Part 1 (1/2)
The Story of Evolution.
by Joseph McCabe.
PREFACE
An ingenious student of science once entertained his generation with a theory of how one might behold again all the stirring chapters that make up the story of the earth. The living scene of our time is lit by the light of the sun, and for every few rays that enter the human eye, and convey the image of it to the human mind, great floods of the reflected light pour out, swiftly and indefinitely, into s.p.a.ce. Imagine, then, a man moving out into s.p.a.ce more rapidly than light, his face turned toward the earth. Flas.h.i.+ng through the void at, let us say, a million miles a second, he would (if we can overlook the dispersion of the rays of light) overtake in succession the light that fell on the French Revolution, the Reformation, the Norman Conquest, and the faces of the ancient empires. He would read, in reverse order, the living history of man and whatever lay before the coming of man.
Few thought, as they smiled over this fairy tale of science, that some such panoramic survey of the story of the earth, and even of the heavens, might one day be made in a leisure hour by ordinary mortals; that in the soil on which they trod were surer records of the past than in its doubtful literary remains, and in the deeper rocks were records that dimly lit a vast abyss of time of which they never dreamed. It is the supreme achievement of modern science to have discovered and deciphered these records. The picture of the past which they afford is, on the whole, an outline sketch. Here and there the details, the colour, the light and shade, may be added; but the greater part of the canvas is left to the more skilful hand of a future generation, and even the broad lines are at times uncertain. Yet each age would know how far its scientific men have advanced in constructing that picture of the growth of the heavens and the earth, and the aim of the present volume is to give, in clear and plain language, as full an account of the story as the present condition of our knowledge and the limits of the volume will allow. The author has been for many years interested in the evolution of things, or the way in which suns and atoms, fishes and flowers, hills and elephants, even man and his inst.i.tutions, came to be what they are. Lecturing and writing on one or other phase of the subject have, moreover, taught him a language which the inexpert seem to understand, although he is not content merely to give a superficial description of the past inhabitants of the earth.
The particular features which, it is hoped, may give the book a distinctive place in the large literature of evolution are, first, that it includes the many evolutionary discoveries of the last few years, gathers its material from the score of sciences which confine themselves to separate aspects of the universe, and blends all these facts and discoveries in a more or less continuous chronicle of the life of the heavens and the earth. Then the author has endeavoured to show, not merely how, but why, scene succeeds scene in the chronicle of the earth, and life slowly climbs from level to level. He has taken nature in the past as we find it to-day: an interconnected whole, in which the changes of land and sea, of heat and cold, of swamp and hill, are faithfully reflected in the forms of its living population. And, finally, he has written for those who are not students of science, or whose knowledge may be confined to one branch of science, and used a plain speech which a.s.sumes no previous knowledge on the reader's part.
For the rest, it will be found that no strained effort is made to trace pedigrees of animals and plants when the material is scanty; that, if on account of some especial interest disputable or conjectural speculations are admitted, they are frankly described as such; and that the more important differences of opinion which actually divide astronomers, geologists, biologists, and anthropologists are carefully taken into account and briefly explained. A few English and American works are recommended for the convenience of those who would study particular chapters more closely, but it has seemed useless, in such a work, to give a bibliography of the hundreds of English, American, French, German, and Italian works which have been consulted.
THE STORY OF EVOLUTION
CHAPTER I. THE DISCOVERY OF THE UNIVERSE
The beginning of the victorious career of modern science was very largely due to the making of two stimulating discoveries at the close of the Middle Ages. One was the discovery of the earth: the other the discovery of the universe. Men were confined, like molluscs in their sh.e.l.ls, by a belief that they occupied the centre of a comparatively small disk--some ventured to say a globe--which was poised in a mysterious way in the middle of a small system of heavenly bodies. The general feeling was that these heavenly bodies were lamps hung on a not too remote ceiling for the purpose of lighting their ways. Then certain enterprising sailors--Vasco da Gama, Maghalaes, Columbus--brought home the news that the known world was only one side of an enormous globe, and that there were vast lands and great peoples thousands of miles across the ocean. The minds of men in Europe had hardly strained their sh.e.l.ls sufficiently to embrace this larger earth when the second discovery was reported. The roof of the world, with its useful little system of heavenly bodies, began to crack and disclose a profound and mysterious universe surrounding them on every side. One cannot understand the solidity of the modern doctrine of the formation of the heavens and the earth until one appreciates this revolution.
Before the law of gravitation had been discovered it was almost impossible to regard the universe as other than a small and compact system. We shall see that a few daring minds pierced the veil, and peered out wonderingly into the real universe beyond, but for the great ma.s.s of men it was quite impossible. To them the modern idea of a universe consisting of hundreds of millions of bodies, each weighing billions of tons, strewn over billions of miles of s.p.a.ce, would have seemed the dream of a child or a savage. Material bodies were ”heavy,”
and would ”fall down” if they were not supported. The universe, they said, was a sensible scientific structure; things were supported in their respective places. A great dome, of some unknown but compact material, spanned the earth, and sustained the heavenly bodies. It might rest on the distant mountains, or be borne on the shoulders of an Atlas; or the whole cosmic scheme might be laid on the back of a gigantic elephant, and--if you pressed--the elephant might stand on the hard sh.e.l.l of a tortoise. But you were not encouraged to press.
The idea of the vault had come from Babylon, the first home of science.
No furnaces thickened that clear atmosphere, and the heavy-robed priests at the summit of each of the seven-staged temples were astronomers.
Night by night for thousands of years they watched the stars and planets tracing their undeviating paths across the sky. To explain their movements the priest-astronomers invented the solid firmament. Beyond the known land, encircling it, was the sea, and beyond the sea was a range of high mountains, forming another girdle round the earth. On these mountains the dome of the heavens rested, much as the dome of St. Paul's rests on its lofty masonry. The sun travelled across its under-surface by day, and went back to the east during the night through a tunnel in the lower portion of the vault. To the common folk the priests explained that this framework of the world was the body of an ancient and disreputable G.o.ddess. The G.o.d of light had slit her in two, ”as you do a dried fish,” they said, and made the plain of the earth with one half and the blue arch of the heavens with the other.
So Chaldaea lived out its 5000 years without discovering the universe.
Egypt adopted the idea from more scientific Babylon. Amongst the fragments of its civilisation we find representations of the firmament as a G.o.ddess, arching over the earth on her hands and feet, condemned to that eternal posture by some victorious G.o.d. The idea spread amongst the smaller nations which were lit by the civilisation of Babylon and Egypt.
Some blended it with coa.r.s.e old legends; some, like the Persians and Hebrews, refined it. The Persians made fire a purer and lighter spirit, so that the stars would need no support. But everywhere the blue vault hemmed in the world and the ideas of men. It was so close, some said, that the birds could reach it. At last the genius of Greece brooded over the whole chaos of cosmical speculations.
The native tradition of Greece was a little more helpful than the Babylonian teaching. First was chaos; then the heavier matter sank to the bottom, forming the disk of the earth, with the ocean poured round it, and the less coa.r.s.e matter floated as an atmosphere above it, and the still finer matter formed an ”aether” above the atmosphere.
A remarkably good guess, in its very broad outline; but the solid firmament still arched the earth, and the stars were little undying fires in the vault. The earth itself was small and flat. It stretched (on the modern map) from about Gibraltar to the Caspian, and from Central Germany--where the entrance to the lower world was located--to the Atlas mountains. But all the varied and conflicting culture of the older empires was now pa.s.sing into Greece, lighting up in succession the civilisations of Asia Minor, the Greek islands, and then Athens and its sister states. Men began to think.
The first genius to have a glimpse of the truth seems to have been the grave and mystical Pythagorus (born about 582 B.C.). He taught his little school that the earth was a globe, not a disk, and that it turned on its axis in twenty-four hours. The earth and the other planets were revolving round the central fire of the system; but the sun was a reflection of this central fire, not the fire itself. Even Pythagoras, moreover, made the heavens a solid sphere revolving, with its stars, round the central fire; and the truth he discovered was mingled with so much mysticism, and confined to so small and retired a school, that it was quickly lost again. In the next generation Anaxagoras taught that the sun was a vast globe of white-hot iron, and that the stars were material bodies made white-hot by friction with the ether. A generation later the famous Democritus came nearer than any to the truth. The universe was composed of an infinite number of indestructible particles, called ”atoms,” which had gradually settled from a state of chaotic confusion to their present orderly arrangement in large ma.s.ses. The sun was a body of enormous size, and the points of light in the Milky Way were similar suns at a tremendous distance from the earth. Our universe, moreover, was only one of an infinite number of universes, and an eternal cycle of destruction and re-formation was running through these myriads of worlds.
By sheer speculation Greece was well on the way of discovery. Then the mists of philosophy fell between the mind of Greece and nature, and the notions of Democritus were rejected with disdain; and then, very speedily, the decay of the brilliant nation put an end to its feverish search for truth. Greek culture pa.s.sed to Alexandria, where it met the remains of the culture of Egypt, Babylonia, and Persia, and one more remarkable effort was made to penetrate the outlying universe before the night of the Middle Ages fell on the old world.
Astronomy was ardently studied at Alexandria, and was fortunately combined with an a.s.siduous study of mathematics. Aristarchus (about 320-250 B.C.) calculated that the sun was 84,000,000 miles away; a vast expansion of the solar system and, for the time, a remarkable approach to the real figure (92,000,000) Eratosthenes (276-196 B.C.) made an extremely good calculation of the size of the earth, though he held it to be the centre of a small universe. He concluded that it was a globe measuring 27,000 (instead of 23,700) miles in circ.u.mference. Posidonius (135-51 B.C.) came even nearer with a calculation that the circ.u.mference was between 25,000 and 19,000 miles; and he made a fairly correct estimate of the diameter, and therefore distance, of the sun. Hipparchus (190-120 B.C.) made an extremely good calculation of the distance of the moon.
By the brilliant work of the Alexandrian astronomers the old world seemed to be approaching the discovery of the universe. Men were beginning to think in millions, to gaze boldly into deep abysses of s.p.a.ce, to talk of vast fiery globes that made the earth insignificant But the splendid energy gradually failed, and the long line was closed by Ptolemaeus, who once more put the earth in the centre of the system, and so imposed what is called the Ptolemaic system on Europe. The keen school-life of Alexandria still ran on, and there might have been a return to the saner early doctrines, but at last Alexandrian culture was extinguished in the blood of the aged Hypatia, and the night fell.
Rome had had no genius for science; though Lucretius gave an immortal expression to the views of Democritus and Epicurus, and such writers as Cicero and Pliny did great service to a later age in preserving fragments of the older discoveries. The curtains were once more drawn about the earth. The glimpses which adventurous Greeks had obtained of the great outlying universe were forgotten for a thousand years. The earth became again the little platform in the centre of a little world, on which men and women played their little parts, preening themselves on their superiority to their pagan ancestors.
I do not propose to tell the familiar story of the revival at any length. As far as the present subject is concerned, it was literally a Renascence, or re-birth, of Greek ideas. Constantinople having been taken by the Turks (1453), hundreds of Greek scholars, with their old literature, sought refuge in Europe, and the vigorous brain of the young nations brooded over the ancient speculations, just as the vigorous young brain of Greece had done two thousand years before. Copernicus (1473-1543) acknowledges that he found the secret of the movements of the heavenly bodies in the speculations of the old Greek thinkers.
Galilei (1564-1642) enlarged the Copernican system with the aid of the telescope; and the telescope was an outcome of the new study of optics which had been inspired in Roger Bacon and other medieval scholars by the optical works, directly founded on the Greek, of the Spanish Moors.
Giordano Bruno still further enlarged the system; he pictured the universe boldly as an infinite ocean of liquid ether, in which the stars, with retinues of inhabited planets, floated majestically. Bruno was burned at the stake (1600); but the curtains that had so long been drawn about the earth were now torn aside for ever, and men looked inquiringly into the unfathomable depths beyond. Descartes (1596-1650) revived the old Greek idea of a gradual evolution of the heavens and the earth from a primitive chaos of particles, taught that the stars stood out at unimaginable distances in the ocean of ether, and imagined the ether as stirring in gigantic whirlpools, which bore cosmic bodies in their orbits as the eddy in the river causes the cork to revolve.
These stimulating conjectures made a deep impression on the new age.