 CHAPTER 2 THE STORY OF EVOLUTION The beginning of the earth, making a home for life, the first living creatures. The evolution idea is a master key that opens many doors. It is a luminous interpretation of the world, throwing the light of the past upon the present. Everything is seen to be an antiquity, with a history behind it, a natural history, which enables us to understand in some measure how it has come to be as it is. We cannot say more than understand in some measure, for while the fact of evolution is certain, we are only beginning to discern the factors that have been at work. The evolution idea is very old, going back to some of the Greek philosophers, but it is only in modern times that it has become an essential part of our metal equipment. It is now an everyday intellectual tool. It was applied to the origin of the solar system and to the making of the earth before it was applied to plants and animals. It was extended from these to man himself. It spread to language, to folk ways, to institutions. Within recent years the evolution idea has been applied to the chemical elements, for it appears that uranium may change into radium, that radium may produce helium, and that lead is the final stable result when the changes of uranium are complete. Perhaps all the elements may be the outcome of an inorganic evolution. Not less important is the extension of the evolution idea to the world within, as well as to the world without. For alongside of the evolution of bodies and brains is the evolution of feelings and emotions, ideas and imagination. Organic evolution means that the present is the child of the past and the parent of the future. It is not a power or a principle. It is a process, a process of becoming. It means that the present day animals and plants and all the subtle interrelations between them have arisen in a natural, knowable way from a preceding state of affairs on the whole somewhat simpler, and that again from forms and interrelations simpler still, and so on backwards and backwards for millions of years till we lose all clues and the thick mists that hang over life's beginnings. Our solar system was once represented by a nebula of some sort, and we may speak of the evolution of the sun and the planets, but since it has been the same material throughout that has changed in its distribution and forms, it might be clearer to use some word like Genesis. Similarly, our human institutions were once very different from what they now are. And we may speak of the evolution of government or of cities, but man works with a purpose, with ideas and ideals, in some measure controlling his actions and guiding his achievements, so that it is probably clearer to keep the good old word history for all processes of social becoming in which man has been a conscious agent. Now, between the Genesis of the solar system and the history of civilization and there comes the vast process of organic evolution, the word development should be kept for the becoming of the individual, the chick out of the egg, for instance. Organic evolution is a continuous natural process of racial change by successive steps in a definite direction whereby distinctively new individualities arise, take root, and flourish. Sometimes alongside of, and sometimes sooner or later, in place of, the originative stock. Our domesticated breeds of pigeons and poultry are the results of evolutionary change whose origins are still with us in the rock dove and the jungle fowl. But in most cases in wild nature the ancestral stocks of present-day forms are long since extinct, and in many cases they are unknown. Evolution is a long process of coming and going, appearing and disappearing, a long drawn out, sublime process like a great piece of music, the beginning of the earth. When we speak the language of science we cannot say, in the beginning, for we do not know of, but in the beginning of science we cannot say, in the beginning of science we cannot know of and cannot think of any condition of things that did not arise from something that went before. But we may qualify the phrase and legitimately inquire into the beginning of the earth within the solar system. If the result of this inquiry is to trace the sun and the planets back to a nebula we reach only a relative beginning. The nebula has to be accounted for, and even before matter there may have been a prematerial world. If we say, as was said long ago, in the beginning was mind, we may be expressing or trying to express a great truth, but we have gone beyond science. The Nebular Hypothesis One of the grandest pictures that the scientific mind has ever thrown upon the screen is that of the nebular hypothesis. According to Laplace's famous form of this theory, 1796, the solar system was once a gigantic glowing mass spinning slowly and uniformly around its center. As the incandescent world cloud of gas cooled and its speed of rotation increased, the shrinking mass gave off a separate whirling ring, which broke up and gathered together again as the first and most distant planet. The main mass gave off another ring and another, till all the planets, including the earth, were formed. The central mass persisted as the sun. Laplace spoke of his theory, which Kant had anticipated forty-one years before, with scientific caution. Conjectures which I present with all the distrust which everything not the result of observation or of calculation ought to inspire. Subsequent research justified his distrust, for it has been shown that the original nebula need not have been hot and need not have been gaseous. Moreover, there are great difficulties in Laplace's theory of the separation of successive rings from the main mass and of the condensation of a whirling gaseous ring into a planet. So it has come about that the picture of a hot gaseous nebula revolving as a unit body has given place to other pictures. Thus Sir Norman Lockyer pointed out, 1890, that the earth is gathering to itself millions of meteorites every day. This has been going on for millions of years. In distant ages the accretion may have been vastly more rapid and voluminous, and so the earth is grown. Now the meteoric contributions are undoubted, but they require a center to attract them, and the difficulty is to account for the beginning of a collecting center or planetary nucleus. Moreover, meteorites are sporadic and erratic, scattered hither and thither rather than collecting into unit bodies. As Professor Chamberlain says, meteorites have rather the characteristics of the wreckage, of some earlier organization, of the parentage of our planetary system. Several other theories have been propounded to account for the origin of the earth, but the one that is found most favor in the eyes of authorities is that of Chamberlain and Moulton. According to this theory a great nebular mass condensed to form the sun, from which under the attraction of passing stars, planet after planet, the earth included, was heaved off in the form of knotted spiral nebulae, like many of these now observed in the heavens. Of great importance were the knots, for they served as collecting centers drawing flying matter into their clutches. Whatever part of the primitive bolt escaped and scattered was drawn out into independent orbits round the sun, forming the planetesimals which behave like minute planets. These planetesimals formed the food on which the knots subsequently fed. The Growth of the Earth It has been calculated that the newborn earth, the earth-knot of Chamberlain's theory, had a diameter of about 5,500 miles. But it grew by drawing planetesimals into itself until it had a diameter of over 8,100 miles at the end of its growing period. Thus then it is shrunk by periodic shrinkages which have meant the buckling up of successive series of mountains, and it has now a diameter of 7,918 miles. But during the shrinking the earth became more varied. A sort of slow boiling of the internally hot earth often forced molten matter through the cold outer crust, and there came about a gradual assortment of lighter materials nearer the surface and heavier materials deeper down. The continents are built of the lighter materials, such as granites, while the beds of the great oceans are made of the heavier materials, such as basalts. In limited areas land has often become sea, and sea is often given place to land. But the probability is that the distinction of the areas corresponding to the great continents and oceans goes back to a very early stage. The lithosphere is the more or less stable crust of the earth, which may have been to begin with about 50 miles in thickness. It seems that the young earth had no atmosphere, and that ages passed before water began to accumulate on its surface. Before, in other words, there was any hydrosphere. The water came from the earth itself to begin with, and it was long before there was any rain dissolving out saline matter from the exposed rocks and making the sea salt. The weathering of the high grounds of the ancient crust by air and water furnished the material which formed the sandstones and mudstones and other sedimentary rocks, which are said to amount to a thickness of over 50 miles in all. Making a Home for Life It is interesting to inquire how the callous, rough and tumble conditions of the outer world in the early days were replaced by others that allowed of the germination and growth of that tender plant we call life. There are very tough living creatures, but the average organism is ill-suited for violence. Most living creatures are adapted to mild temperatures and gentle reactions. Hence the fundamental importance of the early atmosphere, heavy with planetesimal dust in blanketing the earth against intensities of radiance from without, as Chamberlain says, and inequalities of radiance from within. This was the first preparation for life, but it was an atmosphere without free oxygen. What less important was the appearance of pools and lakelets of lakes and seas. Perhaps the early waters covered the earth, and water was the second preparation for life, water that can dissolve a larger variety of substances in greater concentration than any other liquid, water that in summer does not readily evaporate altogether from a pond, nor in winter freeze throughout its whole extent, water that is such a mobile vehicle and such a subtle cleaver of substances, water that forms over eighty percent of living matter itself. Of great significance was the abundance of carbon, hydrogen, and oxygen in the form of carbonic acid and water in the atmosphere of the cooling earth, for these three wonderful elements have a unique ensemble of properties ready to enter into reactions and relations, making great diversity and complexity possible, favoring the formation of the plastic and permeable materials that build up living creatures. We must not pursue the idea, but it is clear that the stones and mortar of the inanimate world are such that they built a friendly home for life. Origin of Living Creatures Upon the Earth During the early chapters of the earth's history, no living creature that we can imagine could possibly have lived there. The temperature was too high. There was neither atmosphere nor surface water. Therefore it follows that at some uncertain but inconceivably distant date living creatures appeared upon the earth. Now one knows how, but it is interesting to consider possibilities. From ancient times it has been a favorite answer that the dust of the earth may have become living in a way which is outside scientific description. This answer forecloses the question, and it is far too soon to do that. Science must often say, Ignoramus. Science should be slow to say, Ignorabubus. A second position held by Helmholtz, Lord Kelvin, and others suggests that minute living creatures may have come to the earth from elsewhere in the cracks of a meteorite or among cosmic dust. It must be remembered that seeds can survive prolonged exposure to very low temperatures, that spores of bacteria can survive high temperature, that seeds of plants and germs of animals in a state of latent life can survive prolonged drought and absence of oxygen. It is possible, according to Berthelot, that as long as there is not molecular disintegration, vital activities may be suspended for a time and may afterwards recommence when appropriate conditions are restored. Therefore one should be slow to say that a long journey through space is impossible. The obvious limitation of Lord Kelvin's theory is that it only shifts the problem of the origin of organisms, i.e. living creatures, from the earth to elsewhere. The third answer is that living creatures of a very simple sort may have emerged on the earth's surface from not living material, that is, from some semi-fluid carbon compounds activated by ferments. The tenability of this view is suggested by the achievements of the synthetic chemists, who are able artificially to build up substances such as oxalic acid, indigo, salicylic acid, caffeine, and grape sugar. We do not know, indeed, what a nature's laboratory would take the place of the clever synthetic chemist, but there seems to be a tendency to complexity. Corpuscles form atoms, atoms form molecules, small molecules, large ones. This concrete suggestions have been made in regard to the possible origin of living matter, which will be dealt with in a later chapter. So far as we know of what goes on today, there is no evidence of spontaneous generation. Organisms seem always to arise from pre-existing organisms of the same kind. Where any suggestion of the contrary has been fancied, there have been flaws in the experimenting. But it is one thing to accept the verdict, om ne vivum e vivum, as a fact to which experiment has not yet discovered an exception, and another thing to maintain that this must always have been true, or must always remain true. If the synthetic chemists should go on surpassing themselves, if substances like white of eggs should be made artificially, and if we should get more light on possible steps by which simple living creatures may have arisen from not living materials, this would not greatly affect our general outlook on life. So it would increase our appreciation of what is often libeled as inert matter. If the dust of the earth did naturally give rise very long ago to living creatures, if they are in a real sense born of her and of the sunshine, then the whole world becomes more continuous and more vital, and all the inorganic groaning and travailing becomes more intelligible. The First Organisms Upon the Earth We cannot have more than a speculative picture of the first living creatures upon the earth, or rather in the waters that cover the earth. A basis for speculation is to be found, however, in the simplest creatures living today, such as some of the bacteria and one-celled animicules, especially those called protists, which have not taken any very definite step towards becoming either plants or animals. No one can be sure, but there is much to be said for the theory that the first creatures were microscopic globules of living matter, not unlike the simplest bacteria of today, but able to live on air, water, and dissolve salts. From such a source may have originated a race of one-celled marine organisms which were able to manufacture chlorophyll, or something like chlorophyll, that is to say the green pigment which makes it possible for plants to utilize the energy of the sunlight in breaking up carbon dioxide and in building up, by photosynthesis, carbon compounds like sugars and starch. These little units were probably encased in the cell wall of cellulose, but their boxed-in energy expressed itself in the undulatory movement of a lash or flagellum, by means of which they propelled themselves energetically through the water. There are many similar organisms today, mostly in water, but some of them, simple one-celled plants, paint the tree stems and even the paving-stones green in wet weather. According to Professor A. H. Church there was a long chapter in the history of the earth when the sea that covered everything teemed with these green flagellates, the originators of the vegetable kingdom. On another tack, however, there probably evolved a series of simple predatory creatures, not able to build up organic matter from air, water and salts, but devouring their neighbors. These units were not closed in with cellulose, but remained naked, with their living matter or protoplasm flowing out in changeful processes, such as we see in the amoebae, in the ditch or in our own white blood-core puzzles and other amoeboid cells. These were the originators of the animal kingdom. This from very simple protists, the first animals and the first plants may have arisen. All were still very minute, and it is worth remembering that had there been any scientific spectator after our kind upon the earth during these long ages, he would have lamented the entire absence of life, although the seas were teeming. The simplest forms of life in the protoplasm, which Huxley called the physical basis of life, will be dealt with in the chapter on biology in a later section of this work. First Great Steps in Evolution The first plants, the first animals, beginnings of bodies, evolution of sex, beginnings of natural death, the contrast between plants and animals. However it may have come about, there is no doubt at all that one of the first great steps in organic evolution was the forking of the genealogical tree into plants and animals, the most important parting of the ways in the whole history of nature. Typical plants have chlorophyll, they are able to feed at a low chemical level on air, water, and salts, using the energy of the sunlight in their photosynthesis. They have their cells boxed in by cellulose walls, so that their opportunities for motility are greatly restricted. They manufacture much more nutritive material than they need and live far below their income. They have no ready way of getting rid of any nitrogenous waste matter that they may form, and this probably helps to keep them sluggish. Animals on the other hand feed at a high chemical level, on the carbohydrates such as starch and sugar, fats and proteins, for instance gluten, albumin, casein, which are manufactured by other animals or to begin with by plants. Their cells have not cellulose walls, nor in most cases much wall of any kind, and motility in the majority is unrestricted. Animals live much more nearly up to their income. If we could make for an animal and a plant of equal weight, two fractions showing the ratio of the upbuilding, constructive, chemical processes to the downbreaking, disruptive chemical processes that go on in their respective bodies, the ratio for the plant would be much greater than the corresponding ratio for the animal. In other words, animals take the munitions which plants laboriously manufacture and explode them in locomotion and work, and the entire system of animate nature depends upon the photosynthesis that goes on in green plants. As the result of much more explosive life, animals have to deal with much in the way of nitrogenous waste products, the ashes of the living fire, but these are usually got rid of very effectively. For instance, in the kidney filters, and do not clog the system by being deposited as crystals than the like as happens in plants. Sluggish animals like sea squirts, which have no kidneys, are exceptions that prove the rule, and it need hardly be said that the statements that have been made in regard to the contrast between plants and animals are general statements. There is often a good deal of the plant about the animal, as in sedentary sponges, zoophytes, corals, and sea squirts, and there's often a little of the animal about the plant, as we see in the movements of all shoots and roots and leaves, and occasionally in the parts of the flower. But the important fact is that on the early forking of the genealogical tree, that is, the divergence of plants and animals, there depended and depends all the higher life of the animal kingdom, not to speak of, mankind. The continuance of civilization, the upkeep of the human and animal population of the globe, and even the supply of oxygen to the air we breathe depend on the silent laboratories of the green leaves, which are able with the help of the sunlight to use carbonic acid, water, and salts to build up the bread of life. The Beginnings of Land Plants It is highly probable that for long ages the waters covered the earth and that all the primeval vegetation consisted of simple flagellates and universal open sea. But contraction of the earth's crust brought about elevations and depressions of the sea floor, and in places the solid substratum was brought near enough the surface to allow the floating plants to begin to settle down without getting out of the light. This is how Professor Church pictures the beginning of a fixed vegetation, a very momentous step in evolution. It was perhaps among this early vegetation that animals had their first successes. As the floor of the sea in these shallow areas was raised higher and higher there was a beginning of dry land. The sedentary plants already spoken of were the ancestors of the shore seaweeds, and there was no doubt that when we go down at the lowest tide and wade cautiously out among the jungle of vegetation only exposed on such occasions we are getting a glimpse of very ancient days. This is the forest primeval, the protozoa. Animals below the level of zoophytes and sponges are called protozoa. The word obviously means first animals, but all that we can say is that the very simplest of them may give us some hint of the simplicity of the original first animals, for it is quite certain that the vast majority of the protozoa today are far too complicated to be thought of as primitive. Though most of them are microscopic, each is an animal complete in itself with the same fundamental bodily attributes as are manifested in our cells. They differ from animals of higher degree and not being built up of the unit areas or corpuscles called cells. They have no cells, no tissues, no organs, and the ordinary acceptation of these words, but many of them show a great complexity of internal structure, far exceeding that of the ordinary cells that build up the tissues of higher animals. They are complete living creatures which have not gone in for body-making. In the dim and distant past there was a time when the only animals were of the nature of protozoa, and it is safe to say that one of the great steps in evolution was the establishment of three great types of protozoa. A. Some were very active, the infusorians, like the slipper animacul, the nightlight, noctiluca, which makes the seas phosphorescent at night, and the deadly trepanosome, which causes sleeping sickness. B. Others were very sluggish, the parasitic sporozoa, like the malaria organism which the mosquito introduces into man's body. C. Others were neither very active nor very passive, the rhizopods, with outflowing processes of living matter. This amseboid line of evolution has been very successful. It is represented by the rhizopods, such as amoebae and the choc forming formanifera, and the exquisitely beautiful flint-shelled radiolarians of the open sea. They have their counterparts in the amoeboid cells of most multicellular animals, such as the phegocytes, which migrate about in the body, engulfing and digesting intruding bacteria, serving as sappers and miners when something has to be broken down and build up again, and performing other useful offices. THE MAKING OF A BODY The great naturalist Louis Agassiz once said that the biggest gulf in organic nature was that between the unicellular and the multicellular animals, protozoa and metazoa. But the gulf was bridged very long ago when sponges, stinging animals, and simple worms were evolved, and shewed for the first time a body. What would one not give to be able to account for the making of a body, one of the great steps in evolution? No one knows, but the problem is not altogether obscure. When an ordinary protozoan or one-celled animal divides into two or more, which is its way of multiplying, the daughter units thus formed, float apart, and live independent lives. But there are a few protozoa in which the daughter's units are not quite separated off from one another, but remain coherent. Thus volvox, a beautiful green ball, found in some canals and the like, is a colony of a thousand or even ten thousand cells. It is almost formed a body. But in this colony making protozoan, and in others like it, the component cells are all of one kind, whereas in true multicellular animals there are different kinds of cells showing division of labor. There are some other protozoa in which the nucleus or kernel divides into many nuclei within the cell. This is seen in the great amoeba, paleomixa, sometimes found in duck ponds, or the beautiful opalina, which always lives in the hind part of the frog's food canal. If a portion of the living matter of these protozoa should gather round each of the nuclei, then that would be the beginning of a body. It would be still nearer the beginning of a body if division of labor set in, and if there was a setting apart of egg cells and sperm cells distinct from body cells. It was possible in some such way that animals and plants with a body were first evolved. Two points should be noted that body making is not essentially a matter of size, although it has made large size possible. For the body of a many-celled wheel, animicule, or rotifer, is no bigger than many a protozoan. Yet the rotifer, we are thinking of hydratina, has nine hundred odd cells, whereas the protozoan has only one, except in forms like vulvox. Secondly, it is a luminous fact that every many-celled animal from sponge to man that multiplies in the ordinary way begins at the beginning again as a single cell, the fertilized egg cell. It is of course not an ordinary single cell that develops into an earthworm, or a butterfly, an eagle, or a man. It is a cell in which a rich inheritance, the fruition of ages, is somehow condensed. But it is interesting to bear in mind the elementary fact that every many-celled creature reproduced in the ordinary way and not by budding or the like, starts as a fertilized egg cell. The coherence of the daughter cells into which the fertilized egg cell divides is a reminiscence, as it were, of the primeval coherence of daughter units that made the first body possible. The Beginnings of Sexual Reproduction A freshwater hydra growing on the duckweed usually multiplies by budding. It forms daughter buds, living images of itself. A check comes to nutrition and these daughter buds go free. A big sea anemone may divide into two or more parts, which becomes separate animals. This is asexual reproduction, which means that the multiplication takes place by dividing into two or many portions, and not by liberating egg cells and sperm cells. Among plants as among animals asexual reproduction is very common, but it has great disadvantages for it is apt to be physiologically expensive, and it is beset with difficulties when the body shows great division of labor, and is very intimately bound into unity. Thus no one can think of a bee or a bird multiplying by division or by budding. Moreover, if the body of the parrot has suffered from injury or deterioration, the result of this is bound to be handed on to the next generation if asexual reproduction is the only method. Splitting into two or many parts was the old-fashioned way of multiplying, but one of the great steps in evolution was the discovery of a better method, namely sexual reproduction. The gist of this is simply that during the process of body building by the development of the fertilized egg cell, production units, the germ cells, do not share in forming ordinary tissues or organs, but remain apart, continuing the full inheritance which was condensed in the fertilized egg cell. These cells, kept by themselves, are the originators of the future reproductive cells of the mature animal that give rise to the egg cells and the sperm cells. The advantages of this method are great. One, the new generation is started less expensively, for it is easier to shed germ cells into the cradle of the water than to separate off half of the body. Two, it is possible to start a great many new lives at once, and this may be of vital importance when the struggle for existence is very keen, and when parental care is impossible. Three, the germ cells are little likely to be prejudicially affected by disadvantageous dents impressed on the body of the parent, little likely unless the dents have peculiarly penetrating consequences, as in the case of poisons. Four, a further advantage is implied in the formation of two kinds of germ cells, the ovum or egg cell, where the considerable amount of building material and often with the legacy of nutritive yolk, the spermatozoan or sperm cell, adapted to move in fluids and to find the ovum from a distance, thus securing change-provoking cross fertilization. THE EVOLUTION OF SEX Another of the great steps in organic evolution was the differentiation of two different physiological types, the male or sperm producer and the female or egg producer. It seems to be a deep-seated difference in constitution, which leads one egg to develop into a male and another lying beside it in the nest into a female. In the case of pigeons it seems almost certain from the work of Professor Oscar Riddle that there are two kinds of egg, a male producing egg and a female producing egg, which differ in their yolk-forming and other physiological characters. In sea urchins we often find two creatures superficially indistinguishable, but the one is a female with large ovaries and the other is a male with equally large testes. Here the physiological difference does not affect the body as a whole, but the reproductive organs or gonads only, though more intimate physiology would doubtless discover differences in the blood or in the chemical routine, metabolism. In a large number of cases, however, there are marked superficial differences between the sexes, and everyone is familiar with such contrasts as peacock and peahen, stag and hind. In such cases the physiological difference between the sperm producer and the ovum producer, for this is the essential difference, saturates through the body and expresses itself in masculine and feminine structures and modes of behavior. The expression of the masculine and feminine characters is in some cases under the control of hormones or chemical messengers which are carried by the blood from the reproductive organs throughout the body, and pull the trigger which brings about the development of an antler or a wattle or a decorative plume or a capacity for vocal and saltatory display. In some cases it is certain that the female carries in a latent state the masculine features, but these are kept from expressing themselves by other chemical messengers from the ovary. Of these chemical messengers more must be said later on. Recent research has shown that while the difference between male and female is very deep-rooted, corresponding to a difference in gearing, it is not always clear cut. Thus a hen pigeon may be very masculine, and a cockpige in very feminine. The difference is in degree, not in kind. What is the meaning of the universal or almost universal inevitableness of death? A sequoir or big tree of California has been known to live for over two thousand years, but eventually it died. A centenarian tortoise has been known, and a sea anemone sixty years of age, but eventually they die. What is the meaning of this apparently inevitable stoppage of bodily life? The beginning of natural death. There are three chief kinds of death. A. The great majority of animals come to a violent end, being devoured by others or killed by sudden and extreme changes in their surroundings. B. When an animal enters a new habitat, or comes into new associations with other organisms, it may be invaded by a microbe or by some larger parasite to which it is unaccustomed, and to which it can offer no resistance. With many parasites a live and let live compromise has arrived at, but new parasites are apt to be fatal, as man knows to his cost when he is bitten by a tzitzi fly, which infects him with the microscopic animal, a trepanosome, that causes sleeping sickness. In many animals the parasites are not troublesome as long as the host is vigorous, but if the host is out of condition the parasites may get the upper hand, as in the so-called grouse disease, and become fatal. C. But besides violent death and microbic or parasitic death there is natural death. This is in great part to be regarded as the price paid for a body. A body worth having implies complexity or division of labor, and this implies certain internal furnishings of a more or less stable kind in which the effects of wear and tear are apt to accumulate. It is not the living matter itself that grows old so much as the framework in which it works, the furnishings of the vital laboratory. There are various processes of rejuvenessence, for instance rest, repair, change, reorganization, which work against the inevitable processes of senescence, but sooner or later the victory is with aging. Another deep reason for natural death is to be found in the physiological expansiveness of reproduction, for many animals, from worms to eels, illustrate natural death as the nemesis of starting new lives. Now it is a very striking fact that to a large degree the simplest animals or protozoa are exempt from natural death. They are so relatively simple that they can continually recuperate by rest and repair. They do not accumulate any bad debts. Moreover, their modes of multiplying, by dividing into two or many units, are very inexpensive physiologically. It seems that in some measure this bodily immortality of the protozoa is shared by some simple many-celled animals, like the freshwater hydra and planarian worms. Here is an interesting chapter in evolution, the evolution of means of evading or staving off natural death. Thus there is the well-known case of the palala worm of the coral reefs where the body breaks up in liberating the germ cells, but the head end remains fixed in a crevice of the coral and buds out a new body at leisure. Even with the evolution of the waves of avoiding death should be considered also the gradual establishment of the length of life best suited to the welfare of the species and the punctuation of the life history to suit various conditions. Great Acquisitions In animals like sea anemones and jellyfishes the general symmetry of the body is radial. That is to say there is no right or left, and the body might be halved along many planes. It is a kind of symmetry well-suited for sedentary or for drifting life. But worms began the profitable habit of moving with one end of the body always in front, and from worms to man the great majority of animals have bilateral symmetry. They have a right and a left side, and there is only one cut that halves the body. This kind of symmetry is suited for a more strenuous life than radial animals show. It is suited for pursuing food, for avoiding enemies, for chasing mates, and with the establishment of bilateral symmetry must be associated the establishment of head-brains, the beginnings of which is to be found in some simple worm-types. The beginning of which is to be found in some simple worm-types. Among the other great acquisitions gradually evolved we may notice a well-developed head with sense-organs, the establishment of large internal surfaces such as the digestive and absorptive wall of the food canal, the origin of quickly contracting striped muscle and of muscular appendages, the formation of blood as a distributing medium throughout the body, from which all the parts take what they need and to which they also contribute. Another very important acquisition, almost confined, so far as is known, to back-boned animals, was the evolution of what are called glands of internal secretion, such as the thyroid and the supra-renal. These manufacture subtle chemical substances which are distributed by the blood throughout the body, and have a manifold influence in regulating and harmonizing the vital processes. Some of these chemical messengers are called hormones, which stimulate organs and tissues to greater activity. Others are called chalones, which put on a break. Some regulate growth and others rapidly alter the pressure and composition of the blood. Some of them call into active development certain parts of the body which have been, as it were, waiting for an appropriate trigger-pulling. Thus at the proper time the milk glands of a mammalian mother are awakened from their dormancy. This very interesting work of evolution will be dealt with in another portion of this work. End of the first part of Chapter 2 Chapter 2 Part 2 of the Outline of Science This is the LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. This recording is by Mark Smith of Simpsonville, South Carolina. The Outline of Science, Volume 1 by J. Arthur Thompson. Chapter 2 Part 2 The Inclined Plane of Animal Behavior Before passing to a connected story of the gradual emergence of higher and higher forms of life in the course of the successive ages, the procession of life, as it may be called, it will be useful to consider the evolution of animal behavior. Evolution of Mind A human being begins as a microscopic fertilized egg cell, within which there is condensed the long result of time, man's inheritance. The long period of nine months before birth, with its intimate partnership between mother and offspring, is passed as it were in sleep, and no one can make any statement in regard to the mind of the unborn child. Even after birth the dawn of mind is as slow as it is wonderful. To begin with, there is in the ovum and early embryo no nervous system at all, and it develops very gradually from simple beginnings. Not as mentality cannot come in from outside, we seem bound to conclude that the potentiality of it, whatever that means, resides in the individual from the very first. The particular kind of activity known to us as thinking, feeling, and willing is the most intimate part of our experience, known to us directly apart from our senses, and the possibility of that must be implicit in the germ cell, just as the genius of Newton was implicit in a very miserable specimen of an infant. Now what is true of the individual is true also of the race. There is a gradual evolution of that aspect of the living creature's activity which we call mind. We cannot put our finger on any point and say, before this stage there was no mind. Indeed many facts suggest the conclusion that wherever there is life there is some degree of mind, even in the plants. Or it might be more accurate to put the conclusion in another way, that the activity we call life is always in some degree an inner or mental aspect. In another part of this book there is an account of the dawn of mind in back-boned animals. What we aim at here is an outline of what may be called the inclined plane of animal behavior. A very simple animal accumulates a little store of potential energy and it proceeds to expend this like an explosive by acting on its environment. It does so in a very characteristic self-preservative fashion, so that it burns without being consumed and explodes without being blown to bits. It is characteristic of the organism that it remains a going concern for a longer or shorter period its length of life. Living creatures that expended their energy ineffectively or self-destructively would be eliminated in the struggle for existence. When a simple one-celled organism explores a corner of the field seen under a microscope behaving to all appearance very like a dog scouring a field seen through a telescope it seems permissible to think of something corresponding to mental endeavor associated with its activity. This impression is strengthened when an amoeba pursues another amoeba, overtakes it, engulfs it, loses it, pursues it again, recaptures it, and so on. What is quite certain is that the behavior of the anemocule is not like that of a potassium pill fizzing about in a basin of water, nor like the lurching movements of a gun that has got loose and taken charge on board ship. Another feature is that the locomotor activity of an anemocule often shows a distinct individuality. It may swim, for instance, in a loose spiral. But there is another side to vital activity besides acting upon the surrounding world. The living creature is acted on by influences from without. The organism acts on its environment, that is, the one side of the shield. The environment acts upon the organism, that is, the other side. If we are to see life whole we must recognize these two sides of what we call living, and it is missing an important part of the history of animal life. If we fail to see that evolution implies becoming more advantageously sensitive to the environment, making more of its influences, shutting out profitless stimuli, and opening more gateways to knowledge. The bird's world is a larger and finer world than in earthworms. The world means more to the bird than to the worm. The trial and error method. Animal creatures act with a certain degree of spontaneity on their environment, and they likewise react effectively to surrounding stimuli. Animals come to have definite answers back. Sometimes several, sometimes only one, as in the case of the slipper anemocule, which reverses its cilia when it comes within the sphere of some disturbing influence, retreats, and, turning upon itself tentatively, sets off again in the same general direction as before, but at an angle to the previous line. If it misses the disturbing influence, well and good. If it strikes it again, the tactics are repeated until a satisfactory way out is discovered, or the stimulation proves fatal. It may be said that the slipper anemocule has but one answer to every question, but there are many protozoa which have several in-registered reactions. And there are alternative reactions which are tried one after another. The animal is pursuing what is called the trial and error method, and a higher note is struck. There is an endeavor after satisfaction and a trial of answers. When the creature profits by experience to the extent of giving the right answer first, there is the beginning of learning. Reflex actions. Using simple multicellular animals, such as sea anemones, we find the beginnings of reflex actions, and a considerable part of the behavior of the lower animals is reflex. That is to say, there are laid down in the animal in the course of its development certain pre-arrangements of nerve cells and muscle cells, which secure that a fit and proper answer is given to a frequently recurrent stimulus. An earthworm half out of its burrow becomes aware of the light shred of a thrush's foot and jerks itself back into its hole before anyone can say, reflex action. What is it that happens? Certain sensory nerve cells in the earthworm's skin are stimulated by vibrations in the earth. The message travels down a sensory nerve fiber from each of the stimulated cells and enters the nerve cord. The sensory fibers come into vital connection with branches of intermediary, associative, or communicating cells, which are likewise connected with motor nerve cells. To these the message is thus shunted. From the motor nerve cells an impulse or command travels by motor nerve fibers, one from each cell, to the muscles, which contract. If this took as long to happen as it takes to describe even an outline, it would not be of much use to the earthworm. But the motor answer follows the sensory stimulus almost instantaneously. The great advantage of establishing or in registering these reflex chains is that the answers are practically ready-made or inborn, not requiring to be learned. It is not necessary that the brain should be stimulated if there is a brain, nor does the animal will to act, though in certain cases it may, by means of higher controlling nerve fibers, keep the natural reflex response from being given, as happens, for instance, when we control a cough or a sneeze on some solemn occasion. The evolutionary method, if we may use the expression, has been to enregister ready-made responses, and as we ascend the animal kingdom we find reflex actions becoming complicated and often linked together, so that the occurrence of one pulls the trigger of another, and so on, in a chain. The advantage of the insectivorous plant called Venus' flytrap, when it shuts on an insect, is like a reflex action in an animal, but plants have no definite nervous system. What Are Called Tropisms A somewhat higher level on the inclined plane is illustrated by what are called tropisms, obligatory movements which the animal makes, adjusting its whole body so that physiological equilibrium results in relation to gravity, pressure, currents, moisture, heat, light, electricity, and surfaces of contact. A moth is flying past a candle. The eye next, the light, is more illumined than the other. A physiological inequilibrium results, affecting nerve cells and muscle cells. The outcome is that the moth automatically adjusts its flight so that both eyes become equally illumined. In doing this it often flies into the candle. It may seem bad business that the moth should fly into the candle, but the flame is an utterly artificial item in its environment, to which no one can expect it to be adapted. These tropisms play an important role in animal behavior. Instinctive Behavior What a higher level is instinctive behavior, which reaches such remarkable perfection in ants, bees, and wasps. In its typical expression instinctive behavior depends on inborn capacities. It does not require to be learned. It is independent of practice or experience, though it may be improved by both. It is shared equally by all members of the species of the same sex, for the female's instincts are often different from the male's. It refers to particular conditions of life that are of vital importance, though they may occur only once in a lifetime. The female yucca moth emerges from the cocoon when the yucca flower puts forth its bell-like blossoms. She flies to a flower, collects some pollen from the stamens, needs it into a pill-like ball, and stows this away under her chin. She flies to an older yucca flower and lays her eggs in some of the ovules within the seed-box. But before she does so she has to deposit on the stigma the ball of pollen. From this the pollen tubes grow down and the pollen nucleus of a tube fertilizes the egg cell in an ovule, so that the possible seeds become real seeds, for it is only a fraction of them that the yucca moth has destroyed by using them as cradles for her eggs. Now it is plain that the yucca moth has no individual experience of yucca flowers, yet she secures the continuance of her race by a concatenation of actions which form part of her instinctive repertory. From a physiological point of view instinctive behavior is like a chain of compound reflex actions, but in some cases, at least, there is reason to believe that the behavior is suffused with awareness and backed by endeavor. This is suggested in exceptional cases where the stereotyped routine is departed from to meet exceptional conditions. It should also be noted that Justice Ants, Hive Bees, and Wasps exhibit in most cases purely instinctive behavior, but move on occasion on the main line of trial and error or of experimental initiative. So among birds and mammals the intelligent behavior is sometimes replaced by instinctive routine. Perhaps there is no instinctive behavior without a spice of intelligence, and no intelligent behavior without an instinctive element. The old view that instinctive behavior was originally intelligent, and that instinctive lapsed intelligence is attempting one, and is suggested by the way in which habitual intelligent actions cease in the individual to require intelligent control, but it rests on the unproved hypothesis that the acquisitions of the individual can be entailed on the race. It is almost certain that instinct is on a line of evolution quite different from intelligence, and that it is nearer to the inborn inspirations of the calculating boy or the musical genius than to the plotting methods of intelligent learning—animal intelligence. The higher reaches of the inclined plane of behavior show intelligence in the strict sense. They include those kinds of behavior which cannot be described without the suggestion that the animal makes some sort of perceptual inference, not only profiting by experience but learning by ideas. Such intelligent actions show great individual variability. They are plastic and adjustable in a manner rarely hinted at in connection with instincts where routine cannot be departed from without the creature being nonplussed. They are not bound up with particular circumstances as instinctive actions are, but imply an appreciative awareness of relations. When there is an experimenting with general ideas, when there is conceptual as contrasted with perceptual inference, we speak of reason, but there is no evidence of this below the level of man. It is not indeed always that we can credit man with rational conduct, but he has the possibility of it ever within his reach. General instinct and intelligence will be illustrated in another part of this work. We are here concerned simply with the general question of the evolution of behavior. There is a main line of tentative experimental behavior, both below and above the level of intelligence, and has been part of the tactics of evolution to bring about the hereditary and registration of capacities of effective response. The advantage is being that the answers come more rapidly and that the creature is left free if it chooses for higher adventures. There is no doubt as to the big fact that in the course of evolution animals have shown an increasing complexity and masterfulness of behavior that they have become at once more controlled and more definitely free agents, and that the inner aspect of the behavior experimenting, learning, thinking, feeling, and willing has come to count for more and more. Mammals furnish a crowning instance of a trend of evolution which expresses itself at many levels, the tendency to bring forth the young at a well-advanced stage and to an increase of parental care associated with a decrease in the number of offspring. There is a British starfish called Luidia, which has two hundred millions of eggs in a year, and there are said to be several millions of eggs in conger eels and some other fishes. These illustrate the spawning method of solving the problem of survival. Some animals are naturally prolific and the number of eggs which they sow broadcast in the waters allows for enormous infantile mortality and obviates any necessity for parental care. But some other creatures, by nature less prolific, have found an entirely different solution of the problem. They practice parental care, and they secure survival with greatly economized reproduction. This is a trend of evolution, particularly characteristic of the higher animals. So much so that Herbert Spencer formulated the generalization that the size and frequency of the animal family is inverse ratio to the degree of evolution to which the animal has attained. Now there are many different methods of parental care which secure the safety of the young, and one of these is called vivaparity. The young ones are not liberated from the parrot until they are relatively well advanced and more or less able to look after themselves. This gives the young a good send-off in life and their chances of death are greatly reduced. In other words, the animals that have varied in the direction of economized reproduction may keep their foothold in the struggle for existence if they have varied at the same time in the direction of parental care. In other cases, it may have worked the other way round. In the interesting archaic animal called parapatis, which has to face a modern world too severe for it, one of the methods of meeting the enviring difficulties is the retention of the offspring for many months within the mother, so that it is born a fully formed creature. There are only a few offspring at a time, and although there are exceptional cases like the summer green flies, which are very prolific, though viviparous, the general rule is that vivaparity is associated with a very small family. The case of flowering plants stands by itself, for although they illustrate a kind of vivaparity, the seed being embryos, an individual plant may have a large number of flowers and therefore a huge family. Vivaparity naturally finds its best illustrations among terrestrial animals, where the risk to the young life are many, and it finds its climax among mammals. Now it is an interesting fact that the three lowest mammals, the duck mole and the two spiny ant-eaters, lay eggs, that is, are oviparous, that the marsupials on the next grade bring forth their young as it were prematurely, and in most cases stow them away in an external pouch. All the others, the placentals, show a more prolonged antinatal life and intimate partnership between the mother and the unborn young. There is another way of looking at the sublime process of evolution. It has implied a mastery of all the possible haunts of life. It has been a progressive conquest of the environment. 1. It is highly probable that living organisms found their foothold in the stimulating conditions of the shore of the sea. The shallow water, brightly illumined, seaweed-growing shelf, fringing the continents. This littoral zone was a propitious environment where sea and fresh water, earth and air all meet, where there is stimulating change, abundant oxygenation, and a copious supply of nutritive material in what the streams bring down and in the rich seaweed vegetation. It is not an easy haunt of life, but none the worse for that, and it is teneted today by representatives of practically every class of animals from infusorians to sea-shored birds and mammals. 2. The open sea or pelagic haunt includes all the brightly illumined surface waters beyond the shallow water of the shore area. It is perhaps the easiest of all the haunts of life, for there is no crowding, there is considerable uniformity, and an abundance of food for animals is afforded by the inexhaustible floating sea meadows of microscopic algae. These are reincarnated in minute animals like the open sea crustaceans, which again are utilized by fishes, these in turn making life possible for higher forms like carnivorous turtles and toothed whales. It is quite possible that the open sea was the original cradle of life, and perhaps Professor Church is right in picturing a long period of pelagic life before there was any sufficiently shallow water to allow the floating plants to anchor. It is rather in favor of this view that many shore animals such as crabs and starfishes spend their youthful stages in their relatively safe cradle of the open sea, and only return to the more strenuous conditions of their birthplace after they have gained considerable strength of body. It is probably safe to say that the honor of being the original cradle of life lies between the shore of the sea and the open sea. The Great Deepes 3. A third haunt of life is the floor of the deep sea, the abyssal area, which occupies more than a half of the surface of the globe. It is a region of extreme cold, an eternal winter of utter darkness, an eternal night, relieved only by the fitful gleams of phosphorescent animals, of enormous pressure, two and a half tons on the square inch at a depth of 2,500 fathoms, a profound calm, unbroken silence, immense monotony. And as there are no plants in the Great Abysses, the animals must live on one another, and at the long run, on the range of moribund animacules which sink from the surface through the miles of water. It seems a very unpromising haunt of life, but it is abundantly tenanted, and it gives us a glimpse of the insurgent nature of the living creature that the difficulties of the deep sea should have been so effectively conquered. It is probable that the colonizing of the Great Abysses took place in relatively recent times, for the fauna does not include many very antique types. It is practically certain that the colonization was due to littoral animals, which followed the food, debris, millennium after millennium, further and further down the long slope from the shore. The Fresh Waters IV A fourth haunt of life is that of the Fresh Waters, including river and lake, pond and pool, swamp and marsh. It may have been colonized by gradual migration up estuaries and rivers, or by more direct passage from the seashore into the brackish swamp. Or it may have been in some cases that partially landlocked corners of ancient seas became gradually turned into freshwater basins. The animal population of the Fresh Waters is very representative, and is diversely adapted to meet the characteristic contingencies. The risk of being dried up, the risk of being frozen hard in winter, and the risk of being left high and dry after floods, or of being swept down to the sea, conquest of the dry land. V The terrestrial haunt has been invaded age after age by contingents from the sea or from the Fresh Waters. We must recognize the worm invasion, which led eventually to the making of the fertile soil. The invasion due to air-breathing arthropods, which led eventually to the important linkage between flowers and their insect visitors, and the invasion due to air-breathing amphibians, which led eventually to the higher terrestrial animals and to the development of intelligence and family affection. Besides these three great invasions, there were minor ones, such as that leading to slain snails, for there has been a widespread and persistent tendency among aquatic animals to try to possess the dry land. Living on to dry land has had a manifold significance. It implied getting into a medium with a much larger supply of oxygen than there is dissolved in the water. But the oxygen of the air is more difficult to capture, especially when the skin becomes hard or well protected, as it is almost bound to become an animal's living on dry ground. Thus, this leads to the development of internal surfaces, such as those of lungs, where the oxygen taken into the body may be absorbed by the blood. In most animals, the blood goes to the surface of oxygen capture, but in insects and their relatives there is a different idea of taking the air to the blood, or in greater part to the area of oxygen combustion, the living tissues. A system of branching air tubes takes air into every hole and corner of the insect's body, and this thorough aeration is doubtless in part the secret of the insect's intense activity. The blood never becomes impure. The conquest of the dry land also implied a predominance of that kind of locomotion, which may be compared to punting, when the body is pushed along by pressing a lever against a hard substratum. And it also followed that with few exceptions the body of the terrestrial animal tended to be compact, readily lifted off the ground by the limbs or adjusted in some other way, so that there may not be too large a surface trailing on the ground. An animal like a jellyfish easily supported in the water would be impossible on land. Such apparent exceptions as earthworms, centipedes, and snakes are not difficult to explain, for the earthworm is a burrower which eats its way through the soil, the centipede's long body is supported by numerous hard legs, and the snake pushes itself along by means of the large ventral scales to which the lower ends of very numerous ribs are attached. Methods of Mastering the Difficulties of Terrestrial Life A great restriction attended on the invasion of the dry land is that locomotion becomes limited to one plane, namely the surface of the earth. This is in great contrast to what is true in the water, where the animal can move up or down, to right or to left, at any angle and in three dimensions. It surely follows from this that the movements of land animals must be rapid and precise, unless indeed safety is secured in some other way. Hence it is easy to understand why most land animals have very finely developed striped muscles, and why a beetle running on the ground has far more numerous muscles than a lobster swimming in the sea. Land animals were also handicapped by the risks of drought and of frost, but these were met by defences of the most diverse description, from the hairs of woolly caterpillars to the fur of mammals, from the carapace of tortoises, to the armor of armadillos. In other cases it is hardly necessary to say the difficulties may be met in other ways, as frogs meet the winter by falling into a lethargic state in some secluded retreat. Another consequence of getting on to dry land is that the eggs or young can no longer be set free anyhow, as is possible when the animal is surrounded by water, which is in itself more or less of a cradle. If the eggs were laid or the young liberated on dry ground, the chances are many that they would be dried up or devoured. So there are numerous ways in which land animals secure the safety of their young, for instance by burying them in the ground, or by hiding them in nests, or by carrying them about for a prolonged period either before or after birth. This may mean great safety for the young, this may make it possible to have only a small family, and this may tend to the evolution of parental care and the kindly emotions. Thus it may be understood that from the conquest of the land many far-reaching consequences have followed. Finally, it is worth dwelling on the risks of terrestrial life, because they enable us better to understand why so many land animals had become burrowers and others climbers of trees, why some have returned to the water and others have taken to the air. It may be asked, perhaps, why the land should have been colonised at all when the risks and difficulties are so great. The answer must be that the necessity and curiosity are the mother and father of invention. Animals left the water because the pools dried up, or because they were overcrowded, or because of inveterate enemies, but also because of that curiosity and spirit of adventure which, from first to last, has been one of the spurs of progress. CONCORING THE AIR 6. The last great haunt of life is the air, a mastery of which must be placed to the credit of insects, pterodactyls, birds, and bats. These have been the successes, but it should be noted that there have been many brilliant failures, which have not attained to much more than parachuting. These include the flying fishes, which take leaps from the water and are carried for many yards and to considerable heights, holding their enlarged pectoral fins taut, or with little more than a slight fluttering. There is a so-called flying frog, Rackophorus, that skims from branch to branch, and the much more effective flying dragon, Draco-Volans of the Far East, which has been mentioned already. Among mammals there are flying phalangers, flying lemurs, and more besides, all attaining to great skill as parachutists and illustrating the endeavor to master the air which man has realized in a way of his own. The power of flight brings obvious advantages. A bird feeding on the ground is able to evade the stalking carnivore by suddenly rising into the air. Food and water can be followed rapidly and to great distances. The eggs or the young can be placed in safe situations, and birds and their migrations have made a brilliant conquest both of time and space. Many of them know no winter in their year, and the migratory flight of the Pacific golden plover from Hawaii to Alaska and back again does not stand alone.