, and pipes and ducts for
many purposes installed throughout the system. Telegraph wires have next been
stretched in every direction to keep up connection between the endless parts;
and other cells developed into bony pillars for support. Finally, the whole
delicate structure has been shielded by a variety of protective coverings, and
after months and years of further elaboration and adjustment the elaborate
fabric is complete. Now all these complicated contrivances --bones, muscles,
nerves, heart, brain, lungs--are made out of cells; they are themselves, and in
their furthest development, simply masses or suites of cells modified in
various ways for the special department of household work they are meant to
serve. No new thing, except building material, has entered into the embryo
since its first appearing. It seized whatever matter lay to hand, incorporated
it with its own quickening substance, and built it in to its appropriate place.
So the structure rose in size and symmetry, till the whole had climbed, a
miracle of unfolding, to the stature of a Man.
But the beauty of this development is not the
significant thing to the student of Evolution; nor is it the occultness of the
process nor the perfection of the result that fill him with awe as he surveys
the finished work. It is the immense distance Man has come. Between the early
cell and the infant's formed body, the ordinary observer sees the uneventful
passage of a few brief months. But the evolutionist sees concentrated into
these few months the labour and the progress of incalculable ages. Here before
him is the whole stretch of time since life first dawned upon the earth; and as
he watches the nascent organism climbing to its maturity he witnesses a
spectacle which for strangeness and majesty stands alone in the field of
biological research. What he sees is not the mere shaping or sculpturing of a
Man. The human form does not begin as a human form. It begins as an animal; and
at first, and for a long time to come, there is nothing wearing the remotest
semblance of humanity. What meets the eye is a vast procession of lower forms
of life, a succession of strange inhuman creatures emerging from a crowd of
still stranger and still more inhuman creatures; and it is only after a
prolonged and unrecognizable series of metamorphoses that they culminate in
some faint likeness to the image of him who is one of the newest yet the oldest
of created things. Hitherto we have been taught to look among the fossiliferous
formations of Geology for the buried lives of the earth's past. But Embryology
has startled the world by declaring that the ancient life of the earth is not
dead. It is risen. It exists to-day in the embryos of still-living things, and
some of the most archaic types find again a resurrection and a life in the
frame of man himself.
It is an amazing and almost incredible story. The
proposition is not only that Man begins his earthly existence in the guise of a
lower animal embryo, but that in the successive transformations of the human
embryo there is reproduced before our eyes a visible, actual, physical
representation of part of the life-history of the world. Human Embryology is a
condensed account, a recapitulation or epitome of some of the main chapters in
the Natural History of the world. The same processes of development which once
took thousands of years for their consummation are here condensed,
foreshortened, concentrated into the space of weeks. Each platform reached by
the human embryo in its upward course represents the embryo of some lower
animal which in some mysterious way has played a part in the pedigree of the
human race, which may itself have disappeared long since from the earth, but is
now and for ever built into the inmost being of Man. These lower animals, each
at its successive stage, have stopped short in their development; Man has gone
on. At each fresh advance his embryo is found again abreast of some other
animal-embryo a little higher in organization than that just passed. Continuing
his ascent that also is overtaken, the now very complex embryo making up to one
animal-embryo after another until it has distanced all in its series, and
stands alone. As the modern stem-winding watch contains the old clepsydra and
all the most useful features in all the timekeepers that were ever made; as the
Walter printing-press contains the rude hand-machine of Gutenberg, and all the
best in all the machines that followed it; as the modern locomotive of to-day
contains the engine of Watt, the locomotive of Hedley, and most of the
improvements of succeeding years, so Man contains the embryonic bodies of
earlier and humbler and clumsier forms of life. Yet in making the Walter press
in a modern workshop, the artificer does not begin by building again the press
of Gutenberg, nor in constructing the locomotive does the engineer first make a
Watt's machine and then incorporate the Hedley, and then the Stephenson, and so
on through all the improving types of engines that have led up to this. But the
astonishing thing is that, in making a Man, Nature does introduce the framework
of these earlier types, displaying each crude pattern by itself before
incorporating it in the finished work. The human embryo, to change the figure,
is a subtle phantasmagoria, a living theatre in which a weird transformation
scene is being enacted, and in which countless strange and uncouth characters
take part. Some of these characters are well known to science, some are
strangers. As the embryo unfolds, one by one these animal actors come upon the
stage, file past in phantom-like procession, throw off their drapery, and
dissolve away into something else. Yet, as they vanish, each leaves behind a
vital portion of itself, some original and characteristic memorial, something
itself has made or won, that perhaps it alone could make or win--a bone, a
muscle, a ganglion, or a tooth-- to be the inheritance of the race. And it is
only after nearly all have played their part and dedicated their gift, that a
human form, mysteriously compounded of all that has gone before, begins to be
discerned in their midst.
The duration of this process, the profound
antiquity of the last survivor, the tremendous height he has scaled, are
inconceivable by the faculties of Man. But measure the very lowest of the
successive platforms passed in the ascent, and see how very great a thing it is
even to rise at all. The single cell, the first definite stage which the human
embryo attains, is still the adult form of countless millions both of animals
and plants. Just as in modern England the millionaire's mansion--the evolved
form--is surrounded by labourers' cottages--the simple form--so in Nature,
living side by side with the many-celled higher animals, is an immense
democracy of unicellular artizans. These simple cells are perfect living
things. The earth, the water, and the air teem with them everywhere. They move,
they eat, they reproduce their like. But one thing they do not do--they do not
rise. These organisms have, as it were, stopped short in the ascent of life.
And long as Evolution has worked upon the earth, the vast numerical majority of
plants and animals are still at this low stage of being. So minute are some of
these forms that if their one-roomed huts were arranged in a row it would take
twelve thousand to form a street a single inch in length. In their watery
cities--for most of them are Lake-Dwellers--a population of eight hundred
thousand million could be accommodated within a cubic inch. Yet, as there was a
period in human history when none but cave-dwellers lived in Europe, so was
there a time when the highest forms of life upon the globe were these
microscopic things. See, therefore, the meaning of Evolution from the want of
it. In a single hour or second the human embryo attains the platform which
represents the whole life-achievement of myriads of generations of created
things, and the next day or hour is immeasurable centuries beyond them.
Through all what zoological regions the embryo
passes in its great ascent from the one-celled forms, one can never completely
tell. The changes succeed one another with such rapidity that it is impossible
at each separate stage to catch the actual likeness to other embryos. Sometimes
a familiar feature suddenly recalls a form well-known to science, but the
likeness fades, and the developing embryo seems to wander among the ghosts of
departed types. Long ago these crude ancestral forms were again the highest
animals upon the earth. For a few thousand years they reigned supreme,
furthered the universal evolution by a hair-breadth, and passed away. The
material dust of their bodies is laid long since in the Palaeozoic rocks, but
their life and labour are not forgotten. For their gains were handed on to a
succeeding race. Transmitted thence through an endless series of descendants,
sifted, enriched, accentuated, still dimly recognizable, they re-appeared at
last in the physical frame of Man. After the early stages of human development
are passed, the transformations become so definite that the features of the
contributary animals are almost recognizable. Here, for example, is a stage at
which the embryo in its anatomical characteristics resembles that of the Vermes
or Worms. As yet there is no head, nor neck, nor backbone, nor waist, nor
limbs. A roughly cylindrical headless trunk--that is all that stands for the
future man. One by one the higher Invertebrates are left behind, and then
occurs the most remarkable change in the whole life-history. This is the laying
down of the line to be occupied by the spinal chord, the presence of which
henceforth will determine the place of Man in the Vertebrate sub-kingdom. At
this crisis, the eye which sweeps the field of lower Nature for an analogue
will readily find it. It is a circumstance of extraordinary interest that there
should be living upon the globe at this moment an animal representing the
actual transition from Invertebrate to Vertebrate life. The acquisition of a
vertebral column is one of the great marks of height which Nature has bestowed
upon her creatures; and in the shallow waters of the Mediterranean she has
preserved for us a creature which, whether degenerate or not, can only be
likened to one of her first rude experiments in this direction. This animal is
the Lancelet, or Amphioxus, and so rudimentary is the backbone that it does not
contain any bone at all, but only a shadow or prophecy of it in cartilage. The
cartilaginous notochord of the Amphioxus nevertheless is the progenitor
of all vertebral columns, and in the first instance this structure appears in
the human embryo exactly as it now exists in the Lancelet. But this is only a
single example. In living Nature there are a hundred other animal
characteristics which at one stage or another the biologist may discern in the
ever-changing kaleidoscope of the human embryo.
Even with this addition, nevertheless, the human
infant is but a first rough draft, an almost formless lump of clay. As yet
there is no distinct head, no brain, no jaws, no limbs; the heart is imperfect,
the higher visceral organs are feebly developed, everything is elementary. But
gradually new organs loom in sight, old ones increase in complexity. By a magic
which has never yet been fathomed the hidden Potter shapes and re-shapes the
clay. The whole grows in size and symmetry. Resemblances, this time, to the
embryos of the lower vertebrate series, flash out as each new step is
attained--first the semblance of the Fish, then of the Amphibian, then of the
Reptile, last of the Mammal. Of these great groups the leading embryonic
characters appear as in a moving panorama, some of them pronounced and
unmistakable, others mere sketches, suggestions, likenesses of infinite
subtlety. At last the true Mammalian form emerges from the crowd. Far ahead of
all at this stage stand out three species--the Tailed Catarrhine Ape, the
Tailless Catarrhine, and last, differing physically from these mainly by an
enlargement of the brain and a development of the larynx, Man.
Whatever views be held of the doctrine of
Evolution, whatever theories of its cause, these facts of Embryology are
proved. They have taken their place in science wholly apart from the discussion
of theories of Evolution, and as the result of laboratory investigation, made
for quite other ends. What is true for Man, moreover, is true of all other
animals. Every creature that lives climbs up its own genealogical tree before
it reaches its mature condition. "All animals living, or that ever have lived,
are united together by blood relationship of varying nearness or remoteness,
and every animal now in existence has a pedigree stretching back, not merely
for ten or a hundred generations, but through all geologic time since life
first commenced on the earth. The study of development has revealed to us that
each animal bears the mark of its ancestry, and is compelled to discover its
parentage in its own development; the phases through which an animal passes in
its progress from the egg to the adult are no accidental freaks, no mere
matters of developmental convenience, but represent more or less closely, in
more or less modified manner, the successive ancestral stages through which the
present condition has been acquired."[32]
Almost foreseen by Agassiz, suggested by Von Baer, and finally applied by Fritz
Muller, this singular law is the key-note of modern Embryology. In no case, it
is true, is the recapitulation of the past complete. Ancestral stages are
constantly omitted, others are over-accentuated, condensed, distorted, or
confused; while new and undecipherable characters occasionally appear. But it
is a general scientific fact, that over the graves of a myriad aspirants the
bodies of Man and of all higher Animals have risen. No one knows why this
should be so. Science, at present, has no rationale of the process adequate to
explain it. It was formerly held that the entire animal creation had
contributed something to the anatomy of Man; or that as Serres expressed it,
"Human Organogenesis is a transitory Comparative Anatomy." But though Man has
not such a monopoly of the past as is here inferred--other types having here
and there diverged and developed along lines of their own--it is certain that
the materials for his body have been brought together from an unknown multitude
of lowlier forms of life.
Those who know the Cathedral of St. Mark's will
remember how this noblest of the Stones of Venice owes its greatness to the
patient hands of centuries and centuries of workers, how every quarter of the
globe has been spoiled of its treasures to dignify this single shrine. But he
who ponders over the more ancient temple of the Human Body will find
imagination fail him as he tries to think from what remote and mingled sources,
from what lands, seas, climates, atmospheres, its various parts have been
called together, and by what innumerable contributory creatures, swimming,
creeping, flying, climbing, each of its several members was wrought and
perfected. What ancient chisel first sculptured the rounded columns of the
limbs? What dead hands built the cupola of the brain, and from what older ruins
were the scattered pieces of its mosaic-work brought? Who fixed the windows in
its upper walls? What winds and weathers wrought strength into its buttresses?
What ocean-beds and forest glades worked up its colourings? What Love and
Terror and Night called forth the Music? And what Life and Death and Pain and
Struggle put all together in the noiseless workshop of the past, and removed
each worker silently when its task was done? How these things came to be,
Biology is one long record. The architects and builders of this mighty temple
are not anonymous. Their names, and the work they did, are graven forever on
the walls and arches of the Human Embryo. For this is a volume of that Book in
which Man's members were written, which in continuance were fashioned, when as
yet there was none of them.
The Descent of Man from the Animal Kingdom is
sometimes spoken of as a degradation. It is an unspeakable exaltation. Recall
the vast antiquity of that primal cell from which the human embryo first sets
forth. Compass the nature of the potentialities stored up in its plastic
substance. Watch all the busy processes, the multiplying energies, the
mystifying transitions, the inexplicable chemistry of this living laboratory.
Observe the variety and intricacy of its metamorphoses, the exquisite gradation
of its ascent, the unerring aim with which the one type unfolds--never pausing,
never uncertain of its direction, refusing arrest at intermediate forms,
passing on to its flawless maturity without waste or effort or fatigue. See the
sense of motion at every turn, of purpose and of aspiration. Discover how, with
identity of process and loyalty to the type, a hair-breadth of deviation is yet
secured to each so that no two forms come out the same, but each arises an
original creation, with features, characteristics, and individualities of its
own. Remember, finally, that even to make the first cell possible, stellar
space required to be swept of matter, suns must needs be broken up, and planets
cool, the agents of geology labour millennium after millennium at the
unfinished earth to prepare a material resting-place for the coming guest.
Consider all this, and judge if Creation could have a sublimer meaning, or the
Human Race possess a more splendid genesis.
From the lips of the Prophet another version, an
old and beautiful story, was told to the childhood of the earth, of how God
made Man; how with His own hands He gathered the Bactrian dust, modelled it,
breathed upon it, and it became a living soul. Later, the insight of the Hebrew
Poet taught Man a deeper lesson. He saw that there was more in Creation than
mechanical production. He saw that the Creator had different kinds of Hands and
different ways of modelling. How it was done he knew not, but it was not the
surface thing his forefathers taught him. The higher divinity and mystery of
the process broke upon him. Man was a fearful and wonderful thing. He was
modelled in secret. He was curiously wrought in the lowest parts of the earth.
When Science came, it was not to contradict the older versions. It but gave
them content and a still richer meaning. What the Prophet said, and the Poet
saw, and Science proved, all and equally will abide forever. For all alike are
voices of the Unseen, commissioned to different peoples and for different ends
to declare the mystery of the Ascent of Man.
[31] When the multicellular globe, made up of
countless offshoots or divisions of the original pair, has reached a certain
size, its centre becomes filled with a tiny lakelet of watery fluid. This fluid
gradually increases in quantity, and, pushing the cells outward, packs them
into a single layer, circumscribing it on every side as with an elastic wall.
At one part a dimple soon appears, which slowly deepens, until a complete
hollow is formed. So far does this invagination of the sphere go on that the
cells at the bottom of the hollow touch those at the opposite side. The ovum
has now become an open bag or cup, such as one might make by doubling in an
india-rubber ball, and thus is formed the gastrula of biology. The
evolutional interest of this process lies in the fact that probably all animals
above the Protozoa pass through this gastrula stage. That some of the lower
Metazoa, indeed, never develop much beyond it, a glance at the structure
of the humbler Coelenterates will show--the simplest of all illustrations of
the fact that embryonic forms of higher animals are often permanently
represented by the adult forms of lower. The chief thing however to mark here
is the doubling-in of the ovum to gain a double instead of a single wall of
cells. For these two different layers, the ectoderm and the endoderm, or the
animal layer and the vegetal layer, play a unique part in the after-history.
All the organs of movement and sensation spring from the one, all the organs of
nutrition and reproduction develop from the other.
[32] Marshall, Vertebrate
Embryology. p. 26.