CHAPTER I. Primitive Ancestors

PRIMITIVE ANCESTORS

ORIGIN AND EARLY DAYS OF THE BRAIN

Since every well-arranged biography should start at the beginning, we may first inquire into the origin of the brain. The early history of such an important organ must be closely interwoven with the genesis of man. If man were the result of a separate creative miracle, so also was his brain.

But we are not obliged to accept this view which attributes the universe and all living things to creative miracles. There is another and equally reasonable possibility. We may, for example, assume that man and all else came into existence by that process of continuous change and progressive development called evolution. We have excellent grounds for accepting such an assumption. Astronomy, geology, biology, chemistry, and all of the sciences relating to mankind have revealed the essential facts. Any other interpretation must disregard or repudiate this convincing record. With such a record as this to guide us we may turn our attention to the origin of the brain.

Earliest Forms of Animal Life

The inception of life on our planet was simple in the extreme. The earliest animals, although well organized, possessed no special organs in the strict sense. In the beginning there was nothing which could be specifically called a stomach or a heart, a lung or a kidney. Certainly there was nothing even remotely resembling a brain. The business of living was transacted within a single cell. This cell was so small that it could not be seen by the naked eye. Each of these cells was sufficient unto itself. Each played its own separate part with a simple programme of existence. Each was required to get its own food, to carry on its own chemical activities of digestion and elimination. Finally, after it had been successful in this remarkable process, it was called upon to produce offspring, to perpetuate its species. This last act was the crown and climax of its life, for in this way it conferred a material immortality upon its kind.

The amœba, among living animals, is a good example of this simple life. It is wholly intent upon carrying on within itself the earliest traditions of existence. All of its life is conducted within a single microscopic cell, which is at once its office and workshop. It has nothing in its make-up that could in the ordinary sense be called an organ. In such amœban animals as these there seems to be nothing progressive, nothing to suggest the possibilities of further advancement. Each amœba might, if such a thing were possible, look back over a long line of ancestors exactly like itself. In looking forward it might see no great possibility of progress. Perhaps it might reach the more specialized conditions of its present-day relatives with contractile threads in their substance and vibrating hairs by which to move themselves about. At best the outlook of the amœba for progress was restricted within very narrow limits.

Familiar Animals of Earliest Type

Certain events in the long history of these little animals have acquired much human interest. At times some of these simple lives become strikingly dramatic. Their monotonous existence is changed and they pass through certain exciting phases. Such a drama is often enacted when certain amœbæ gain entrance into the body of another animal and there become parasites. The other animal may be some huge beast or even man himself. One unpretentious amœba (Amœba histolytica), if it gains entrance into the intestinal tract of man, may cause amœbic dysentery and abscess of the liver. Another single cell animal (Trypanosome Gambiense) living in the blood of certain cattle is often conveyed by the tsetse fly to human blood where it produces the fatal disease known as “African sleeping sickness.” This small animal claims hundreds of thousands of victims a year. In tropical Africa its devastations go on unchecked over an area of more than a million square miles. In this region sleeping sickness kills as many persons as all other diseases combined. From five to seventy per cent. of the inhabitants in different localities are stricken. Cattle, horses, and other domestic animals cannot be kept because of this disease. On this account, and also because the area in which the sickness rages is extremely fertile, it has been said that the conquering of this malignant protozoan would be equivalent to the discovery of a new continent.

Even better known are the several acts in the cycle of the plasmodium malaria. This protozoan animal is often borne by the Anopheles mosquito and injected into the blood of man. Then follows the familiar series of pathological events consisting of chill, fever, and sweat, called malaria. In certain respects it seems like retributive justice when this animal is injected into the body of man to cure the effects produced by another microörganism. The other organism is the spirochæte which causes syphilis. It often produces changes which destroy the human brain in consequence of a disease known as paresis. Many other protozoan animals are parasites, but in the main they live and have lived simple, unobtrusive lives.

Notwithstanding their apparent simplicity of structure and action, these minute animals, like all other things, have been subject to the influence of continuous change. They have responded to this influence in different ways. In many instances, through generations of reproduction, they have effected combinations and recombinations of their essential constituents out of which have emerged modifications of their original structure. Often these changes have proved progressive and contributed to more complex modes of living. Often they have been regressive or non-progressive. It was the progressive modifications in these earliest animals that were of utmost importance to the origin of the brain. This organ was not yet in sight, but adaptations working toward it were soon to appear.

Critical Changes in Animal Existence

In the course of time certain critical changes took place in the lowly scheme of animal existence. These were distinctly progressive changes. Some of the single-cell animals began to live in colonies. Circumstances thus conferred upon them a community life. They began to exist in close contact with others like themselves and were compelled to forego their simple, independent habits. They were, in fact, actually joined to each other by rather slender bonds of their own vital substance--protoplasm. This was an epochal stride forward. It was the first step which led to progress. In some instances it brought about entirely new relations between these animals and the world in which they lived. Now, since these small cells were grouped together as colonies, each individual cell lost much of its own independence. Its interests became, in some degree at least, the interests of the group. If, as a single cell by itself, it had been thoroughly self-contained, now it was necessary for it to follow the needs and inclinations of its neighbours. It was forced to observe the conventions and habits of its colony. This condition of affairs exists in what are known as the colonized protozoans. In addition to the advantages of community life there was another and far more important reason why this new kind of existence was a critical step. It introduced for the first time the principle of differentiation or class distinction. A division of labour was thus made possible. Some of the cells in each group were forced to take up positions on the outer surface of the colony. Others occupied places inside of the group. This arrangement immediately created a distinction between “outer cells” and “inner cells.” It was destined to have far-reaching consequences because it established a difference in the responsibilities of two great classes. The outer cells made an immediate and direct contact with the world. They were nearest to the water, to the light, and to all of the outer chemical substances necessary for living. They were like guards and outposts about a camp, defending the colony from adverse influences. They might be likened to the first line of battle in the aggressive struggles for life, acting as foragers and procurers of food. The rôle of the inner cells was different. Their contacts with the world were more indirect and established largely through the outer cells. Their offices were especially confined to the inner workings of the colony. They became the germ cells whose function it was to insure the immortality of the species. This arrangement was a momentous advance in the direction of progress. It was particularly momentous because it laid the foundations upon which all of the great developments in the animal world were to be built. In a certain way, it was also a prophecy, for it foretold the coming of animals that were to follow the protozoans. These newcomers, the metazoans (animals which came after the first forms of animal life), were to possess a body with outer cells engaged chiefly in the efforts of life, while the inner cells would be particularly concerned with the essence of living, such, for example, as digestion, assimilation, and circulation.

This remarkable process of class distinction among cells developed new and useful methods in living. It brought about a division of labour in the business of life. Different parts of the animal now had different obligations to fulfil. Some parts served to move the body about, some were employed in digesting food, some in eliminating waste, some in breathing and circulation, some in reproduction. In the end, this division of labour resulted in the formation of a body made up of many different organs, each having its own particular responsibilities. We may find an excellent example of the very earliest stages of this division of labour in Volvox, one of the colony-forming protozoans. Most of the colonized cells of this minute animal are on the outside, forming a hollow sphere. These cells are equipped with minute hairs or flagellæ which, by their constant motion, keep the animal rolling around in the water like a hollow rubber ball. In this manner it seeks and finds its food, and thus also it may escape when threatened. But all of the cells of Volvox are not on the outside. A number of them are tucked away from the actual surface of the animal. These are the sex cells to which is entrusted the important duty of reproduction.

Early Influences at Work to Form the Brain

Even by this time in the history of the earth, although animal life had been developing for millions of years, there was no sign of anything like a brain. The forces, however, which would eventually bring such an organ into existence were already at work. Perhaps from this great distance it may be difficult to recognize the exact nature of these forces as they began to act at this particular stage of life. They were present nevertheless, faintly discernible like the first streaks of dawn which precede the sunrise. This figure of speech may seem to imply that in the end the brain was the actual sun destined to rise above the horizon of animal life and ultimately to dominate all progressive achievement. The rest of this biography must prove whether this is an extravagant figure or not. One important influence behind those forces that eventually produced the brain stands out clearly. It seems to have been the direct result of that class distinction among cells which caused such effectual division of labour. With this subtle influence at work it required one further critical step to set in motion the events which were to end in the formation of a brain. This step was taken when the sponges (Poriphara), the simplest of metazoan animals, came into existence. They differed from the protozoans, even the colonized protozoans, because their bodies were more complexly organized. The individual cells forming them had lost most of their separate independence. All of these cells were now incorporated in a single living individual, and each cell was subordinate to the interests of the whole.

Cell distinction had become still more important because of the increase in size of these animals. The outer cells now formed a covering or skin called the “ectoderm.” The inner cells constituted the wall of a cavity, which might be likened to the lining of the stomach. The lining is called the “entoderm.” Many minute openings or pores in the outer covering established communication by means of small canals with the inner cavity of the animal. Through these pores water is inhaled and carries with it particles of food into the inner chambers. These particles are absorbed, and the water is then exhaled through a larger opening called the “osculum.”

It was at this critical point that a decisive factor leading to the formation of the brain made its appearance. Some of the deep cells around the pores and outlets of the sponge formed “muscles.” In many respects this was a new device, and the sponges become especially interesting because of this innovation in animal life. The innovation itself resulted in a special machine for producing motion; namely, the muscle cell. Such muscle cells in the sponge are extremely simple. They form rings around the pores and the outlets which, by contracting, regulate the flow of water through the animal. But such muscle action as this is extremely important because if the water in the sponge contains an abundance of food particles, muscular contraction prevents too rapid outflow. This slowing of the ex-current stream, among other things, allows more time for absorption and digestion. The muscles in different parts of the sponge act independently. Each one is, so to speak, a free agent, occupying its position at its own particular pore or outlet. If, however, it became necessary for all of these muscles to contract at the same instant in a concerted effort, let us say, to make the sponge move, there would be no mechanism to assure harmony of action. The muscle cells at each outlet would react according to their own inclinations--some relaxing, others contracting. Confusion of action could scarcely fail to result. The sponge, however, does not need to move about in order to get its food. Being stationary, it obtains its nourishment by sucking the water through its pores, and by regulating the flow the muscle cells do all that is required of them.

A New Motor Device

Simple as is this muscular equipment, it possesses great possibilities for further development. It clearly indicates how such mechanisms for producing motion might be expanded to create all of the surprising varieties of motors which in time enabled animals to move about over the earth, in the water, and through the air. It is true that the simple strands of muscle in the sponge are far from powerful; but when a number of muscular strands are collected together they may take form in such muscles as the biceps of the arm, the great extensors of the leg, or those covering the entire body.

The presence of the muscle cells created the need for a nervous system to control and regulate their activities. In order to act together muscles require a supervisor. The first important step in this direction was taken when certain simple animals like hydras and sea anemones (Metridium) made their appearance. These animals are equipped with muscles in several parts of their bodies. Some of them, unlike the sponges, have the power to move about a little, crawling slowly like snails. They are also capable of moving their many tentacles, and thus are able to reach out and grasp food. All of these movements call for the action of the many different muscles. The sea anemone has thirteen different sets of such muscles, the exact coöperation of which requires the closest harmony of action. Each part must be mutually adjusted to the others. It must act in the right rhythm and with the proper force. Such delicate adjustment as this could not be left to chance. It needed an adjuster and regulator. It required also a system of communication between the cells in order that each might sense how the others were acting during any given interval of time. In consequence of these requirements many cells were specialized as timers, signallers, and dispatchers. They acted like independent telephone stations, each serving separate districts; such, for example, as the individual tentacles of hydra or of sea anemones. These separate stations were known as nerve cells. In them the first elements needed for the origin of the brain made their appearance. At first they were scattered and had limited communication by means of slender strands, the nerve fibres. There was as yet no central operator for receiving and routing their messages which were transmitted rather diffusely by a loose nerve net.

Foundation Stones of the Brain

In spite of this apparent simplicity, these nerve cells were the foundation stones of the brain. Scattered as they were, they lacked that unity of action which is the real secret of nerve power. A more constructive plan for utilizing their capacity was requisite at this stage. Such a plan was eventually forthcoming. It was exactly what might have been expected in the progressive development of any good business concern; namely, consolidation. In effect, it was a merger uniting the separate nerve units into one centralized system. How this merger was brought about may be recognized in such animals as the jellyfish (Cœlenterates). In them the body equipment consists of an outside layer called the “exumbrella,” and an inner layer, the “subumbrella.” In the latter the older arrangement of the nerve cells as scattered, more or less independent stations still persists. These stations form a net of communication on the under surface of the animal. But where the subumbrella joins the exumbrella, making the rim of the jellyfish, the nerve fibres and the nerve cells form a nervous ring entirely surrounding the animal. This is the first time in the history of animal life that an actual central nervous system makes its appearance. This ring of nerve fibres and cells acts as a central receiving and dispatching station. It is a central office for receiving information from the outside world and a dispatcher for sending orders to different portions of the animal so that all parts may coöperate harmoniously. Certain special organs develop along the rim of the jellyfish, whose functions have some bearing upon the sense of direction. These structures are known as the marginal sense organs or “lithocysts.” They are in direct communication with the central nervous system. Certain other sense organs are also present in the form of red or black specks of pigment at the bases of the tentacles; they are the “ocelli,” which are sensitive to light and are, in fact, the simplest form of eyes. Thus, in such low forms of animal life as the jellyfish, the first signs of special sense organs made their appearance, and the nervous elements were for the first time organized to form a central governing mechanism for the animal.

Nerve Concentration in Forming the Head

Following the merger of the scattered nerve cells to form a central system, the process of developing a brain had opportunity to advance along another new line. The circular nervous system of the jellyfish passed through many modifications as it adapted itself to the form of different types of lowly animals. The great impulse thus imparted toward the formation of the brain veered off in numerous directions until a new and decisive change occurred in the arrangement of the muscles. At this juncture certain animals appeared whose bodies were much elongated and slender. Their muscles were arranged in straight rows, one behind the other. Such an arrangement had definite advantages for transportation, and these advantages were utilized by such animals as the flat worms (Platyhelminthes). Many of the nerve cells and fibres became concentrated in the head end of these animals. This head region in a general way took the lead in directing the activities of motion and transportation. It also had centralized in and about it many of the most important structures of life. The animal at this critical stage now possessed a head and a body. In the broadest sense the development of such a head may be likened to the creation of a definite executive office within which was established a supreme organ to preside over the rest of the body.

Further concentration of nerve cells in the head of the animal was the next step in this constructive process. This advance added materially to the centralization of nerve power, which was the keynote in the formation and growth of the brain.

If this process of successive upbuilding seems mysterious and almost miraculous, especially from its feeble beginnings in a single cell, it is scarcely more remarkable than the commonplace miracle that has resulted in the development and birth of every newly created animal since the dawn of time. The offspring of each species--fish or fowl, beast or man--has its beginning in a single cell. It passes through stages of cell colonization, of class distinction among cells, and of specialization of organs for the various functions of life.

In the main, these two processes have run parallel in their programmes of construction--the beginning and development of life on our planet, the beginning and growth of every new life created. Summarized thus briefly, these successive stages necessary to bring the brain into existence may appear unimpressive. But when we consider that each forward step required ages for its achievement, we may appreciate that this was indeed a marvel of progress. From nerve cell to brain is a few short words in print; but it required millions of years for the slow advances to attain even the humble level of the flat worms.

Development of Better Brains

With the head at length in its proper place and the most simple kind of brain installed within it, vast horizons of life still lay ahead. Better mechanisms were needed for a more successful struggle with existence. More capable motors were required for more efficient locomotion. These improvements came after the passage of long intervals of time. By degrees more highly developed animals, such as bees, ants, beetles, or other insects, lobsters, crayfish, and shrimp, began to appear. Their brains were much better organized than those of the lowly worms. The special senses of sight, smell, and taste became highly important, while the central organ which presided over all activities acquired a remarkable complexity in its structure.

How much these animals gained from their better brain power is clearly seen in their behaviour. The achievements of ants and bees and beetles, as well as many other insects, have long been a matter of wonder, a theme of interest and fascination. If we credit these animals with highly capable brains, it is their just due. One detail in their organization, however, became a serious handicap to them in their further development. The passageway from the mouth to the stomach ran directly through the centre of the brain. If the brain grew extensively it would encroach upon the gullet, ultimately shutting off the only channel for food. This embarrassment actually overtook many insects like the mosquito. Here the brain became large. The tube connecting the mouth and the stomach was thus reduced to a fine calibre, and the animal was forced to depend upon the highly concentrated fluid diet obtained by sucking blood. Coarser forms of food could not pass the œsophageal ring which the brain forms about the gullet. Thus the stomach and the brain came into serious competition with each other. If the brain grew larger the stomach would be deprived of food. In consequence, this situation created a dangerous hazard to life.

Advent of Backboned Animals

In addition to this stomach-brain dilemma, animals such as the insects suffered from another handicap because of the outer skeleton which protected their bodies. This skeleton was in the form of a more or less rigid shell, as in the lobster, crab, or crayfish. It was to overcome the effects of such handicaps, according to some authorities, that the great race of backboned animals came into existence. In any event, such animals seem to have circumvented the difficulty of having a brain which surrounded the gullet. They also overcame the necessity of carrying a heavy shell about on the outside of their bodies. An inner skeleton did away with this embarrassment. It is not altogether clear how or when this transition took place. Many students of this matter believe that the basis for this change is to be found in the starfish group of lower animals (Echinoderms). Others maintain that the change began with some creature not unlike the horseshoe crab (Limulus). It is also believed that the animals which served as the intermediate forms for this advance were the ostracoderms, a group which has long since become extinct. They are known to us only through fossil preservations. They possessed, however, so many fishlike features that they may well have served as the forerunners of the earliest animals with backbones. Whatever else is in doubt, one detail of this transition is definite. The brain, already well developed in certain lower creatures, now received a fuller opportunity to advance along more advantageous lines. The first gains of this kind are seen in the fish. Judged by outward appearances the object of such new brain development was to provide a more efficient regulator for a new and more efficient kind of animal. The fish, in one particular at least, showed higher specialization. It was built for speed in locomotion. The shape of its body, the arrangement of its muscles, the position of its fins, the design of its head, and the form of its tail gave it many advantages over lower animals. Equally important were the special organs by which it sensed the world. The fish possessed powerful and remarkably constructed eyes. It had most delicate organs for smell, and an effective apparatus for taste. In fact, all of the senses of the body were now so thoroughly organized that each one of them had its own special department in the brain. According to this new type of administrative organization, an endbrain, an interbrain, a midbrain, and a hindbrain were established for distinct departmental purposes.

In spite of this better arrangement, there were still decided limitations in the brain. The most serious of these deficiencies lay in the mechanism regulating the energy turnover. The fish had little power to withhold its reactions. Its impressions from the outside world produced almost immediate responses. Such rapid reactions precluded the wide range of acts which characterizes more deliberate behaviour.

The brain machinery for the most ample kind of living was not yet present at this stage of animal development. It did begin to make its appearance, however, when certain of the fish assumed partial adjustment to life on land. These adventurous pioneers managed to crawl out of the muddy waters at times when there was a lack of oxygen or when the supply of food was insufficient. They set on foot those progressive changes that gave rise to fore and hind limbs in such amphibians as the frogs. When these latter animals made their appearance nearly all of the fundamental problems of the vertebrate brain had been solved. Nevertheless, there was still the need of certain expansions in brain power and these, in some part, were supplied during the age of reptiles.

As yet, however, that handicap of almost instantaneous reaction which seriously limited the life of fish had not been entirely overcome by the amphibian or by the reptile. These animals still lacked the brain mechanisms needed for the deliberate and varied actions of the most efficient life. They had not yet altogether escaped from the ancient tyranny of automatic or reflex reaction.

At length the mammals, throughout the different periods of their long progressive age, introduced the final detail of brain perfection. The secret of this perfecting detail was the addition of a new mechanism to the brain never possessed by animals before this time. The great and new areas of the cerebral hemispheres now came slowly into existence. With them developed new and greater capacities for action together with far more effective adjustments to life.

Vast Ages of Animal Life

All of these developments reach back a great distance in time, so great that it is difficult to calculate its exact duration. According to modern estimates the first animals came into existence about 1,000,000,000 years ago in the Proterozoic period. This period was followed by the Palæozoic, which began approximately 300,000,000 years ago, and is known as the Age of Fish. Then came the remarkable Age of Reptiles, beginning about 200,000,000 years ago, followed by the Age of Mammals, which commenced in the neighbourhood of 65,000,000 years ago. The present Age of Man has had a short duration, extending back only about 1,000,000 years.

Two methods have been depended upon in determining these figures and the age of the earth. The first is based upon the rate of deposit and upbuilding of sedimentary rocks. The estimated period required for the development of each rock layer has provided a time-table for the age of the different strata of the earth’s crust. The second method calculates the rate at which common salt is extracted from the land and deposited in the oceans. Imprints of fossil animals upon the several rock layers also reveal the age of different strata. The discovery of radium afforded the latest gauge for estimating geologic time. The physicists now tell us that former calculations have been far too modest and that we must go back still further to reach the actual beginnings of our earth. Their “radioactive clock” indicates that the earth is 1,600,000,000 years old.

During all this vast interval there has been a succession of great changes in the earth and its waters. Continents have risen above sea level, to be submerged again. Great inundations of continental oceans have swept inward and made vastly different land divisions from those which exist to-day. North America has been more or less widely flooded by great oceans at least fifteen times. Other continents have been similarly inundated. Mountain ranges have risen and crumbled away by erosion. In point of geologic time most of the present mountains are relatively young. The oldest of these is the Appalachian range which was formed during the Permian period approximately 230,000,000 years ago. The Rocky Mountains appeared at the close of the Cretaceous, 100,000,000 years ago, while the Swiss Alps are of much later development, having been formed at the close of the Miocene about 15,000,000 years ago. Even the Himalayas are relatively young when compared with the earth’s antiquity. They had not taken on their full gigantic proportions until the close of the Eocene about 45,000,000 years ago.

According to many authorities, great continental land connections once existed between Africa and what is now part of South America. This connecting continent disappeared beneath the ocean long ago. So also did the land connection between Asia and North America in the region of the Bering Sea. An important land connection existed between England and the Continent, across what is now the English Channel, in Pliocene times. It was present, therefore, at some time within the last 6,000,000 years. Immense inland seas have drained off or evaporated and left in their places great desert spaces, like the Bad Lands of the West.

The Long Upward March Toward Humanity

While these changes were in process marked alterations in climate affected the surface of the earth. Glacial ice caps descended from the poles, later to recede and leave the earth invested in tropical warmth. Time and again these changes recurred. The crust of the earth, chilled by intense refrigeration for protracted ages, grew warm again for equally long periods when tropical vegetation crept up toward the poles. These changes in vegetation have been accompanied by many changes in the animal inhabitants of the globe. Species of animals in profusion have come into existence only to follow the path which led to extinction. In many cases the forms of life began simply and progressed by graded stages to greater structural complexity. Man is an outstanding example of this rule. He began in much simpler form than that in which he now exists. This relative simplicity is particularly true of his brain.

Thus, as if descending a long stairway, we may pass by the successive terraces of the earth’s history toward the beginnings of geologic time. The expanse of this time is difficult to conceive. From the inception of animal life in the long Proterozoic Age, throughout the ages of Fish, Reptiles, and Mammals, man’s brain was in the making. Irresistible forces molded the various stages of its progress. Species, genera, families, and even entire orders of animals came into existence and disappeared as wastage in a great experiment. Yet, through all vicissitudes of time and change, the long upward march toward humanity held its place. Ultimately it became the dominant feature in creation. The advent of man introduced a new era. It remains to be seen whither the forces moving in this Age of Man will take us. They may be leading to extinction. The way to such a termination is clearly open to our race. On the other hand, the brain has made man what he is and may save him for better things. Its interesting pioneer ancestry, although extremely remote, has left a well-established record. The history of its development through the process of evolution in the backboned animals is still more interesting.