Initiative in Evolution

They are numerous over finger joints and front of elbow joint.

Table II.—(From Schäfer’s Text Book of Physiology):—

Average of Meissner’s corpuscles to each square millimetre, which is approximately one five hundredth part of a square inch:—

* Absent from the cornea, and conjunctiva of the upper eyelid and from the glans penis.

Table III.—Distribution of Touch Spots:—

These must be distinguished, of course, from the touch corpuscles of the preceding list and the subjective element in the study of them must be borne in mind.

If an area, as of the calf of the leg, be prepared, by cutting short the small hairs, and examined, it is found that there are about 15 touch spots in each square centimetre, which is about one-fifth of a square inch.

In another area so treated the hairs are counted and the following result is given:—

Schäfer says: “An area of the dorsum of the distal phalanx of a finger contains about seven times as many touch spots as an equal area between the shoulders. Regions poor in touch spots are the flexor surface of the upper arm, the upper third of the thigh, the leg above the inner malleolus, the neck, and in general the skin over subcutaneous surfaces of bone.”81

Table IV.—Distribution of Cold and Warmth Sensations.

The Scale includes twelve grades of sensation in cold, and eight in warmth sensations, and commences with the regions which yield the maximal intensity of sensation.

Table V.—Distribution of Cold and Warmth Spots.

By stimulation of cold or warmth spots there is shown, not only the quality and quantity of the stimulus, but the locality. When punctiform stimuli are applied to pairs of cold spots and pairs of warmth spots marked “local sign” is found. This Goldscheider showed to be higher for cold than warmth spots.

Thus on the palm of the hand two pairs of cold spots .8 mm. apart are distinguished by this punctiform stimula­tion, whereas on this surface two pairs of warmth spots are only distinguished when they are 2 mm. apart on the cheek, chin or forehead and cold spots are distinguished when .8 mm. apart on the same surfaces warmth spots when 5 mm. apart.

Table VI.—Average lowest distances in millimetres on different areas of skin where two points are felt as two or minimal distances from which double sensation is obtained.

Table VII.—(According to Weber’s Law.) Average differences in different regions of skin of sensation of pressure.

Thus on the forehead differences of pressure are distinguished when they are increased by  1/30, whereas on the dorsum of the foot they have to be increased by  1/10 to be distinguished. This is carried out by impact of little balls of a light substances such as pith.

It may be remarked of these tabulated results that on the one hand they are the results of work extending over some seventy years and numerous observers, and on the other that, broadly looked at, they all tell the same story of stimuli in their incidence on the skin—those of pain, cold, warmth and touch. There is also one thread of origin running through all, and that is that the regions most exposed to the four stimuli show the highest development of specialised function and structure.

Some Aspects of the Nervous System.

It has been said with some truth that the telephone has struck a mortal blow at such serenity of life as the Juggernaut Car of modern progress has left us. But if it has done nothing else it has furnished the physiologist with a good illustra­tion when he sets out to expound the functions and arrangement of the elements of the central nervous system and its peripheral expansion. In addition to this general light upon a great matter the vivid experience of many an Englishman during the recent years of war adds point to a subordinate phase of the general story of the telephone, for it represents my conten­tion as to the origin or initiative of the sensorial areas of the mosaic under considera­tion. Modern persons may be divided into two classes, those who want and those who do not want the telephone, and the former may be sub-divided into A, those who can, and B those who cannot get it (or could not). A and B from the present point of view may be termed Receptors, though to call the B people by that name is to speak Hibernically. With this war-time experience in our minds, we may picture a vast period of time during which the stimuli of pain, cold, warmth and touch were hammering on the skin both before it began to lose its chief hairy covering, and after that process had left man still a hairy animal, but with much-diminished amount of his ancient heritage. These stimuli fell upon the skin very much as the class A, among telephone receptors, spent numerous fruitless stimuli on Postmasters-General, Ministers in Parliament and in “short” bitter letters to our bright little Daily Pope, and who yet found themselves not “connected up,” as the saying goes. There is no knowing how long it was before they had enough effect on the delicate nerve fibrils struggling up into the epidermis and produced receptors or were “connected up” to the exchange or central nervous system. I am inclined to liken the pain stimuli to the short letters referred to, the cold and warmth stimuli to those addressed to the Postmasters-General and the touch stimuli to those which fell upon Ministers at question time.

Another comparison of the peripheral portion of the nervous system to common things has at times forced itself upon my mind when reflecting on the stimuli which are continually assaulting the skin, as I have watched on the Needles’ Downs a flock of sheep on a summer evening returning to their fold. As the sun begins to set they are scattered over the western end of the Downs, still cropping the short grass clothing those chalk and flint slopes which from immemorial time has alone flourished there. They wander singly or in small groups on such parts of the slope as the intrusive golfer still allows, and gradually fall into larger groups which follow somewhat indefinite paths. As they move further and further towards home they are seen to follow one another in single file on some score or more of clearer paths, and finally converge into one well-beaten and broad path until they descend the northern slope and pass out by a single roadway into which a gate opens, and so reach the haven where they would be. Here one has a simple picture of the common stimuli of the skin, at first indefinite and ineffectual, by their cumulative action producing an individual receptor and its nerve connec­tion with the central system.

Professor Leonard Hill82 also gives a view of the general action of the nervous system and compares it to control of the police force. He supposes a murder to have been committed in a village, and that the local policeman telegraphs to the local town ordering the roads to be searched. The policeman is the tactile sense-organ, the telegraph wire is the sensory nerve, the telegraph office in the local town is the spinal cord, from this office a message is sent to the town police-station by another wire and the police are set in motion. The police are the muscles, the wire that sets them in motion in the motor nerve. The message is also sent to neighbouring towns and to London, that is to say, other local offices (parts of the spinal cord) and the head office (the brain) are informed of the crime or sensory impulse. The central office in London directs the operations controlling the local police office. The whole order of events need not be here described because it goes beyond my immediate purpose, but it is enough to say that attached to the head office are the cleverest detectives (higher sense-organs) and in these are kept records of past crimes, lines of action of the police, and success or non-success of their investigations.

Following on this picture he speaks of the way in which conscious actions become automatic and makes a statement to the effect that “There is evidence to show that the axons (or processes of the nerve-cells which extend unbroken from nerve-cell to its termina­tion) become covered with a adulated coat as each new tract is formed. Thus the structure, like the habit, becomes fixed”—and—“It would appear as if, by repeated experiences, tracts and pathways must be beaten through the nervous system”83 (Italics not in original).

Beside this I place a statement from Professor Graham Kerr as to his view of the development of peripheral nerve-trunks. He is reviewing the “outgrowth” theory of His, the “chain cell” theory of Balfour, and the “Primitive Continuity” theory of Hensen, and expresses himself as follows: “It is suggested that the development of the actual nerve fibril is simply the coming into view of a pathway produced by the repeated passage of nerve impulses over a given route.”84 (Italics not in original.)

A passage from Professor McDougall’s Physiological Psychology may also be referred to at more length than it was in Chapter III., page 25. Speaking of the automatiza­tion of voluntarily acquired actions which have been explained by the view that purely reflex actions carried out by mechanisms of the spinal level were also originally acquired by our original ancestors as voluntary actions, he says, “This view is usually associated with the name of Wundt, who has forcibly advocated it. It implies, of course, the assump­tion that acquired characters are in some degree transmitted from one genera­tion to another, a proposi­tion which most biologists at the present time are inclined to deny because they cannot conceive how such transmissions can be effected. Nevertheless, the rejection of this view leaves us with insuperable difficulties when we attempt to account for the evolution of the nervous system, and there are no established facts with which it is incompatible. If, therefore, we accept this view we shall regard the congenital neural dispositions, both those that determine pure reflexes and those that determine instinctive actions, as having been acquired and consolidated under the guidance of individual experience, with the co-operation, to a degree which we cannot determine, of natural selection.”85

These three statements from a physiologist, a zoologist, and a psychologist, all of great eminence, though they differ in particular problems studied, tell very strongly in favour of the position here put forward as to initiative in the produc­tion of specialised innerva­tion of the skin.

Origin of Cold, Warm, Pain and Touch Spots.

The hair-clad skin of primitive man provided ample raw material for the eventual differentia­tion of both end-organs and sensorial areas which is found to-day. Not only did he possess what is called Common Sensation in his skin but in the individual hairs lay a delicate tactile structure, which, though probably inferior in delicacy, serves a similar purpose to that of the vibrissæ on the muzzle of Felidæ. Each hair, being deeply inserted into the skin and supplied with fine nerve fibrils, when it is bent, acts as a lever communicating an impulse to an afferent nerve trunk. In an animal covered with thick hair the sensory impulse conveyed might be exceedingly delicate, but, from the nature of the case, of much more limited range than in one like man in whom the hair is so greatly diminished in length and thickness.

It would be fruitless to speculate as to which of these four forms of stimuli was the earliest to become effective in developing man.

Cold and Pain.

Two of them, cold and pain, may be termed nocuous; one, that of touch, useful, and one, that of warmth, indifferent. If it be true, as Professor Scott Elliott states,86 that man’s earliest home had a climate which “lies between the regular tropical, with wet, steaming, impassable jungles, and the colder temperate zone, so affording chance of acclimatisa­tion in both directions,” the stimuli of cold would even then not be wanting, however much they increased in severity when he passed through glacial periods; but wherever, whenever, and at whatever time he first became man he had to tread the Via Dolorosa in the course of his hard and eventful life, and must have been well accustomed in all regions of his skin to the stimuli of pain, working, as he did, for his living, and fighting for it and his mate, with varied and powerful enemies. Though it is correct to call both these fundamental stimuli “nocuous,” this is all a matter of degree, and both the stimulus of moderate cold, raising blood-pressure and activating metabolism, and that of minor pains, would do little else than good in his education for the higher terrestrial life to which he had descended. If he was to learn effectually to take care of himself the discipline of both moderate cold and pain would be as valuable to him then as in its measure it is to his descendant to-day. The triumphs of medicine and surgery could never have appeared if it were not for the beneficent warning voice of pain that so generally accompanies disease.

Through long ages of exposure to the stimuli of cold and pain came response in the form of cold and pain spots, after minute struggles between the static conservative tissues of the skin and the dynamic force of repeated assaults upon them. In due time then receptors appeared and each became connected with the central organs, by which means better adapted motor reactions against “nocuous” cold and pain became possible. In 1900 Professor Sherrington summed up the evidence in Schafer’s work on Physiology against the existence “of separate afferent fibres with their specific end-organs entrusted specifically with carrying painful impressions to a pain centre,” but Professor Starling in his later work on Human Physiology speaks of “a distinct sense of pain,” probably subserved by a distinct set of nerve fibres, but for the present purpose it is not necessary that agreement on such a problem should be reached, for it is alone with pain spots that we are concerned. He also points out that on the one hand the cornea is sensitive to only one of the four stimuli in question, that is, pain, and on the other that the surface of the glans penis is sensitive to cold and pain, but tactile sensation and warmth sensations are almost entirely absent.

Touch.—This form of stimulus and its response can only be reckoned as useful to the organism, except that it may be, and often must be indifferent. The great number of the touch spots can be understood when it is declared by Professor Sherrington that almost invariably there are one or more touch spots close to the emergence of each hair,87 and that they are very numerous also on the palmar and plantar surfaces of the hand and foot. Of the four forms of cutaneous stimuli those of touch are the only kind that have so far been proved to have specialised corpuscles, the other three having developed the physiological equivalent of cold, pain and warmth spots.

Warmth spots are decidedly the least numerous of the four, those of pain being, as stated by Professor Sherrington, the most numerous. It is obvious that unless thermal stimuli become somewhat excessive they hardly can be described as “stimuli,” being more or less neutral in their action on a warm-blooded animal. This cannot be entirely so, because it has been shown quite conclusively that warmth spots do exist, though much less numerous than others. There is a significant fact as to thermal reaction and that is that there are no pure heat spots like those of cold, for the stimuli of about 49° C are so associated with those of pain that warmth spots alone are distinguished, and among primitive man no stimuli of heat could impinge on his skin, until he had learned the use of fire, more powerful than those of solar heat.

Such stimuli of heat as the rays of the sun would occasionally discharge on the skin would resolve themselves into the general stimulus of pain, and in this direction a far shorter initia­tion occurred than with any of the four normal cutaneous stimuli. The fact, at any rate, of there being no heat spots is to be noted.

It remains now, having quoted three writers eminent in physiology, psychology and zoology in support of the modest thesis here put forward for me to appeal to the authority of the facts contained in the tables for such evidence as they can give, and to give a summary of this.

Summary.

1. Table I. shows that the structures known as touch corpuscles are distributed on those parts of the skin where the stimuli of touch fall most and in propor­tion to the degree in which those parts are employed in tactile discrimina­tion; thus, most of all on the index finger (with the exception of the tip of the tongue) next on the thumb and less on the middle finger. There are 530 of these corpuscles to the upper and 317 to the lower extremity.

2. Table II. bears out the same conclusion, the average number of corpuscles to a square millimetre being twenty-one on the terminal, eight on the second and four on the first phalanges of the index finger, whereas on the foot there are seven on the great toe much exposed to stimuli and only two on the middle of the sole of the foot, which is little exposed. The absence of them from the cornea and conjunctiva, protected by quick and powerful reflexes from such stimuli, and from the (normally) covered glans penis is in accordance with the other results.

3. Table III. dealing with touch spots, shows that these are nearly twice as numerous on the flexor as the dorsal surface of the forearm; and nearly five times as numerous as on the scalp, where tactile stimuli are few, and that the distal phalanx of a finger contains about seven times as many as an area between the shoulders. The regions poor in touch spots are shown to be those where relatively few tactile stimuli can fall.

4. Table IV. gives cold and warmth sensations graded according to the delicacy with which they are perceived in many regions of the skin. The cold sensations are best distinguished on the parts normally most exposed to cold, as the tips of fingers, malleoli, tip of nose, chin, patella, wrist, and least on the protected areas, inner side of thigh, flank, loins and abdomen. The warmth sensations are best distinguished on the regions on which the stimuli of warmth has most frequently fallen, tips of fingers and toes, cavity of mouth, palm of hand, less so on the neck and loin. And the striking fact is noted that warmth sensations are not felt in the lower gums, the inside of the cheek at a certain level and the cornea, which again is protected from these stimuli by its efficient reflex, whereas to the gums and inside of the cheek most warmth stimuli have not been “stimuli” at all.

5. Table V. also gives results of the mode of distribu­tion of cold and warmth spots, examined with punctiform stimuli. The “local sign” for cold is higher than that for warmth spots, and two of these are distinguished as double when only 0.8 millimetres apart on the palm, cheek, chin and forehead, whereas on the upper arm, back and thigh, they are only distinguished as double when separated by two millimetres, and this distance is the minimum at which warmth spots are distinguished as two, that is 2 mm. on the palm, and five on cheek, chin, forehead and back. This tells the same story as Table IV., of past stimuli of cold and warmth.

6. Table VI. deals more elaborately than the others with double sensation in different areas of the skin, the tip of the tongue being the most accurate in this respect of all examined, and the tip of the index finger next, which is to the great toe as 2.3 to 11.3, the palmar surface of a finger half as accurate again as the dorsal surface, the palm of the hand twice as accurate as the surfaces of the forehead and back of ankle, nearly four times as much so as the dorsum of the foot and six times as the skin of the middle of the back.

There is here a very close relation between the amount of exposure of these various regions to tactile stimuli and their present equipment of ability to discriminate between two small objects.

7. Table VII. deals with the sensation of pressure in certain groups of areas, and shows that change of pressure is perceived about three or four times as accurately on the forehead, lips and tongue, as on the finger nail, back of forearm, hand, or fingers, and more than three or four times on the back of the foot, and sole, and surface of leg and thigh. In this group of observations also the rule is followed that the greater and more frequent in man’s ancestral past have been the exposure of his skin to variations of pressure, the greater is his present power of accurate discrimina­tion of them.

There are some scattered facts mentioned by Professor Sherrington which are in keeping with the line here taken, that the formation of receptors in the skin have their origin in accumulated stimuli. He refers to the vain endeavours of Goltz to evoke the reflex croak of the female frog by applying electrical stimuli to the skin, whereas non-nocuous mechanical stimuli were the only stimuli that proved effective.

He never was able to elicit the “extensor thrust” in the “spinal dog” by any form of electrical stimula­tion, but only by a particular kind of mechanical stimulus. This peculiarity was also found in the pinna reflex of the cat.

As to the scratch reflex in the dog it was only when it was easily elicitable that it could be evoked by electrical stimula­tion as well as mechanical, and when it was not easily elicitable electrical stimuli failed altogether while mechanical stimuli still evoked it.

He describes the receptor as a mechanism “attuned to respond specially to a certain one or ones of the agencies that act as stimuli to the body,” and points to the fact that electrical stimuli are not of common occurrence in nature and no chance for adapta­tion to evolve in the organism receptors appropriate for such stimuli has been afforded. Such negative facts are at the least suggestive in considering the question of the mode of origin of receptors and end-organs, electrical stimuli being rare in nature.

The subject of the innerva­tion of the skin and its receptors has been treated here in a great measure by the aid of imagina­tion, with some evidence, and a good deal of reconstruc­tion has been attempted, but perhaps this will be pardoned by those who are prepared to carry out a corresponding process with such as Pithecanthropus, Eoanthropus and Saurian monsters from somewhat scanty osseous remains. Any biological theory of the origin of these receptors than the one here put forward is faced with some formidable difficulties, which are probably insurmountable.

CHAPTER XXIV.
THE BUILDING OF REFLEX ARCS.

Assuming the foregoing origin of the innerva­tion of the skin, I submit that between this rudimentary process and the building of sensori-motor arcs in the spinal cord and brain there is a field, almost unlimited, for initiative in the construc­tion of new forms of animal life. The former is nothing without the latter. To leave it without proceeding further is to leave it “in the air” as military writers say. The formation of Receptors, then, both in the skin field and in the higher sense-organs, leads of necessity to the formation, multiplica­tion and co-ordina­tion of reflex arcs. As in an imperfectly organised telephone service after many a repeated stimuli or “rings” the messages begin to reach their destinations, and as by practice the operators better and better learn their business, so the impulses passing through receptors and nerve-fibrils become organized into more or less efficient systems of arcs, and response is secured to them by some effector of gland or muscle. It is not true of man alone that practice makes perfect.

A certain feature of higher animals which distinguishes them from lower must be remembered, and that is that among them the individual becomes increasingly important. Speaking generally, the latter are born and die in large groups, and their lives resemble those of their group more closely than in the former. The struggle of the individual is vividly pictured by Professor Woods Jones in his descrip­tion of the baby of the perfected arboreal animals. He shows how they and the roaming Ungulates and Pelagic Cetacea cannot indulge in large families, and that it is only those forms which have a safe retreat for their young which can avoid reduction of the size of their families, and how the higher apes still more resemble in these respects mankind, as we know it. For the proper study of the “synthesis of the individual” organism this essential fact must be kept in mind.

Some Illustrations.

It will be expected of course that for the claim here advanced on behalf of the predominant influence of the nervous system in the initiative of the evolutionary process some experimental or other evidence should be produced. Before entering upon this, I think some analogous facts from the story of man, in accordance with the principle laid down in the first chapter should be stated, so as to illustrate the line of thought. These will be in the nature of analogies, and whether or not the accepted accounts of the chosen examples agree precisely with the last word of the critics is immaterial, for if not they will equally well serve the purpose of illustra­tion.

Abraham.

When from his Mesopotamian home an opulent and successful farmer decided for reasons sufficient to himself that he would leave his present prosperity for a promised land, and went out not knowing whither he went, it is manifest that the construc­tion and organiza­tion of Abraham’s cerebral cortex was the motive power which led to this step so fraught with change to himself, his descendants, and the world. By his choice he showed the inherited structure of his brain, its nature, and perhaps its nurture, to be different from those of his family and tribe. Implicit in this venture was the introduc­tion of a new group of people into a new environment, and their reaction to it through many generations is written before our eyes to-day in indelible characters. It was neither stature, muscular development, colour of hair, skin or eyes, properties of digestive or circulatory organs, keenness of sight, hearing, taste, smell, or touch which led to this result even though without a high degree of efficiency of these he could never have “arrived” as he did.

Mohammed.

The conjunc­tion of environment with a certain organized complexity of grey matter was hardly ever more important to the world than that of Mohammed. The powerful frame, abundant black hair, wonderful dark eyes, and great imposing head may well have attracted the rich widow who “made his fortune” by marrying him, and they stood him in good stead in his later adventurous career. But nothing short of a unique arrangement of his reflex-arcs, chiefly in the associa­tion-areas of his brain, could have opened up to him the world of Asia and Europe.

Columbus.

Who can doubt that it was ultimately to the inherited structure of the convolutions of his brain that Columbus owed his great achievement in opening up a New World; or that to the reactionary and intense “character” of Philip’s brain the persecutions in the Netherlands were due; and on the other hand that to the brain of William of Orange with its liberal and enlightened “character” the Seven Provinces that resisted Philip owed their freedom; the results in the two cases being the decay of Spain from that time forward, and the final success in the struggle for religious liberty. In such a view of historical facts it is not necessary either to follow Carlyle in his extreme claims for the influence of great men and heroes, nor to look upon the hero as an epiphenomenon. It is certain that eventually some other great man would have arisen to do what the great Genoese did, if he had not done it, and as it is claimed that Amerigo di Vespucci did, and it is certain that Philip was only the last of the Hapsburg sovereigns who determined the fall of Spain, and that Huss, Jerome, Wycliffe and Luther in their days initiated the struggle for religious liberty which Holland brought to success. But the facts referred to can hardly be disputed, and the men and their “characters” did certainly determine permanent changes in the world.

Napoleon.

Among individual men of modern times none strikes the imagina­tion as does Napoleon. Without ignoring the tremendous outburst of the soul of down-trodden France at the Revolu­tion, it cannot be denied that the “character” or grey matter of brain of the man of whom it is said “nothing where he had passed was as it had been before,” was the dominant and natural fact that changed the face of Europe. What physical quality had Napoleon, except those of his grey cells, which could have led him to such results on the environment into which he was cast?

Migrations.

Similar results in nations and tribes can easily be supplied from the great migrations of the past. The wider movements are but due to comparatively small aggregates of adventurous men, in other words to the aggrega­tion of many similar central nervous systems. The great Western and Southern adventures of the Scythian Tribes had many contributing causes on which the historian has much to say, and they were physically highly efficient for their new career, but, reduced to the simplest elements, it was neither their great stature, strong muscles, flaxen hair, nor blue eyes, but the cerebral constitu­tion of a comparatively small group of them which brought part of the nation to the promised land, and left another and large part in their homes beyond and along the Danube. The subsequent story of the latter may well be compared with the invaders of Gaul and Italy in connec­tion with initiative in evolution.

The successive invasion of Britain by Low German tribes in the fifth century, and the Scandinavian hordes of Swedes, Danes, Norwegians, Letts and Finns in the eighth and ninth teach the same lesson. The later condition and development of the Northmen in France, Italy, Spain, Sicily and Britain have only to be compared for a moment with that of their races who remained in Norway, Sweden and Denmark and their descendants, to bring clearly before one’s mind the profound influence exerted by the cerebral constitu­tion of the original Viking hosts on their career in their new environments, and, indeed, on the environments themselves; as in intermarriage with their conquered foes.

These examples have been chosen for the reason that one feature is common to them all, the introduc­tion of an individual or group into new environments by reason of the constitu­tion of their brains, irrespective of the contributing factors. If these be sound analogies they bear closely on the matter of initiative in the evolution of new forms of life. The men in question came to their task, in their day, with a certain equipment of brain derived from many ancestors and much nurture. Unconscious arbiters of their fate and that of multitudes who should follow them, they initiated a course of physical and cerebral evolution of which we can see much revealed before our eyes. The motive power of their conduct bears a relation to their physical forms that the engines of a motor-car do to its varied forms of body. The latter are modified indefinitely to suit convenience, comfort and grace, but fundamentally they exist and are energised by the former, just as structure is modified for the performance of function.

This fact is occasionally brought vividly to the mind of an observer when he first passes a Rolls-Royce car in all its glory and magnificence, and then a rough squalid kind of trolly in which the engine-parts of a similar future Rolls-Royce are out for trial. In principle it is not a long step from these illustrations to the diverse environments of animals in which their lot is cast, and their reaction to them as to behaviour and structural change.

Some Changes in Habits of Man.

There are two current views as to the present erect posture of man, one which traces it to the adoption of a new posture by a pronograde four-footed ancestor, and the other that man’s ancestors were “never typically pronograde with four supporting limbs,” but derived from an arboreal stock in which the forelimbs were mobile rather than stable. Whenever or wherever man became orthograde he opened up for himself and his descendants immense regions of structural and functional change and became increasingly dominant over his environment. Changes in muscles, joints, bones, bursæ, lungs, heart, and vessels occurred through his employing in new modes the muscles, joints, bones, bursæ, lungs, heart and vessels he already possessed, and the resemblance between these structures of man and the great apes has given to the latter the name of anthropoid, and this similarity of structures in the highest Primates has done much to support in the past that Simian origin of man which is at present questioned. The behaviour of the apes and early man were sufficiently alike to lead either to a parallel or genetic similarity. This point is, perhaps, irrelevant in considering the great field for initiative in the formation of new physical characters, and chief among these new reflex-arcs which have built up the marvellous organ of man’s glory and greatness; but no one can dispute the elementary fact that the ancestor of man who adopted terrestrial bipedal locomo­tion and became orthograde, owed it to his growing brain and the higher integra­tion of his organs for that function. But besides the new posture he had adopted he learned to talk articulately, to make tools, and to use stereoscopic vision. None of these could have been started on the upward way without a long process of trial and error in the course of his total experience and practice of his powers. The results that followed from these three properties of his are inconceivably great, and it is unnecessary to enlarge on such a theme or to add to the number of examples.

Leaving, then, the immediate ancestor to work out his own destiny in his new terrestrial home, we must as before proceed backward in the history of animal life in the line of Primate ancestry.

Primate Ancestry.

It is generally agreed to trace the Primates back to an active pioneer animal form which took to the trees, and which arose out of the widely-spread Insectivores. This deriva­tion will probably satisfy any reasonable genealogist. But, if we may use a parallel in human families, this active animal was as different from its congeners as Napoleon was from his four brothers who played a part in European history, and it is not necessary to say more as to the significance of this fact than that the relative importance of “chassis” and “body” is again a useful analogy. But we need to ask what those congeners did if we are to succeed in understanding the Napoleon-like course of him who became our Primate ancestor. From the original widely-spread and plastic raw material of the Insectivores allied forms took different lines, and their stories are written at great length in one small and the three other great orders of Bats, Carnivores, Ungulates, and Rodents. As it has been pointed out, Carnivores took to attacking larger prey, including their less fortunate relatives, and stepped into the arena as carnivorous animals; the Ungulates-to-be became herbivorous and developed into two great groups of hoofed animals, relying mainly on flight for safety; Rodents took to burrows for defence, ceased to trouble much about attack, and became gnawing animals; Bats adopted an aerial life—a poor form of it indeed like that of the aeroplane—and acquired a degraded fore-limb. Before leaving these great orders of animals, whom I do not desire to compare unfavourably with poor Louis, Jerome, Joseph or Lucien Bonaparte, it is convenient here to refer to a fact which comes to light immediately one looks into such a piece of classifica­tion as this of the orders arising out of the loins of the early Insectivores, and that is the functional concep­tion underlying it. Doubtless pure functional “characters” could never supply a whole system of classifica­tion in the light of the modern doctrine of descent with modifica­tion, and of zoological affinities. This is shown in a change from division of six orders of Birds-Running, Swimming, Wading, Climbing, Predatory and Perching Birds, to that of a few old-fashioned Ratite Birds, and all the rest, one which seems the best that can be offered at present.

Insects, Mollusca, Birds.

The grouping of animals by structural characters, and by affinities which are assumed, though based on almost undeniable evidence, whether into species, families, classes, phyla or sub-phyla, has its apotheosis in Mollusca and Insects. As to the second of these immense groups it has always seemed strange that their colourings and structural characters should have received such intensive study from Weismann to the exclusion of Mollusca, when he set out to prove his stupendous negative, and still more that of Vertebrates, among which his chief difficulty and desired triumph would seem to have lain. Mollusca though invertebrate are held by many to be in the line of ancestry of the highest forms of life, and at any rate insects are not. They are most fruitful fields indeed in which Nature has been able to show what she could do by her stern selective powers, but, from the point of view of descent with modifica­tion, may be fairly compared to a review of an army in time of peace, or the Kriegspiel of a German military staff. He who concerns himself with the fundamental difficulties of the problems at issue in evolution must make his notes of what experts tell him of such groups as those of Insects, Mollusca and Birds, and pass on to the higher forms in which on the one hand function becomes the predominant partner, and on the other individual experience becomes more and more important. He feels indeed at liberty to wish the entomologist and ornithologist all success, and to leave him at peace, in his siding, to pursue his delightful and interminable studies far from the dust and din of controversy.

Insectivores.

The critical territory of vertebrate, and still more of Mammalian forms, in which the genealogist pictures the five main groups of Insectivores, looking about them, if one may so speak, in the world around and pondering which of many paths they shall pursue, resembles certain centres that may be seen in towns where three, four, five, or seven different roads are open to the traveller, each with its incalculable effects on his ultimate career. If one may change here the metaphor it may be said that the Insectivores are the watershed of the Five Rivers of higher life. However much the wayfaring insect-feeders have diverged from this broad centre in structure, and however much the laws of genetics have widened this divergence, the facts of function stare one in the face when such descriptions of three of the four orders outside the Primate stock are pondered—Flesh-feeders, Herbivorous animals, Burrowers and Gnawers. These time-honoured names appealed strongly to older zoologists, and in them is implicit a large body of evidence for initiative in their evolution by pioneering work on the part of their ancestors. Though in these days Prototheria include Monotremes, One-vent animals, Metatheria, Marsupials or pouched animals, and Eutheria Insect-feeders, and though Mammals derive their indispensable name from the function by which they feed their young, the most severe of systematists cannot clear his mind from the old leaven of function in all these terms. They imply momentous potentialities prior to new structures, and the modern fails to ban entirely such functional names. I believe there is here no juggling with names and words on my part, but a stone in the founda­tion of the unambitious building which I am seeking to rear. It is ultimately connected with a directive power as well as the formation of sensori-motor arcs in the central nervous system.

Is it possible or probable that the factors which led some group to the water alone, some to a life in water and on land at different parts of their lives, some to a crawling life on land and partly in water, some to the air and trees, some to nocturnal, some to hybernating, some to burrowing life, some to a diet of flesh, some to one of plants, some to the trees alone, some to the trees and land, some to the land by night and trees by day, and some for ever and wholly to the land—is it probable that any process of selection of suited structures with countless ages of trial and error, could have determined these changes of habit and habitat? At least one may claim that the balance of probabilities is heavily against that view, and that the forging of reflex-arcs, with all it means to the career of an individual, affords a more intelligible hypothesis, and that this is strongly supported by modern discoveries and doctrines arising from the work of physiologists, as will appear later.

The Place of the Nervous System in Evolution.

The constitu­tion of the nervous system is conditioned by conduc­tion, its fundamental and primary function. Its processes consist in the transmission of impulses from receptive fields to effective reactions through devious paths in a region which, even to-day, is a jungle, with many further secrets for physiology to reveal. From this point of view the nervous system may be looked at as a clearing-house and storehouse of impulses on their way in, on their way through, and on their way out. If so, the making of new reflex-arcs is a process which has gone on simultaneously with the formation of receptors in the skin, the higher sense-organs and such deep structures as muscles, and that of effectors of infinite variety—and these are called conveniently adaptations. When we hear from Professor Sherrington that the afferent fibres with their private paths which enter the spinal cord outnumber three times those which leave it, and that those of the cranial nerves should be added, so that the afferent fibres may be reckoned as five times more numerous than the efferent, we get a vivid idea of the fundamental importance of the formation and compounding of reflex-arcs into systems. Without that the most sensitive receptors and the widest range of structures and organs, small and great, would be as nothing and things of naught.

A neurone is the anatomical, as the reflex-arc is the functional unit of a central nervous system. Just as it is profitless to consider apart the engines and body of a motor car, as working machine, so is it to picture neurones and reflex-arcs separately in the living nervous system except for the purpose of an ideal construc­tion. In common with the organs and structures of higher animals they have to pass, as historical structures, through the stages of initia­tion, repeti­tion of rudimentary function, and selection by trial and error, till the “canalizing force of habit” issues in rudimentary and increasingly efficient effectors. It is in this final stage where the triumphs of selection have been won, and where their undeniable value and interest has led some exponents of the distributional laws of genetics to disregard, or accept as data, the early and formative stages. Theirs is a mental state which resembles that of Darwin, who, for once in a moment of haste, declared the question of the origin of life to be rubbish.

In the foregoing considera­tion of the formation of receptors of the skin it was assumed that certain common stimuli of the environment hammer out for themselves paths in the nerve-fibrils of the skin and by ceaseless repeti­tion lay down not only the receptor, which may be called the terminus a quo, but also the afferent fibres which ultimately find their way into the grey matter of the cord and brain. That this is the initial stage of the construc­tion of the higher nervous system can hardly be denied. But it carries the problem of the synthesis of the organism but a little way unless it be coincident with the construc­tion of new reflex-arcs and their co-ordina­tion into systems. Till this stage be reached in a rudimentary form the most cunning and exact adaptations and structures, or, as they may be broadly called effectors, will not advance the efficiency of the organism in the smallest degree. If the receptor be the terminus a quo the effector is the terminus ad quem. This is so obvious that it may be waved aside as a truism not worth the notice of a zoologist concerned with the major problems of biology. It may seem to challenge in a highly speculative region and manner the labours of the biometrician and Mendelian, but, if fairly met it no more encroaches on their territory than do the labours of the engineers who invented the first and crudest chassis of a motor car upon the elaborate and brilliant ingenuity, taste and skill of the coachbuilders who turn out the “body” of a sumptuous Rolls-Royce of 1920. But the latter would never have “arrived” if the former had not made his slow and arduous trials and errors and final success. So here, as in many other subjects, a truism has its use. If the biometrician and Mendelian will only abstain from erecting notice-boards to proclaim “No thoroughfare here,” we shall not be put down as trespassers or poachers on their ground and may range at large in certain fields of specula­tion.

Some Neural Phenomena.

Among numerous phenomena of nervous reactions discovered by the research of physiologists certain have a close bearing on the formation of receptors, afferent fibres and reflex-arcs, especially those of Delay, Summation, Fatigue, Block or Resistance, Localiza­tion, Facilita­tion and Inhibi­tion.

Facilitation.

But of all these important reactions in nervous tissues none bears so closely on the problem of the formation of reflex-arcs as that of Facilita­tion. This is equivalent to the Law of Neural Habit of the physiological psychologist, and is bound up with the highly important Law of Forward Direction, which Professor Starling says might as well be spoken of as the Irreciprocal conduc­tion of nerve-arcs. The Law of Forward Direction of sensori-motor arcs is too well known to need here any descrip­tion. But when this law is taken into account the phenomenon of Facilita­tion is seen to throw a strong light upon the earliest and rudimentary formation of specialized nerve-fibres, reflex-arcs and Final Common Paths leading to the effector glands or muscles. Facilita­tion is described shortly by Professor Starling as follows. If the passage of a nervous impulse across a synapse or series of synapses in the central nervous system be too often repeated, fatigue is produced, and there is an increase of the block at each synapse. If, however the stimulus be not excessive and the impulse not too frequently evoked, the effect of a passage of an impulse once is to diminish the resistance, so that a second applica­tion of the stimulus provokes the reaction more easily, and he adds that the result of summation of stimuli is in fact in the direction of removal of block. When an impulse has passed once through a certain set of neurones to the exclusion of others it will tend, other things being equal, to take the same course on a future occasion, and each time it traverses this path the resistance in the path will be smaller. Education then is the laying down of nerve-channels in the central nervous system, while still plastic, by this process of Facilita­tion along fit paths, combined with inhibi­tion (by pain) in the other unfit paths. He makes the important statement that Facilita­tion is of great interest in connec­tion with the development of “long paths” in the central nervous system and, more especially with the acquirement of new reactions by the higher animals. (Italics not in the original).

Raw Materials of the Central Nervous System.

The raw materials of higher central nervous systems are furnished even in lowly Vertebrates by the neurones and their processes, and the pathways into the grey matter by the “canalizing force of habit” in the receptors and afferent fibres. Facilita­tion, discovered in higher Vertebrates, such as dogs and cats, throws backwards a light on the earliest struggles towards success and integra­tion among phyla, sub-phyla and smaller groups, and here again the well-known may lead to the less-known. We may then frame a legitimate hypothesis, or at least an ideal construc­tion of trials and errors and success, if those of lower levels were ever to be introduced to the career of progress and achievement. But to make good this claim it is necessary that it be based on the important doctrine taught by Hughlings Jackson of the three (or more) levels of sensori-motor arcs—those of the spinal or lowest, of the sensory or intermediate, and those of the third or highest level, in which the associa­tion-areas of the Primate brain are at once the means and the title to his primacy, or headship of the sentient world. The light of this doctrine guides the mind backwards to the frog-stage of animal evolution with its highly organized congenital system of arcs of the spinal level, so efficient for its life that, even when the brain is removed, the frog can execute under certain stimuli a purposeful complicated movement such as that of trying to wipe away with its foot an irritant drop of acid applied to its head or back; or, still more, if touched lightly between the scapulæ, will “lower its head at the first touch, and again more so at a second, and at a third will, besides lowering the head, draw the front half of its trunk slightly backwards; at a fourth the same movement with stronger retrac­tion; at a fifth give an ineffectual sweep with its hind or fore-foot; at a sixth a stronger sweep; at a seventh a feeble jump; at an eighth a free jump, and so on.” Probably such an animal as the frog has all its reflexes congenitally organized, whereas a dog, reaching the sensory level, has added countless reflex-arcs to those inherited from its early ancestors of the Insectivores which had long emerged from the spinal level, retaining its old, perfecting its new inheritance, and eliminating the unfit. Perhaps a faint picture of this long process may be afforded by watching an experienced mountain guide ascending an ice-slope with the aid of ice-axe, hand and foot.

Integration of Raw Materials.

Every group of animals in the higher ranks has its own entailed property of innate reflexes, for example, the reflexes which subserve the reflex functions of the cord: those of locomo­tion, muscular and vascular tone, micturi­tion, defæca­tion, impregna­tion and parturi­tion. These exist in an animal of the spinal level whether or not it remains purely aquatic, partly aquatic, partly terrestrial, arboreal or terrestrial. As the progressive groups ascend the ladder of life they add to this inalienable heritage, gained we need not here ask how, fresh reflex-arcs by response to new initial stimuli, forging them by the incident of use. So, the original acquirements in the past levels serve as starting points for raising the degree of their nervous integra­tion with growing control over their environments. The long story from the simple central nervous system of a fish, with a few or no associa­tion-areas, to that of man with his extensive frontal, parietal, parieto-occipital associa­tion-areas, could never be deciphered, even with the light of the laws of genetics turned on full, without a protracted process of construc­tion of fresh arcs. A common illustra­tion of such a series of changes and results may be seen in the building of a house. Bricks, founda­tion-stones, walls and a roof may serve some of the elementary requirements of a house and much less than these were of use to early man for his shelter. Without them we cannot call any structure a modern house; but also without floors, staircases, windows, chimneys, division into rooms, some degree of decora­tion by paint or paper, and a supply of water, we should refuse in these days the name of house to that rough structure, apart from beauty of design, decora­tion, within and without, and some addition of modern appliances of comfort and convenience. In the history of house-building the stages of supply of raw materials, adapta­tion to needs guided by selection, initia­tion, trial and error have their counterpart in the construc­tion of higher animals.

Evidence.

It will be asked what evidence there is for the view here put forward that such is the order and method of the construc­tion of the central nervous system. There are two classes of evidence. The first direct, and the second indirect and resting on inference. The well-known leads to the less-known and inferred. Direct evidence of the founda­tion of new reflex-arcs and their organiza­tion is of course small. The conditions, such as the duration of human life, preclude any extensive formation under experiment of new reflex-arcs, but enough is known to enable one to follow the backward way with some confidence. As to the inheritance of these, the evidence rests on opinion and tremendous probability, but as the only problem with which I am concerned here is that of initiative I think it better to leave the matter of transmission to a dispassionate considera­tion of the probability of its occurrence.

Direct Evidence.

The prolonged researches of over twelve years of Professor Pawlow and his colleagues on dogs afford a body of evidence as to the possibility of producing new reflexes in the life of an individual which have never been questioned. In 1913 at Groningen, before the International Congress of Physiologists, he gave a brief account of this work. His previous work on the digestive glands carried on by delicate operations in which the œsophagus was diverted from the stomach and made to open externally, and in which a portion of the stomach was diverted from the rest and a new “small stomach” was formed, gave him the opportunity of immensely important insight into the factors governing the work of the various glands of the stomach. The work of others showed similar results in the pancreas. I only refer to these because they lead up to the special artificial results with new reflexes which he described in 1913. He states that the nervous system besides the primitive function of reproducing innate reflexes, possesses another prime function-namely the formation of new reflexes; and that the living thing is enabled to respond, by definite and suitable activities to agencies to which it was formerly indifferent. His experiments on the formation of “conditional reflexes,” as he calls them rather than “acquired” as opposed to “innate,” are grouped around the feeding of the animal and mainly deal with the salivary glands, because they are in direct connec­tion with the external world and their reactions are simply and easily observed. An indifferent stimulus is chosen for the reflexes which it is desired to build up, and this is applied at the same time as food or acid is introduced in the mouth. After a few sittings it is found that this indifferent stimulus alone is now capable of calling forth a secretion of saliva. “The conditional reflex has been formed; the formerly indifferent stimulus has now found a path to the requisite part of the central nervous system. The reflex-arc has now a different afferent neurone.” He gives a good example of this in the result of the applica­tion of painful stimuli by a strong electrical current to the skin, systematically accompanying each feeding of the animal. He finds that the strongest electrical stimuli applied to the skin give rise merely to the “feeding reaction,” that is, the secretion of saliva, and no indications of any fright or pain appear. “The skin of a dog can be subjected to cutting, pinching or burning, and the only result we shall obtain will be the manifesta­tion of what, judging from our own experience, we should call the symptoms of the keenest appetite; the animal follows the experimenter about, licks himself, and saliva flows in abundance.” This, it must be remembered, occurs in the absence of the offer or sight of food, at the time in question. He adds: “In this way we have been able to divert the impulses from one path to another according to the conditions, and we cannot avoid the conclusion that the diversion of an impulse from one path to another represents one of the most important functions of the highest parts of the central nervous system.” The presence of certain special conditions, he points out, causes the indifferent stimulus, which would otherwise be dispersed in the higher centres, to be directed to a particular focus, and eventually to lay down for itself a path to that part. A very interesting detail of such a building of a new reflex is that “the stimuli from which the new reflex is to be worked out shall be rigidly isolated.” Therefore to avoid any interference with the certainty of the experiment, such matters as a personal bodily odour or kind of movement, or even such a slight fact as a change in the mode of breathing familiar to the dog on the part of the experimenter, has in the latest experiments been removed by the applica­tion of the stimuli by mechanical devices worked from another room, with results similar to the earlier ones. Conditional reflexes can also be obtained from stimuli arising from the locomotor apparatus, as the joints, eliminating the stimuli arising from the skin. Also certain parts of the frontal lobes were extirpated and “when one part is extirpated the reflex is obtained from the flexion of the joint, but not from the skin; if a different part be removed we can get the skin-reflex, but not the reflex from the joint.” He extirpated in one case the greater portion of the posterior part of the brain and the dog lived for several years after this in complete health. It was found easy to obtain a conditional reflex for various intensities of illumina­tion, also for sound, and even a fine differentia­tion of tones. In another dog the anterior half of the brain was removed and all the reflexes before worked out in this animal disappeared, and yet in this helpless condition of the dog he could train it to give that response of the salivary glands which he called the “water-reflex,” in which first of all an irritating acid was introduced into the mouth and the subsequent administra­tion of water provoked an abundant secretion of saliva which does not occur when water is poured into the mouth of a normal dog. This was confirmed in another example in which alone the centre for smell had been spared, and yet it was possible in it to train the smell-reflexes also. I add one striking sentence from Pawlow’s address which, though an opinion, must be received with the respect it deserves from such a source. “It is perhaps not rash to think that some of the newly-formed conditional reflexes can be transmitted hereditarily and become unconditional thereby.”