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The Story of Evolution

Joseph McCabe

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THE STORY OF EVOLUTION BY JOSEPH McCABE

1912




PREFACE

An ingenious student of science once entertained his generation
with a theory of how one might behold again all the stirring
chapters that make up the story of the earth. The living scene of
our time is lit by the light of the sun, and for every few rays
that enter the human eye, and convey the image of it to the human
mind, great floods of the reflected light pour out, swiftly and
indefinitely, into space. Imagine, then, a man moving out into
space more rapidly than light, his face turned toward the earth.
Flashing through the void at, let us say, a million miles a
second, he would (if we can overlook the dispersion of the rays
of light) overtake in succession the light that fell on the
French Revolution, the Reformation, the Norman Conquest, and the
faces of the ancient empires. He would read, in reverse order,
the living history of man and whatever lay before the coming of
man.

Few thought, as they smiled over this fairy tale of science, that
some such panoramic survey of the story of the earth, and even of
the heavens, might one day be made in a leisure hour by ordinary
mortals; that in the soil on which they trod were surer records
of the past than in its doubtful literary remains, and in the
deeper rocks were records that dimly lit a vast abyss of time of
which they never dreamed. It is the supreme achievement of modern
science to have discovered and deciphered these records. The
picture of the past which they afford is, on the whole, an
outline sketch. Here and there the details, the colour, the light
and shade, may be added; but the greater part of the canvas is
left to the more skilful hand of a future generation, and even
the broad lines are at times uncertain. Yet each age would know
how far its scientific men have advanced in constructing that
picture of the growth of the heavens and the earth, and the aim
of the present volume is to give, in clear and plain language, as
full an account of the story as the present condition of our
knowledge and the limits of the volume will allow. The author has
been for many years interested in the evolution of things, or the
way in which suns and atoms, fishes and flowers, hills and
elephants, even man and his institutions, came to be what they
are. Lecturing and writing on one or other phase of the subject
have, moreover, taught him a language which the inexpert seem to
understand, although he is not content merely to give a
superficial description of the past inhabitants of the earth.

The particular features which, it is hoped, may give the book a
distinctive place in the large literature of evolution are,
first, that it includes the many evolutionary discoveries of the
last few years, gathers its material from the score of sciences
which confine themselves to separate aspects of the universe, and
blends all these facts and discoveries in a more or less
continuous chronicle of the life of the heavens and the earth.
Then the author has endeavoured to show, not merely how, but why,
scene succeeds scene in the chronicle of the earth, and life
slowly climbs from level to level. He has taken nature in the
past as we find it to-day: an interconnected whole, in which the
changes of land and sea, of heat and cold, of swamp and hill, are
faithfully reflected in the forms of its living population. And,
finally, he has written for those who are not students of
science, or whose knowledge may be confined to one branch of
science, and used a plain speech which assumes no previous
knowledge on the reader's part.

For the rest, it will be found that no strained effort is made to
trace pedigrees of animals and plants when the material is
scanty; that, if on account of some especial interest disputable
or conjectural speculations are admitted, they are frankly
described as such; and that the more important differences of
opinion which actually divide astronomers, geologists,
biologists, and anthropologists are carefully taken into account
and briefly explained. A few English and American works are
recommended for the convenience of those who would study
particular chapters more closely, but it has seemed useless, in
such a work, to give a bibliography of the hundreds of English,
American, French, German, and Italian works which have been
consulted.


CONTENTS

I.     THE DISCOVERY OF THE UNIVERSE
II.    THE FOUNDATIONS OF THE UNIVERSE
III.   THE BIRTH AND DEATH OF WORLDS
IV.    THE PREPARATION OF THE EARTH
V.     THE BEGINNING OF LIFE
VI.    THE INFANCY OF THE EARTH
VII.   THE PASSAGE TO THE LAND
VIII.  THE COAL-FOREST
IX.    THE ANIMALS OF THE COAL-FOREST
X.     THE PERMIAN REVOLUTION
XI.    THE MIDDLE AGES OF THE EARTH
XII.   THE AGE OF REPTILES
XIII.  THE BIRD AND THE MAMMAL
XIV.   IN THE DAYS OF THE CHALK
XV.    THE TERTIARY ERA
XVI.   THE FLOWER AND THE INSECT
XVII.  THE ORIGIN OF OUR MAMMALS
XVIII. THE EVOLUTION OF MAN
XIX.   MAN AND THE GREAT ICE-AGE
XX.    THE DAWN OF CIVILISATION
XXI.   EVOLUTION IN HISTORY INDEX



THE STORY OF EVOLUTION



CHAPTER I. THE DISCOVERY OF THE UNIVERSE

The beginning of the victorious career of modern science was very
largely due to the making of two stimulating discoveries at the
close of the Middle Ages. One was the discovery of the earth: the
other the discovery of the universe. Men were confined, like
molluscs in their shells, by a belief that they occupied the
centre of a comparatively small disk--some ventured to say a
globe--which was poised in a mysterious way in the middle of a
small system of heavenly bodies. The general feeling was that
these heavenly bodies were lamps hung on a not too remote ceiling
for the purpose of lighting their ways. Then certain enterprising
sailors--Vasco da Gama, Maghalaes, Columbus--brought home the
news that the known world was only one side of an enormous globe,
and that there were vast lands and great peoples thousands of
miles across the ocean. The minds of men in Europe had hardly
strained their shells sufficiently to embrace this larger earth
when the second discovery was reported. The roof of the world,
with its useful little system of heavenly bodies, began to crack
and disclose a profound and mysterious universe surrounding them
on every side. One cannot understand the solidity of the modern
doctrine of the formation of the heavens and the earth until one
appreciates this revolution.

Before the law of gravitation had been discovered it was almost
impossible to regard the universe as other than a small and
compact system. We shall see that a few daring minds pierced the
veil, and peered out wonderingly into the real universe beyond,
but for the great mass of men it was quite impossible. To them
the modern idea of a universe consisting of hundreds of millions
of bodies, each weighing billions of tons, strewn over billions
of miles of space, would have seemed the dream of a child or a
savage. Material bodies were "heavy," and would "fall down" if
they were not supported. The universe, they said, was a sensible
scientific structure; things were supported in their respective
places. A great dome, of some unknown but compact material,
spanned the earth, and sustained the heavenly bodies. It might
rest on the distant mountains, or be borne on the shoulders of an
Atlas; or the whole cosmic scheme might be laid on the back of a
gigantic elephant, and--if you pressed--the elephant might stand
on the hard shell of a tortoise. But you were not encouraged to
press.

The idea of the vault had come from Babylon, the first home of
science. No furnaces thickened that clear atmosphere, and the
heavy-robed priests at the summit of each of the seven-staged
temples were astronomers. Night by night for thousands of years
they watched the stars and planets tracing their undeviating
paths across the sky. To explain their movements the
priest-astronomers invented the solid firmament. Beyond the known
land, encircling it, was the sea, and beyond the sea was a range
of high mountains, forming another girdle round the earth. On
these mountains the dome of the heavens rested, much as the dome
of St. Paul's rests on its lofty masonry. The sun travelled
across its under-surface by day, and went back to the east during
the night through a tunnel in the lower portion of the vault. To
the common folk the priests explained that this framework of the
world was the body of an ancient and disreputable goddess. The
god of light had slit her in two, "as you do a dried fish," they
said, and made the plain of the earth with one half and the blue
arch of the heavens with the other.

So Chaldaea lived out its 5000 years without discovering the
universe. Egypt adopted the idea from more scientific Babylon.
Amongst the fragments of its civilisation we find representations
of the firmament as a goddess, arching over the earth on her
hands and feet, condemned to that eternal posture by some
victorious god. The idea spread amongst the smaller nations which
were lit by the civilisation of Babylon and Egypt. Some blended
it with coarse old legends; some, like the Persians and Hebrews,
refined it. The Persians made fire a purer and lighter spirit, so
that the stars would need no support. But everywhere the blue
vault hemmed in the world and the ideas of men. It was so close,
some said, that the birds could reach it. At last the genius of
Greece brooded over the whole chaos of cosmical speculations.

The native tradition of Greece was a little more helpful than the
Babylonian teaching. First was chaos; then the heavier matter
sank to the bottom, forming the disk of the earth, with the ocean
poured round it, and the less coarse matter floated as an
atmosphere above it, and the still finer matter formed an
"aether" above the atmosphere. A remarkably good guess, in its
very broad outline; but the solid firmament still arched the
earth, and the stars were little undying fires in the vault. The
earth itself was small and flat. It stretched (on the modern map)
from about Gibraltar to the Caspian, and from Central
Germany--where the entrance to the lower world was located--to
the Atlas mountains. But all the varied and conflicting culture
of the older empires was now passing into Greece, lighting up in
succession the civilisations of Asia Minor, the Greek islands,
and then Athens and its sister states. Men began to think.

The first genius to have a glimpse of the truth seems to have
been the grave and mystical Pythagorus (born about 582 B.C.). He
taught his little school that the earth was a globe, not a disk,
and that it turned on its axis in twenty-four hours. The earth
and the other planets were revolving round the central fire of
the system; but the sun was a reflection of this central fire,
not the fire itself. Even Pythagoras, moreover, made the heavens
a solid sphere revolving, with its stars, round the central fire;
and the truth he discovered was mingled with so much mysticism,
and confined to so small and retired a school, that it was
quickly lost again. In the next generation Anaxagoras taught that
the sun was a vast globe of white-hot iron, and that the stars
were material bodies made white-hot by friction with the ether. A
generation later the famous Democritus came nearer than any to
the truth. The universe was composed of an infinite number of
indestructible particles, called "atoms," which had gradually
settled from a state of chaotic confusion to their present
orderly arrangement in large masses. The sun was a body of
enormous size, and the points of light in the Milky Way were
similar suns at a tremendous distance from the earth. Our
universe, moreover, was only one of an infinite number of
universes, and an eternal cycle of destruction and re-formation
was running through these myriads of worlds.

By sheer speculation Greece was well on the way of discovery.
Then the mists of philosophy fell between the mind of Greece and
nature, and the notions of Democritus were rejected with disdain;
and then, very speedily, the decay of the brilliant nation put an
end to its feverish search for truth. Greek culture passed to
Alexandria, where it met the remains of the culture of Egypt,
Babylonia, and Persia, and one more remarkable effort was made to
penetrate the outlying universe before the night of the Middle
Ages fell on the old world.

Astronomy was ardently studied at Alexandria, and was fortunately
combined with an assiduous study of mathematics. Aristarchus
(about 320-250 B.C.) calculated that the sun was 84,000,000 miles
away; a vast expansion of the solar system and, for the time, a
remarkable approach to the real figure (92,000,000) Eratosthenes
(276-196 B.C.) made an extremely good calculation of the size of
the earth, though he held it to be the centre of a small
universe. He concluded that it was a globe measuring 27,000
(instead of 23,700) miles in circumference. Posidonius (135-51
B.C.) came even nearer with a calculation that the circumference
was between 25,000 and 19,000 miles; and he made a fairly correct
estimate of the diameter, and therefore distance, of the sun.
Hipparchus (190-120 B.C.) made an extremely good calculation of
the distance of the moon.

By the brilliant work of the Alexandrian astronomers the old
world seemed to be approaching the discovery of the universe. Men
were beginning to think in millions, to gaze boldly into deep
abysses of space, to talk of vast fiery globes that made the
earth insignificant But the splendid energy gradually failed, and
the long line was closed by Ptolemaeus, who once more put the
earth in the centre of the system, and so imposed what is called
the Ptolemaic system on Europe. The keen school-life of
Alexandria still ran on, and there might have been a return to
the saner early doctrines, but at last Alexandrian culture was
extinguished in the blood of the aged Hypatia, and the night
fell. Rome had had no genius for science; though Lucretius gave
an immortal expression to the views of Democritus and Epicurus,
and such writers as Cicero and Pliny did great service to a later
age in preserving fragments of the older discoveries. The
curtains were once more drawn about the earth. The glimpses which
adventurous Greeks had obtained of the great outlying universe
were forgotten for a thousand years. The earth became again the
little platform in the centre of a little world, on which men and
women played their little parts, preening themselves on their
superiority to their pagan ancestors.

I do not propose to tell the familiar story of the revival at any
length. As far as the present subject is concerned, it was
literally a Renascence, or re-birth, of Greek ideas.
Constantinople having been taken by the Turks (1453), hundreds of
Greek scholars, with their old literature, sought refuge in
Europe, and the vigorous brain of the young nations brooded over
the ancient speculations, just as the vigorous young brain of
Greece had done two thousand years before. Copernicus (1473-1543)
acknowledges that he found the secret of the movements of the
heavenly bodies in the speculations of the old Greek thinkers.
Galilei (1564-1642) enlarged the Copernican system with the aid
of the telescope; and the telescope was an outcome of the new
study of optics which had been inspired in Roger Bacon and other
medieval scholars by the optical works, directly founded on the
Greek, of the Spanish Moors. Giordano Bruno still further
enlarged the system; he pictured the universe boldly as an
infinite ocean of liquid ether, in which the stars, with retinues
of inhabited planets, floated majestically. Bruno was burned at
the stake (1600); but the curtains that had so long been drawn
about the earth were now torn aside for ever, and men looked
inquiringly into the unfathomable depths beyond. Descartes
(1596-1650) revived the old Greek idea of a gradual evolution of
the heavens and the earth from a primitive chaos of particles,
taught that the stars stood out at unimaginable distances in the
ocean of ether, and imagined the ether as stirring in gigantic
whirlpools, which bore cosmic bodies in their orbits as the eddy
in the river causes the cork to revolve.

These stimulating conjectures made a deep impression on the new
age. A series of great astronomers had meantime been patiently
and scientifically laying the foundations of our knowledge.
Kepler (1571-1630) formulated the laws of the movement of the
planets; Newton (1642-1727) crowned the earlier work with his
discovery of the real agency that sustains cosmic bodies in their
relative positions. The primitive notion of a material frame and
the confining dome of the ancients were abandoned. We know now
that a framework of the most massive steel would be too frail to
hold together even the moon and the earth. It would be rent by
the strain. The action of gravitation is the all-sustaining
power. Once introduce that idea, and the great ocean of ether
might stretch illimitably on every side, and the vastest bodies
might be scattered over it and traverse it in stupendous paths.
Thus it came about that, as the little optic tube of Galilei
slowly developed into the giant telescope of Herschel, and then
into the powerful refracting telescopes of the United States of
our time; as the new science of photography provided observers
with a new eye--a sensitive plate that will register messages,
which the human eye cannot detect, from far-off regions; and as a
new instrument, the spectroscope, endowed astronomers with a
power of perceiving fresh aspects of the inhabitants of space,
the horizon rolled backward, and the mind contemplated a universe
of colossal extent and power.

Let us try to conceive this universe before we study its
evolution. I do not adopt any of the numerous devices that have
been invented for the purpose of impressing on the imagination
the large figures we must use. One may doubt if any of them are
effective, and they are at least familiar. Our solar system--the
family of sun and planets which had been sheltered under a mighty
dome resting on the hill-tops--has turned out to occupy a span of
space some 16,000,000,000 miles in diameter. That is a very small
area in the new universe. Draw a circle, 100 billion miles in
diameter, round the sun, and you will find that it contains only
three stars besides the sun. In other words, a sphere of space
measuring 300 billion miles in circumference--we will not venture
upon the number of cubic miles--contains only four stars (the
sun, alpha Centauri, 21,185 Lalande, and 61 Cygni). However, this
part of space seems to be below the average in point of
population, and we must adopt a different way of estimating the
magnitude of the universe from the number of its stellar
citizens.

Beyond the vast sphere of comparatively empty space immediately
surrounding our sun lies the stellar universe into which our
great telescopes are steadily penetrating. Recent astronomers
give various calculations, ranging from 200,000,000 to
2,000,000,000, of the number of stars that have yet come within
our faintest knowledge. Let us accept the modest provisional
estimate of 500,000,000. Now, if we had reason to think that
these stars were of much the same size and brilliance as our sun,
we should be able roughly to calculate their distance from their
faintness. We cannot do this, as they differ considerably in size
and intrinsic brilliance. Sirius is more than twice the size of
our sun and gives out twenty times as much light. Canopus emits
20,000 times as much light as the sun, but we cannot say, in this
case, how much larger it is than the sun. Arcturus, however,
belongs to the same class of stars as our sun, and astronomers
conclude that it must be thousands of times larger than the sun.
A few stars are known to be smaller than the sun. Some are,
intrinsically, far more brilliant; some far less brilliant.

Another method has been adopted, though this also must be
regarded with great reserve. The distance of the nearer stars can
be positively measured, and this has been done in a large number
of cases. The proportion of such cases to the whole is still very
small, but, as far as the results go, we find that stars of the
first magnitude are, on the average, nearly 200 billion miles
away; stars of the second magnitude nearly 300 billion; and stars
of the third magnitude 450 billion. If this fifty per cent
increase of distance for each lower magnitude of stars were
certain and constant, the stars of the eighth magnitude would be
3000 billion miles away, and stars of the sixteenth magnitude
would be 100,000 billion miles away; and there are still two
fainter classes of stars which are registered on long-exposure
photographs. The mere vastness of these figures is immaterial to
the astronomer, but he warns us that the method is uncertain. We
may be content to conclude that the starry universe over which
our great telescopes keep watch stretches for thousands, and
probably tens of thousands, of billions of miles. There are
myriads of stars so remote that, though each is a vast
incandescent globe at a temperature of many thousand degrees, and
though their light is concentrated on the mirrors or in the
lenses of our largest telescopes and directed upon the
photographic plate at the rate of more than 800 billion waves a
second, they take several hours to register the faintest point of
light on the plate.

When we reflect that the universe has grown with the growth of
our telescopes and the application of photography we wonder
whether we may as yet see only a fraction of the real universe,
as small in comparison with the whole as the Babylonian system
was in comparison with ours. We must be content to wonder. Some
affirm that the universe is infinite; others that it is limited.
We have no firm ground in science for either assertion. Those who
claim that the system is limited point out that, as the stars
decrease in brightness, they increase so enormously in number
that the greater faintness is more than compensated, and
therefore, if there were an infinite series of magnitudes, the
midnight sky would be a blaze of light. But this theoretical
reasoning does not allow for dense regions of space that may
obstruct the light, or vast regions of vacancy between vast
systems of stars. Even apart from the evidence that dark nebulae
or other special light-absorbing regions do exist, the question
is under discussion in science at the present moment whether
light is not absorbed in the passage through ordinary space.
There is reason to think that it is. Let us leave precarious
speculations about finiteness and infinity to philosophers, and
take the universe as we know it.

Picture, then, on the more moderate estimate, these 500,000,000
suns scattered over tens of thousands of billions of miles.
Whether they form one stupendous system, and what its structure
may be, is too obscure a subject to be discussed here. Imagine
yourself standing at a point from which you can survey the whole
system and see into the depths and details of it. At one point is
a single star (like our sun), billions of miles from its nearest
neighbour, wearing out its solitary life in a portentous
discharge of energy. Commonly the stars are in pairs, turning
round a common centre in periods that may occupy hundreds of days
or hundreds of years. Here and there they are gathered into
clusters, sometimes to the number of thousands in a cluster,
travelling together over the desert of space, or trailing in
lines like luminous caravans. All are rushing headlong at
inconceivable speeds. Few are known to be so sluggish as to run,
like our sun, at only 8000 miles an hour. One of the "fixed"
stars of the ancients, the mighty Arcturus, darts along at a rate
of more than 250 miles a second. As they rush, their surfaces
glowing at a temperature anywhere between 1000 and 20,000 degrees
C., they shake the environing space with electric waves from
every tiny particle of their body at a rate of from 400 billion
to 800 billion waves a second. And somewhere round the fringe of
one of the smaller suns there is a little globe, more than a
million times smaller than the solitary star it attends, lost in
the blaze of its light, on which human beings find a home during
a short and late chapter of its history.

Look at it again from another aspect. Every colour of the rainbow
is found in the stars. Emerald, azure, ruby, gold, lilac, topaz,
fawn--they shine with wonderful and mysterious beauty. But,
whether these more delicate shades be really in the stars or no,
three colours are certainly found in them. The stars sink from
bluish white to yellow, and on to deep red. The immortal fires of
the Greeks are dying. Piercing the depths with a dull red glow,
here and there, are the dying suns; and if you look closely you
will see, flitting like ghosts across the light of their luminous
neighbours, the gaunt frames of dead worlds. Here and there are
vast stretches of loose cosmic dust that seems to be gathering
into embryonic stars; here and there are stars in infancy or in
strenuous youth. You detect all the chief phases of the making of
a world in the forms and fires of these colossal aggregations of
matter. Like the chance crowd on which you may look down in the
square of a great city, they range from the infant to the worn
and sinking aged. There is this difference, however, that the
embryos of worlds sprawl, gigantic and luminous, across the
expanse; that the dark and mighty bodies of the dead rush, like
the rest, at twenty or fifty miles a second; and that at
intervals some appalling blaze, that dims even the fearful
furnaces of the living, seems to announce the resurrection of the
dead. And there is this further difference, that, strewn about
the intermediate space between the gigantic spheres, is a mass of
cosmic dust--minute grains, or large blocks, or shoals consisting
of myriads of pieces, or immeasurable clouds of fine gas--that
seems to be the rubbish left over after the making of worlds, or
the material gathering for the making of other worlds.

This is the universe that the nineteenth century discovered and
the twentieth century is interpreting. Before we come to tell the
fortunes of our little earth we have to see how matter is
gathered into these stupendous globes of fire, how they come
sometimes to have smaller bodies circling round them on which
living things may appear, how they supply the heat and light and
electricity that the living things need, and how the story of
life on a planet is but a fragment of a larger story. We have to
study the birth and death of worlds, perhaps the most impressive
of all the studies that modern science offers us. Indeed, if we
would read the whole story of evolution, there is an earlier
chapter even than this; the latest chapter to be opened by
science, the first to be read. We have to ask where the matter,
which we are going to gather into worlds, itself came from; to
understand more clearly what is the relation to it of the forces
or energies --gravitation, electricity, etc.--with which we
glibly mould it into worlds, or fashion it into living things;
and, above all, to find out its relation to this mysterious ocean
of ether in which it is found.

Less than half a century ago the making of worlds was, in popular
expositions of science, a comparatively easy business. Take an
indefinite number of atoms of various gases and metals, scatter
them in a fine cloud over some thousands of millions of miles of
space, let gravitation slowly compress the cloud into a globe,
its temperature rising through the compression, let it throw off
a ring of matter, which in turn gravitation will compress into a
globe, and you have your earth circulating round the sun. It is
not quite so simple; in any case, serious men of science wanted
to know how these convenient and assorted atoms happened to be
there at all, and what was the real meaning of this equally
convenient gravitation. There was a greater truth than he knew in
the saying of an early physicist, that the atom had the look of a
"manufactured article." It was increasingly felt, as the
nineteenth century wore on, that the atoms had themselves been
evolved out of some simpler material, and that ether might turn
out to be the primordial chaos. There were even those who felt
that ether would prove to be the one source of all matter and
energy. And just before the century closed a light began to shine
in those deeper abysses of the submaterial world, and the
foundations of the universe began to appear.
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