£)tate College of ^gricultucc at Cornell ?intbctsiitp Hibrarp Cornell University Library QH 366.H47 The first princi 9les of evolution 3 1924 003 046 509 The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924003046509 THE FIRST PRINCIPLES OF EVOLUTION RY thp: same author THE FIRST PRINCIPLES OF HEREDITY COXTAIN'IN'G 75 DIAGRAMS AND ILLUSTRATION'S Large Ciown 8vo., cloth Pik-c 5s. net (by fost 5s. 4ci.) "Dr. Herbert lias produced a book which we think will be widely read and will al=o serve its oi-jgmal purpose as 4 bvw Uasaak Street, CALCUTTA THE FIRST PRIN^afLES OF EVOLUTION BY S. HERBERT, M.D., M.R.C.S., L.R.C.P. AUTHOR OF "the FIRST PRINCIPLES OF HEREDITY" SECOND (REVISED) EDITION CONTAINING NINETY ILLUSTRATIONS AND TABLES A. & C. BLACK, LTD. 4, 5 & 6 SOHO SQUARE, LONDON 191S TO PROFESSOR L. T. HOBHOUSE IN ADMIRATION OF HIS WORK FOR PROGRESS PREFACE This book, like a previous one, "The First Principles of Heredity," is the outcome of a series of lectures given to a class of working-men and others. Though there are hosts of books dealing with Evolution, they are either too com- pendious and specialized, or, if intended for the average reader, too limited in their treatment of the subject. Indeed, there exists no textbook which presents the problem of Evolution comprehensively in all its aspects. To do this in the following pages in a simple, yet scientific manner, and thus to supply a real want — the only excuse for a new book — ^has been my aim. The task of embracing in one survey so many fields of science has proved an immense one, and I must therefore crave the indulgence of the critical reader of this book for its unavoidable imperfections. I cannot omit expressing my great indebtedness to my friend Mr. David Isaacs for his unwearying help, so ungrudgingly given, in the preparation of this work. S. H. Manchester, March, 1913. PREFACE TO SECOND EDITION The publication of a second edition after the short lapse of two years has made it possible for me to give an account of Professor L. T. Hobhouse's latest book on " Develop- ment and Purpose," which, unfortunately, came too late to be incorporated in the first edition of this work. S. H. April, 1915. [Thefirsl edition of this book was fublished in June. 1913.] vi CONTENTS INTRODUCTION Chapter I. EVOLUTION IN GENERAL - PACE I SECTION I.— INORGANIC EVOLUTION Chapter II. THE EVOLUTION OF MATTER - 7 1. COSMIC EVOLUTION 2. GEOLOGICAL EVOLUTION 3. ATOMIC EVOLUTION - 4. EVOLUTION OF LIFE - . . . 7 17 30 43 SECTION II.— ORGANIC EVOLUTION PART I.— THE FACTS OF EVOLUTION Chapter III. MORPHOLOGY - . - 52 1. HOMOLOGOUS STRUCTURES - - . - 54 2. RUDIMENTARY STRUCTURES - - - "59 3. VESTIGIAL STRUCTURES IN MAN - . -63 Chapter IV. EMBRYOLOGY - - - 69 1. EMBRYOGENY - - ■ - 71 2. THE BIOGENETIC LAW - - . - 74 Chapter V. CLASSIFICATION . . -83 Chapter VI. PALAEONTOLOGY - . - 89 Chapter VII- GEOGRAPHICAL DISTRIBUTION- . 99 viii CONTENTS PART II.— THEORIES OF EVOLUTION PACE ChaI'ter viii. theories OF EVOLUTION - 107 1. HISTORICAL - - - 107 2. LAMARCKISM - - - - - III DARWINISM - - - - -117 A. NATURAL SELECTION - - - - 117 ADAPTATIONS - - - - 1 24 (a) PLANT STRUCTURES - - - I25 (6) ANIMAL COLOURATION - - 13I (c) INSTINCTS - - 152 (d) HUMAN FACULTY 157 (e) DEGENERATION - - * 1 59 B. SEXUAL SELECTION - - I63 4. DIFFICULTIES OF THE THEORIES - - 1 72 A. NEO-LAMARCKISM - 1 75 B. NEO-DARWINISM 1 78 AUXILIARY THEORIES OF NATURAL SELECTION - I90 (a) PANMIXIA - 191 (6) INTRA-SELECTION - - 193 (c) GERMINAL SELECTION - - 194 {d) COINCIDENT SELECTION - - 197 (fi) ISOLATION - - 1 98 Chapter IX. THEORIES OF EVOhVTlON— Continued 205 1. heterogenesis - - - 206 2. orthogenesis - - 214 (a) mechanistic theories - - 214 (6) VITALISTIC theories - - 21 8 conclusion - - . - 223 SECTION III.— SUPERORGANIC EVOLUTION Chapter X. SOCIAL EVOLUTION . 226 I. mental evolution - 226 (a) behaviour of lower organisms - - 227 (6) instinct - . 235 (c) intelligence - - . . 240 (d) reason ^ , . . - 24-^ CONTENTS IX Chapter X. SOCIAL KVOLVTION— Continued PACK 2. MORAL EVOLUTION ..... 247 (a) ANIMAL ORIGINS .... 249 (6) HUMAN DEVELOPMENTS . - 253 3. EVOLUTION OF MAN - . - -. , 258 4. EVOLUTION OF SOCIETY . - . ' - 27I A. THE FAMILY ..... 272 (a) THE PATRIARCHAL THEORY - 272 (6) THE MATRIARCHAL THEORY 274 (c) THE MONOGAMOUS THEORY . 278 B. THE STATE ... 280 (a) PRIMITIVE COMMUNISM 28o (6) FEUDALISM AND ITS OUTCOME . 284 C. RELIGION ..... 288 {a) ANIMISM . . . . .289 (6) OTHER THEORIES ... 293 APPENDIX : A PRECIS OF SCIENCE . 297 D. EVOLUTION AND PROGRESS ... 298 CONCLUSION Chapter XI. THE FORMULA OF EVOLUTION - - 30 5 1. EVOLUTION ..... 306 2. DISSOLUTION - - . - "313 Chapter XIL THE PHILOSOPHY OF CHANGE- . 316 Literature - • . - - - 319 Glossary ....... 327 Index -.--.... 337 LIST OF ILLUSTRATIONS FIG. I'AGE 1. Spectra of Sun, Sodium, and Calcium. (In colour) facing lo 2. Diffuse Nebula in Orion ,, 12 3. Spiral Nebula - - ,, 16 4. Table of Geological Periods - - 23 5. Crookes Tube 35 6. Table of Uranium, Radium, etc. - 39 7. Free-Floating Magnets - - 41 8. Arrangement of Corpuscles - 42 9. Skeleton of Greenland Whale 53 10. Anterior Limbs compared 54 11. Wings of Reptile, Mammal, and Bird compared 55 12. Mouth-Parts of Cockroach 56 13. Head of Bee 57 14. Head of Butterfly - 58 15. Upper and Lower Limb of Man compared 59 16. Skeleton of Seal 60 17. Rudimentary Hind-Limbs of Python 61 18. Apteryx (52 19. Sacrum of Man and External Tail of Human Embryo 63 20. Vermiform Appendix 6^ 21. Eye of Owl and Man compared 64 22. Young Gorilla - gr 23. Young Child - 6g 24. Swinging Infant 67 25. Ear of Man and of Foetus of Orang 67 26. Spermatozoa - 70 27. Ovum of Sea-Urchin 70 28. Fertilization - -j 29. Embryogeny of Sagitta - 72 30. Section of a Young Sagitta - 7^ 31. Amoeba Dividing - -. 32. Cell Colony of Goniura . - ■ LIST OF ILLUSTRATIONS xi Kir. PAGE. 33. Magosphara Planula - 75 34., Trophysema Primordiale - 76 35. Amphioxus Lanceolatus - 77 36, Series of Embryos - 80, 81 37. Classification of Plants and Animals 84, 85 38. Tree of Life facing 86 39. Archaeopteryx 92 39(1. Archfeopteryx restored - 93 40. Evolution of Horse 9.5 41. Paludina Shells 96 42. Development of the Fish-Tail - 97 43. Development of the Bird's Tail 98 44. Pigeons 118, 119 45. Vitcher oi Nepenthes Villosa 126 46. Sundew 127 47. Flower of Meadow gage 129 48. Cowslip 13a 49. Caterpillar, striped longitudinally - 131 50. Caterpillar, striped diagonally 135 51. Stick Insect 136 52. Slick Caterpillar 137 53. Stick Moth 138 54. Leaf Insect 139 55. Kallima Butterfly - 139 56. Indian Mantis 140 57. Larva of Puss Moth 141 58. Eyed Hawk Moth - 142 59. Gazella Scemmeringi 142 60. African Plovers 144 61. Brarilian Skunk 145 62. Mimicry among Butterflies - 149 63. Hornet Clearwing - 15° 64. Mimicking Flies - 151 65. Hermit Crab 155 66. Sacculina - 161 67. Chondracanihus Gibbosus - 162 68. Acariis Equi - 163 69. Chalcosoma Atlas - - - . - 164 70. CalUonymus Lyra - - 165 7J. Chamakon Owenii ' 166 xii LIST OF ILLUSTRATIONS FtG. 72. Bell-Bird - - . 73. Diagram of Evolution 74. Brush and Comb of Bee 75. Development of Lungs 76. Curve of Stature 77. Mutations of (Enothera Lamarckiana 78. Colour-Markings of Laceria Miirahs 79. Spiral Path of Paramecium 80. Avoiding Reaction of Paramecin") Si. Orientation of Euglena 82. Stenior Roesclii 83. Wasp using Stone 84. Skeletons of Higher Apes and Man 85. Outhne of Skulls 86. Skull of an Orang 85a. Skull of the Fossil Apc-Man of Java 866. Skull of Negro S6c. Skull of Kalmuck - 87. Palaeolithic Implements 88. Sketch of a Mammoth 89. Neolithic Implements go. Stonehenge THE FIRST PRINCIPLES OF' EVOLUTION INTRODUCTION CHAPTER I EVOLUTION IN GENERAL There is perhaps nothing more significant of our age than the change which has taken place in our conception of the universe. The old notion of eternal unchangeableness, with occasional upheavals — the static view — has given way to the newer idea of progressive development in nature. Gradually, within the last half-century, this new inter- pretation, which regards all things from the evolutionary or dynamic point of view, has extended from one field of human inquiry to another, creating everjrwhere fresh interests, giving novel aspects to old problems — nay, colouring and transforming the whole purpose and meaning of modern life. At last we seem to be on the threshold of nature's long-kept secret. After ages of darkness, the first gleam of a deeper understanding of her intentions has dawned upon us. Showing as it does the small beginnings of all things, their gradual transformation, step by step, towards higher stages of perfection, this new philosophy has opened out to us new possibilities, new visions and aspirations. It takes in with one grand sweep all the phenomena of existence, and stands as the embodiment of a new ideal which cannot fail to widen our outlook upon life. 2 THE FIRST PRINCIPLES OF EVOLUTION For this end it is necessary not only that we should know a few isolated facts of evolution, but that we should digest and thoroughly understand its principle ; in short, we must learn to think in terms of evolution. But what is evolution ? Though the doctrine has been before the world for over fifty years, and has become an accepted fact of science, the general public still has only a very hazy notion of it and all it involves. It is often thought to imply nothing more than the belief in " the descent of man from monkey " ; or sometimes people somewhat better informed will go so far as to connect it with the theory of the Origin of Species, propounded by Darwin. As usual, the popular fancy has seized on the most outstanding feature of the doctrine of evolution. We must make clear from the outset that evolution, properly understood, is neither the one nor the other of these theories, but rather includes, as we shall presently see, immeasurably more than both. As we term the growth of the individual his develop- ment, so we call the development of the cosmos from a simple primitive state to complex and higher states its evolution. The unending process of evolution is a uni- versal phenomenon, a /fact of nature, for which an ex- planation is attempted in the various theories of evolution. Evolution and the theory of evolution are accordingly not identical terms, the first being a process of nature, the second a hypothesis or theory, formulated to explain this process. That the universe is not static, but is, on the contrary, undergoing a continual change, is a truth which had already dawned on the ancient Greeks. " Flux or move- ment," said Heraclitus, " is the all-pervading law of things." After the passing of the dark Middle Ages, the idea of the gradual transformation of all the forms of life found ex- pression here and there, but without gaining any wide acceptance. It is only when we approach our own times that we find the principle of evolution established on a EVOLUTION IN GENERAL 3 scientific basis. Erasmus Darwin, Lamarck, and others had made ineffectual attempts towards a solution of the problem ; but it was Charles Darwin who, in his book on the " Origin of Species," at one stroke not only offered an acceptable theory of the transmutation of species, but firmly established the fundamental principle of evolution. Since that time the world has become more and more convinced of the correctness of that principle ; though, as we shall see later, this can by no means be said of the special theory which Darwin advanced as an explanation of organic evolution — a vital point which has already been aUuded to, and which has to be carefully borne in mind by the reader. For Darwinism, or the theory of evolution as pro- pounded by Darwin, refers only to organic evolution — i.e., to the evolution of plants and animals. His epoch-making book, which appeared in 1859, explains, as the title in- dicates, the " Origin of Species by Means of Natural Selection." It must therefore be understood that Darwin- ism is not identical with evolution, but is a theory, — and a theory of organic evolution only. StiU less can evolution be taken to be synonjnnous with the descent of man from the ape ; for the descent of the species man from the lower animals is only a particular case of the origin of species. Evolution in the fullest sense covers a much wider field ; it is coterminous with the whole range of cosmic phenomena. It holds good not less of the great stars, millions of miles away, than of the tiny microbes barely discernible under the highest magnifying power. By its light we are enabled to decipher the ancient history of suns and planets, of our earth, and all it contains ; we can explain the onward path of all things existent, and to a certain extent foretell their further progress. To have discovered a unifjdng principle of such far- reaching application, covering such various phenomena, to have given us the grand conception of a world-embracing evolution, is the great achievement of Herbert Spencer. 4 THE FIRST PRINCIPLES OF EVOLUTION Not only was he the first independently to adopt the evolutionary principle as a means for the solution of various problems of matter and mind, actually anticipating Darwin's discovery by a few years — a fact very little known by the general public — but he gradually elaborated a complete theory of evolution, comprising in one great formula the law of all existence. Dealing in his " First Principles " (ist edition, 1862) with the general aspect of the problem of evolution, he completed the tremendous task of working out all the successive sections of his great " Synthetic Philosophy " in full, applying the " master-key of evolu- tion " in turn to the phenomena of life, the problems of society, and last, but not least, to the fundaments of ethics. " Indeed, this last part of the task it is," he writes, " to which I regard all preceding parts as subsidiary." " To find for the principles of right and wrong a scientific basis " is, he declares, his ultimate aim. And here we are face to face with the profound impor- tance of the results flowing" from the scheme of evolu- tionary doctrine. Giving us a unifying principle for the totality of manifestations, and recognizing the con- stant transformation of all things, spiritual as well as material, through a never-ending series to higher and more perfect states) it is specially suited to deepen our inmost sense of life, making us tolerant towards the past and hope- ful of the future. SECTION I INORGANIC EVOLUTION Nature is one and indivisible. She knows nothing of the categories we are wont to make in order to render her understandable to oiirselves in parts. We are apt to over- look this truth when we apply ourselves to the study of any definite range of phenomena ; we so easily forget the connections which exist between the different manifesta- tions of the universe. For, it must be understood, all these distinctions are of our own making — they are ab- stractions serving the useful purpose of defining the separate parts of our human knowledge. Of this unity in diversity science has at last become fully conscious, ever since the theory of evolution opened out to us the possi- bility of combining under one principle all natural phe- nomena, which had appeared until then as so many frag- mentary records of an inscrutable whole. The hitherto isolated facts of nature have become, thanks to Herbert Spencer, comprehensible from one common point of view. He applied, as already mentioned, this new central idea of progressive development to all phases of existence ; and in the exposition of the succeeding pages we shall have to follow largely the masterly account of his doctrine laid down in his " Synthetic Philosophy." It is customary to divide the whole realm of nature into two great parts : the inorganic and the organic. The former comprises all lifeless things, as stones, rocks, planets, suns, etc. ; the latter contains the living beings with more 5 6 THE FIRST PRINCIPLES OF EVOLUTION or less differentiated parts (organs), from the lowest plants ,to the highest animals, including man. In addition to the facts presented by organic bodies taken singly, there are certain other phenomena, such as constitute the social life of a community, which are the result of the aggregation of a number of organisms. These phenomena were called by Herbert Spencer " superorganic." In dealing, then, with evolution, we shall treat it in three separate sections — namely, (i) inorganic, (2) organic, and {3) superorganic evolution. CHAPTER II THE EVOLUTION OF MATTER Before entering into the subject proper of inorganic evolution, we must remark that whatever we may be able to find out about the evolution of matter, we must take its somehow-existence for granted. Evolution only traces back the transformation of matter through its various stages ; it does not at all pronounce as to an original creation of matter out of nothing.* Starting, then, with the world-stuff as given, we shall discuss (i) the evolution of the universe, or cosmic evolu- tion ; (2) the evolution of the earth, or geological evolu- tion ; (3) the evolution of the chemical elements, or atomic evolution ; and (4) the evolution of organic forms from inorganic matter, or the evolution of life. I. Cosmic Evolution. It has ever been the natural tendency of man to assign to himself a unique position in the scheme of creation, which he is but slowly being forced to abandon by the hard facts of science. To the ancients the earth, the abode of man, was the centre of the universe, and around it the sun, stars, and planets moved in their courses. This idea pre- vailed until deep into the Middle Ages. It was only in the sixteenth century that Copernicus finally overthrew the old Ptolemsean geocentric system by showing that the movements of the heavenly bodies could be accounted for much more plausibly by assiuning the earth, in common with tlie other planets, to revolve round the sun as a fixed * We shall see later on that the evolution of matter out of electrical units is the latest subject of speculation. 7 8 THE FIRST PRINCIPLES OF EVOLUTION centre. About a century later Kepler discovered the famous law of motion, according to which the paths or orbits described by the planets around the sun are not circles, as was previously supposed, but ellipses. The heliocentric theory of the solar system, then, posits a mighty central sun (866,000 miles in diameter), and round it, coursing at various distances of millions of miles, the planets, all many times smaller than the sun, each accompanied in its turn by one or more satellites, which move round their primaries according to the same law of motion. But this solar system of ours is, as is well known, only a very 'small portion of the entire visible universe. For, as will appear later, the sun is nothing but a star, and there are known to the astronomers at least a hundred millions of stars, the nearest of them many billions of miles away from our sun, each star having, in all probability, mightier and vaster systems than our own. These, in- cluding the passing comets and shooting stars, were con- sidered to form the whole contents of the heavenly spheres, until at the end of the eighteenth century Sir William Herschel, by his extensive observations on nebulse, showed them to be an integral part of the cosmic system, thereby opening a new outlook into the constitution of the universe. Though faint luminosities in the heavens had been observed before his time, it was he who, by a systematic study of the nebulse, was enabled to bring them into line with the other stellar phenomena ; indeed, he first gave scientific evidence, by means of his improved telescopic methods, of a hypothesis which had already been advanced before him on merely theoretical grounds, independently by the German philosopher Kant and by the great French mathematician and astronomer Laplace. This Kant-Laplacean theory, which is generally known as the " nebular hypothesis," we shall now deal with more in detail. COSMIC EVOLUTION 9 {a) The Nebular Hypothesis. It is a somewhat startling fact in the history of evolu- tion to find that the first successful attempt of applying the principle of progressive development in nature was made with regard to celestial bodies which are miUions and millions of miles away. The nebular theory first suggested by Kant in 1755, and afterwards worked out more fully by Laplace in 1796, has been amply confirmed by later scientific researches, and still holds the foremost place as an explanation of the origin of the solar system. According to Laplace, the matter which now constitutes our solar system — i.e., the sun, planets, and their satellites — ^was once, seons ago, a vast mass of intensely heated gas, extending beyond the confines of the orbit of the outer- most planet, Neptune, a radius of nearly three thousand million miles. This rarefied " fire-mist," millions of times more tenuous than air, was, in fact, at that time nothing else than a nebula, such as can be observed by the thousand in the heavens with our improved telescopes. If there was any doubt left as to the true nature of such a nebula, the marvellous advancement of astrophysics has been able to set that at rest. For by means of spectrum analysis the constitution of the heavenly bodies coursing at such enormous distances can be analyzed as certainly as if we had them in our chemical laboratories. It is a well-known fact that sunlight, when passed through a prism, is spread out into a beautiful coloured band or spectrum, exhibiting all the colours of the rainbow from red on one side through orange, yellow, green and blue to violet on the other. When suitably examined, this continuous spectrum of the sun can be seen to be crossed by a great number of dark lines, constant in posi- tion and relative intensity, which were first detected by Fraunhofer in the beginning of the nineteenth century, and are since known as " Fraunhofer lines." Kirchhoff was first able, in 1859, to give the meaning of these lines. He 10 THE FIRST PRINCIPLES OF EVOLUTION showed that light emitted from any given chemical element made gaseous by incandescence, when examined through a spectroscope (an arrangement of various prisms and lenses), gave bright coloured lines on a dark background — the discontinuous bright-line spectrum — each element being characterized by a definite set of Unes, which were found to correspond with certain groups of Fraunhofer lines in the continuous sun spectnmi ; indeed, the dark lines in the sun spectrum indicate the presence of the various chemical substances in the sun. The Unes appear dark, because the hot, vaporous atmosphere surrounding the sun, which by itself gives a bright-line spectrum, absorbs — i.e., extinguishes — the identical rays coming from the still hotter white central body of the sun. We are therefore enabled to determine the nature of any given body, however far distant, by the kind of spectrum it gives. A discontinuous bright-Une spectrum indicates an incandescent gas ; a continuous spectrum without lines indicates an incandescent soUd or liquid bcdy (or a gaseous body under high pressure) ; while the addition of dark lines gives the absorption spectrum, and indicates an atmosphere of cooler vapour around a central heated body. Distinctive groups of lines stand for the separate elements constituting such bodies (Fig. i). It was in 1864 that Sir WiUiam Huggins first demon- strated the real gaseous nature of the nebulae by showing that they give a bright-Une spectnim, the Unes being those of hydrogen, heUum, and another gas, not yet found on our earth, and provisionaUy caUed " nebuUum." Such a nebula, spread out flat and rotating in the same direction as the solar system, is assumed to have been the origin of our planetary world. As cooUng would take place in this intensely hot, vast mass by the radiation of heat into space, the nebula would gradually contract, and its outermost equatorial parts would in consequence detach themselves as a separate ring, similar to the rings seen in the planet Saturn. At a further stage this ring would cool and Q O cn o U COSMIC EVOLUTION il condense into a liquid or solid. As the cooling would not go on uniformly in all parts of the ring, it would break up and tend to aggregate into a globular mass, forming a planet. This process would not only repeat itself successively in the main parent mass, thus leading to the formation of the different planets coursing round the central remaining body as a sun, but the planets themselves, being fiery balls, would throw off their own satellites in a similar manner.* This theory of the formation of the sun and all its attendant bodies out of one original nebula accounts in a most simple and satisfactory manner for a host of phe- nomena exhibited by the solar system. It explains the facts : (i) That the sun and larger planets are much hotter than the earth and smaller planets, for the larger the mass of a body the longer it takes to cool down ; (2) that the motion of the planets and their attending satellites is in the same direction ; (3) that the rotation of these different bodies, including that of the sun, on their own axis is in the same direction ; (4) that the orbits of these different bodies are nearly in the same plane ; (5) that the earth, being originally a rotating fluid mass, is flattened at both poles and bulged out at the equator, etc. Further proof has been forthcoming of late ; indeed, the whole science of stellar evolution may be said to have resulted from the application of this fruitful hypothesis. Not only have nebulae been found in all stages of develop- ment from the diffuse nebula in Orion (Fig. 2) through greater and greater condensation to planetary nebulae, which appear like bright discs, but the stars themselves give evidence of their birth from these nebular masses ; indeed, there are nebulous stars, still surrounded by a sort of glow of nebulosity, while spectroscopically stars can be arranged in a continuous series according to their age, * According to the newest theory, by Professor G. H. Darwin, the moon has not been formed in this manner, but broke off, as it were, from the earth as a result of tidal action, after the earth had become liquid or nearly solid. 12 THE FIRST PRINCIPLES OF EVOLUTION As stars take their origin from a hot incandescent gas which is gradually cooling down and condensing, we should naturally find that stars in the earlier stages would be hotter than those of a more advanced type. The hottest stars are white. With gradual cooling down the colour of the stars changes to orange, yellow, and finally red, just as a heated iron cools from a white heat through yellow to red with the decrease of temperature. Furthermore, in the immense heat prevailing in these glowing stars, all substances are vaporized and broken up into their con- stituent elements ; nay, the elements themselves, as will appear later, are dissociated — i.e., split up into their more primitive units. It follows that the earlier the evolutionary stage of a star, the more primitive wiU be its constituents and the simpler its spectrum. The classification of stars is by no means simple, and has not been definitely settled. But on the whole four stages can be distinguished. We have, firstly, the earliest stars, hke those of the Trapezium in the Orion nebula, which seem intimately connected with the surrounding nebular mass, and have the most primitive spectrum, showing only the helium and hydrogen lines. After these come the white or bluish-white stars, like Sirius, which give the lines of hydrogen, and in addition, faint lines of iron, sodium, magnesium, etc. At first the shrinking of the stars which takes place, more than counterbalances the loss of heat due to radiation, so that in the beginning the stars grow hotter instead of cooler. But ultimately a stage is reached when cooling of the outermost parts goes on rapidly enough to lead to their condensation. These stars show, in conse- quence, an orange or yellow colour, their spectrum giving faint hydrogen lines, while the metallic lines become more pronounced. (Our sun, which, as we have said before, is nothing but a star seen from a relatively short distance, belongs to this class.) Finally, we have the red stars in the declining age, showing a very complex spectrum. The appearance of the planets, too, depends, as already Fig. 2. — Diffuse Nebula in Orion (W. H. Pickering). {From '^Problems hi Astrophysics" by Agnes M. Gierke.) COSMIC EVOLUTION 13 mentioned, on the stage of their development. We know that the earth has sufficiently cooled down to have a solid crust and a cool atmosphere, which made the evolution of organic life possible ; while the much larger planet Jupiter is still a glowing ball surrounded by an intensely hot, vaporous envelope. ' The moon, on the other hand, much smaller than both these planets, has long since cooled down completely, and is now barren and atmosphereless. The ultimate question arises : Whence these nebulae ? We can only surmise. The generally accepted idea is that they are due to the collision of two mighty celestial bodies. The heat generated by their tremendous impact would be sufficient to dissipate both of them into thin vapour, forming the substance of a new nebula. It must be added finally that the large nebulae usually observed have not given rise to such a small system as ours ; they represent rather a system of such systems. Though, as we have seen, the nebular hypothesis brings into one harmonious scheme many phenomena of cosmic evolution, still, many facts have been forthcoming which are not in agreement with this theory. Of these we shall only mention the principal ones : 1. The formation of coherent rings has been doubted, because, according to dynamical principles, it would be more likely that the outermost portions would separate particle by particle. 2. According to Professor F. R. Moulton, the drawing together of the ring material into a spheroid to form a planet meets with great mechanical difficulties. 3. If the planets were formed in this manner, they should, as Professor Faye has shown, rotate in the opposite direc- tion to that of their primaries. 4. While the satellites accompanying the earth, Mars and Jupiter, and eight of the satellites of Saturn, revolve, in accordance with the theory, in the same direction as their planets, the satellites of Uranus and Neptune, and 14 THE FIRST PRINCIPLES OF EVOLUTION the newly discovered ninth satellite of Saturn, revolve in the opposite direction. 5. The planes of the orbits of the four satelhtes of Uranus are almost perpendicular to the plane of the planet's orbit. 6. According to the nebular theory, the loss of heat leads to contraction, and in consequence thereof to a con- stantly accelerated rotation of the planets. It follows from this that, as the satellites are thrown off at an early stage of the planet's existence, the time taken for a revolu- tion of the satellite round its primary should be longer than the time of rotation of the primary round its own axis ; but Phobos, one of the satellites of Mars, revolves in less than a third of the time of the planet's rotation.* 7. Serious dynamical objections, too technical to be discussed here, have been raised by Professor Moulton. 8. Finally, and this is perhaps the weightiest argument against the theory, no nebulae have been found with rings, the only heavenly body with ring formation being Saturn. On the contrary, the discoveries of Professor Keeler have shown that out of nearly a hundred and twenty thousand nebulae now recorded, by far the greater number are spiral in form, a fact with which we shall deal presently. It would appear, then, that grave difficulties stand in the way of the complete acceptance of the nebular theory as propounded by Kant and Laplace ; indeed, as has just been mentioned, it does not take account at all of the majority of nebulas, which, with the modern powerful instruments, have been found to exhibit a typical spiral structure. Professors Th. C. Chamberlin and F. R. Moulton have advanced a new hypothesis as to the origin of our solar system more in accordance with modern knowledge. To this we now turn. * This objection has been met by Professor G. H. Darwin, who explains the difference as due to tidal retardation of the rotation of Mars. COSMIC EVOLUTION 15 (6) The Planetesimal Hypothesis. The starting-point of the solar system, according to this theory, is a spiral nebula, which is, as has just been said, the most common type observed. Such a nebula, as Fig. 3 well illustrates, shows a distinct central mass around which are coiled two long arms, which give the impression of having been produced by rotation of the whole mass, though sufficient time has not yet elapsed for proving such rotatory movement by actual observation. On the arms " knots " or partial concentrations of matter can be distinguished. The whole spiral is more or less flat, lying, when seen edgewise, in one plane. The spectrum of these nebulae is continuous, thereby proving that we have to deal, not with a finely dispersed gas, but with either liquid or, more probably, solid bodies. There seems to be no doubt that we have in these nebulas aggregates of small bodies revolving round a common central mass, and immersed in a more tenuous medium. These bodies have been called " planetoids " or " planetesimals," on account of their resemblance to the planets, the theory of their origin and further evolution being the Planetesimal Theory. It would appear, then, that we have in such a spiral nebula the rough outline of a planetary system, in which the process of further development is a relatively simple one. The knots forming the nuclei of the future planets, and coursing in their orbits around the central body, aggregate by coalescing into larger and larger masses, the planets gathering up at the same time the remnants of nebulous matter, while the central body remains the controlling sun. It follows from this that the planets are at no time of their life-history entirely gaseous, but rather cool, solid bodies, including a greater or smaller, amount of gaseousi matter. As to the origin of the spiral nebula, it has been ex- plained by Professor Moulton as due to the effect of the tidal i6 THE FIRST PRINCIPLES OF EVOLUTION action of two more or less spheroidal nebulae on each other. Given two such rotating bodies approaching near to each other without colliding, the effect of the mutual attraction on such loosely aggregated bodies would be an elongation of the main masses, the formation of bulging parts at the two opposite poles, and the final disruption of these pro- tuberances into long streamer-like arms, which, on account of the rotatory movement of the whole mass, would tend to coil closer and closer round the central body. These coils would cool down through rapid radiation, and con- dense at various points into knots, forming finely divided solids and planetoids. According to Chamberlin, the gaseous nebulae have nothing to do with the evolution of our planetary system, though they may be connected with the origin of the stars. We are thus left face to face with two theories of cosmic evolution, which cannot be reconciled with each other ; nor does either of them fit in at present with all the observed facts of astronomy. (c) The Meteoritic Hypothesis. There is a third theory in the field, propounded by Sir N. Lockyer, and supported by Professor G. H. Darwin, which we must briefly mention for the sake of complete- ness, though it has found little recognition among scientists. According to this hypothesis, the original cosmic material consists of meteorites. " Nebulae are really swarms of meteorites in the celestial space. The meteorites are sparse, and the colhsions among them bring about a rise of temperature sufficient to render luminous some of their chief constituents." The meteorites swarm indiscrimin- ately in all directions, and with widely different velocities. But Chamberlin has argued that if this is so, they must soon be vapourized ; and therewith this theory would merge into the gaseous one of Laplace. Furthermore, the main evidence of Lockyer, based on the appearance of a certain characteristic line in the nebular spectrum, and attributed Fig. 3. — Spiral Nebula (taken bv ^Ir. W. E. "Wilsox, March 6, 1897). (F)Oin " Problems in Astrophysia^ by A^ncs M. Citrkc.') GEOLOGICAL EVOLUTION 17 by him to magnesium oxide, has broken down, as this line is now generally interpreted as due to nebulium, a gas peculiar to nebulae, and not yet found on our earth. We must point out here, in order to avoid misunder- standing, that the inability to formulate at present one thoroughgoing theory in explanation of stellar evolution, does not mihtate in the least against the evolution of the cosmos as a fact. The proofs of the. latter are entirely independent of any theory that may be propounded to explain any particular method of evolution. We have seen that the harmony of the observed heavenly phenomena fits in well with a general scheme of cosmic evolution ; and the time may not be far off when all these phenomena will be brought into one comprehensive whole. 2. Geological Evolution. The most primitive idea of the earth was that of a vast extended flat disc, with the expanse of the heavens stretch- ing over it Uke a mighty dome. This gave way in very early times to the more correct interpretation of the earth as a spherical globe poised in space, the sun and stars coursing round it in their regular paths. The next stage was reached when, as has already been pointed out in the first part of this chapter, the centre of the whole system was transferred from the earth to the sun. Of course, there was at this period of geological history no possible thought of a continuous development of the earth. The most fanciful notions prevailed. The biblical theory of creation held sway in place of scientific research. Fossils were looked upon as " sports of Nature," and the belief in a iK:Jversal deluge which once overtook the earth and all its inhabitants was general. Though here and there the truth was guessed at — ^thus, among others, the famous painter Leonardo da Vinci recognized fossils to be the bmried remains of once-existing animals, and Steno of Padua {1669) deduced from the marine deposits of Tuscany the 3 i8 THE FIRST PRINCIPLES OF EVOLUTION successive configurations of tliat district — it was not until the end of the eighteenth century that the Scotch geologist Hutton (1788) promulgated the first coherent theory of geological formations. He was the first to explain the former changes of the earth's crust by means of natural forces only. According to him, " all past changes have been brought about by the slow agency of existing causes." Unfortunately his work met with great opposition for religious reasons. Furthermore, he expounded a one-sided theory of the formation of the rocks, attributing their origin to igneous action only (vulcanism), in contra- distinction to the so-called " Neptunists," who, led by the German geologist Werner, supposed all existing rocks to be due to a chemical precipitation from a " chaotic fluid." The true founder of modern geology is Charles Lyell, who in his " Principles of Geology" (ist edition, 1830) elaborated all the natural means now recognized as factors in earth- sculpture. The wearing down of the high land by the action of the rain and the atmosphere, the erosion of valleys by streams, the encroachment of the waves upon the sea- shore, and the deposition of the resulting debris either upon lowlands or within the sea as sedimentary strata ; further, the activity of volcanoes and underground waters ; — in fact, the uniform action in aU past ages of the same agencies as can now be studied, determines, according to modern geological science, the ultimate features of the face of the earth. Not catastrophism, but slow and orderly develop- ment, reigns in geological phenomena as in all other realins of nature. The uniformitarian doctrine of Lyell, it is true, recognized neither beginning nor end in the earth's history ; but since then the new evolutionary ideas in con- junction with recent astronomical discoveries have enabled us to trace the earth's progress in a continuous line from its first beginnings up to the latest stages of the present time. Of +hese the early stages are in the nature of the case largely hypothetical, while the later geological formations of the earth have been worked out with more definiteness and accuracy. GEOLOGICAL EVOLUTION 19 {a) The Hypothetical Stages. We have seen that, according to the theory of cosmic evolution, the earth was born from a primeval nebula, and revolves, with its sister planets, around the central sun. We have further seen that in course of time the planets pass through various phases, starting as shining white-hot globes, and cooling down gradually to duU, non-luminous bodies receiving their light from the central sun. Now, we must assume the earth to have passed through all these successive stages. Originating as a great fiery ball, our globe, in whirling round its own axis, assumed its present shape, being flattened at the two poles and bulged out at the equator. On account of the enormous heat, all the substances making up the planet would be vapourized, the compound bodies being dissociated into their constituent elements. Gradually, as cooling took place through the radiation of heat into space, a molten mass would result, the heavier metals, like iron, etc., gravitating towards the centre, the lighter towards the surface, while the lightest elements would form a vast atmosphere around it laden with the waters of the future oceans and heavy with carbonic acid (CO2). The moon was thrown off, according to Professor G. H. Darwin, by a tidal wave, from the earth, while it was still in this plastic condition, which is reckoned to have taken place about fifty-six to fifty-seven million years ago. With the further fall of temperature, the planet tended to consolidate. It is still a moot point in science where solidification first started. The opinion most widely held assumes the interior of the earth to be an intensely hot, partly gaseous, partly fluid mass ; though it must be under- stood that at the enormous pressure which prevails at this depth such a mass would behave practically like a rigid body. According to this view, the surface of the globe congealed first, forming a comparatively thin shell, which gradually extended towards the centre. Lord Kelvin, on 20 THE FIRST PRINCIPLES OF EVOLUTION the other hand, argued that with the high pressure at the centre, the interior must have consolidated first. It must not be imagined, however, that the primitive crust was smooth and uniform. Floating on a sea of fluid rock, and exposed to mighty tidal waves and strong atmospheric currents from above, it was repeatedly broken up into enormous irregular slabs, and acquired stability only after many successive corrugations. The first permanent configuration assumed by the earth, according to Professor J. H. Jeans, was pear-shaped (as if the earth had been arrested in the protrusion of a second body like the moon) ; the equator was not circular, but oval, the broader end corresponding to the middle of the African continent, while the stalked end formed an island — assumed to have once been in existence in the midst of the Pacific Ocean. With a further fall of temperature, the steam suspended in the atmosphere liquefied and settled on the uneven surface of the land, thus giving rise to the first oceans, which consisted of boiling water. The original shape of the earth determined the primary distribution of land and sea, the latter accumulating mainly round the neck of the pear, forming a broad girdle of water round the globe corresponding to the present Pacific Ocean.* As the con- densation going on in the overlying atmosphere must have been irregular, areas of high pressure and low pressure ensued, with the result that the thin crust was corre- spondingly depressed or raised. The solid earth became " dimpled and embossed," the water gathering in the hollows. But the very distribution of land and water would lead to a further differentiation of land and sea level. For the enormous weight of the oceans, exerting a steady downward pressure, would increase the oceanic depression, while, on the other hand, the release of pressure over the land area, produced by the withdrawal of the dense, heavy, watery atmosphere above it, would tend to * Later on the land hemisphere collapsed at the two sides, which led to the formation of the Atlantic and Indian Oceans respectively. GEOLOGICAL EVOLUTION 21 expand and elevate the crust. It must be understood, however, that the early formation of continents has nothing to do with the upheaval of gigantic mountain-ranges, which appear at a much later period of the earth's history. We have thus at last reached the final arrangement of the accessible parts of the earth, the threefold zone of matter encircling our globe — " the lithosphere, or girdle of rock ; the hydrosphere, or belt of water ; and the atmosphere, or mantle of air " — the latter still dense and heavy, because it contained all the carbonic acid that was later on used up for the growth of the carboniferous forests, and all that went otherwise into the formation of the rocks. The further stages of the geological record consist, henceforth, mainly in the alternate process of wearing down the land surface and building up new rocks out of the detritus. Weathering, stream and coast erosion, etc., gradually disintegrate the rock substance, which is carried into the sea, and laid down at the bottom of it as sedi- mentary beds. These in their turn, after having been consolidated into sedimentary rocks by the enormous com- bined pressure of ocean and superimposed strata, emerge gradually, as we shall see hereafter, above the sea-level, only to be worn down again in order to form new strata ; until by constant repetition of this process the whole structure of the successive geological formations has been built up. Before we enter upon this part of our subject we must point out that the hypothetical stages outlined above are by no means free from doubt. There are difficulties in the way of their acceptance, which we can only mention briefly. If the original earth crust furnished the material for the successive sedimentary rocks, it should form the lowest stratum underlying all the other geological forma- tions. But, as the latest discoveries seem to indicate, the earliest accessible Archaean rocks do not seem to correspond well with such an assumption. They are rather igneous rocks, interposed generally between the stratified rocks 22 THE FIRST PRINCIPLES OF EVOLUTION and the supposed original crust, which is nowhere accessible. We should have to assume that after the formation of the primitive crust a prolonged era of widespread volcanic action ensued, completely burying the crust under a mass of poured-out lava. Such eruptive activity on a grand scale, however, could only take place if a great deal of the gases and steam, supposed to have been forced out into the atmosphere by the fiery-hot globe, was retained within it for a long time, to be given off gradually in volcanic ex- plosions. Besides, a dense, heavy atmosphere, overcharged with steam and carbonic acid, and acting, as it were, as a warm blanket to the earth, is hardly consistent with the existence of organic life-forms, such as are known to have abounded in the very earliest geological times. At least their organization does not warrant our postulating funda- mentally different atmospheric and thermal conditions for them. According to the planetesimal theory, which was based by Chamberlin largely on geological considerations, the early phases of the earth would read rather differently. We would have firstly the nuclear stage, at which the globe, small as yet, is not able to hold an atmosphere, the light gases, not being attracted sufficiently by gravitation, flying off into space.* By gradual accretion an atmospheric envelope was gathered round the globe, partly by accumu- lation of the surrounding nebular masses, partly by ex- trusion of the gases occluded in the nucleus itself. The gases ultimately condensed and led to the appearance of water, which first accumulated within the lithosphere, because saturation ensued there most quickly. Gradually the water oozed out to the surface to form oceans. Violent extrusion of gas and steam would at the same time bring about a stage of vulcanism, and therewith lead to the formation of the oldest geological strata of igneous rocks. * The atmosphereless stage is thus seen to precede the later stages, in contradistinction to the usual theory which ascribes the want of an atmosphere (as, e.g., of the moon) to the absorption of it in the declining age of the orb, GEOLOGICAL EVOLUTION 23 From thence the further geological stages are the same according to both cosmic theories. (6) The Known Geological Stages. The known geological strata which form the supercrust of the earth can be arranged into five great divisions, each being subdivided into systems, etc. (see Table, Fig. 4). Epoch. Archean Proterozoic Palaeozoic or Primary Mesozoic or Secondary If Cenozoic System. Precam- brian Cambrian Silurian Devonian Carboni- ferous Permian Triassic Jurassic Cretaceous Eocene Oligocene Miocene \ Pliocene / Pleistocene or Glacial Post- glacial Fauna. Flora. Foraminifera ; crus-l tacea / Sponges ; corals ; Crus- tacea ; shellfish Fish; insects Land snails ; fresh- water shells Amphibians Reptiles Marsupials Flying reptiles Birds Placental mammals Manlike apes Man 83 S Algas /Mosses ; j ferns ; I horsetails Gymno- sperms (conifers ; cycads) Angio- sperms SO H 3i 7 Si Fig. 4. — Table of Geologicai- Periods with Successive Appearance of Typical Life-Forms. (Modified from E, Clodd.) As these beds were superimposed upon each other in course of time, their position still gives us, on the whole, the order of their origin, the lowest being the oldest, the uppermost the newest strattmi. Very often, however, the whole series 24 THE FIRST PRINCIPLES OF EVOLUTION has been upturned and disturbed by violent upheavals and distortions. But whatever may be the actual position of a given stratum, its place in the earth's history can be deter- mined by the kind of fossils it contains. WiUiam Smith, about a century ago, was the first to show that each geological period has its own characteristic organic remains, by which its chronological position can be ascertained. Later palaeontological researches, based on the theory of evolution, which assumes an actual succession of pro- gressive life-forms in time, have borne out his contention to the full, his method having been greatly improved. Being here concerned only with a general view of the earth's history, we shall merely indicate briefly the course of the events. We have already noted that the most ancient geological formation is the Archaean, which consists chiefly of rocks of igneous origin, while the later divisions are mainly made up of sedimentary strata. The Archaean land, most prob- ably sparsely clothed with primitive vegetation, was gradually worn down by weathering and the encroaching sea ; and its vast detritus, accumulating for ages reckoned to exceed all the other geological periods together, went to form the sedimentary rocks of the Proterozoic era. The oldest definite fossils yet found belong to the latter stage, and, though occurring very sparsely, they are of a rather advanced type, representing the crusters, thus indicating that life must have been in existence for a very long time previously in order to be able to attain to such high organization. The Archaean and Proterozoic formations are often classed together under the term of " Precambrian," coming as they do before the Cambrian system, the first which, by its abundance of preserved fossils, allows us more precise knowledge. The story of all successive stages is the same — a heaving up of the accumulated sedimentary deposits, their gradual denudation, and the building up out of their detritus of the next geological stage. At the beginning of the Cambrian period we find the GEOLOGICAL EVOLUTION 25 distribution of land and sea settled in its main outline very much as at present : a large, low-lying mass of land stretching across the northern hemisphere of the globe, covering, according to some accounts, a great part of what is now the North Atlantic Ocean. No mountains existed as yet, for these were slowly uplifted during later periods. The Cambrian Sea abounded in a rich variety of animal life, from the lowest Protozoa, sponges, etc., up to the crusters and molluscs, the most prominent class being a kind of cruster. Only doubtful fossils of plants have been found, though no doubt many must have existed at that time. During the next stage, the Silurian system, the sea stood over a large part of the continents, only once more to with- draw slowly from the land at the close of the period. The prominent feature of this stage is the appearance of the first air-breathing animals, the insects, while its end witnessed the advent of the earliest type of fishes. Of plants, alg£e mainly have been recovered. The climate during the last two periods must have been, judging from the wide distribution of the marine fauna, uniformly waim all over the globe. The following system, the Devonian, is known in England chiefly as the age of " Old Red Sandstone." The sea inun- dated the greater part of Europe, leading there to marine deposits, while in England vast inland lakes were formed, where the accumulating sediments were transformed into rocks, of which red sandstone, so prevalent on the Devon coast, is the most characteristic. This period yields the fir.st confident traces of terrestrial life, the earliest land animal preserved being the snaiL A primeval vegetation of giant clubmosses, ferns, and horsetails, covered the country. The immense development of the carboniferous forests of the next period is well known. Enormous fern-trees, huge mosses, and mighty horsetails flourished in the vast swamps of the Carboniferous age, the remains of which now furnish the coal-seams all over the world. There were 4 26 THE FIRST PRINCIPLES OF EVOLUTION only few terrestrial animals, of which the most interesting are the earliest types of amphibians. The luxuriant vegetation, favoured by a very moist and warm cUmate, largely absorbed the excess of carbon dioxide (COj) of the atmosphere, though, according to Chamberlin, the evidence of the superabundance of CO2 during the Carboniferous age is by no means unequivocal. Whatever carbonic acid was needed for vegetal growth was, according to him, supplied from volcanic and cosmic sources. Into this period falls the first beginning of mountain-formation, for it was then that the so-called Palaeozoic Alps, remnants of which can be seen to-day in the Vosges, Black Forest, Harz, and Sudetes Mountains, began their development. The Ural Mountains, too, seem to date from the same time. The main cause of the formation of mountain-chains is generally considered to be the contraction of the earth due to secular cooling. The shrinkage of the interior of the globe causes the crust to crumple into huge folds, which rise over the continents and sink at the bottom of the sea. For not only does the great weight of the superimposed sediments, accumulating for millions of years, tend to crush the oceanic segments downwards, but it would, according to Professor Sollas, thrust up the adjoining land by lateral pressure. During the Permian period the uplifting of mountains went on apace. In America the Appalachian mountain- range arose, while large tracts of land emerged in the southern hemisphere, which bridged over the sea between Africa and South America on the one hand, and between India and Australia on the other, but have since disappeared again. The characteristic feature of this time is the general decrease of temperature, and the first indication of definite climatic zones and seasons. This has been ascribed to various causes, partly to the depletion of carbonic acid, which acts Uke a thermal blanket, partly to the reduction of humidity by the restriction of the oceanic area, etc. One thing is certain, that though traces of glacial action GEOLOGICAL EVOLUTION 27 have been found as far back as the Cambrian times, the Permian period is distinguished by the first authentic Ice- age, the causes of which we shall discuss later. This period, too, saw the rise of the first primitive reptiles. It is unnecessary for our purpose to follow the whole series of successive strata by describing the essential characteristics of each. We shall confine ourselves to the main facts, which prove of general interest from the evolutionary point of view. The second great era, following upon the Palaeozoic era, is the Mesozoic, which is divided into the Triassic, Jurassic, and Cretaceous systems. During the first period the sea overspread the greater part of Europe, which then again had a semi-tropical climate. The greatest significance is attached to the appearance of the lowest non-placental mammals, and the first flowering plants, represented by the conifers and cycads. The Jurassic age saw the origin of the first forerunners of the birds, evolving from the flying reptiles, which abounded during the Secondary epoch. Mountain-building, too, now started in full vigour, slowly giving rise during the next stages to the Rocky Mountains and Andes in America, and the P3rrenees and Alps in Europe. The third epoch, the Cretaceous, takes its name from the vast beds of chalk which were formed out of the shell-remains of lowly minute organisms swarming in the ocean which covered the whole of Southern Europe. True birds and the advent of true flowering plants characterize the life of this geological series. The Tertiary era, which is divided by geologists into the Eocene, Oligocene, Miocene, and Pliocene epochs, is dis- tinguished by a revival of great volcanic activity, which had ceased during the past ages. The configuration of the continents assumed its present shape, the great mountain-ranges, the Alps and the Himalayas, being finally reared, while the land which had connected North America with Europe and South America with Africa and Asia ultimately disappeared. The climate, temperate during 28 THE FIRST PRINCIPLES OF EVOLUTION the Eocene period, became tropical during the Oligocene, only to grow cold again, and finally to end in what is known as the great Ice-age of the Pleistocene period. The evolution of the animal species reached its crucial point in the development of the ape-man {Pithecanthropus erectus), leading later to the appearance of man himself. The Quaternary era was ushered in by the great Ice-age, a time when not only the poles and the high mountain- summits were covered by mighty ice-fields, but when a great mantle of ice, extending over 6 to 8 million square miles, and up to io,ooo feet in thickness, reached down over half North America and North Europe. Signs of glaciation have been found as far south as the Thames and the Danube, and on the top of mountains even in tropical regions. There is sufficient evidence to show that there was not one ice invasion only, but that the ice retreated at intervals, only to advance again. Six separate such invasions, with interglacial intervals, have been made out in America and Europe. As to the cause of the glacial period, with its alternate atctic and temperate climates, various explanations have been brought forward. Repeated elevation and depression of the glaciated regions have been adduced, but such periodical oscillations of great continents within comparatively brief periods seem to be improbable. Atmospheric conditions, connected with the depletion of the carbonic acid of the atmosphere, the interruption of oceanic currents, etc., are also scarcely able to account for the periodicity of the glacial phenomena. According to the astronomical hypothesis of James Croll, the regular recurrence of glacial periods is due to the variations of the earth's orbit, which produces at definite long intervals exceptionally short summers and long winters. Though perhaps the most widely accepted theory, this has by no means remained uncontroverted, so that at the present time we are still left in doubt as to the real cause or causes of the Ice-age. Finally, the Postglacial or Human period embraces the GEOLOGICAL EVOLUTION 29 stages of human development from prehistoric times of the Stone-age through the Bronze and Iron ages to our own historical period ; upon which stages, however, we do not need to enlarge here, as they more properly belong to archaeology than geology. In concluding this subject it will perhaps be advisable to give an indication of the time evolved in the past periods of geological evolution. The computation arrived at is founded partly on geological, partly on physico- astronomical arguments. As to the latter. Lord Kelvin calculated from the rate of secular cooling of the globe, based on the known rate of increase of heat towards the earth's centre, that superficial congelation of the globe must have taken place between 20 and 40 million years ago ; while the age of the sun, according to the same authority, lies between the limits of 100 and 500 million years. Now, since Darwin postulated for the evolution of species a much greater length of time, there has long been a serious discrep- ancy between biological needs and physical calculation. The geological data themselves are very little reUable. For though the rate of denudation can be approximately reckoned out — it would, for instance, take about 7 million years for the European land-complex to be carried piece- meal into the sea — yet as the time that elapsed between the several geological strata is beyond our calculation, no definite figures can be given which are at all useful. Indeed, the figures given in the Table, Fig. 4, indicate more the relative duration of each period than its actual age. Lately Professor J. Joly estimated the age of the earth by the quan- tity of salt contained in the ocean. As the sea-water was originally precipitated on to the earth from the atmosphere, it contained no salts. These were carried into the sea by the rivers, which dissolved the saline constituents out of the rocks they traversed. Professor Joly arrived at a probable age of our globe of 90 to 100 million years. The deadlock which existed so long between biologists and geologists on the one band, and physicists on the other, as regards 30 THE FIRST PRINCIPLES OF EVOLUTION geological time, and which at one time threatened to prove a very serious obstacle to the acceptance of the gradual evolution of species, has now at last been fortunately solved in favour of evolution. Since radium, which is one of the constituents of the earth and most probably of the sun, is known to be a great liberator of cosmic energy, producing it by its own disintegration, as we shall see in the next section, the source of energy available is now no longer restricted to the contraction of the cosmic bodies. Accord- ing to G. H. Darwin, we may safely multiply the time given by Lord Kelvin by a number between ten or twenty. It would appear, then, that evolution has at its disposal any time it may require for the origin of species. It is now roughly put at about loo million years, while the date of the great Ice-age lies anywhere between 60,000 and 300,000, or more years. 3. Atomic Evolution. Ever since John Dalton, in 1803, formulated the atomic theory, the permanence and fixity of the chemical elements has been an accepted axiom of science. He showed that the elements combine with each other in certain unalterable proportions ; and also that, if several compounds are formed by the same elements, the relative weights of any one element entering into such combinations are simple multiples of each other. If, as Dalton assumed, matter is made up of ultimate atoms which cannot further be subdivided, then the atoms uniting with each other to form chemical compounds can only combine in whole numbers. As each atom of a given chemical element has its own definite atomic weight, the law of chemical combination, as enunciated above, follows as a matter of course. But while the fundamental basis of this theory remains unshaken, facts have gradually accumulated which tend to show that atoms are by no means the indivisible units they were originally held to be. ATOMIC EVOLUTION 31 (a) The Periodic Law. In determining the relative weights of the atoms, taking hydrogen as unity = i, it was found that many of the elements have atomic weights expressible by whole or very nearly whole numbers : thus the atomic weight of carbon is 12, that of nitrogen 14, etc. This suggested to Prout as early as 18 15 the idea that the heavier elements were nothing but condensations of hydrogen atoms, each element being made up of a certain number of such atoms — viz., 12 or 14, etc. — according to the atomic weight of the element. But more precise work soon revealed the fallacy of this assumption, as it was definitely ascertained that the atomic weights of the majority of the elements are certainly not whole numbers. Of more value was the discovery of Dobereiner, who found that certain elements had a very great resemblance to each other, forming little groups of triads which showed strongly correlated chemical properties. Such groups are, e.g., calcium, strontium, barium, or chlorine, bromine, iodine, etc. The interesting fact is that the atomic weight of the middle element of any one triad is the mean of the combined atomic weights of the first and third elements of the group. The next important step was taken by John Newlands, who in 1863 showed that the elements, if arranged in order of their atomic weight from the lowest to the highest, fall naturally into a number of series, the elements which occupy the same place in each series forming a natural group, and being chemically closely related to each other. This law, which was independently worked out in full by Mendel6ef and Lothar Meyer, is called the " Periodic Law." Its great significance lies in the fact that it shows the properties of the elements to be in some wise dependent on their atomic weights. Seeing that each such related group, as it were, forms a natural family of elements, this curious kinship seemed best explainable by assuming that the similarity 32 THE FIRST PRINCIPLES OF EVOLUTION of the related elements was due to an underlying unity in their composition. What this common factor was, chemistry was unable to tell. But other sciences gradually opened out new methods of inquiry, revealing hitherto unknown phenomena, which have brought this great fundamental problem of matter much nearer a solution. (b) The Dissociation of Elements, New evidence in favour of the view that the eighty-odd elements known at present are but different aggregations of one primordial substance, was furnished by the advance of the study of spectrum analysis. Sir Norman Lockyer, by his extensive researches on the spectroscopic behaviour of the elements under the most varying conditions, was able to carry the theory of the dissociation of the elements one step further. We have seen in the section on cosmic evolution that each element, when suitably examined through a spectroscope, exhibits a characteristic spectrum of its own, by which it is readily distinguishable from any other element. It was soon found, however, that the idea of " one element — one spectrimi " was by no means correct, for '■ certain elementary substances, when differently treated, furnish two kinds of spectra of quite a different character, not having any line or band in common." Lockyer was able to show by the appUcation of various degrees of heat that the spectrum of a given element changes with the intensity of the temperature employed. Not only this, but, applying the same reasoning to the sun and the stars, he found corresponding changes in the spectroscopic appearance of the elements according to the temperature prevailing in the celestial bodies — tempera- tures which far exceed any attainable by artificial means, and which thus provide a natural means for the dissociation of the elements. As the temperature of the stars can be determined by the extension of their spectra into the ultra- violet — the hottest stars having the longest spectrum, the coldest the shortest — Lockyer was enabled to arrange the ATOMIC EVOLUTION 33 stars into a series according to their temperature, and to compare their respective spectra with each other. As a result, he discovered that the gaseous stars, which are the hottest, have the simplest spectrum, showing only the lines of hydrogen, helium, and asterium (the latter a gas unknown as yet on earth). In the next order of stars, those of medium temperature, the gases (except hydrogen) begin to die out, while the lines of the metals appear, characteristic of the high temperature of the electric spark. As these are totally different from the metallic lines at a low temperature, the suggestion occurred to connect these simplified metallic spectra with an elemental state different from that of the ordinary metals. Lockyer therefore called these substances " proto-metals," since they form the stage before the real metals. For the ordinary metallic lines appear in the stars of the lowest grade of temperature, the gases (with the exception of hydrogen once more) having disappeared. It would seem, then, that with an increase of temperature a progressive disintegration of the elements takes place. Or, putting it the other way, as the stars gradually cool down, there are given the conditions for the successive births of the chemical elements. The hottest stars contain only a few gases ; slowly, with a lower- ing of the temperature, more and more of the known substances make their appearance. Furthermore, as a general rule, the lightest elements appear first, then the proto-metals ; the heaviest and most complex coming latest. All these facts find their simple explanation in the assump- tion that the elements, as observed by the chemist, consist of units which vary in number with the degree of the complexity of the atom. ■ There are many other phenomena of spectrum analysis tending to strengthen this hypothesis, of which we shall only give a few. Thus it is known that the so-called iron- vapour in the sun is in rapid motion. But the up-rush and down-rush of the incandescent gas are not registered by all iron-Unes alike ; thereby showing that in the sun " we are 5 34 THE FIRST PRINCIPLES OF EVOLUTION not dealing with iron itself, but with primitive forms of matter contained in iron," which are represented by different sets of spectroscopic lines. Other corroborative facts in favour of the dissociation theory are the possibihty of sorting out the apparently haphazard arrangement of the multitude of spectroscopic lines into a number of harmon- ious series, each of which must be assumed to stand for a different set of vibrating particles of the atom in question ; also the splitting up of yttria by Sir William Crookes in 1883 into at least five components, each giving a distinct spectrum of its own. But it must be admitted that, while there is no doubt of the facts, scientific opinion has been slow to accept the interpretation advanced by Lockyer. There are weighty objections, and the question of the ultimate constitution of the atom would have had to remain in abeyance once more, had not a new knowledge arisen — the science of. radio-activity — which put the compound nature of the so-called elements finally beyond doubt. (c) Radio- Activity Radio-activity is a property of matter which was first discovered by Henri Becquerel in the element uranium in 1896, whilst he was studying the action of X rays and phosphorescent bodies. Uranium occurs in the mineral pitchblende. Monsieur and Madame Curie, experimenting with the latter, found that it is four times more radio-active than uranium itself. This led them to the conclusion that there must be a substance in pitchblende many times more radio-active than uranium. They succeeded in isolating two such elements, which were named by them" polonium " and " radium." Radium was discovered in 1898, and its discovery has well-nigh revolutionized the fundamental ideas of science. What, then, is radio-activity ? It is nothing else than a disintegration of the atom going on spontaneously before our very eyes. ATOMIC EVOLUTION 35 If two poles of an electric current are fused into a sealed glass bulb from which the air has been exhausted to a verj- high degree of vacuum (the Crookes Tube, see Fig. 5), and an electric discharge is passed through the tube, rays are given off from the negative pole or cathode. These cathode rays were studied in detail by Sir William Crookes, who declared them to be " radiant matter," or " matter in the fourth state," thus anticipating in a remarkable degree the modern theory of matter. These rays were shown to travel in straight lines, producing vivid phosphorescence wherever ■ ■ ^^^7 -'''PMkM WW: ^^^H mZ-- '^^tJ^^H ^^^^^H u^^m^mHH Sh ^ Hi Fig. 5, — Crookes Tube in Action. + , Positive pole. - , negative pole. I From " The New Knowledge" by R, K. Duncan.) they strike the glass. They are charged with negative electricity, and are deviated from their path by a strong magnet. They are capable of penetrating through solid bodies, and generate the X rays. In fact, the cathode rays are, as Crookes had already pointed out, particles of matter projected with great velocity from the negative pole. The same corpuscles are found in burning gases, in glowing metals, and in incandescent carbon, which act as conductors of electricity. Indeed, these corpuscles are identical with the electrons, which, according to the modern electrical 36 THE FIRST PRINCIPLES OF EVOLUTION theory, are the carriers of electricity, and which must be present wherever electric phenomena take place. These very same rays are given off by radio-active substances, the radio-active phenomena being due to the emission of rays from such substances as radium, uranium, thorium, actinium, etc. Professor Rutherford demonstrated three kinds of rays given off from radium, which were called by him a, p, and y rays. The /3 rays have all the characteristics of the corpusoles just described ; in fact, they are nothing but negative electrons shot out from radio-active substances with a much higher velocity than the cathode rays, attaining nearly the speed of hght.* They cause phosphorescence in certain substances, affect photographic plates in the dark, dis- charge electrified bodies, penetrate through opaque matter, etc. The mass of a corpuscle has been determined to be a thousand times smaller than that of a hydrogen atom, which is the lightest element existing. The u. rays are also particles of matter ; their speed is much less than that of the /3 rays, their velocity being only 12,000 miles per second. The weight of an a particle is four times as much as that of hydrogen — i.e., its atomic weight is 4. Now, helium, which was discovered by Lockyer in the sun in 1868, and was found by Ramsay in 1895 on our earth, has the same atomic weight. In fact, as Ramsay and Soddy showed in 1903, the a rays are swarms of helium atoms constantly expelled with great velocity from radium and other radio-active substances. . In contra- distinction to the fi rays, which are negatively electric, they carry a positive electric charge. They cause phosphores- cence, are but feebly penetrating, and are only with difficulty deviated by a magnet. The y rays are always associated with the /3 rays, and are most probably produced by them. They are * Velocity of light equals 186,000 miles per second ; speed of shooting stars, 20 to 40 miles per second ; swiftest rifJe-buUet, about J mile per second, ATOMIC EVOLUTION 37 identical, according to some authorities, with the X rays. Little as yet is known about their nature ; they are not corpuscles, but most likely waves set up in the ether. Now, the remarkable feature of the production of these rays lies in the fact that we have here before us an actual splitting up of a radium atom into several components. The disintegration of elements, from being a mere theory, has become an established fact of science. Not only this, but a successive series of changes has been made out in the radio-active substances, leading step by step from one element to another, and thus exhibiting a real transmutation of matter. The dream of the alchemists, discarded by scientists as a useless chimera, has become true, though not exactly in the manner they had anticipated. If radium bromide is dissolved in water, a gas escapes which is intensely radio-active, and has been called by Professor Rutherford the " emanation." While the atomic weight of radium is 226, that of the emanation is 222 ; in other words, emanation is an atom of radium minus an atom of helium. But this emanation in its turn decomposes spontaneously. It has the property of causing objects brought into its immediate neighbourhood to become radio- active. This " induced radio-activity " is due to the deposition of an invisible film of radio-active substances. This " active deposit " of radium is non-gaseous, and represents the successive steps in the disintegration of the emanation. For by the repeated emission of rays a series of new substances is formed, each changing into the next ; these have been named Radium A, B, C, D, E,~ and F respectively. The atomic weight is reduced by 4 with each emission of a, or helium, particles. Some of the substances are very fleeting, while Radium F, which has an atomic weight of 210, has been found to be identical with the previously discovered element polonium. Finally, by the emission of a further a particle, the atom of poloniunj 38 THE FIRST PRINCIPLES OF EVOLUTION changes into Radium G, wiiich has an atomic weight oi 206, and is in all probability identical with the well-known element lead, though its identity has not yet been finally settled. But the question arises : If radium continually transforms itself in the manner described, how is it that there is any radium left in the world ? However great the store may have been in past times, it must, one would think, have disappeared by constant decay. Now, radium emanation decays too, but we know that it is continuously reproduced by radium at exactly the same rate as it decomposes, so that by means of this " radio-active equilibrium " the amount of emanation present in radium at any given time is always constant. If the same holds good for radium, there must be a parent substance which produces radium as fast as the latter disappears. This source of radium was discovered by a train of reasoning which we can only just outline here. Not all the atoms of a given mass of radium break up simultaneously,* but only a certain number, which is pro- portionate to the number present, so that it would take a certain definite time before the whole mass of radium had undergone disintegration. Now, it has been found that half of the total mass of radium disintegrates in 1,300 years, another half of what is left — i.e., a quarter — in the next 1,300 years, and so on, until practically the whole mass has disappeared. In the same way the time (T) for emanation to lose half its radio-activity has been found to be 3-8 days. As both radium and emanation change at a given rate, the latter much faster than the former, there will always exist a certain proportionate amount of emanation to radium, which is a definite fixed quantity dependent on the relative rates of change of the two bodies. Now, radium is always found associated with uranium in constant proportions, i part of radium * It must be understood, though, that the disintegration of each individual atom takes place instantaneously by a sort of small explosion. ATOMIC EVOLUTION 39 to 3 million parts of uranium. This means that if uranium is the parent of radium, it must change more slowly than radium, its duration of life being three million times longer than that of radium. In fact, uranium is radio-active, as we have already learnt, but very much less so than radium. It emits a rays and changes into a sub- stance called " uranium X." The further stages have not all been elucidated as yet, but we know that the ultimate result of these changes is the element radium. The im- Products. Atomic Weight. T.» R.iyi Emitted. Uranium 238 about 4,000 million a Uranium X . . Ionium 234 230 22 days a Radium Emanation 226 222 1,300 years 3-8 days a a Radium A"l o^ 218 3 minutes a .. bU| .. 214 21 minutes /3 „ c