The Meaning of Evolution

by Samuel Christian Schmucker

CHAPTER VI

Life in the Past

Anyone who earnestly studies plants and animals as they exist in the world to-day cannot help wondering how the earth began and where it got its life. This is the true end and aim of geological study. The history of man seems to run back into a far distant and gloomy past. Except for the poetical account in Genesis and the traditions of various peoples throughout the world, real history fades away into an earlier time of which there are no written records. When the delvers in the Mesopotamian plain talk to us of kingdoms running back through seven or eight or nine thousand years, we seem to be getting back to the beginnings of things. But seven or eight or nine thousand years are as nothing in comparison with the age of the earth, which runs back into a past so limitless that no man can safely assign any set figure to it. In a recent paper, Dr. Walcott, of the Smithsonian Institution, says that the antiquity of the earth must be measured not in millions, for they are too short, nor hundreds of millions, for this carries us too far, but must surely be measured in tens of millions of years.

When we attempt to study the past we find its various epochs unequally clear to us. In human history only quite modern times are absolutely clear. The history of the Middle Ages is distinct enough for us to build for ourselves a picture of the time with reasonable hope of gaining a correct view of the state of affairs. Back of this comes the long stretch of the Dark Ages, in which here and there we have bright spots, but it will perhaps long be impossible to portray clearly the life of the people. Getting back to the Romans, things once more become reasonably plain, as is true also in the case of Greek history. Back of this stretches the Egyptian with fair precision, and, older than it, the Babylonian and Chaldean. But these past three have not left nearly so definite an account for us as did the later civilizations of Greece and Rome.

When we try to go back of these we must change our method of study entirely. Writing is absent, and all we know of earlier men must be inferred from a few pictures that were daubed on the rocks or carved in ivory or bone, from tools made of stone or bone, from a few metal or stone ornaments, or from the bones of the men themselves. Even so, the history fades out without telling us its own beginnings. It is quite as impossible for history to write its origins as it is for man, from his own knowledge, to describe his birth.

What is true of the human story is quite as true of that of the earth. Recent steps are very plain. We may read them with considerable confidence. As we go deeper into the rocks and find older fossils, the evidence becomes less certain. The animals differed enough from those of to-day for us to be less sure what they were like. As we keep on moving backward through time, and downward through the rocks, we find, after a while, strata in which there are evidences of life that existed long ago, but in which these traces are so altered that it is impossible to tell what sort of living things existed; we learn only that they were alive. Going back still further, these fade out. There is no knowing when the earth began; there is no knowing when life began upon the earth. It is not meant that men have not wondered, even reckoned carefully, as to how long ago each of these events occurred. Many speculations have proved entirely useless, a few remain as yet neither confirmed nor disproved, and of such we shall speak.

For the last hundred years the theory of the earth's origin suggested by the Marquis Pierre Simon De La Place, of France, near the end of the eighteenth century, has held almost undisputed sway among men who were willing to consider the question as open to human solution. This theory is known as La Place's Nebular Hypothesis. When men began to study the heavenly bodies with the newly invented telescope, new ideas naturally sprang up. Among the objects which the glass disclosed were the nebulæ, which are great clouds of fire mist, glowing masses of gas. They are scarcely visible to the naked eye, but are among the most interesting objects in the heavens when seen through a telescope. The other suggestive heavenly body was our sister planet, Saturn. Besides having a full complement of moons, Saturn has around it, as distant as we would expect moons to be, three great rings. These look very much as if one's hat, with an enormously wide brim, should have the connection between the rim and the hat broken out completely, but the rim should still float around the hat without touching it and should steadily revolve as it stood there. The rings of Saturn are not solid like the suggested hat rim. They are evidently made up of a great number of very small particles, each moving around the center of Saturn. But the great cloud of them is spread out flat. At the distance which Saturn is from the earth they look as if they made a solid sheet. Furthermore, they do not form, as it were, one continuous hat rim, but it is as if the rim were broken into three circular sections, each bigger than the one inside it and separated from the next by an area nearly as wide as the ring itself.

With such material in the heavens to guide him, La Place suggested that the sun had once been an enormous fire mist scattered over an area billions of miles in diameter. This gaseous material, by the attraction of its particles for each other, began to condense and contract. When the plug is pulled from a washbasin the particles of water, in moving toward the center, in order to get out of the basin, invariably set up a rotary motion. As the particles of this diffused nebula began to gather together they, too, gave to the mass a rotary movement. This grew more and more rapid, with greater contraction, until the particles on the outer edge of the rotating mass had just so much speed that the least bit more would make them tend to fly off as mud would fly from a revolving wheel. When this point was reached there was a balance of forces which made the outermost portion remain as a ring while the rest contracted away from it, leaving it behind.

It was La Place's idea that this process had repeated itself, and ring after ring had been left behind. Finally the sun condensed and grew into a ball, occupying the center of the system. At varying distances from it were to be found either rings or planets which had been formed out of such rings. For La Place suggested that in a ring like this the material could not be quite evenly distributed. While every particle in the ring kept revolving around the sun, those in front of the densest part were slowly held back by the attraction of the thicker portion, while those behind it in rotation had their speed hastened until finally all the material in the ring had collected at one spot and a new planet was born. La Place believed that these planets formed their moons in exactly the same way, and that Saturn was simply a planet not all of whose moons had yet been formed. He believed that this happy accident served to tell us how the universe had been created.

Of course, so detailed a theory concerning anything of which we know so little has always had much ridicule thrown upon it, and yet no truly competing theory has been proposed until very recent times.

Within a few years a Planetesimal Theory has been announced, and is gaining considerable prominence, although it is too early yet to say whether it will supersede La Place's idea. In this theory, also, the suggestion comes from the heavenly bodies. With the increasing study of the nebulæ, many forms of these interesting bodies have been discovered. A very common type consists of a great coherent central mass, with two or more arms extending from opposite sides in the form of a spiral. This is as if gaseous revolving nebulæ had come into comparatively close proximity to a passing body. The visitor, by its attraction, drew from the nebula a wisp of gas. The revolving motion of the nebula gave to the attracted arm the spiral form.

These twisted arms are not equally dense throughout, but have thickened knots here and there in their course. The Planetesimal Theory suggests that these thickened knots are embryo planets and the central portion of the nebulæ an embryo sun. After all the material in such a body has condensed either around the knots or about the central mass a new solar system will be complete. As before stated, neither of these theories can be said to be demonstrated. Each of them has points in its favor and each has its difficulties. It is pleasant to know what men have clearly thought concerning such questions, but for a man not a trained geologist neither will carry much conviction. He will still rest with his own early conclusion that whichever shall prove to be true, for him his old formula is still valid, "in the beginning God made the heavens and the earth." He will no longer think of God as having shaped the balls with his own hand and thrown them into space; he will no longer dream that it all occurred within a week not more than six thousand years ago; but still to him will come the reverent conviction that, whatever the plan by which it was accomplished, it was still God's plan and God carried it out.

Now that we have tried to stretch our imagination back to the origin of our globe, the question not unnaturally comes to our mind, how long ago did all this happen? Is there any possible means of telling when the history of the earth began? All such attempts lead either to indefinite or to uncertain conclusions. Each man who essays the problem approaches it from a different side and ends with a different result. But no matter what the method of approach, all are agreed on at least one point, the enormous length of time, as counted in years, through which the earth has lasted.

One great mathematician worked on the basis of the rate of the present cooling of the earth. Counting backward to the time when the earth's surface must have been hotter, according to La Place's idea, he decided that our globe has been cool enough for the existence of life upon it for a period of somewhere in the neighborhood of one hundred million years. Those who try to study the rate at which mud is being deposited in our bays and at the mouth of our rivers, and who hence try to deduce how long it has taken to produce the thickness of all the stratified rock we know, arrive at a figure larger, rather than smaller, than that mentioned above. The same is true of those who try to count the age of the earth by the rate at which the present rivers are carrying away their river basins, and hence who calculate how long it has taken the rivers of the globe to wash away all the rocks which it is quite clear have been carried out. Still others have attempted to solve the problem by seeing how much salt the rivers are carrying into the sea, and consequently how long it must have taken the sea to become as salt as it is. A very late attempt has been based on the alteration in the minerals that show radio-activity. Conservative estimates, based on all of these, would give us a figure on which we must not count with any exactness, but which will serve at least to mark the present trend of opinion. We may put this figure at one hundred millions of years.

The following [table] gives us the names of the periods into which the geologist has divided the past history of the earth. The first column gives a simple name, which, in each case, is a translation of the technical name the geologist gives to the era. This technical name is also given in parenthesis. The second column shows the number of years ago at which this period may be placed, while the third column gives a series of names most of which are in use in geology and which are intended to indicate the stage of advancement of the higher animals in that particular period. Some of these names are perhaps giving way to later terms, but all of them will be understood by any geologist. Most of them will serve to keep very clearly before the mind of the ungeological the period which he is studying. Like all such tables, this must be read from the bottom up. This arrangement is used because the oldest rocks in the series are naturally at the bottom and the newest rocks are on the top, though occasionally a region is sufficiently upset partly to reverse the order.

TABLE OF GEOLOGICAL TIMES

ERAS	MILLIONS OF YEARS AGO (VERY UNCERTAIN)	STAGES OF ANIMAL DEVELOPMENT
Recent Life (Cenozoic)	0 to 5	Age of Man (Quaternary) Age of Mammals (Tertiary)
Middle Life (Mesozoic)	5 to 10	Age of Reptiles
Ancient Life (Palæozoic)	10 to 25	Age of Amphibians (Carboniferous) Age of Fishes (Devonian) Age of Invertebrates (Silurian and Cambrian)
Dawn Life (Eozoic)	25 to 50	Earliest Animals and Plants

Having seen what the scientist supposes to be the method of formation of the earth itself, it will be interesting next to consider what the biologist surmises as to the origin of the life upon the earth. Here again two explanations hold. The one, and distinctly the older of the two, says that at some time in the far distant past, under conditions which are rarely if ever duplicated, out of the lifeless material of the globe were produced simple and low forms of life. These could not properly be called either animal or plant, but partook somewhat of the nature of both. Of this there is at present no evidence whatever. The only reason we have for suggesting it is that, if we understand the past conditions on the earth, there was a time when life was impossible. Now we find life. Hence it must have arisen. This of itself, of course, furnishes no proof, but leads us to try to imagine how the transition might have come about. Every scientist who believes in this form of origin holds that if the exact conditions are repeated the result will occur once more. He may believe that no such repetition is possible, but he is confident that, if it could be, life would arise again from lifeless matter.

This process of life arising from matter that is not alive is known as Spontaneous Generation. Two hundred years ago it was supposed to occur frequently. It was common belief that the beautiful pickerel weed which borders our Northern lakes, after freezing, went into a sort of protoplasmic slime out of which pickerel were produced. The eelgrass of the river was supposed to yield eels in a similar fashion. The dead bodies of animals were supposed to turn into maggots. Such crude ideas of spontaneous generation are no longer possible. The whole science of bacteriology absolutely presupposes the impossibility of spontaneous generation in the flasks and test tubes of the laboratory. One or two men of otherwise good standing in science still maintain that they are getting new life in their own test tubes, but they fail utterly to persuade the scientific world. I think it is a fair statement of the position of science to-day to say that there is no evidence whatever of spontaneous generation, excepting the presence of life upon the globe.

Not all has been said, however, on this question. The chemist is learning in the laboratory to produce many substances which, until very recent times, were produced only in the bodies of animals or plants. Dye-stuffs were originally gotten almost entirely from animal or plant material. At present the great majority of them are made in the laboratory, and in not a few cases they not only imitate the color of the older material, but actually have identically the same composition and constitution. The laboratory-made material is exactly like that made by the animals or the plants.

The same is true with regard to a large number of the fruit flavors. These are due to the presence of ethereal oils in the plant, and their exact counterparts can now be produced in the laboratory, and can serve every purpose of the fruit flavor itself. Alcohol has been produced artificially, and alcohols, which nature never dreamed of making, so far as we can tell, but which are made on her plan, are manufactured by the chemist. Last of all, sugar has recently been built up by the chemist, though the method at present is so expensive that it cannot possibly compete with the production of the commodity from the cane and the beet. As in the case of alcohol, all the sugars that nature makes can now be made artificially, and others of the same general plan which she seems not to have as yet devised can be produced within the laboratory.

Attempts have been made to manufacture proteids, but these have as yet eluded the efforts of the chemist. He is beginning, however, to come nearer understanding their composition, and when he once clearly comprehends that he may be able to reproduce them.

One of the German chemists is convinced that the nuclein in the nucleus of the cell is not a very complicated compound. Under such conditions it is not a matter of surprise that the physiological chemist should be constantly dreaming that he may at some time produce living matter in the laboratory. To the ordinary mind it scarcely seems possible. We are so entirely sure that life is not amenable to physics or chemistry that we can hardly conceive of the possibility of its originating out of matter in the test tube. If it does so come, and when it does so come, this will not prove that life is a less noble and less wonderful thing than we thought. It will only prove that chemistry and physics are more noble and more wonderful than we dreamed.

There is another way of approaching this life problem, though it seems to be rather a begging of the question than a solution of it. Of recent years it has been discovered that even the very low temperatures obtained by evaporating liquid air, say three hundred degrees below zero, Fahrenheit, do not kill seeds or spores of mold. The space between the planets is undoubtedly extremely cold. We have always supposed it to be entirely too cold for life to exist in it. But we laid little stress on the fact because we had no thought of any possible life existing there. But the discovery that seeds and spores can live uninjured through extreme cold has led to an interesting suggestion. This is that when the earth became adapted to the presence of life it was infected by germs transported on meteors from some other system. According to this theory, organic dust through space is ready to infect any planet which offers the conditions under which life may arise. Of course this theory does not explain the origin of life. It pushes back that origin a little farther or supposes that life is as old as matter itself. Again we may leave to the scientist the discussion and the elaboration of this or any other theory he may promulgate concerning the origin of life. When he has established clearly the process and can produce life we will accept his explanation; meanwhile, we will always be interested in his attempts to solve the problem, but still our simple formula, "in the beginning God," serves our present needs and will satisfy us better than any as yet unverified hypothesis.

When we find through scientific investigation how life arises we will simply know how God created it in the beginning.

The next step in the understanding of early life is to study under the microscope the simplest forms which we can find in existence to-day. This, while far easier of execution than the problems which we have thus far considered, is still not without serious difficulties. But every day brings us nearer to the understanding of the structure of living things. Life the scientist cannot see. All he can study is living matter. Whether life can exist separate from living things is a problem outside the range of his, at least present, possibilities. Therefore, concerning it he has no answer whatever to give. But when we come to study living things we find that all life is associated with protoplasm. This apparently foamy, jellylike, transparent material is the only living substance in all the world. Animals and plants are larger or smaller collections of the little masses of protoplasm which we know as cells. The lowest animals are each made up of but a single cell. This consists of a small mass of protoplasm surrounded almost always by a thicker skin or covering, known as the cell wall and enclosing a complicated kernel known as the nucleus. The protoplasm seems to be the living substance itself. The cell wall is not a simple dead scum on the outside of the protoplasm, but is itself able to do certain things which can only, so far as we know, be done by living substances. For instance, of two materials dissolved in the water in which the cell floats, the wall may permit one to soak into the animal and keep the other out. The one allowed to enter will usually be found good to be used for food by the cell. The nucleus seems to store within itself the record of its past history and thus enable the cell to do in the future what its ancestors did in the past.

Such simple cells can exhibit in very low form all the activities the higher animals show in much more elaborate development. A one-celled animal can move about, can recognize the proximity of food, can engulf its food and digest it, can build up its own substance out of the digested food, can absorb oxygen, can use this oxygen in the burning of its own substance to produce its own activities, can act in response to sensation gained from outside, can throw off its waste matter produced by its own activities, and can grow. When the proper time comes its nucleus can split in two, the cell itself enclosing the nucleus can separate into two cells, each of which can grow to the size of the parent cell and repeat its life. This is as simple an animal as we have yet discovered. Every kitchen drain swarms with such creatures. On a summer day the stagnant pools are full of them. The simplest microscope will show them clearly. This is life in its lowest terms with which we are acquainted. With such life, it seems to us, the animal and plant world must have started their existence, when first the earth began to teem with living matter.

If, then, we may form any judgment concerning the first living things upon the globe by considering the simplest creatures that live here to-day, certain facts seem clear. In the first place, life began in the water, and for a long time was only to be found in the water. Single cells are so small and dry out so easily that it is necessary to their existence that they should be kept entirely moist by the presence of water all about them. It is true many of them will stand drying, but while they are thus dried they can scarcely be said to be much more than just alive. They are utterly inactive, or, as we say, they are dormant. In such conditions they become covered with a tough skin, almost a shell, and their protoplasm is itself nearly dry. Under these circumstances the life processes hardly continue at all. The protozoa, as these small animals are called, tolerate drought for a time; but they only live, in any sense worth calling living, when water is abundant and is neither very warm nor very cold. It is safe to say that the early life of the world formed in the oceans of the time. So absolutely is the habit fixed upon cells of protoplasm that even to-day the activities of the cells of higher animals depend upon the presence of moisture. The cells of our own bodies are to-day living, as it were, in an ocean. Everyone can remember far enough back to recall some time at which a tear slipped from his own eye onto his own tongue; we know our tears are salt. The tongue has tasted, undoubtedly, the perspiration from the lip on more than one summer day; this perspiration tasted as salt as the tear itself. The lymph that constitutes the "water" of a so-called "water blister" is also salty, and even the little blood one gets into his mouth in trying nature's method of stanching the flow from a cut finger gives the impression that it contains a little salt. Every fluid of the body is salty, and every cell of the body is bathed in salt water. It is too long since the ancestors of our cells swam in the seas of the Eozoic time for us to assert with any positiveness that the ancestral habit is responsible for this trait in the descendants. Sure it is that to-day our cells, like their ancestors of old, live in water, and this water is slightly salty—as were probably the Archæan seas.

The geologist tries as best he may to build up the geography of the earth in the past. He endeavors to judge from the rocks as he now finds them, where the seas, the bays, the dry land, and the mountains of earlier geological times lay. The present aspect of the earth is very recent, and earlier ages must have shown an entirely different distribution of land and water. The North American continent was certainly very much smaller than it is now. The first known lands lay close to the Atlantic seaboard and probably extended out into the water some distance beyond the present shoreline. The stretch of continent was narrow, and grew narrower as it went southward. In what is now the Canadian district, a considerable expanse probably existed in very early times. Then a great internal sea, shallower than the Atlantic, stretched its unbroken sheet over almost the entire area now occupied by the United States, while only a comparatively small hump of earth, ending in a narrower strip, lay where the great Western plateau now rears its enormous bulk.

A large portion of the history of the North American continent, with its developing animals and plants, is tied up with the gradual shrinkage of this interior sea. Slowly across the Canadian district, the Eastern and Western lands became connected with each other, while the waters progressively were pushed down the continent, which was steadily growing from the east and from the north, though less slowly from the west, into this internal sea. To-day only the Gulf of Mexico remains as evidence of the broad stretch that once extended through to the Arctic Ocean and west beyond the present position of the Rocky Mountains.

How this great Eastern backbone of the continent was produced, what sort of animals lived while these rocks were being formed, or whether this preceded entirely the existence of life upon the earth, no man to-day may surely say. In the oldest of the rocks there are beds of graphite, from which lead pencils are made. This substance is believed by the geologists to be, like coal, the remains of vegetable life. But these early rocks have been so heated and baked, so twisted and bent, that whatever forms of life they once held are now obliterated, or so altered as to give us no idea of what may have been their character.

So far as anyone can now see, this past history is wiped out forever and it will be impossible for men ever to demonstrate the character of this early life. Speculations, more or less certain, will arise. They may, after a while, seem so clear as to receive the acceptance of the scientific mind. Yet the truth remains that the early history of the earth, so far as animals and plants are concerned, is probably lost forever.

The most striking feature concerning the earliest layers of rocks in which good fossils are found abundantly is the complexity of the life. With the exception of the backboned animals, every important branch of the animal kingdom is represented, and it is just possible that we have even earlier forms of the vertebrates themselves. This, to the evolutionist, is very disconcerting. To find the great groups all well developed at least twenty-five million years ago and to find only fossils built on the same lines since almost nonplusses him. When the geologist tells him what an enormous length of time preceded the rocks in which he finds these fossils and how absolutely these earlier strata have been altered by the later geological activities he easily understands why it is impossible to find fossils in them. As a consequence, the evolutionist is forced to believe that all the earliest animals have left no clear traces behind them. Life as he first surely knows it is already extremely varied and quite well developed in some of its groups. The early animals were as well adapted to the times in which they lived as are the great majority of the animals of to-day. The reader must not infer this to mean that the animals of those days were like our present animals. They were not. No one traveling in a far country could find there animals as strange to him as would be those of the earlier stratified rocks. In these there were no fishes as we know them to-day, not a single member of the frog and salamander class, not a reptile, not a bird, not a mammal, and probably no air-living insects. It is highly doubtful whether there was any animal living upon the land and breathing the air twenty-five million years ago.

We start our study, then, at the period known as the Palæozoic era, the era of the ancient life of the globe, beginning twenty-five million and ending ten million years ago. The first of the three sections into which this period of life is divided is known as the Silurian age, the age of invertebrates. The word invertebrate is an unscientific but convenient term under which we embrace all the animals below those having backbones. This period is called the age of invertebrates because, although there is an enormous wealth of animal and plant life in the Silurian, there are no backboned animals except the lowest kinds of fishes. It was supposed for a long time that even fishes were absent. Now we know they existed, but they were small and inconspicuous. In this period corals were wonderfully abundant, particularly in the great internal sea which spread over what is now known as the Mississippi Valley. Everywhere over this region must have grown in the shallow water great numbers of creatures called crinoids or stone lilies. They were attached to the bottom by slender stems, sometimes many feet long. These stems are jointed, and when they became fossilized the sections were apt to separate, with the result that over a wide area in the Mississippi Valley it is very common to find these little segments which look not unlike checkers. At the end of the stem was a rounded head, with a mouth at the top, and around the mouth were branched, feathery arms. The creatures must have been exquisitely beautiful, but they have completely disappeared from the face of the earth, with the exception of a very few, found in the obscurity of the almost fathomless depths of the great ocean. Here they remain as peculiar relics, only preserved by the unvarying conditions in the deep sea from the extinction that has met their sisters.

Those who are familiar with our seacoast will know an interesting creature known as the horseshoe crab, or king crab, though in reality it is not a crab at all. It is rather more nearly related to the spiders than the crabs, though no one but a technical zoölogist could possibly associate them together. The ancestors of these king crabs were the finest and best developed animals in this early Palæozoic time. These creatures had bodies jointed like the tail of a lobster. They were wide and flat, instead of narrow and rounded like a lobster, and each joint of the body was highest in the middle and distinctly lower at the two sides, thus forming three regions along their backs. This structure gives to these creatures the name of trilobites. These animals were the kings of the early ocean. They had an interesting habit of curling up nose to tail before they died, and, as a result, a large proportion of all the trilobite fossils we find are curled in this peculiar manner.

After these forms the most abundant fossils we find in Silurian times were creatures that at first sight looked as if they might be related to the clams. These are known as lampshells, because one shell projects beyond the other and curls up at the tip so as to resemble the clay lamps which are dug out of old Roman towns. The lampshells also have nearly disappeared in modern times. Simple creatures belonging with our present crab and snail had begun to make their appearance, but they were not as abundant as we find them later on.

The third group of the mollusks to which the nautilus and squid of to-day belong is very abundantly represented in the Silurian by fossils with coiled-up shells. As for the plant life of the time, it is exceedingly difficult to say much about it. There must have been nothing but marine plants, and these must have been on the general line of the seaweeds. Little can be definitely said concerning them.

The next period of the Palæozoic is known as the Devonian age, or the age of fishes. Now the backboned animals first make their clear and unmistakable appearance. There are remains in the Silurian which show that there must have been a few fishes at that time. The Devonian is so full of them and they are so well developed and so diversified that this period is definitely known as the "age of fishes." They do not closely resemble the fishes of to-day, but anyone would recognize most of them for what they are. Their bodies were covered, not so much with scales as with heavy plates, often arranged like tiles, those on the forward half of the animal being often larger than those surrounding the rest of the body. The creature was encased, as it were, in armor. These were the rulers of the Devonian seas. The land, as yet, was probably nearly without animal life, the creatures thus far being almost confined to the water. A few insects make their appearance and a few thousand-leggers are running around among the lowly plants; a few spider-like animals have arisen; there are a few snails that have left the water and taken to the land. Altogether only the dawn of a land fauna is to be noticed. In the Devonian the plants are creeping up upon the ground. Ferns are growing about everywhere, though they are not exactly our ferns, but are rather a sort of intermediate form between these and the present seed plants.

Now comes an entire change in the history of the world. By some means a rise in the bottom seems to have cut off a great part of the internal sea from the outer ocean and to have converted it into a widespread shallow bay, much like the sounds which lie back of the islands that line the Atlantic Coast from New Jersey to Florida. Just as this coastal region to-day is covered with salt marshes, so the whole internal sea of the Carboniferous period was converted into a great swamp. Sometimes an oscillation of the crust of the earth brought this marsh above the surface of the sea and a luxuriant growth of plants spread over it. Then a sinking of the bottom allowed the mud and sand to wash down the shores, and spread out over the marsh, and enclose the muck of the marsh under a layer of sand or clay. Another lift of the bottom would start the swamp growing once more, and a series of alternations between marsh land and sound seems to have followed. The plants of this period are not the plants of to-day, though we still have some very degenerate representatives of them. The common horse-tail, with its angular, slender, leaflike branches and its club-shaped spore-bearing body, is a modern degenerate descendant of the treelike calamites of the Carboniferous forest. A creeping evergreen, known by the name of clubmoss, is in like manner the modern degenerate remnant of the scalestem and sealstem, which were the great trees of the forests of the coal period.

All over the surface of the marsh, between these big trees, grew the ferns. While the coal itself was formed generally from the scalestems and sealstems, the most common fossils found in the shales that lie upon the coal beds are the ferns which covered the surface of the marsh.

It is believed by many geologists that this great luxuriant forest points to a time when the climate was far warmer than it is to-day, when the air was moist and heavily laden with carbon dioxide, and when a great mass of clouds practically enveloped the earth. In this way only do most geologists account for the enormous wealth of vegetation in the Carboniferous period and for the abundance of plants up to the Arctic Ocean, of the kinds that now grow chiefly in the tropics. But of recent years a few geologists point to the fact that the peat bogs of to-day, which seem to be the beginnings of future coal deposits, are found almost entirely in cold countries. Hence it is a serious matter to attempt to describe the climate of any part of the Palæozoic era. Certainly of the climate earlier than the Carboniferous it is very risky to say anything definite.

The forests of the coal period seem actually to have cleared the air; at least now we begin to find creatures related to our salamanders and frogs moving about among the stumps of the marshes. These amphibians are evidently the descendants of some of the fishes of the Devonian times. Among these fishes were some which bear a great resemblance to a few found in South America, in Africa and Australia to-day, and which we know as lungfish. Anyone who has cleaned our fresh water fishes in preparation for the table will remember that inside of them there is a long slender bladder filled with air. This bladder assists in making the fish light, hence making it easier for it to support itself in the water. In certain swampy regions these lungfish swim freely in the water of the marshes. When the dry season comes, however, the water evaporates, draining the marshes completely. This would prove the death of most fishes. The lungfish have a curious habit which keeps them over the dry season. They cover themselves with a coat of mud, inside of which there is a lining of slime produced from their bodies. In such cocoon-like cases they survive the drought. The means by which they breathe during this dry season is interesting. The swim-bladder which we have just described in other fishes is, with this lungfish, peculiarly spongy in its walls, presenting a large surface full of blood vessels which absorb the air on the inside of the bladder. This air the fish changes with moderate frequency, the result being that the swim-bladder serves him exactly as the lung serves a higher animal. To this fact he owes his name of lungfish.

We sometimes gain much light concerning the past history of any particular form of animal by studying the development of that animal in the egg, or, in the case of the mammals, before birth. It is an interesting fact that when the lung begins to form in the embryo it starts as a simple sac which is an offspring from the gullet, and occupies the position of the swim-bladder of the fish. This sac later divides into two, and develops into the lungs of the animal. This assures the zoölogist that the origin of the lungs in the higher animals is found in the swim-bladder of the so-called lungfish. In this Silurian time certain of these lungfish were perhaps trapped in the basin in the marsh by the uplifting of the border. The waters becoming progressively shallower and more crowded, these fishes took to the land, their fins developing into awkward limbs which slowly became more perfect.

To state the fact in this simple fashion is to make it seem far less probable than is really the case. The simple forms of the life of lowly creatures, as well as the simple character of the legs and feet in the salamander class, make the explanation not so unlikely as would at first sight appear. Suffice it to say that the scientist now believes that out of the lungfish of the Devonian came the amphibians of the Carboniferous period.

At the end of the coal period came the greatest change the face of the globe had seen for many millions of years. Slowly the continent rose on both sides of the old interior sea. A great plateau formed in the region of the Alleghenies and another in the western district, though this latter uplift was to be completely washed away, and later to rise again into the Rocky Mountains and the Sierras. With the uplift at the edges of the continent came a steady rise of the internal marshes, until what had previously been swamp land became progressively first dry land and, in the western part, even desert, in that respect being somewhat like what it is now.

The amphibians of to-day (animals like the salamander and frog) all lay their eggs in the water and their young have a tadpole stage. This doubtless was true of the amphibians of the coal period. With the beginning of the Mesozoic, or "middle life" period, a change and a progression comes over the animal world. The tadpole life of the frog is a rather lengthened one, while the toad has learned to crowd its tadpole life within a few weeks. It would seem as if, in the earlier times of the Mesozoic, this same change of habit had been going on. With the drying up of the swamp, some of the amphibians crowded their tadpole stage further and further back, until it was completely accomplished before their young left the egg. An examination of the development of the reptile in the egg will show a stage very similar to the fish and to the amphibians, but this is all experienced before the reptile emerges from the egg. The reptilian egg, unlike that of the frog, is covered with a shell, packed away under the surface of the ground, and left to its own fate. If, as most geologists believe, the climate of the Mesozoic was distinctly warm, this habit of the parent of forsaking the egg was not a serious matter. However the creatures arose, it is certain that in this Mesozoic age reptiles roamed the forests, swam the seas, and even flew in the air. Probably at no other time in the earth's history has any one class of animals so completely dominated the situation as did the reptiles of this age. They were not only abundant; they were frequently enormously large. Their skeletons are among the most interesting that we find to-day. Gigantic lizards, seventy feet long and eighteen feet high at the shoulders, dragged their heavy bodies through the marshy edges of the lakes. Out upon the land others, not quite so heavy nor so large, roamed about, some of them feeding upon the soft vegetation, others having teeth fitted to tear down their herbivorous cousins. In some of them the hind legs and tail were very heavy and the front legs so light that it is quite clear they must have hopped around as do the kangaroos to-day. Others of these reptiles went back to the sea, lost the leglike development of their limbs and regained the flipper form, though the bones of the fingers and toes are singularly distinguishable in the paddle.

Strangest of all, a considerable group of these wonderful reptiles lengthened their little fingers, sometimes to three or four feet in length, and had a skin stretched from these fingers over to the body in such a fashion as to give them wings not unlike those of the bat. In the wing of the bat, however, four of the fingers of the hand run through the membrane and support it. In the pterodactyl, as these flying reptiles are called, the middle finger supports the web, while the remaining fingers can still be used to clasp objects or serve the animal to lift himself, as the bat can do with his thumbs.

Meanwhile an entire change is coming over the plant world. The last third of this age of reptiles is known as the Cretaceous or chalk period. Now, for the first time, the forests begin to take on more of the character of our forests of to-day. Plants like our willow and beech, poplar and sassafras appear in great abundance. Their broad leaves serve better than those of any earlier plants to catch the sunlight. But in addition they offered such effective evaporating surface that they cast off rapidly the moisture obtained from the ground by the plant. Accordingly in the winter season, when the water in the ground is frozen and not available for plant purposes, they were forced to throw away their leaves. It is quite possible that up to and including the time of the Carboniferous, plants were all evergreen. There had been before this little variation in climate over the globe. Life in the Cretaceous begins to take on distinctly its modern form.

Among the reptiles of the forest there appear to have been a few small creatures which to an observer of those times, if there could have been an observer, would have seemed of the utmost insignificance compared with their giant cousins.

These little creatures climbed up into the trees to escape their enemies. There were some in whom the skin, in front of the elbow and behind the wrist, was loose, and stretched across the joint a little like the wing of a bat. This reptile, climbing into the trees to escape its enemies, found that this loose flap of skin served it nicely, and sailed out of the trees in a manner not unlike that of the flying squirrel of to-day. Among these experimenters in aviation, certain forms produced scales which became elongated and finally slit up along the side. These slit scales slowly developed into the feathers of the birds of to-day. Whether the steps by which the change occurred have been correctly stated or not, the result is sure. In the rocks of the chalk period we find the remains of an interesting creature. If nothing but its bones had been found it would have been called a reptile. It had a long tail, it had claws on its front limbs; it had teeth in its mouth; it had a flexible backbone. All of these are reptilian rather than bird characters. Yet on the rocks surrounding these bones are the unmistakable impressions of the feathers of the wings and of the tail. Nothing in the world to-day has feathers excepting the birds, and in this "ancient winged thing," for this is the significance of its name—archæopteryx—we have perhaps the most remarkable link in the world between two distinct sections of the animal kingdom. Here is a creature half reptile, half bird; perhaps one-third reptile and two-thirds bird. It was about the size of the crow. A little later unmistakable bird skeletons will appear, but still their jaws are provided with long conical teeth.

Still more interesting from our standpoint is another set of primitive animals, utterly insignificant in appearance, but of momentous importance on account of their later history. Among these reptiles were a few small creatures perhaps not much bigger than mice or moles. Their teeth were a little more complicated and specialized than the teeth of their reptilian cousins. Between their scales were small and sparse hairs. Almost nothing but their jaws remain to-day to tell us anything about them. But in this humble little creature of the Mesozoic, utterly insignificant beside the tremendous reptiles of the time, we discern the ancestor of the mammals. These were the progenitors of the horses and cows, of the cats and dogs, of the monkeys and apes, of the men of to-day.

During this chalk period, which forms the last portion of the age of reptiles, life for the first time grew to look much as it does to-day. Now, apparently, the cold of winter and the heat of summer followed each other in regular succession. There have been colder and warmer periods at various times in the previous history of the earth, but undoubtedly they were more uniformly cold or uniformly warm than now. Ages were warm, or ages were cold, but now the earth clearly shows the annual alternations of summer and winter, and for the first time clearly shows the bands of climate on the earth which we know as zones.

In the chalk period this new factor of cold works mightily in favor of the mammals. Their reptilian ancestors were cold blooded. When the climate was warm they were active; when the climate was cold they were sluggish. With the continuation of the annual alternations of cold and warm weather that had now set in upon the earth, the little birds and mammals had in their warm blood an advantage which, in the long run, enables them not simply to compete with their reptile forefathers, but to outdistance them absolutely in the race. Here and there, on earth to-day, exist a few big reptiles like the crocodiles and the boa constrictors. But they are few and comparatively insignificant among the multitudinous population of the globe and are confined to the hotter portions of the earth. For the most part, the reptiles now play an insignificant and unobtrusive part. The little molelike creatures, practically unnoticed between their feet in the later Mesozoic, have come to supplant them entirely, and almost to rival them in size. While the reptiles have grown steadily smaller, the mammals have steadily become larger.

While there is no land mammal to-day as big as the heaviest of the reptiles in the Mesozoic, the whale, which is one of the mammals that has again taken to the ocean, surpasses in size even those gigantic creatures. There never lived in the world before a creature quite so big as the biggest of our whales. Size, however, is not the most important point in any animal. Speed, sagacity, variability, and power of adaptation, these are the qualities which the world prizes, and these the new mammals possessed.

The next geological era is the Cenozoic, or period of modern life. This is divided into two quite distinct sections, the Tertiary and the Quaternary. This era began about five million years ago, roughly speaking, and is still going on. The greater half of it is known as the Tertiary. It was during this time that the mammals came to their own. At first these creatures belonged to what the scientist knows as generalized types. They are jacks-of-all-trades. The student of early animal life finds in the little Phenacodus, which was scarcely bigger than a good-sized setter dog, the beginnings from which many forms have subsequently developed. This creature showed points of structure which to-day may be seen in such diversified animals as the dog, the horse, the rabbit, and the monkey. It is not, of course, suggested that Phenacodus was the immediate ancestor of any of these. But there were no animals in those times more like these I have mentioned than was Phenacodus, and from forms like it in main features all of these other animals have since been derived, each species of animal having become adapted to one particular kind of life. The development of diversified situations on the earth, the varieties of climate, the variation between marsh and upland, between valley and plateau, furnish a complexity of environment into each niche of which a new form of animal fitted itself.

With the increased complexity of mammals comes the submergence of the reptiles and amphibians to-day. In all sorts of situations we find mammals. The old-fashioned continent of Australia is separated from everything about it by deep water, impassable to any animal which lives upon it. In this secluded country evolution is very slow and animals are very antiquated. We still find there mammals with the ancient habit of laying eggs in a hollow in the ground, though after these eggs are hatched the young are nursed on the milk of the mother. But on the great continental stretches, where competition is keen, where the animal must battle for his life against a wide field of other animals, where migration into new situations is possible, the rapidity of the development has been very much greater.

It is in such a situation that man has arisen. In the extreme southeastern portion of Asia, and on the islands lying close to the coast, his highest non-human relatives, members of the ape family, have reached their best development. These, of course, are not man's ancestors. They are the less progressive members who are left behind entirely in the race. Whether we have to-day any traces of the steps by which man arose from the animal beneath him is vigorously disputed. Eminent scientists will be found on both sides of this question.

Many scientific writers to-day take it for granted that one form, discovered in Java, while it may not be in the absolutely direct line, must be very close indeed to the line of ascent toward man out of the apelike forms. A scientist by the name of DuBois, working in the banks of a stream in south-central Java, found a thigh bone which seemed to him exceedingly human in its general character and yet not absolutely like the human thigh bone. The oncoming of the rainy season raised the water in the river so that DuBois could not continue his search. Returning a year later, and digging back deeper into this bank, he found a skull cap and two molar teeth which seemed to him to belong to the thigh bone, although they lay several yards farther back, but at the same level in the bank.

When these bones were subsequently presented to a meeting of European scientists by DuBois, he claimed to have found the "missing link" for which there was so eager a demand. Some of the best anatomists of the meeting, notably Virchow, laughed at his claim and said that the skull cap was simply that of a human idiot, and could be duplicated in any large asylum. A committee of twelve naturalists was appointed to report upon DuBois' find. Of this committee three asserted the bones to be those of a low-grade man, three insisted that they belonged to a high ape, of a type somewhat higher than any we know to-day, but still distinctly an ape. Six members of the committee of twelve agreed that the remains were those of a creature higher than an ape and lower than any normal man, and represented, in their opinion, a stage distinctly along the line of development out of the apes and into man.

This so-called "Java find" is known in science by the name of Pithecanthropus, which means the ape-man. Whether we look upon this fossil as a serious find or not, it is very certain that in the caves of Europe belonging to the Quaternary period we find abundant evidences of primitive man. The older these evidences are, the more likely they are to be distinctly below the grade of man of to-day, in the size and shape of the brain case and in the length and massiveness of the jaw.

There are probably more races than one represented among these skulls. Some of them are surely well-deserving of the title of low brow. Their heavy ridges over the eyes, their small foreheads, their massive, heavy-set jaws show a race of men far less endowed mentally and much better endowed in the matter of brute force than the men of to-day. These skeletons, or parts of skeletons, are turning up every year, and we are just beginning to know much about them. Capable men are studying them with much care. The next fifty years may not improbably make the history of the ascent of man as clear as is now that of the horse, to which we shall refer later.

The whole question of the descent of man from the lower animals, or his ascent from them, as Drummond aptly termed it, is to most people so entirely repugnant as to set them at once, and finally, against all willingness to consider the question of Evolution. This, however, does not solve the problem. Even though truth be horribly unpalatable, it is still to be believed if it is only the truth. There is practically no doubt left among scientific men of the origin of man in lower forms. The evidences grow more and more complete year by year, and from every line of investigation. Whether we study his anatomy, his embryology, his history, his language, or his civilization, all indications point in the same direction. Constant discoveries indicate the fact of an enormously long development from a very humble form. If this proves to be true and remains unpalatable, the fault lies in the palate and not in the truth. Gradually we are coming to understand that there is no reason why this truth should be unpalatable. We consider a rise from humble conditions to be the glory of our heroes; we esteem it an added charm in their strength that they should have developed from untoward surroundings. It is not a disgrace to man to have descended from the apes. It is to the glory of man that he should have ascended from forms not much more promising-looking than the apes of to-day. We must repeat, however, that the apes were the unprogressive members, and hence we must not judge man's ancestors too harshly. It must have been in them to rise. But the great glory in the thought of the humble ancestry lies in the possibilities of his future. If out of a creature not materially unlike the gibbering ape of to-day there should have come, under the guiding hand of an Almighty God, creatures with the endowments and capabilities of man of to-day, then this is only an earnest and foretaste of that which may be expected in the future. A time will come when man shall have risen to heights as far above anything he now is as to-day he stands above the ape. Even then there seems no end. With Infinite Power as the agent, and limitless time in which to work, man would be limiting God to an extent unwarranted by the history of the past to imagine that His process had stopped to-day, and that man, with his many imperfections of body, of mind, and of morals, should be the best that is yet to come. There cling to him still the limitations and dregs of his brute life. Often the brute in him comes to the surface. Little by little he is coming to be dominated by the qualities God has last given him. Slowly the brute shall sink away, slowly the divine in him shall advance, until such heights are attained as we to-day can scarcely imagine. As we can scarcely conceive the beginnings of this process, so we can with difficulty imagine its end. This only can be seen by the Eternal through whom it shall all come to pass, and by whom all will in time be accomplished.