§ 1. No one primitive language 150
§ 2. The Aryan languages 151
§ 3. The Semitic languages 153
§ 4. The Hamitic languages 154
§ 5. The Ural-Altaic languages 156
§ 6. The Chinese languages 157
§ 7. Other language groups 157
§ 8. Submerged and lost languages 161
§ 9. How languages may be related 163
BOOK III
THE DAWN OF HISTORY
CHAPTER XV. THE ARYAN-SPEAKING PEOPLES IN PREHISTORIC TIMES
§ 1. The spreading of the Aryan-speakers 167
§ 2. Primitive Aryan life 169
§ 3. Early Aryan daily life 176
CHAPTER XVI. THE FIRST CIVILIZATIONS
§ 1. Early cities and early nomads 183
§ 2A. The riddle of the Sumerians 188
§ 2B. The empire of Sargon the First 191
§ 2C. The empire of Hammurabi 191
§ 2D. The Assyrians and their empire 192
§ 2E. The Chaldean empire 194
§ 3. The early history of Egypt 195
§ 4. The early civilization of India 201
§ 5. The early history of China 201
§ 6. While the civilizations were growing 206
CHAPTER XVII. SEA PEOPLES AND TRADING PEOPLES
§ 1. The earliest ships and sailors 209
§ 2. The Ægean cities before history 213
§ 3. The first voyages of exploration 217
§ 4. Early traders 218
§ 5. Early travellers 220
CHAPTER XVIII. WRITING
§ 1. Picture writing 223
§ 2. Syllable writing 227
§ 3. Alphabet writing 228
§ 4. The place of writing in human life 229
CHAPTER XIX. GODS AND STARS, PRIESTS AND KINGS
§ 1. Nomadic and settled religion 232
§ 2. The priest comes into history 234
§ 3. Priests and the stars 238
§ 4. Priests and the dawn of learning 240
§ 5. King against priests 241
§ 6. How Bel-Marduk struggled against the kings 245
§ 7. The god-kings of Egypt 248
§ 8. Shi Hwang-ti destroys the books 252
CHAPTER XX. SERFS, SLAVES, SOCIAL CLASSES, AND FREE INDIVIDUALS
§ 1. The common man in ancient times 254
§ 2. The earliest slaves 256
§ 3. The first “independent” persons 259
§ 4. Social classes three thousand years ago 262
§ 5. Classes hardening into castes 266
§ 6. Caste in India 268
§ 7. The system of the Mandarins 270
§ 8. A summary of five thousand years 272
BOOK IV
JUDEA, GREECE, AND INDIA
CHAPTER XXI. THE HEBREW SCRIPTURES AND THE PROPHETS
§ 1. The place of the Israelites in history 277
§ 2. Saul, David, and Solomon 286
§ 3. The Jews a people of mixed origin 292
§ 4. The importance of the Hebrew prophets 294
CHAPTER XXII. THE GREEKS AND THE PERSIANS
§ 1. The Hellenic peoples 298
§ 2. Distinctive features of the Hellenic civilization 304
§ 3. Monarchy, aristocracy, and democracy in Greece 307
§ 4. The kingdom of Lydia 315
§ 5. The rise of the Persians in the East 316
§ 6. The story of Crœsus 320
§ 7. Darius invades Russia 326
§ 8. The battle of Marathon 332
§ 9. Thermopylæ and Salamis 334
§ 10. Platæa and Mycale 340
CHAPTER XXIII. GREEK THOUGHT AND LITERATURE
§ 1. The Athens of Pericles 343
§ 2. Socrates 350
§ 3. What was the quality of the common Athenians? 352
§ 4. Greek tragedy and comedy 354
§ 5. Plato and the Academy 355
§ 6. Aristotle and the Lyceum 357
§ 7. Philosophy becomes unworldly 359
§ 8. The quality and limitations of Greek thought 360
CHAPTER XXIV. THE CAREER OF ALEXANDER THE GREAT
§ 1. Philip of Macedonia 367
§ 2. The murder of King Philip 373
§ 3. Alexander’s first conquests 377
§ 4. The wanderings of Alexander 385
§ 5. Was Alexander indeed great? 389
§ 6. The successors of Alexander 395
§ 7. Pergamum a refuge of culture 396
§ 8. Alexander as a portent of world unity 397
CHAPTER XXV. SCIENCE AND RELIGION AT ALEXANDRIA
§ 1. The science of Alexandria 401
§ 2. Philosophy of Alexandria 410
§ 3. Alexandria as a factory of religions 410
CHAPTER XXVI. THE RISE AND SPREAD OF BUDDHISM
§ 1. The story of Gautama 415
§ 2. Teaching and legend in conflict 421
§ 3. The gospel of Gautama Buddha 422
§ 4. Buddhism and Asoka 426
§ 5. Two great Chinese teachers 433
§ 6. The corruptions of Buddhism 438
§ 7. The present range of Buddhism 440
BOOK V
THE RISE AND COLLAPSE OF THE ROMAN EMPIRE
CHAPTER XXVII. THE TWO WESTERN REPUBLICS
§ 1. The beginnings of the Latins 445
§ 2. A new sort of state 454
§ 3. The Carthaginian republic of rich men 466
§ 4. The First Punic War 467
§ 5. Cato the Elder and the spirit of Cato 471
§ 6. The Second Punic War 475
§ 7. The Third Punic War 480
§ 8. How the Punic War undermined Roman liberty 485
§ 9. Comparison of the Roman republic with a modern state 486
CHAPTER XXVIII. FROM TIBERIUS GRACCHUS TO THE GOD EMPEROR
IN ROME
§ 1. The science of thwarting the common man 493
§ 2. Finance in the Roman state 496
§ 3. The last years of republican politics 499
§ 4. The era of the adventurer generals 505
§ 5. Caius Julius Cæsar and his death 509
§ 6. The end of the republic 513
§ 7. Why the Roman republic failed 516
CHAPTER XXIX. THE CÆSARS BETWEEN THE SEA AND THE GREAT
PLAINS OF THE OLD WORLD
§ 1. A short catalogue of emperors 52
§ 2. Roman civilization at its zenith 529
§ 3. Limitations of the Roman mind 539
§ 4. The stir of the great plains 541
§ 5. The Western (true Roman) Empire crumples up 552
§ 6. The Eastern (revived Hellenic) Empire 560
BOOK VI
CHRISTIANITY AND ISLAM
CHAPTER XXX. THE BEGINNINGS, THE RISE, AND THE DIVISIONS
OF CHRISTIANITY
§ 1. Judea at the Christian era 569
§ 2. The teachings of Jesus of Nazareth 573
§ 3. The universal religions 582
§ 4. The crucifixion of Jesus of Nazareth 584
§ 5. Doctrines added to the teachings of Jesus 586
§ 6. The struggles and persecutions of Christianity 594
§ 7. Constantine the Great 598
§ 8. The establishment of official Christianity 601
§ 9. The map of Europe, A.D. 500 605
§ 10. The salvation of learning by Christianity 609
CHAPTER XXXI. SEVEN CENTURIES IN ASIA (CIRCA 50 B.C. TO A.D. 650)
§ 1. Justinian the Great 614
§ 2. The Sassanid Empire in Persia 616
§ 3. The decay of Syria under the Sassanids 619
§ 4. The first message from Islam 623
§ 5. Zoroaster and Mani 624
§ 6. Hunnish peoples in Central Asia and India 627
§ 7. The great age of China 630
§ 8. Intellectual fetters of China 635
§ 9. The travels of Yuan Chwang 642
LIST OF MAPS AND ILLUSTRATIONS
PAGE
Life in the Early Palæozoic 11
Time-chart from Earliest Life to 40,000,000 Years Ago 14
Life in the Later Palæozoic Age 19
Australian Lung Fish 26
Some Reptiles of the Late Palæozoic Age 27
Astronomical Variations Affecting Climate 33
Some Mesozoic Reptiles 40
Later Mesozoic Reptiles 42
Pterodactyls and Archæopteryx 45
Hesperornis 48
Some Oligocene Mammals 53
Miocene Mammals 58
Time-diagram of the Glacial Ages 60
Early Pleistocene Animals, Contemporary with Earliest Man 64
The Sub-Man Pithecanthropus 65
The Riddle of the Piltdown Sub-Man 71
Map of Europe 50,000 Years Ago 77
Neanderthal Man 78
Early Stone Implements 81
Australia and the Western Pacific in the Glacial Age 82
Cro-magnon Man 87
Europe and Western Asia in the Later Palæolithic Age 89
Reindeer Age Articles 90
A Reindeer Age Masterpiece 93
Reindeer Age Engravings and Carvings 94
Diagram of the Estimated Duration of the True Human Periods 97
Neolithic Implements 107
Restoration of a Lake Dwelling 111
Pottery from Lake Dwellings 112
Hut Urns 115
A Menhir of the Neolithic Period 128
Bronze Age Implements 132
Diagram Showing the Duration of the Neolithic Period 133
Heads of Australoid Types 139
Bushwoman 141
Negro Types 142
Mongolian Types 143
Caucasian Types 144
Map of Europe, Asia, Africa 15,000 Years Ago 145
The Swastika 147
Relationship of Human Races (Diagrammatic Summary) 149
Possible Development of Languages 155
Racial Types (after Champollion) 163
Combat between Menelaus and Hector 176
Archaic Horses and Chariots 178
The Cradle of Western Civilization 185
Sumerian Warriors in Phalanx 189
Assyrian Warrior (_temp._ Sargon II) 193
Time-chart 6000 B.C. to A.D. 196
The Cradle of Chinese Civilization (Map) 202
Boats on Nile about 2500 B.C. 211
Egyptian Ship on Red Sea, 1250 B.C. 212
Ægean Civilization (Map) 214
A Votary of the Snake Goddess 215
American Indian Picture-Writing 225
Egyptian Gods--Set, Anubis, Typhon, Bes 236
Egyptian Gods--Thoth-lunus, Hathor, Chnemu 239
An Assyrian King and His Chief Minister 243
Pharaoh Chephren 248
Pharaoh Rameses III as Osiris (Sarcophagus relief) 249
Pharaoh Akhnaton 251
Egyptian Peasants (Pyramid Age) 257
Brawl among Egyptian Boatmen (Pyramid Age) 260
Egyptian Social Types (From Tombs) 261
The Land of the Hebrews 280
Aryan-speaking Peoples 1000-500 B.C. (Map) 301
Hellenic Races 1000-800 B.C. (Map) 302
Greek Sea Fight, 550 B.C. 303
Rowers in an Athenian Warship, 400 B.C. 306
Scythian Types 319
Median and Second Babylonian Empires (in Nebuchadnezzar’s Reign) 321
The Empire of Darius 329
Wars of the Greeks and Persians (Map) 333
Athenian Foot-soldier 334
Persian Body-guard (from Frieze at Susa) 338
The World According to Herodotus 341
Athene of the Parthenon 348
Philip of Macedon 368
Growth of Macedonia under Philip 371
Macedonian Warrior (bas-relief from Pella) 373
Campaigns of Alexander the Great 381
Alexander the Great 389
Break-up of Alexander’s Empire 393
Seleucus I 395
Later State of Alexander’s Empire 398
The World According to Eratosthenes, 200 B.C. 405
The Known World, about 250 B.C. 406
Isis and Horus 413
Serapis 414
The Rise of Buddhism 419
Hariti 428
Chinese Image of Kuan-yin 429
The Spread of Buddhism 432
Indian Gods--Vishnu, Brahma, Siva 437
Indian Gods--Krishna, Kali, Ganesa 439
The Western Mediterranean, 800-600 B.C. 446
Early Latium 447
Burning the Dead: Etruscan Ceremony 449
Statuette of a Gaul 450
Roman Power after the Samnite Wars 451
Samnite Warriors 452
Italy after 275 B.C. 453
Roman Coin Celebrating the Victory over Pyrrhus 455
Mercury 457
Carthaginian Coins 468
Roman _As_ 471
Rome and its Alliances, 150 B.C. 481
Gladiators 489
Roman Power, 50 B.C. 506
Julius Cæsar 512
Roman Empire at Death of Augustus 518
Roman Empire in Time of Trajan 524
Asia and Europe: Life of the Period (Map) 544
Central Asia, 200-100 B.C. 547
Tracks of Migrating and Raiding Peoples, 1-700 A.D. 555
Eastern Roman Empire 561
Constantinople (Maps to show value of its position) 563
Galilee 571
Map of Europe, 500 A.D. 608
The Eastern Empire and the Sassanids 620
Asia Minor, Syria, and Mesopotamia 622
Ephthalite Coin 629
Chinese Empire, Tang Dynasty 633
Yuan Chwang’s Route from China to India 643
BOOK I
THE MAKING OF OUR WORLD
THE OUTLINE OF HISTORY
I
THE EARTH IN SPACE AND TIME
The earth on which we live is a spinning globe. Vast though it seems to
us, it is a mere speck of matter in the greater vastness of space.
Space is, for the most part, emptiness. At great intervals there are in
this emptiness flaring centres of heat and light, the “fixed stars.”
They are all moving about in space, notwithstanding that they are called
fixed stars, but for a long time men did not realize their motion. They
are so vast and at such tremendous distances that their motion is not
perceived. Only in the course of many thousands of years is it
appreciable. These fixed stars are so far off that, for all their
immensity, they seem to be, even when we look at them through the most
powerful telescopes, mere points of light, brighter or less bright. A
few, however, when we turn a telescope upon them, are seen to be whirls
and clouds of shining vapour which we call nebulæ. They are so far off
that a movement of millions of miles would be imperceptible.
One star, however, is so near to us that it is like a great ball of
flame. This one is the sun. The sun is itself in its nature like a fixed
star, but it differs from the other fixed stars in appearance because it
is beyond comparison nearer than they are; and because it is nearer men
have been able to learn something of its nature. Its mean distance from
the earth is ninety-three million miles. It is a mass of flaming matter,
having a diameter of 866,000 miles. Its bulk is a million and a quarter
times the bulk of our earth.
These are difficult figures for the imagination. If a bullet fired from
a Maxim gun at the sun kept its muzzle velocity unimpaired, it would
take seven years to reach the sun. And yet we say the sun is near,
measured by the scale of the stars. If the earth were a small ball, one
inch in diameter, the sun would be a globe of nine feet diameter; it
would fill a small bedroom. It is spinning round on its axis, but since
it is an incandescent fluid, its polar regions do not travel with the
same velocity as its equator, the surface of which rotates in about
twenty-five days. The surface visible to us consists of clouds of
incandescent metallic vapour. At what lies below we can only guess. So
hot is the sun’s atmosphere that iron, nickel, copper, and tin are
present in it in a gaseous state. About it at great distances circle not
only our earth, but certain kindred bodies called the planets. These
shine in the sky because they reflect the light of the sun; they are
near enough for us to note their movements quite easily. Night by night
their positions change with regard to the fixed stars.
It is well to understand how empty space is. If, as we have said, the
sun were a ball nine feet across, our earth would, in proportion, be the
size of a one-inch ball, and at a distance of 323 yards from the sun.
The moon would be a speck the size of a small pea, thirty inches from
the earth. Nearer to the sun than the earth would be two other very
similar specks, the planets Mercury and Venus, at a distance of 125 and
250 yards respectively. Beyond the earth would come the planets Mars,
Jupiter, Saturn, Uranus, and Neptune, at distances of 500, 1806, 3000,
6000, and 9500 yards respectively. There would also be a certain number
of very much smaller specks, flying about amongst these planets, more
particularly a number called the asteroids circling between Mars and
Jupiter, and occasionally a little puff of more or less luminous vapour
and dust would drift into the system from the almost limitless emptiness
beyond. Such a puff is what we call a comet. _All the rest of the space
about us and around us and for unfathomable distances beyond is cold,
lifeless, and void._ The nearest fixed star to us, _on this minute
scale_, be it remembered,--the earth as a one-inch ball, and the moon a
little pea--would be over 40,000 miles away.
The science that tells of these things and how men have come to know
about them is Astronomy, and to books of astronomy the reader must go to
learn more about the sun and stars. The science and description of the
world on which we live are called respectively Geology and Geography.
The diameter of our world is a little under 8000 miles. Its surface is
rough; the more projecting parts of the roughness are mountains, and in
the hollows of its surface there is a film of water, the oceans and
seas. This film of water is about five miles thick at its deepest
part--that is to say, the deepest oceans have a depth of five miles.
This is very little in comparison with the bulk of the world.
About this sphere is a thin covering of air, the atmosphere. As we
ascend in a balloon or go up a mountain from the level of the sea-shore
the air is continually less dense, until at last it becomes so thin that
it cannot support life. At a height of twenty miles there is scarcely
any air at all--not one hundredth part of the density of air at the
surface of the sea. The highest point to which a bird can fly is about
four miles up--the condor, it is said, can struggle up to that; but most
small birds and insects which are carried up by aeroplanes or balloons
drop off insensible at a much lower level, and the greatest height to
which any mountaineer has ever climbed is under five miles. Men have
flown in aeroplanes to a height of over four miles, and balloons with
men in them have reached very nearly seven miles, but at the cost of
considerable physical suffering. Small experimental balloons, containing
not men, but recording instruments, have gone as high as twenty-two
miles.
It is in the upper few hundred feet of the crust of the earth, in the
sea, and in the lower levels of the air below four miles that life is
found. We do not know of any life at all except in these films of air
and water upon our planet. So far as we know, all the rest of space is
as yet without life. Scientific men have discussed the possibility of
life, or of some process of a similar kind, occurring upon such kindred
bodies as the planets Venus and Mars. But they point merely to
questionable possibilities.
Astronomers and geologists and those who study physics have been able to
tell us something of the origin and history of the earth. They consider
that, vast ages ago, the sun was a spinning, flaring mass of matter,
not yet concentrated into a compact centre of heat and light,
considerably larger than it is now, and spinning very much faster, and
that as it whirled, a series of fragments detached themselves from it,
which became the planets. Our earth is one of these planets. The flaring
mass that was the material of the earth broke as it spun into two
masses, a larger, the earth itself, and a smaller, which is now the
dead, still moon. Astronomers give us convincing reasons for supposing
that sun and earth and moon and all that system were then whirling about
at a speed much greater than the speed at which they are moving to-day,
and that at first our earth was a flaming thing upon which no life could
live. The way in which they have reached these conclusions is by a very
beautiful and interesting series of observations and reasoning, too long
and elaborate for us to deal with here. But they oblige us to believe
that the sun, incandescent though it is, is now much cooler than it was,
and that it spins more slowly now than it did, and that it continues to
cool and slow down. And they also show that the rate at which the earth
spins is diminishing and continues to diminish--that is to say, that our
day is growing longer and longer, and that the heat at the centre of the
earth wastes slowly. There was a time when the day was not a half and
not a third of what it is to-day; when a blazing hot sun, much greater
than it is now, must have moved visibly--had there been an eye to mark
it--from its rise to its setting across the skies. There will be a time
when the day will be as long as a year is now, and the cooling sun,
shorn of its beams, will hang motionless in the heavens.
It must have been in days of a much hotter sun, a far swifter day and
night, high tides, great heat, tremendous storms and earthquakes, that
life, of which we are a part, began upon the world. The moon also was
nearer and brighter in those days and had a changing face.[3]
II
THE RECORD OF THE ROCKS
§ 1. _The First Living Things._ § 2. _How Old Is the World?_
§ 1
We do not know how life began upon the earth.[4]
Biologists, that is to say, students of life, have made guesses about
these beginnings, but we will not discuss them here. Let us only note
that they all agree that life began where the tides of those swift days
spread and receded over the steaming beaches of mud and sand.
The atmosphere was much denser then, usually great cloud masses obscured
the sun, frequent storms darkened the heavens. The land of those days,
upheaved by violent volcanic forces, was a barren land, without
vegetation, without soil. The almost incessant rain-storms swept down
upon it, and rivers and torrents carried great loads of sediment out to
sea, to become muds that hardened later into slates and shales, and
sands that became sandstones. The geologists have studied the whole
accumulation of these sediments as it remains to-day, from those of the
earliest ages to the most recent. Of course the oldest deposits are the
most distorted and changed and worn, and in them there is now no certain
trace to be found of life at all. Probably the earliest forms of life
were small and soft, leaving no evidence of their existence behind them.
It was only when some of these living things developed skeletons and
shells of lime and such-like hard material that they left fossil
vestiges after they died, and so put themselves on record for
examination.
The literature of geology is very largely an account of the fossils that
are found in the rocks, and of the order in which layers after layers of
rocks lie one on another. The very oldest rocks must have been formed
before there was any sea at all, when the earth was too hot for a sea to
exist, and when the water that is now sea was an atmosphere of steam
mixed with the air. Its higher levels were dense with clouds, from which
a hot rain fell towards the rocks below, to be converted again into
steam long before it reached their incandescence. Below this steam
atmosphere the molten world-stuff solidified as the first rocks. These
first rocks must have solidified as a cake over glowing liquid material
beneath, much as cooling lava does. They must have appeared first as
crusts and clinkers. They must have been constantly remelted and
recrystallized before any thickness of them became permanently solid.
The name of Fundamental Gneiss is given to a great underlying system of
crystalline rocks which probably formed age by age as this hot youth of
the world drew to its close. The scenery of the world in the days when
the Fundamental Gneiss was formed must have been more like the interior
of a furnace than anything else to be found upon earth at the present
time.
After long ages the steam in the atmosphere began also to condense and
fall right down to earth, pouring at last over these warm primordial
rocks in rivulets of hot water and gathering in depressions as pools and
lakes and the first seas. Into those seas the streams that poured over
the rocks brought with them dust and particles to form a sediment, and
this sediment accumulated in layers, or as geologists call them,
_strata_, and formed the first Sedimentary Rocks. Those earliest
sedimentary rocks sank into depressions and were covered by others; they
were bent, tilted up, and torn by great volcanic disturbances and by
tidal strains that swept through the rocky crust of the earth. We find
these first sedimentary rocks still coming to the surface of the land
here and there, either not covered by later strata or exposed after vast
ages of concealment by the wearing off of the rock that covered them
later--there are great surfaces of them in Canada especially; they are
cleft and bent, partially remelted, recrystallized, hardened and
compressed, but recognizable for what they are. And they contain no
single certain trace of life at all. They are frequently called _Azoic_
(lifeless) Rocks. But since in some of these earliest sedimentary rocks
a substance called graphite (black lead) occurs, and also red and black
oxide of iron, and since it is asserted that these substances need the
activity of living things for their production, which may or may not be
the case, some geologists prefer to call these earliest sedimentary
rocks _Archæozoic_ (primordial life). They suppose that the first life
was soft living matter that had no shells or skeletons or any such
structure that could remain as a recognizable fossil after its death,
and that its chemical influence caused the deposition of graphite and
iron oxide. This is pure guessing, of course, and there is at least an
equal probability that in the time of formation of the Azoic Rocks, life
had not yet begun.
Long ago there were found in certain of these ancient first-formed rocks
in Canada, curious striped masses, and thin layers of white and green
mineral substance which Sir William Dawson considered were fossil
vestiges, the walls or coverings of some very simple sort of living
thing which has now vanished from the earth. He called these markings
_Eozoon Canadense_ (the Canadian dawn-animal). There has been much
discussion and controversy over this Eozoon, but to-day it is agreed
that Eozoon is nothing more than a crystalline marking. Mixed minerals
will often intercrystallize in blobs or branching shapes that are very
suggestive of simple plant or animal forms. Any one who has made a lead
tree in his schooldays, or lit those queer indoor fireworks known as
serpents’ eggs, which unfold like a long snake, or who has seen the
curious markings often found in quartz crystals, or noted the tree-like
pattern on old stone-ware beer mugs, will realize how closely non-living
matter can sometimes mock the shapes of living things.
Overlying or overlapping these Azoic or Archæozoic rocks come others,
manifestly also very ancient and worn, which do contain traces of life.
These first remains are of the simplest description; they are the
vestiges of simple plants, called algæ, or marks like the tracks made by
worms in the sea mud. There are also the skeletons of the microscopic
creatures called Radiolaria. This second series of rocks is called the
Proterozoic (beginning of life) series, and marks a long age in the
world’s history. Lying over and above the Proterozoic rocks is a third
series, which is found to contain a considerable number and variety of
traces of living things. First comes the evidence of a diversity of
shellfish, crabs, and such-like crawling things, worms, seaweeds, and
the like; then of a multitude of fishes and of the beginnings of land
plants and land creatures. These rocks are called the Palæozoic (ancient
life) rocks. They mark a vast era, during which life was slowly
spreading, increasing, and developing in the seas of our world. Through
long ages, through the earliest Palæozoic time, it was no more than a
proliferation of such swimming and creeping things in the water. There
were creatures called trilobites; they were crawling things like big sea
woodlice that were probably related to the American king-crab of to-day.
There were also sea-scorpions, the prefects of that early world. The
individuals of certain species of these were nine feet long. These were
the very highest sorts of life. There were abundant different sorts of
an order of shellfish called brachiopods. There were plant animals,
rooted and joined together like plants, and loose weeds that waved in
the waters.
It was not a display of life to excite our imaginations. There was
nothing that ran or flew or even swam swiftly or skilfully. Except for
the size of some of the creatures, it was not very different from, and
rather less various than, the kind of life a student would gather from
any summer-time ditch nowadays for microscopic examination. Such was the
life of the shallow seas through a hundred million years or more in the
early Palæozoic period. The land during that time was apparently
absolutely barren. We find no trace nor hint of land life. Everything
that lived in those days lived under water for most or all of its life.
[Illustration: Life in the Early Palæozoic
Note its general resemblance, except for size, to the microscopic summer
ditch-water life of to-day.]
Between the formation of these Lower Palæozoic rocks in which the sea
scorpion and trilobite ruled, and our own time, there have intervened
almost immeasurable ages, represented by layers and masses of
sedimentary rocks. There are first the Upper Palæozoic Rocks, and above
these the geologists distinguish two great divisions. Next above the
Palæozoic come the Mesozoic (middle life) rocks, a second vast system of
fossil-bearing rocks, representing perhaps a hundred millions of swift
years, and containing a wonderful array of fossil remains, bones of
giant reptiles and the like, which we will presently describe; and above
these again are the Cainozoic (recent life) rocks, a third great volume
in the history of life, an unfinished volume of which the sand and mud
that was carried out to sea yesterday by the rivers of the world, to
bury the bones and scales and bodies and tracks that will become at last
fossils of the things of to-day, constitute the last written leaf.
(It is, we may note, the practice of many geologists to make a break
between the rest of the Cainozoic system of rocks and those which
contain traces of humanity, which latter are cut off as a separate
system under the name of Quaternary. But that, as we shall see, is
rather like taking the last page of a book, which is really the
conclusion of the last chapter, and making a separate chapter of it and
calling it the last chapter.)
These markings and fossils in the rocks and the rocks themselves are our
first historical documents. The history of life that men have puzzled
out and are still puzzling out from them is called the Record of the
Rocks. By studying this record men are slowly piecing together a story
of life’s beginnings, and of the beginnings of our kind, of which our
ancestors a century or so ago had no suspicion. But when we call these
rocks and the fossils a record and a history, it must not be supposed
that there is any sign of an orderly keeping of a record. It is merely
that whatever happens leaves some trace, if only we are intelligent
enough to detect the meaning of that trace. Nor are the rocks of the
world in orderly layers one above the other, convenient for men to read.
They are not like the books and pages of a library. They are torn,
disrupted, interrupted, flung about, defaced, like a carelessly arranged
office after it has experienced in succession a bombardment, a hostile
military occupation, looting, an earthquake, riots, and a fire. And so
it is that for countless generations this Record of the Rocks lay
unsuspected beneath the feet of men. Fossils were known to the Ionian
Greeks in the sixth century B.C.,[5] they were discussed at Alexandria
by Eratosthenes and others in the third century B.C., a discussion which
is summarized in Strabo’s _Geography_ (?20-10 B.C.). They were known to
the Latin poet Ovid, but he did not understand their nature. He thought
they were the first rude efforts of creative power. They were noted by
Arabic writers in the tenth century. Leonardo da Vinci, who lived so
recently as the opening of the sixteenth century (1452-1519), was one of
the first Europeans to grasp the real significance of fossils,[6] and it
has been only within the last century and a half that man has begun the
serious and sustained deciphering of these long-neglected early pages of
his world’s history.
§ 2
[Illustration: graph of eras]
Speculations about geological time vary enormously.[7] Estimates of the
age of the oldest rocks by geologists and astronomers starting from
different standpoints have varied between 1,600,000,000, and 25,000,000.
The lowest estimate was made by Lord Kelvin in 1867. Professor Huxley
guessed at 400,000,000 years. There is a summary of views and the
grounds upon which the estimates have been made in Osborn’s _Origin and
Evolution of Life_; he inclines to the moderate total of 100,000,000. It
must be clearly understood by the reader how sketchy and provisional all
these time estimates are. They rest nearly always upon theoretical
assumptions of the slenderest kind. That the period of time has been
vast, that it is to be counted by scores and possibly by hundreds of
millions of years, is the utmost that can be said with certainty in the
matter. It is quite open to the reader to divide every number in the
appended time diagram by ten or multiply it by two; no one can gainsay
him. Of the relative amount of time as between one age and another we
have, however, stronger evidence; if the reader cuts down the
800,000,000 we have given here to 400,000,000, then he must reduce the
40,000,000 of the Cainozoic to 20,000,000. And be it noted that whatever
the total sum may be, most geologists are in agreement that _half or
more than half of the whole of geological time had passed before life
had developed to the Later Palæozoic level_. The reader reading quickly
through these opening chapters may be apt to think of them as a mere
swift prelude of preparation to the apparently much longer history that
follows, but in reality that subsequent history is longer only because
it is more detailed and more interesting to us. It looms larger in
perspective. For ages that stagger the imagination this earth spun hot
and lifeless, and again for ages of equal vastness it held no life above
the level of the animalculæ in a drop of ditch-water.
Not only is Space from the point of view of life and humanity empty, but
Time is empty also. Life is like a little glow, scarcely kindled yet, in
these void immensities.
III
NATURAL SELECTION AND THE CHANGES OF SPECIES
Now here it will be well to put plainly certain general facts about this
new thing, _life_, that was creeping in the shallow waters and
intertidal muds of the early Palæozoic period, and which is perhaps
confined to our planet alone in all the immensity of space.
Life differs from all things whatever that are without life in certain
general aspects. There are the most wonderful differences among living
things to-day, but all living things past and present agree in
possessing _a certain power of growth_, all living things _take
nourishment_, all living things _move about_ as they feed and grow,
though the movement may be no more than the spread of roots through the
soil, or of branches in the air. Moreover, living things reproduce; they
give rise to other living things, either by growing and then dividing or
by means of seeds or spores or eggs or other ways of producing young.
_Reproduction_ is a characteristic of life.
No living thing goes on living forever. There seems to be a _limit of
growth_ for every kind of living thing. Among very small and simple
living things, such as that microscopic blob of living matter the
_Amæba_, an individual may grow and then divide completely into two new
individuals, which again may divide in their turn. Many other
microscopic creatures live actively for a time, grow, and then become
quiet and inactive, enclose themselves in an outer covering and break up
wholly into a number of still smaller things, spores, which are released
and scattered and again grow into the likeness of their parent. Among
more complex creatures the reproduction is not usually such simple
division, though division does occur even in the case of many creatures
big enough to be visible to the unassisted eye. But the rule with almost
all larger beings is that the individual grows up to a certain limit of
size. Then, before it becomes unwieldy, its growth declines and stops.
As it reaches its full size it _matures_, it begins to produce young,
which are either born alive or hatched from eggs. But all of its body
does not produce young. Only a special part does that. After the
individual has lived and produced offspring for some time, it ages and
dies. It does so by a sort of necessity. There is a practical limit to
its life as well as to its growth. These things are as true of plants as
they are of animals. And they are not true of things that do not live.
Non-living things, such as crystals, grow, but they have no set limits
of growth or size, they _do not move of their own accord_ and there is
_no stir within them_. Crystals once formed may last unchanged for
millions of years. There is _no reproduction_ for any non-living thing.
This growth and dying and reproduction of living things leads to some
very wonderful consequences. The young which a living thing produces are
either directly, or after some intermediate stages and changes (such as
the changes of a caterpillar and butterfly), like the parent living
thing. But they are never exactly like it or like each other. There is
always a slight difference, which we speak of as _individuality_. A
thousand butterflies this year may produce two or three thousand next
year; these latter will look to us almost exactly like their
predecessors, but each one will have just that slight difference. It is
hard for us to see individuality in butterflies because we do not
observe them very closely, but it is easy for us to see it in men. All
the men and women in the world now are descended from the men and women
of A.D. 1800, but not one of us now is exactly the same as one of that
vanished generation. And what is true of men and butterflies is true of
every sort of living thing, of plants as of animals. Every species
changes all its individualities in each generation. That is as true of
all the minute creatures that swarmed and reproduced and died in the
Archæozoic and Proterozoic seas, as it is of men to-day.
Every species of living things is continually dying and being born
again, as a multitude of fresh individuals.
Consider, then, what must happen to a new-born generation of living
things of any species. Some of the individuals will be stronger or
sturdier or better suited to succeed in life in some way than the rest,
many individuals will be weaker or less suited. In particular single
cases any sort of luck or accident may occur, but _on the whole_ the
better equipped individuals will live and grow up and reproduce
themselves and the weaker will _as a rule_ go under. The latter will be
less able to get food, to fight their enemies and pull through. So that
in each generation there is as it were a picking over of a species, a
picking out of most of the weak or unsuitable and a preference for the
strong and suitable. This process is called _Natural Selection_ or the
_Survival of the Fittest_.[8]
It follows, therefore, from the fact that living things grow and breed
and die, that every species, so long as the conditions under which it
lives remain the same, becomes more and more perfectly fitted to those
conditions in every generation.
But now suppose those conditions change, then the sort of individual
that used to succeed may now fail to succeed and a sort of individual
that could not get on at all under the old conditions may now find its
opportunity. These species will change, therefore, generation by
generation; the old sort of individual that used to prosper and dominate
will fail and die out and the new sort of individual will become the
rule,--until the general character of the species changes.
Suppose, for example, there is some little furry whitey-brown animal
living in a bitterly cold land which is usually under snow. Such
individuals as have the thickest, whitest fur will be least hurt by the
cold, less seen by their enemies, and less conspicuous as they seek
their prey. The fur of this species will thicken and its whiteness
increase with every generation, until there is no advantage in carrying
any more fur.
[Illustration: DIAGRAM OF LIFE IN THE LATER PALÆOZOIC AGE.
Life is creeping out of the water. An insect like a dragon fly is shown.
There were amphibia like gigantic newts and salamanders, and even
primitive reptiles in these swamps.]
Imagine now a change of climate that brings warmth into the land, sweeps
away the snows, makes white creatures glaringly visible during the
greater part of the year and thick fur an encumbrance. Then every
individual with a touch of brown in its colouring and a thinner fur will
find itself at an advantage, and very white and heavy fur will be a
handicap. There will be a weeding out of the white in favour of the
brown in each generation. If this change of climate come about too
quickly, it may of course exterminate the species altogether; but if it
come about gradually, the species, although it may have a hard time, may
yet be able to change itself and adapt itself generation by generation.
This change and adaptation is called the _Modification of Species_.
Perhaps this change of climate does not occur all over the lands
inhabited by the species; maybe it occurs only on one side of some great
arm of the sea or some great mountain range or such-like divide, and not
on the other. A warm ocean current like the Gulf Stream may be
deflected, and flow so as to warm one side of the barrier, leaving the
other still cold. Then on the cold side this species will still be going
on to its utmost possible furriness and whiteness and on the other side
it will be modifying towards brownness and a thinner coat. At the same
time there will probably be other changes going on; a difference in the
paws perhaps, because one half of the species will be frequently
scratching through snow for its food, while the other will be scampering
over brown earth. Probably also the difference of climate will mean
differences in the sort of food available, and that may produce
differences in the teeth and the digestive organs. And there may be
changes in the sweat and oil glands of the skin due to the changes in
the fur, and these will affect the excretory organs and all the internal
chemistry of the body. And so through all the structure of the creature.
A time will come when the two separated varieties of this formerly
single species will become so unlike each other as to be recognizably
different species. Such a splitting up of a species in the course of
generations into two or more species is called the _Differentiation of
Species_.
And it should be clear to the reader that given these elemental facts of
life, given growth and death and reproduction with individual variation
in a world that changes, life _must_ change in this way, modification
and differentiation _must_ occur, old species _must_ disappear, and new
ones appear. We have chosen for our instance here a familiar sort of
animal, but what is true of furry beasts in snow and ice is true of all
life, and equally true of the soft jellies and simple beginnings that
flowed and crawled for hundreds of millions of years between the tidal
levels and in the shallow, warm waters of the Proterozoic seas.
The early life of the early world, when the blazing sun rose and set in
only a quarter of the time it now takes, when the warm seas poured in
great tides over the sandy and muddy shores of the rocky lands and the
air was full of clouds and steam, must have been modified and varied and
species must have developed at a great pace. Life was probably as swift
and short as the days and years; the generations, which natural
selection picked over, followed one another in rapid succession.
Natural selection is a slower process with man than with any other
creature. It takes twenty years or more before an ordinary human being
in western Europe grows up and reproduces. In the case of most animals
the new generation is on trial in a year or less. With such simple and
lowly beings, however, as first appeared in the primordial seas, growth
and reproduction was probably a matter of a few brief hours or even of a
few brief minutes. Modification and differentiation of species must
accordingly have been extremely rapid, and life had already developed a
very great variety of widely contrasted forms before it began to leave
traces in the rocks. The Record of the Rocks does not begin, therefore,
with any group of closely related forms from which all subsequent and
existing creatures are descended. It begins in the midst of the game,
with nearly every main division of the animal kingdom already
represented.[9] Plants are already plants, and animals animals. The
curtain rises on a drama in the sea that has already begun, and has been
going on for some time. The brachiopods are discovered already in their
shells, accepting and consuming much the same sort of food that oysters
and mussels do now; the great water scorpions crawl among the seaweeds,
the trilobites roll up into balls and unroll and scuttle away. In that
ancient mud and among those early weeds there was probably as rich and
abundant and active a life of infusoria and the like as one finds in a
drop of ditch-water to-day. In the ocean waters, too, down to the utmost
downward limit to which light could filter, then as now, there was an
abundance of minute and translucent, and in many cases phosphorescent,
beings.
But though the ocean and intertidal waters already swarmed with life,
the land above the high-tide line was still, so far as we can guess, a
stony wilderness without a trace of life.
IV
THE INVASION OF THE DRY LAND BY LIFE
§ 1. _Life and Water._ § 2. _The Earliest Animals._
§ 1
Wherever the shore line ran there was life, and that life went on in and
by and with water as its home, its medium, and its fundamental
necessity.
The first jelly-like beginnings of life must have perished whenever they
got out of the water, as jelly-fish dry up and perish on our beaches
to-day. Drying up was the fatal thing for life in those days, against
which at first it had no protection. But in a world of rain-pools and
shallow seas and tides, any variation that enabled a living thing to
hold out and keep its moisture during hours of low tide of drought met
with every encouragement in the circumstances of the time. There must
have been a constant risk of stranding. And, on the other hand, life had
to keep rather near the shore and beaches in the shallows because it had
need of air (dissolved of course in the water) and light.
No creature can breathe, no creature can digest its food, without water.
We talk of breathing air, but what all living things really do is to
breathe oxygen dissolved in water. The air we ourselves breathe must
first be dissolved in the moisture in our lungs; and all our food must
be liquefied before it can be assimilated. Water-living creatures which
are always under water, wave the freely exposed gills by which they
breathe in that water, and extract the air dissolved in it. But a
creature that is to be exposed for any time out of the water, must have
its body and its breathing apparatus protected from drying up. Before
the seaweeds could creep up out of the Early Palæozoic seas into the
intertidal line of the beach, they had to develop a tougher outer skin
to hold their moisture. Before the ancestor of the sea scorpion could
survive being left by the tide it had to develop its casing and armour.
The trilobites probably developed their tough covering and rolled up
into balls, far less as a protection against each other and any other
enemies they may have possessed, than as a precaution against drying.
And when presently, as we ascend the Palæozoic rocks, the fish appear,
first of all the backboned or vertebrated animals, it is evident that a
number of them are already adapted by the protection of their gills with
gill covers and by a sort of primitive lung swimming-bladder, to face
the same risk of temporary stranding.
Now the weeds and plants that were adapting themselves to intertidal
conditions were also bringing themselves into a region of brighter
light, and light is very necessary and precious to all plants. Any
development of structure that would stiffen them and hold them up to the
light, so that instead of crumpling and flopping when the waters
receded, they would stand up outspread, was a great advantage. And so we
find them developing fibre and support, and the beginning of _woody
fibre_ in them. The early plants reproduced by soft spores, or
half-animal “gametes,” that were released in water, were distributed by
water and could only germinate under water. The early plants were tied,
and most lowly plants to-day are tied, by the conditions of their life
cycle, to water. But here again there was a great advantage to be got by
the development of some protection of the spores from drought that would
enable reproduction to occur without submergence. So soon as a species
could do that, it could live and reproduce and spread above the
high-water mark, bathed in light and out of reach of the beating and
distress of the waves. The main classificatory divisions of the larger
plants mark stages in the release of plant life from the necessity of
submergence by the development of woody support and of a method of
reproduction that is more and more defiant of drying up. The lower
plants are still the prisoner attendants of water. The lower mosses must
live in damp, and even the development of the spore of the ferns demands
at certain stages extreme wetness. The highest plants have carried
freedom from water so far that they can live and reproduce if only
there is some moisture in the soil below them. They have solved their
problem of living out of water altogether.
The essentials of that problem were worked out through the vast æons of
the Proterozoic Age and the early Palæozoic Age by nature’s method of
experiment and trial. Then slowly, but in great abundance, a variety of
new plants began to swarm away from the sea and over the lower lands,
still keeping to swamp and lagoon and watercourse as they spread.
§ 2
And after the plants came the animal life.
There is no sort of land animal in the world, as there is no sort of
land plant, whose structure is not primarily that of a water-inhabiting
being which has been adapted through the modification and
differentiation of species to life out of the water. This adaptation is
attained in various ways. In the case of the land scorpion the
gill-plates of the primitive sea scorpion are sunken into the body so as
to make the lung-books secure from rapid evaporation. The gills of
crustaceans, such as the crabs which run about in the air, are protected
by the gill-cover extensions of the back shell or carapace. The
ancestors of the insects developed a system of air pouches and air
tubes, the tracheal tubes, which carry the air all over the body before
it is dissolved. In the case of the vertebrated land animals, the gills
of the ancestral fish were first supplemented and then replaced by a
bag-like growth from the throat, the primitive lung swimming-bladder. To
this day there survive certain mudfish which enable us to understand
very clearly the method by which the vertebrated land animals worked
their way out of the water. These creatures (_e.g._ the African lung
fish) are found in tropical regions in which there is a rainy full
season and a dry season, during which the rivers become mere ditches of
baked mud. During the rainy season these fish swim about and breathe by
gills like any other fish. As the waters of the river evaporate, these
fish bury themselves in the mud, their gills go out of action, and the
creature keeps itself alive until the waters return by swallowing air,
which passes into its swimming-bladder. The Australian lung fish, when
it is caught by the drying up of the river in stagnant pools, and the
water has become deaerated and foul, rises to the surface and gulps air.
A newt in a pond does exactly the same thing. These creatures still
remain at the transition stage, the stage at which the ancestors of the
higher vertebrated animals were released from their restriction to an
under-water life.
The amphibia (frogs, newts, tritons, etc.) still show in their life
history all the stages in the process of this liberation. They are still
dependent on water for their reproduction; their eggs must be laid in
sunlit water, and there they must develop. The young tadpole has
branching external gills that wave in the water; then a gill cover grows
back over them and forms a gill chamber. Then, as the creature’s legs
appear and its tail is absorbed, it begins to use its lungs, and its
gills dwindle and vanish. The adult frog can live all the rest of its
days in the air, but it can be drowned if it is kept steadfastly below
water. When we come to the reptile, however, we find an egg which is
protected from evaporation by a tough egg case, and this egg produces
young which breathe by lungs from the very moment of hatching. The
reptile is on all fours with the seeding plant in its freedom from the
necessity to pass any stage of its life cycle in water.
[Illustration: _Australian Lung fish breathing air_]
The later Palæozoic Rocks of the northern hemisphere give us the
materials for a series of pictures of this slow spreading of life over
the land. Geographically, all round the northern half of the world it
was an age of lagoons and shallow seas very favourable to this invasion.
The new plants, now that they had acquired the power to live this new
aerial life, developed with an extraordinary richness and variety.
[Illustration: Some Reptiles of the Late Palæozoic Age]
There were as yet no true flowering plants,[10] no grasses nor trees
that shed their leaves in winter;[11] the first “flora” consisted of
great tree ferns, gigantic equisetums, cycad ferns, and kindred
vegetation. Many of these plants took the form of huge-stemmed trees, of
which great multitudes of trunks survive fossilized to this day. Some of
these trees were over a hundred feet high, of orders and classes now
vanished from the world. They stood with their stems in the water, in
which no doubt there was a thick tangle of soft mosses and green slime
and fungoid growths that left few plain vestiges behind them. The
abundant remains of these first swamp forests constitute the main
coal-measures of the world to-day.
Amidst this luxuriant primitive vegetation crawled and glided and flew
the first insects. They were rigid-winged, four-winged creatures, often
very big, some of them having wings measuring a foot in length. There
were numerous dragon flies--one found in the Belgian coal-measures had a
wing span of twenty-nine inches! There were also a great variety of
flying cockroaches. Scorpions abounded, and a number of early spiders,
which, however, had no spinnerets for web making.[12] Land snails
appeared. So too did the first-known step of our own ancestry upon land,
the amphibia. As we ascend the higher levels of the Later Palæozoic
record, we find the process of air adaptation has gone as far as the
appearance of true reptiles amidst the abundant and various amphibia.
The land life of the Upper Palæozoic Age was the life of a green swamp
forest without flowers or birds or the noises of modern insects. There
were no big land beasts at all; wallowing amphibia and primitive
reptiles were the very highest creatures that life had so far produced.
Whatever land lay away from the water or high above the water was still
altogether barren and lifeless. But steadfastly, generation by
generation, life was creeping away from the shallow sea-water of its
beginning.
V
CHANGES IN THE WORLD’S CLIMATE
§ 1. _Why Life Must Change Continually._ § 2. _The Sun a Steadfast
Star._ § 3. _Changes from Within the Earth._ § 4. _Life May Control
Change._
§ 1
The Record of the Rocks is like a great book that has been carelessly
misused. All its pages are torn, worn, and defaced, and many are
altogether missing. The outline of the story that we sketch here has
been pieced together slowly and painfully in an investigation that is
still incomplete and still in progress. The Carboniferous Rocks, the
“coal-measures,” give us a vision of the first great expansion of life
over the wet lowlands. Then come the torn pages known as the Permian
Rocks (which count as the last of the Palæozoic), that preserve very
little for us of the land vestiges of their age. Only after a long
interval of time does the history spread out generously again.
It must be borne in mind that great changes of climate have always been
in progress, that have sometimes stimulated and sometimes checked life.
Every species of living thing is always adapting itself more and more
closely to its conditions. And conditions are always changing. There is
no finality in adaptation. There is a continuing urgency towards fresh
change.
About these changes of climate some explanations are necessary here.
They are not regular changes; they are slow fluctuations between heat
and cold. The reader must not think that because the sun and earth were
once incandescent, the climatic history of the world is a simple story
of cooling down. The centre of the earth is certainly very hot to this
day, but we feel nothing of that internal heat at the surface; the
internal heat, except for volcanoes and hot springs, has not been
perceptible at the surface since first the rocks grew solid. Even in the
Azoic or Archæozoic Age there are traces in ice-worn rocks and the like
of periods of intense cold. Such cold waves have always been going on
everywhere, alternately with warmer conditions. And there have been
periods of great wetness and periods of great dryness throughout the
earth.
A complete account of the causes of these great climatic fluctuations
has still to be worked out, but we may perhaps point out some of the
chief of them.[13] Prominent among them is the fact that the earth does
not spin in a perfect circle round the sun. Its path or orbit is like a
hoop that is distorted; it is, roughly speaking, elliptical
(ovo-elliptical), and the sun is nearer to one end of the ellipse than
the other. It is at a point which is a focus of the ellipse. And the
shape of this orbit never remains the same. It is slowly distorted by
the attractions of the other planets, for ages it may be nearly
circular, for ages it is more or less elliptical. As the ellipse becomes
most nearly circular, then the focus becomes most nearly the centre.
When the orbit becomes most elliptical, then the position of the sun
becomes most remote from the middle or, to use the astronomer’s phrase,
most eccentric. When the orbit is most nearly circular, then it must be
manifest that all the year round the earth must be getting much the same
amount of heat from the sun; when the orbit is most distorted, then
there will be a season in each year when the earth is nearest the sun
(this phase is called _Perihelion_) and getting a great deal of heat
comparatively, and a season when it will be at its farthest from the sun
(_Aphelion_) and getting very little warmth. A planet at _aphelion_ is
travelling its slowest, and its fastest at _perihelion_; so that the hot
part of its year will last for a much less time than the cold part of
its year. (Sir Robert Ball calculated that the greatest difference
possible between the seasons was thirty-three days.) During ages when
the orbit is most nearly circular there will therefore be least extremes
of climate, and when the orbit is at its greatest eccentricity, there
will be an age of cold with great extremes of seasonal temperature.
These _changes in the orbit of the earth_ are due to the varying pull of
all the planets, and Sir Robert Ball declared himself unable to
calculate any regular cycle of orbital change, but Professor G. H.
Darwin maintained that it is possible to make out a kind of cycle
between greatest and least eccentricity of about 200,000 years.
But this change in the shape of the orbit is only one cause of the
change of the world’s climate. There are many others that have to be
considered with it. As most people know, the change in the seasons is
due to the fact that the equator of the earth is inclined at an angle to
the plane of its orbit. If the earth stood up straight in its orbit, so
that its equator was in the plane of its orbit, there would be no change
in the seasons at all. The sun would always be overhead at the equator,
and the day and night would each be exactly twelve hours long throughout
the year everywhere. It is this inclination which causes the difference
in the seasons and the unequal length of the day in summer and winter.
There is, according to Laplace, a possible variation of nearly three
degrees (from 22° 6’ to 24° 50’) in this inclination of the equator to
the orbit, and when this is at a maximum, the difference between summer
and winter is at its greatest. Great importance has been attached to
this variation in the inclination of the equator to the orbit by Dr.
Croll in his book _Climate and Time_. At present the angle is 23° 27’.
Manifestly when the angle is at its least, the world’s climate, other
things being equal, will be most equable.
And as a third important factor there is what is called the _precession
of the equinoxes_. This is a slow wabble of the pole of the spinning
earth that takes 25,000 odd years. Any one who watches a spinning top as
it “sleeps,” will see its axis making a slow circular movement, exactly
after the fashion of this circling movement of the earth’s axis. The
north pole, therefore, does not always point to the same north point
among the stars; its pointing traces out a circle in the heavens every
25,000 years.
Now, there will be times when the earth is at its extreme of aphelion or
of perihelion, when one hemisphere will be most turned to the sun in
its midsummer position and the other most turned away at its midwinter
position. And as the precession of the equinoxes goes on, a time will
come when the summer-winter position will come not at aphelion and
perihelion, but at the half-way points between them. When the summer of
one hemisphere happens at perihelion and the winter at aphelion, it will
be clear that the summer of the other hemisphere will happen at aphelion
and its winter at perihelion. One hemisphere will have a short hot
summer and a very cold winter, and the other a long cold summer and a
briefer warmish winter. But when the summer-winter positions come at the
half-way point of the orbit, and it is the spring of one hemisphere and
the autumn of the other that is at aphelion or perihelion, there will
not be the same wide difference between the climate of the two
hemispheres.
Here are three wavering systems of change all going on independently of
each other; the precession of the equinoxes, the change in the obliquity
of the equator to the orbit, and the changes in the eccentricity of the
orbit. Each system tends by itself to produce periods of equability and
periods of greater climatic contrast. And all these systems of change
interplay with each other. When it happens that at the same time the
orbit is most nearly circular, the equator is at its least inclination
from the plane of the earth’s orbit, and the spring and autumn are at
perihelion and aphelion, then all these causes will be conspiring to
make climate warm and uniform; there will be least difference of summer
and winter. When, on the other hand, the orbit is in its most eccentric
stage of deformation, when also the equator is most tilted up and when
further the summer and winter are at aphelion and perihelion, then
climates will be at their extremest and winter at its bitterest. There
will be great accumulations of ice and snow in winter; the heat of the
brief hot summer will be partly reflected back into space by the white
snow, and it will be unequal to the task of melting all the winter’s ice
before the earth spins away once more towards its chilly aphelion. The
earth will accumulate cold so long as this conspiracy of extreme
conditions continues.
[Illustration: DIAGRAM TO ILLUSTRATE ONE SET OF CAUSES, THE ASTRONOMICAL
VARIATIONS, WHICH MAKE THE CLIMATE OF THE WORLD CHANGE SLOWLY BUT
CONTINUOUSLY.
It does not change in regular periods. It fluctuates through vast ages.
As the world’s climate changes, life must change too or perish.]
So our earth’s climate changes and wavers perpetually as these three
systems of influence come together with a common tendency towards
warmth or severity, or as they contradict and cancel each other.
We can trace in the Record of the Rocks an irregular series of changes
due to the interplay of these influences; there have been great ages
when the separate rhythms of these three systems kept them out of
agreement and the atmosphere was temperate, ages of world-wide warmth,
and other ages when they seemed to concentrate bitterly to their utmost
extremity, to freeze out and inflict the utmost stresses and hardship
upon life.
And in accordance we find from the record in the rocks that there have
been long periods of expansion and multiplication when life flowed and
abounded and varied, and harsh ages when there was a great weeding out
and disappearance of species, genera, and classes, and the learning of
stern lessons by all that survived. Such a propitious conjunction it
must have been that gave the age of luxuriant low-grade growth of the
coal-measures; such an adverse series of circumstances that chilled the
closing æons of the Palæozoic time.
It is probable that the warm spells have been long relatively to the
cold ages. Our world to-day seems to be emerging with fluctuations from
a prolonged phase of adversity and extreme conditions. Half a million
years ahead it may be a winterless world with trees and vegetation even
in the polar circles. At present we have no certainty in such a
forecast, but later on, as knowledge increases, it may be possible to
reckon with more precision, so that our race will make its plans
thousands of years ahead to meet the coming changes.
§ 2
Another entirely different cause of changes in the general climate of
the earth may be due to variations in the heat of the sun. We do not yet
understand what causes the heat of the sun or what sustains that undying
fire. It is possible that in the past there have been periods of greater
and lesser intensity. About that we know nothing; human experience has
been too short; and so far we have been able to find no evidence on this
matter in the geological record. On the whole, scientific men are
inclined to believe that the sun has blazed with a general steadfastness
throughout geological time. It may have been cooling slowly, but,
speaking upon the scale of things astronomical, it has certainly not
cooled very much.
§ 3
A third great group of causes influencing climate are to be found in the
forces within the world itself. Throughout the long history of the earth
there has been a continuous wearing down of the hills and mountains by
frost and rain and a carrying out of their material to become
sedimentary rocks under the seas. There has been a continuous process of
wearing down the land and filling up the seas, by which the seas, as
they became shallower, must have spread more and more over the land. The
reverse process, a process of crumpling and upheaval, has also been in
progress, but less regularly. The forces of upheaval have been
spasmodic; the forces of wearing down continuous. For long ages there
has been comparatively little volcanic upheaval, and then have come
periods in which vast mountain chains have been thrust up and the whole
outline of land and sea changed. Such a time was the opening stage of
the Cainozoic period, in which the Alps, the Himalayas, and the Andes
were all thrust up from the sea-level to far beyond their present
elevations, and the main outlines of the existing geography of the world
were drawn.
Now, a time of high mountains and deep seas would mean a larger dry land
surface for the world, and a more restricted sea surface, and a time of
low lands would mean a time of wider and shallower seas. High mountains
precipitate moisture from the atmosphere and hold it out of circulation
as snow and glaciers, while smaller oceans mean a lesser area for
surface evaporation. Other things being equal, lowland stages of the
world’s history would be ages of more general atmospheric moisture than
periods of relatively greater height of the mountains and greater depth
of the seas. But even small increases in the amount of moisture in the
air have a powerful influence upon the transmission of radiant heat
through that air. The sun’s heat will pass much more freely through dry
air than through moist air, and so a greater amount of heat would reach
the land surfaces of the globe under the conditions of extremes of
elevation and depth, than during the periods of relative lowness and
shallowness. Dry phases in the history of the earth mean, therefore, hot
days. But they also mean cold nights, because for the same reason that
the heat comes abundantly to the earth, it will be abundantly radiated
away. Moist phases mean, on the other hand, cooler days and warmer
nights. The same principle applies to the seasons, and so a phase of
great elevations and depressions of the surface would also be another
contributory factor on the side of extreme climatic conditions.
And a stage of greater elevation and depression would intensify its
extreme conditions by the gradual accumulation of ice caps upon the
polar regions and upon the more elevated mountain masses. This
accumulation would be at the expense of the sea, whose surface would
thus be further shrunken in comparison with the land.
Here, then, is another set of varying influences that will play in with
and help or check the influence of the astronomical variations stated in
§ 1 and § 2. There are other more localized forces at work into which we
cannot go in any detail here, but which will be familiar to the student
of the elements of physical geography; the influence of great ocean
currents in carrying warmth from equatorial to more temperate latitudes;
the interference of mountain chains with the moisture borne by prevalent
winds and the like. As in the slow processes of nature these currents
are deflected or the mountain chains worn down or displaced by fresh
upheavals, the climate over great areas will be changed and all the
conditions of life changed with it. Under the incessant slow variations
of these astronomical, telluric, and geographical influences life has no
rest. As its conditions change it must change or perish.
§ 4
And while we are enumerating the forces that change climate and the
conditions of terrestrial life, we may perhaps look ahead a little and
add a fourth set of influences, at first unimportant in the history of
the world so far as the land surface is concerned, but becoming more
important after the age of Reptiles, to which we shall proceed in our
next chapter. These are the effects produced upon climate by life
itself. Particularly great is the influence of vegetation, and
especially that of forests. Every tree is continually transpiring water
vapour into the air; the amount of water evaporated in summer by a lake
surface is far less than the amount evaporated by the same area of beech
forest. As in the later Mesozoic and the Cainozoic Age, great forests
spread over the world, their action in keeping the air moist and
mitigating and stabilizing climate by keeping the summer cool and the
winter mild must have become more and more important. Moreover, forests
accumulate and protect soil and so prepare the possibility of
agricultural life.
Water-weeds again may accumulate to choke and deflect rivers, flood and
convert great areas into marshes, and so lead to the destruction of
forests or the replacement of grass-lands by boggy wildernesses.
Finally, with the appearance of human communities, came what is perhaps
the most powerful of all living influences upon climate. By fire and
plough and axe man alters his world. By destroying forests and by
irrigation man has already affected the climate of great regions of the
world’s surface. The destruction of forests makes the seasons more
extreme; this has happened, for instance, in the northeastern states of
the United States of America. Moreover, the soil is no longer protected
from the scour of rain, and is washed away, leaving only barren rock
beneath. This has happened in Spain and Dalmatia and, some thousands of
years earlier, in South Arabia. By irrigation, on the other hand, man
restores the desert to life and mitigates climate. This process is going
on in Northwest India and Australia. In the future, by making such
operations worldwide and systematic, man may be able to control climate
to an extent at which as yet we can only guess.
VI
THE AGE OF REPTILES
§ 1. _The Age of Lowland Life._ § 2. _Flying Dragons._ § 3. _The
First Birds._ § 4. _An Age of Hardship and Death._ § 5. _The First
Appearance of Fur and Feathers._
§ 1
We know that for hundreds of thousands of years the wetness and warmth,
the shallow lagoon conditions that made possible the vast accumulations
of vegetable matter which, compressed and mummified,[14] are now coal,
prevailed over most of the world. There were some cold intervals, it is
true; but they did not last long enough to destroy the growths. Then
that long age of luxuriant low-grade vegetation drew to its end, and for
a time life on the earth seems to have undergone a period of world-wide
bleakness.
When the story resumes again, we find life entering upon a fresh phase
of richness and expansion. Vegetation has made great advances in the art
of living out of water. While the Palæozoic plants of the coal-measures
probably grew with swamp water flowing over their roots, the Mesozoic
flora from its very outset included palm-like cycads and low-ground
conifers that were distinctly land plants growing on soil above the
water level. The lower levels of the Mesozoic land were no doubt covered
by great fern brakes and shrubby bush and a kind of jungle growth of
trees. But there existed as yet no grass, no small flowering plants, no
turf nor greensward. Probably the Mesozoic was not an age of very
brightly coloured vegetation. It must have had a flora green in the wet
season and brown and purple in the dry. There were no gay flowers, no
bright autumn tints before the fall of the leaf, because there was as
yet no fall of the leaf. And beyond the lower levels the world was still
barren, still unclothed, still exposed without any mitigation to the
wear and tear of the wind and rain.
When one speaks of conifers in the Mesozoic the reader must not think of
the pines and firs that clothe the high mountain slopes of our time. He
must think of low-growing evergreens. The mountains were still as bare
and lifeless as ever. The only colour effects among the mountains were
the colour effects of naked rock, such colours as make the landscape of
Colorado so marvellous to-day.
Amidst this spreading vegetation of the lower plains the reptiles were
increasing mightily in multitude and variety. They were now in many
cases absolutely land animals. There are numerous anatomical points of
distinction between a reptile and an amphibian; they held good between
such reptiles and amphibians as prevailed in the carboniferous time of
the Upper Palæozoic; but the fundamental difference between reptiles and
amphibia which matters in this history is that the amphibian must go
back to the water to lay its eggs, and that in the early stages of its
life it must live in and under water. The reptile, on the other hand,
has cut out all the tadpole stages from its life cycle, or, to be more
exact, its tadpole stages are got through before the young leave the egg
case. The reptile has come out of the water altogether. Some had gone
back to it again, just as the hippopotamus and the otter among mammals
have gone back, but that is a further extension of the story to which we
cannot give much attention in this _Outline_.
[Illustration: Some Mesozoic Reptiles]
In the Palæozoic period, as we have said, life had not spread beyond the
swampy river valleys and the borders of sea lagoons and the like; but in
the Mesozoic, life was growing ever more accustomed to the thinner
medium of the air, was sweeping boldly up over the plains and towards
the hillsides. It is well for the student of human history and the human
future to note that. If a disembodied intelligence with no knowledge of
the future had come to earth and studied life during the early Palæozoic
age, he might very reasonably have concluded that life was absolutely
confined to the water, and that it could never spread over the land. It
found a way. In the Later Palæozoic Period that visitant might have been
equally sure that life could not go beyond the edge of a swamp. The
Mesozoic Period would still have found him setting bounds to life far
more limited than the bounds that are set to-day. And so to-day, though
we mark how life and man are still limited to five miles of air and a
depth of perhaps a mile or so of sea, we must not conclude from that
present limitation that life, through man, may not presently spread out
and up and down to a range of living as yet inconceivable.
[Illustration: Some
Late Mesozoic
Reptiles]
The earliest known reptiles were beasts with great bellies and not very
powerful legs, very like their kindred amphibia, wallowing as the
crocodile wallows to this day; but in the Mesozoic they soon began to
stand up and go stoutly on all fours, and several great sections of them
began to balance themselves on tail and hind legs, rather as the
kangaroos do now, in order to release the fore limbs for grasping food.
The bones of one notable division of reptiles which retained a
quadrupedal habit, a division of which many remains have been found in
South African and Russian Early Mesozoic deposits, display a number of
characters which approach those of the mammalian skeleton, and because
of this resemblance to the mammals (beasts) this division is called the
_Theriomorpha_ (beastlike). Another division was the crocodile branch,
and another developed towards the tortoises and turtles. The
_Plesiosaurs_ and _Ichthyosaurs_ were two groups which have left no
living representatives; they were huge reptiles returning to a
whale-like life in the sea. _Pliosaurus_, one of the largest
plesiosaurs, measured thirty feet from snout to tail tip--of which half
was neck. The _Mosasaurs_ were a third group of great porpoise-like
marine lizards. But the largest and most diversified group of these
Mesozoic reptiles was the group we have spoken of as kangaroo-like, the
_Dinosaurs_, many of which attained enormous proportions. In bigness
these greater _Dinosaurs_ have never been exceeded, although the sea can
still show in the whales creatures as great. Some of these, and the
largest among them, were herbivorous animals; they browsed on the rushy
vegetation and among the ferns and bushes, or they stood up and grasped
trees with their fore legs while they devoured the foliage. Among the
browsers, for example, were the _Diplodocus carnegii_, which measured
eighty=four feet in length, and the _Atlantosaurus_. The
_Gigantosaurus_, disinterred by a German expedition in 1912 from rocks
in East Africa, was still more colossal. It measured well over a hundred
feet! These greater monsters had legs, and they are usually figured as
standing up on them; but it is very doubtful if they could have
supported their weight in this way, out of water. Buoyed up by water or
mud, they may have got along. Another noteworthy type we have figured is
the _Triceratops_. There were also a number of great flesh-eaters who
preyed upon these herbivores. Of these, _Tyrannosaurus_ seems almost the
last word in “frightfulness” among living things. Some species of this
genus measured forty feet from snout to tail. Apparently it carried this
vast body kangaroo fashion on its tail and hind legs. Probably it reared
itself up. Some authorities even suppose that it leapt through the air.
If so, it possessed muscles of a quite miraculous quality. A leaping
elephant would be a far less astounding idea. Much more probably it
waded half submerged in pursuit of the herbivorous river saurians.
§ 2
One special development of the dinosaurian type of reptile was a light,
hopping, climbing group of creatures which developed a bat-like web
between the fifth finger and the side of the body, which was used in
gliding from tree to tree after the fashion of the flying squirrels.
These bat-lizards were the _Pterodactyls_. They are often described as
_flying_ reptiles, and pictures are drawn of Mesozoic scenery in which
they are seen soaring and swooping about. But their breastbone has no
keel such as the breastbone of a bird has for the attachment of muscles
strong enough for long-sustained flying. They must have flitted about
like bats. They must have had a grotesque resemblance to heraldic
dragons, and they played the part of bat-like birds in the Mesozoic
jungles. But bird-like though they were, they were not birds nor the
ancestors of birds. The structure of their wings was altogether
different from that of birds. The structure of their wings was that of a
hand with one long finger and a web; the wing of a bird is like an arm
with feathers projecting from its hind edge. And these Pterodactyls had
no feathers.
§ 3
Far less prevalent at this time were certain other truly birdlike
creatures, of which the earlier sorts also hopped and clambered and the
later sorts skimmed and flew. These were at first--by all the standards
of classification--Reptiles. They developed into true birds as they
developed wings and as their reptilian scales became long and
complicated, fronds rather than scales, and so at last, by much
spreading and splitting, feathers. Feathers are the distinctive covering
of birds, and they give a power of resisting heat and cold far greater
than that of any other integumentary covering except perhaps the
thickest fur. At a very early stage this novel covering of feathers,
this new heatproof contrivance that life had chanced upon, enabled many
species of birds to invade a province for which the pterodactyl was ill
equipped. They took to sea fishing--if indeed they did not begin with
it--and spread to the north and south polewards beyond the temperature
limits set to the true reptiles. The earliest birds seem to have been
carnivorous divers and water birds. To this day some of the most
primitive bird forms are found among the sea birds of the Arctic and
Antarctic seas, and it is among these sea birds that zoologists still
find lingering traces of teeth, which have otherwise vanished completely
from the beak of the bird.
The earliest known bird (the _Archæopteryx_) had no beak; it had a row
of teeth in a jaw like a reptile’s. It had three claws at the forward
corner of its wing. Its tail too was peculiar. All modern birds have
their tail feathers set in a short compact bony rump; the _Archæopteryx_
had a long bony tail with a row of feathers along each side.
§ 4
[Illustration: Archæopteryx
(the earliest known bird)]
This great period of Mesozoic life, this second volume of the book of
life, is indeed an amazing story of reptilian life proliferating and
developing. But the most striking thing of all the story remains to be
told. Right up to the latest Mesozoic Rocks we find all these reptilian
orders we have enumerated still flourishing unchallenged. There is no
hint of an enemy or competitor to them in the relics we find of their
world. Then the record is broken. We do not know how long a time the
break represents; many pages may be missing here, pages that may
represent some great cataclysmal climatic change. When next we find
abundant traces of the land plants and the land animals of the earth,
this great multitude of reptile species had gone. For the most part they
have left no descendants. They have been “wiped out.” The pterodactyls
have gone absolutely; of the plesiosaurs and ichthyosaurs none is alive;
the mosasaurs have gone; of the lizards a few remain, the monitor of
the Dutch East Indies is the largest; all the multitude and diversity of
the dinosaurs have vanished. Only the crocodiles and the turtles and
tortoises carry on in any quantity into Cainozoic times. The place of
all these types in the picture that the Cainozoic fossils presently
unfold to us is taken by other animals not closely related to the
Mesozoic reptiles and certainly not descended from any of their ruling
types. A new kind of life is in possession of the world.
This apparently abrupt ending up of the reptiles is, beyond all
question, the most striking revolution in the whole history of the earth
before the coming of mankind. It is probably connected with the close of
a vast period of equable warm conditions and the onset of a new austerer
age, in which the winters were bitterer and the summers brief but hot.
The Mesozoic life, animal and vegetable alike, was adapted to warm
conditions and capable of little resistance to cold. The new life, on
the other hand, was before all things capable of resisting great changes
of temperature.
Whatever it was that led to the extinction of the Mesozoic reptiles, it
was probably some very far-reaching change indeed, for the life of the
seas did at the same time undergo a similar catastrophic alteration. The
crescendo and ending of the Reptiles on land was paralleled by the
crescendo and ending of the Ammonites, a division of creatures like
squids with coiled shells which swarmed in those ancient seas. All
through the rocky record of this Mesozoic period there is a vast
multitude and variety of these coiled shells; there are hundreds of
species, and towards the end of the Mesozoic period they increased in
diversity and produced exaggerated types. When the record resumes, these
too have gone. So far as the reptiles are concerned, people may perhaps
be inclined to argue that they were exterminated because the Mammals
that replaced them competed with them, and were more fitted to survive;
but nothing of the sort can be true of the Ammonites, because to this
day their place has not been taken. Simply they are gone. Unknown
conditions made it possible for them to live in the Mesozoic seas, and
then some unknown change made life impossible for them. No genus of
Ammonite survives to-day of all that vast variety, but there still
exists one isolated genus very closely related to the Ammonites, the
Pearly Nautilus. It is found, it is to be noted, in the warm waters of
the Indian and Pacific oceans.[15]
And as for the Mammals competing with and ousting the less fit reptiles,
a struggle of which people talk at times, there is not a scrap of
evidence of any such direct competition. To judge by the Record of the
Rocks as we know it to-day, there is much more reason for believing that
first the reptiles in some inexplicable way perished, and then that
later on, after a very hard time for all life upon the earth, the
mammals, as conditions became more genial again, developed and spread to
fill the vacant world.
§ 5
Were there mammals in the Mesozoic period?
This is a question not yet to be answered precisely. Patiently and
steadily the geologists gather fresh evidence and reason out completer
conclusions. At any time some new deposit may reveal fossils that will
illuminate this question. Certainly either mammals, or the ancestors of
the mammals, must have lived throughout the Mesozoic period. In the very
opening chapter of the Mesozoic volume of the Record there were those
Theriomorphous Reptiles to which we have already alluded, and in the
later Mesozoic a number of small jaw-bones are found, entirely mammalian
in character. But there is not a scrap, not a bone, to suggest that
there lived any Mesozoic Mammal which could look a dinosaur in the face.
The Mesozoic mammals or mammal-like reptiles--for we do not know clearly
which they were--seem to have been all obscure little beasts of the size
of mice and rats, more like a down-trodden order of reptiles than a
distinct class; probably they still laid eggs and were developing only
slowly their distinctive covering of hair. They lived away from big
waters, and perhaps in the desolate uplands, as marmots do now; probably
they lived there beyond the pursuit of the carnivorous dinosaurs. Some
perhaps went on all fours, some chiefly went on their hind legs and
clambered with their fore limbs. They became fossils only so
occasionally that chance has not yet revealed a single complete
skeleton in the whole vast record of the Mesozoic rocks by which to
check these guesses.
[Illustration: _Hesperornis_
(_Reptilian wingless water-bird_)]
These little Theriomorphs, these ancestral mammals, developed hair.
Hairs, like feathers, are long and elaborately specialized scales. Hair
is perhaps the clue to the salvation of the early mammals. Leading lives
upon the margin of existence, away from the marshes and the warmth,
they developed an outer covering only second in its warmth-holding (or
heat-resisting) powers to the down and feathers of the Arctic sea-birds.
And so they held out through the age of hardship between the Mesozoic
and Cainozoic ages, to which most of the true reptiles succumbed.
All the main characteristics of this flora and sea and land fauna that
came to an end with the end of the Mesozoic age were such as were
adapted to an equable climate and to shallow and swampy regions. But in
the case of their Cainozoic successors, both hair and feathers gave _a
power of resistance to variable temperatures_ such as no reptile
possessed, and with it they gave a range far greater than any animal had
hitherto attained.
The range of life of the Lower Palæozoic Period was confined to warm
water.
The range of life of the Upper Palæozoic Period was confined to warm
water or to warm swamps and wet ground.
The range of life of the Mesozoic Period as we know it was confined to
water and fairly low-lying valley regions under equable conditions.
Meanwhile in each of these periods there were types involuntarily
extending the range of life beyond the limits prevailing in that period;
and when ages of extreme conditions prevailed, it was these marginal
types which survived to inherit the depopulated world.
That perhaps is the most general statement we can make about the story
of the geological record; it is a story of widening range. Classes,
genera, and species of animals appear and disappear, but the range
widens. It widens always. Life has never had so great a range as it has
to-day. Life to-day, in the form of man, goes higher in the air than it
has ever done before; man’s geographical range is from pole to pole, he
goes under the water in submarines, he sounds the cold, lifeless
darkness of the deepest seas, he burrows into virgin levels of the
rocks, and in thought and knowledge he pierces to the centre of the
earth and reaches out to the uttermost star. Yet in all the relics of
the Mesozoic time we find no certain memorials of his ancestry. His
ancestors, like the ancestors of all the kindred mammals, must have
been creatures so rare, so obscure, and so remote that they have left
scarcely a trace amidst the abundant vestiges of the monsters that
wallowed rejoicing in the steamy air and lush vegetation of the Mesozoic
lagoons, or crawled or hopped or fluttered over the great river plains
of that time.[16]
VII
THE AGE OF MAMMALS
§ 1. _A New Age of Light._ § 2. _Tradition Comes into the World._ §
3. _An Age of Brain Growth._ § 4. _The World Grows Hard Again._ §
5. _Chronology of the Ice Age._
§ 1
The third great division of the geological record, the Cainozoic, opens
with a world already physically very like the world we live in to-day.
Probably the day was at first still perceptibly shorter, but the scenery
had become very modern in its character. Climate was, of course,
undergoing, age by age, its incessant and irregular variations; lands
that are temperate to-day have passed, since the Cainozoic age began,
through phases of great warmth, intense cold, and extreme dryness; but
the landscape, if it altered, altered to nothing that cannot still be
paralleled to-day in some part of the world or other. In the place of
the cycads, sequoias, and strange conifers of the Mesozoic, the plant
names that now appear in the lists of fossils include birch, beech,
holly, tulip trees, ivy, sweet gum, bread-fruit trees. Flowers had
developed concurrently with bees and butterflies. Palms were now very
important. Such plants had already been in evidence in the later levels
of the (American Cretaceous) Mesozoic, but now they dominated the scene
altogether. Grass was becoming a great fact in the world. Certain
grasses, too, had appeared in the later Mesozoic, but only with the
Cainozoic period came grass plains and turf spreading wide over a world
that was once barren stone.
The period opened with a long phase of considerable warmth; then the
world cooled. And in the opening of this third part of the record, this
Cainozoic period, a gigantic crumpling of the earth’s crust and an
upheaval of mountain ranges was in progress. The Alps, the Andes, the
Himalayas, are all Cainozoic mountain ranges; the background of an early
Cainozoic scene, to be typical, should display an active volcano or so.
It must have been an age of great earthquakes.
Geologists make certain main divisions of the Cainozoic period, and it
will be convenient to name them here and to indicate their climate.
First comes the _Eocene_ (dawn of recent life), an age of exceptional
warmth in the world’s history, subdivided into an older and newer
Eocene; then the _Oligocene_ (but little of recent life), in which the
climate was still equable. The _Miocene_ (with living species still in a
minority) was the great age of mountain building, and the general
temperature was falling. In the _Pliocene_ (more living than extinct
species), climate was very much at its present phase; but with the
_Pleistocene_ (a great majority of living species) there set in a long
period of extreme conditions--it was the Great Ice Age. Glaciers spread
from the poles towards the equator, until England to the Thames was
covered in ice. Thereafter to our own time came a period of partial
recovery.
§ 2
In the forests and following the grass over the Eocene plains there
appeared for the first time a variety and abundance of mammals. Before
we proceed to any description of these mammals, it may be well to note
in general terms what a mammal is.
[Illustration: Some Oligocene Mammals]
From the appearance of the vertebrated animals in the Lower Palæozoic
Age, when the fish first swarmed out into the sea, there has been a
steady progressive development of vertebrated creatures. A fish is a
vertebrated animal that breathes by gills and can live only in water. An
amphibian may be described as a fish that has added to its
gill-breathing the power of breathing air with its swimming-bladder in
adult life, and that has also developed limbs with five toes to them in
place of the fins of a fish. A tadpole is for a time a fish; it becomes
a land creature as it develops. A reptile is a further stage in this
detachment from water; it is an amphibian that is no longer amphibious;
it passes through its tadpole stage--its fish stage, that is--in an
egg. From the beginning it must breathe in air; it can never breathe
under water as a tadpole can do. Now, a modern mammal is really a sort
of reptile that has developed a peculiarly effective protective
covering, hair; and that also retains its eggs in the body until they
hatch so that it brings forth living young (viviparous), and even after
birth it cares for them and feeds them by its mammæ for a longer or
shorter period. Some reptiles, some vipers for example, are viviparous,
but none stand by their young as the real mammals do. Both the birds and
the mammals, which escaped whatever destructive forces made an end to
the Mesozoic reptiles, and which survived to dominate the Cainozoic
world, have these two things in common: first, a far more effective
protection against changes of temperature than any other variation of
the reptile type ever produced; and, secondly, a peculiar care for their
eggs, the bird by incubation and the mammal by retention, and a
disposition to look after the young for a certain period after hatching
or birth. There is by comparison the greatest carelessness about
offspring in the reptile.
Hair was evidently the earliest distinction of the mammals from the rest
of the reptiles. It is doubtful if the particular Theriodont reptiles
who were developing hair in the early Mesozoic were viviparous. Two
mammals survive to this day which not only do not suckle their
young,[17] but which lay eggs, the _Ornithorhynchus_ and the _Echidna_,
and in the Eocene there were a number of allied forms. They are the
survivors of what was probably a much larger number and variety of small
egg-laying hairy creatures, hairy reptiles, hoppers, climbers, and
runners, which included the Mesozoic ancestors of all existing mammals
up to and including man.
Now we may put the essential facts about mammalian reproduction in
another way. _The mammal is a family animal._ And the family habit
involved the possibility of a new sort of continuity of experience in
the world. Compare the completely closed-in life of an individual lizard
with the life of even a quite lowly mammal of almost any kind. The
former has no mental continuity with anything beyond itself; it is a
little self-contained globe of experience that serves its purpose and
ends; but the latter “picks up” from its mother, and “hands on” to its
offspring. All the mammals, except for the two genera we have named, had
already before the lower Eocene age arrived at this stage of pre-adult
dependence and imitation. They were all more or less imitative in youth
and capable of a certain modicum of education; they all, as a part of
their development, received a certain amount of care and example and
even direction from their mother. This is as true of the hyæna and
rhinoceros as it is of the dog or man; the difference of educability is
enormous, but the fact of protection and educability in the young stage
is undeniable. So far as the vertebrated animals go, these new mammals,
with their viviparous, young-protecting disposition, and these new
birds, with their incubating, young-protecting disposition, introduce at
the opening of the Cainozoic period a fresh thing into the expanding
story of life, namely, social association, the addition to hard and
inflexible instinct of _tradition_, and the nervous organization
necessary to receive tradition.
All the innovations that come into the history of life begin very
humbly. The supply of blood-vessels in the swimming-bladder of the
mudfish in the lower Palæozoic torrent-river, that enabled it to pull
through a season of drought, would have seemed at that time to that
bodiless visitant to our planet we have already imagined, a very
unimportant side fact in that ancient world of great sharks and plated
fishes, sea-scorpions, and coral reefs and seaweed; but it opened the
narrow way by which the land vertebrates arose to predominance. The
mudfish would have seemed then a poor refugee from the too crowded and
aggressive life of the sea. But once lungs were launched into the world,
every line of descent that had lungs went on improving them. So, too, in
the upper Palæozoic, the fact that some of the Amphibia were losing
their “amphibiousness” by a retardation of hatching of their eggs, would
have appeared a mere response to the distressful dangers that threatened
the young tadpole. Yet that prepared the conquest of the dry land for
the triumphant multitude of the Mesozoic reptiles. It opened a new
direction towards a free and vigorous land-life along which all the
reptilian animals moved. And this viviparous, young-tending training
that the ancestral mammalia underwent during that age of inferiority and
hardship for them, set going in the world a new continuity of
perception, of which even man to-day only begins to appreciate the
significance.
§ 3
A number of types of mammal already appear in the Eocene. Some are
differentiating in one direction, and some in another, some are
perfecting themselves as herbivorous quadrupeds, some leap and climb
among the trees, some turn back to the water to swim, but all types are
unconsciously exploiting and developing the brain which is the
instrument of this new power of acquisition and educability. In the
Eocene rocks are found small early predecessors of the horse (Eohippus),
tiny camels, pigs, early tapirs, early hedgehogs, monkeys and lemurs,
opossums and carnivores. Now, all these were more or less ancestral to
living forms, and all have brains relatively much smaller than their
living representatives. There is, for instance, an early rhinoceros,
_Titanotherium_, with a brain not one tenth the size of that of the
existing rhinoceros. The latter is by no means a perfect type of the
attentive and submissive student, but even so it is ten times more
observant and teachable than its predecessor. This sort of thing is true
of all the orders and families that survive until to-day. All the
Cainozoic mammals were doing this one thing in common under the urgency
of a common necessity; they were all growing brain. It was a parallel
advance. In the same order or family to-day, the brain is usually from
six to ten times what it was in the Eocene ancestor.
Grass was now spreading over the world, and with this extension arose
some huge graminivorous brutes of which no representative survives
to-day. Such were the Uintatheres and the Titanotheres. And in pursuit
of such beasts came great swarms of primitive dogs, some as big as
bears, and the first cats, one in particular (_Smilodon_), a small
fierce-looking creature with big knife-like canines, the first
sabre-toothed tiger, which was to develop into greater things. American
deposits in the Miocene display a great variety of camels, giraffe
camels with long necks, gazelle camels, llamas, and true camels. North
America, throughout most of the Cainozoic period, appears to have been
in open and easy continuation with Asia, and when at last the glaciers
of the Great Ice Age, and then the Bering Strait, came to separate the
two great continental regions, the last camels were left in the old
world and the llamas in the new.
In the Eocene the first ancestors of the elephants appear in northern
Africa as snouted creatures; the elephant’s trunk dawned on the world in
the Miocene.
One group of creatures is of peculiar interest in a history that is
mainly to be the story of mankind. We find fossils in the Eocene of
monkeys and lemurs, but of one particular creature we have as yet not a
single bone. It was half ape, half monkey; it clambered about the trees
and ran, and probably ran well, on its hind legs upon the ground. It was
small-brained by our present standards, but it had clever hands with
which it handled fruits and beat nuts upon the rocks and perhaps caught
up sticks and stones to smite its fellows. It was our ancestor.
§ 4
Through millions of simian generations the spinning world circled about
the sun; slowly its orbit, which may have been nearly circular during
the equable days of the early Eocene, was drawn by the attraction of the
circling outer planets into a more elliptical form. Its axis of
rotation, which had always heeled over to the plane of its orbit, as the
mast of a yacht under sail heels over to the level of the water, heeled
over by imperceptible degrees a little more and a little more. And each
year its summer point shifted a little further from perihelion round its
path. These were small changes to happen to a one-inch ball, circling at
a distance of 330 yards from a flaming sun nine feet across, in the
course of a few million years. They were changes an immortal astronomer
in Neptune, watching the earth from age to age, would have found almost
imperceptible. But from the point of view of the surviving mammalian
life of the Miocene, they mattered profoundly. Age by age the winters
grew on the whole colder and harder and a few hours longer relatively to
the summers in a thousand years; age by age the summers grew briefer. On
an average the winter snow lay a little later in the spring in each
century, and the glaciers in the northern mountains gained an inch this
year, receded half an inch next, came on again a few inches....
[Illustration: Miocene Mammals]
The Record of the Rocks tells of the increasing chill. The Pliocene was
a temperate time, and many of the warmth-loving plants and animals had
gone. Then, rather less deliberately, some feet or some inches every
year, the ice came on.
An arctic fauna, musk ox, woolly mammoth, woolly rhinoceros, lemming,
ushers in the Pleistocene. Over North America, and Europe and Asia
alike, the ice advanced. For thousands of years it advanced, and then
for thousands of years it receded, to advance again. Europe down to the
Baltic shores, Britain down to the Thames, North America down to New
England, and more centrally as far south as Ohio, lay for ages under the
glaciers. Enormous volumes of water were withdrawn from the ocean and
locked up in those stupendous ice caps so as to cause a world-wide
change in the relative levels of land and sea. Vast areas were exposed
that are now again sea bottom.
The world to-day is still coming slowly out of the last of four great
waves of cold. It is not growing warmer steadily. There have been
fluctuations. Remains of bog oaks, for example, which grew two or three
thousand years ago, are found in Scotland at latitudes in which not even
a stunted oak will grow at the present time. And it is amidst this
crescendo and diminuendo of frost and snow that we first recognize forms
that are like the forms of men. The Age of Mammals culminated in ice and
hardship and man.
§ 5
Guesses about the duration of the great age of cold are still vague, but
in the Time diagram on page 60 we follow H. F. Osborn in accepting as
our guides the estimates of Albrecht Penck[18] and C. A. Reeds.[19]
[Illustration: TIME DIAGRAM OF THE GLACIAL AGES.
The reader should compare this diagram carefully with our first time
diagram, Chapter II, § 2, p. 14. That diagram, if it were on the same
scale as this one, would be between 41 and 410 feet long. The position
of the Eoanthropus is very uncertain: it may be as early as the
Pliocene]
BOOK II
THE MAKING OF MEN
VIII
THE ANCESTRY OF MAN[20]
§ 1. _Man Descended from a Walking Ape._ § 2. _First Traces of
Man-like Creatures._ § 3. _The Heidelberg Sub-man._ § 4. _The
Piltdown Sub-man._ § 5. _The Riddle of the Piltdown Remains._
§ 1
The origin of man is still very obscure. It is commonly asserted that he
is “descended” from some man-like ape such as the chimpanzee, the
orang-utang, or the gorilla, but that of course is as reasonable as
saying that I am “descended” from some Hottentot or Esquimaux as young
or younger than myself. Others, alive to this objection, say that man is
descended from the common ancestor of the chimpanzee, the orang-utang,
and the gorilla. Some “anthropologists” have even indulged in a
speculation whether mankind may not have a double or treble origin; the
negro being descended from a gorilla-like ancestor, the Chinese from a
chimpanzee-like ancestor, and so on. These are very fanciful ideas, to
be mentioned only to be dismissed. It was formerly assumed that the
human ancestor was “probably arboreal,” but the current idea among those
who are qualified to form an opinion seems to be that he was a “ground
ape,” and that the existing apes have developed in the arboreal
direction.
[Illustration: Early Pleistocene Animals]
Of course, if one puts the skeleton of a man and the skeleton of a
gorilla side by side, their general resemblance is so great that it is
easy to jump to the conclusion that the former is derived from such a
type as the latter by a process of brain growth and general refinement.
But if one examines closely into one or two differences, the gap widens.
Particular stress has recently been laid upon the tread of the foot. Man
walks on his toe and his heel; his great toe is his chief lever in
walking, as the reader may see for himself if he examines his own
footprints on the bathroom floor and notes where the pressure falls as
the footprints become fainter. His great toe is the king of his toes.
Among all the apes and monkeys, the only group that have their great
toes developed on anything like the same fashion as man are some of the
lemurs. The baboon walks on a flat foot and all his toes, using his
middle toe as his chief throw off, much as the bear does. And the three
great apes all walk on the outer side of the foot in a very different
manner from the walking of man.
[Illustration: POSSIBLE APPEARANCE OF THE SUB-MAN _PITHECANTHROPUS_.
The face, jaws, and teeth are mere guess work (_see_ text). The creature
may have been much less human looking than this.]
The great apes are forest dwellers; their walking even now is
incidental; they are at their happiest among trees. They have very
distinctive methods of climbing; they swing by the arms much more than
the monkeys do, and do not, like the latter, take off with a spring from
the feet. They have a specially developed climbing style of their own.
But man walks so well and runs so swiftly as to suggest a very long
ancestry upon the ground. Also, he does not climb well now; he climbs
with caution and hesitation. His ancestors may have been running
creatures for long ages. Moreover, it is to be noted that he does not
swim naturally; he has to learn to swim, and that seems to point to a
long-standing separation from rivers and lakes and the sea. Almost
certainly that ancestor was a smaller and slighter creature than its
human descendants. Conceivably the human ancestor at the opening of the
Cainozoic period was a running ape, living chiefly on the ground, hiding
among rocks rather than trees. It could still climb trees well and hold
things between its great toe and its second toe (as the Japanese can to
this day), but it was already coming down to the ground again from a
still remoter, a Mesozoic arboreal ancestry. It is quite understandable
that such a creature would very rarely die in water in such
circumstances as to leave bones to become fossilized.