Initiative in Evolution

Indirect Evidence.

From these limited but cogent pieces of evidence I turn to the larger but confirmatory lines of indirect evidence and inference, of which such works as those of Professors Sherrington, Bayliss, and Starling, the notable address of Professor Macdonald at Portsmouth in 1911, as well as the recent work of Professor Woods Jones on Arboreal Man, are full. Indeed if the construc­tion of new reflexes and reflex-arcs in organic evolution “forged by an incident of use” as Professor Macdonald puts it, were expunged from these works, their treatment of the physiology of the central nervous system of higher animals would be emasculated, to say the least of it. And yet not one of these eminent men is writing ad hoc, or for the confusion of Weismann and his followers. At this point it may perhaps gain for the remaining pages a little more considera­tion from opponents if I give a few quotations from these writers in support of the foregoing statement—perhaps the breeze of authority may then carry my little bark a little further on its perilous voyage. Professor Sherrington remarks on the first page of his well known work, in reference to the cell-theory, “with the progress of natural knowledge, biology has passed beyond the confines of the study of merely visible form, and is turning more and more to the subtle and deeper sciences that are branches of energetics. The cell-theory and the doctrine of evolution find their scope more and more, therefore, in the problems of function, and have become more and more identified with the aim and incorporated among the methods of physiology.” Again, “Mere experience can apart from reason mould nervous reactions in so far as they are plastic. The ‘bahnung’ (or facilita­tion) of a reflex exhibits this in germ.” He uses more than once the pregnant phrase, “The canalizing force of habit”; again, “Progress of knowledge in regard to the nervous system has been indissolubly linked with the determina­tion of function in it.” Speaking of the receptive-field he says of the central nervous system, “To analyse its action we turn to the receptor organs, for to them is traceable the initia­tion of the reactions of the centres”; of the extero-ceptive field he says, “facing outwards on the general environment it feels and has felt for countless ages the full stream of the varied agencies for ever pouring upon it from the external world,” page 20, and “each animal has experience only of those qualities of the environment which as stimuli excite its receptors, it analyses its environment in terms of them exclusively. The integra­tion of the animal associated with these leading segments can be briefly with partial justice expressed by saying that the rest of the animal, so far as its motor machinery goes, is but the servant, of them. Volitional movements can certainly become involuntary, and conversely, involuntary movements can sometimes be brought under the subjec­tion of the will. From this subjec­tion it is but a short step to the acquisi­tion of co-ordinations which express themselves as movements newly acquired by the individual,” and, “The integrating power of the nervous system has, in fact, in the higher animal more than in the lower, constructed from a mere collec­tion of organs and segments a functional unity, an individual of more perfected solidarity,” also “a single momentary shock produces in the nervous arc a facilitating influence on a subsequent stimulus applied even 1400σ later.” I will give but one more statement from this work which seems to tell against my humble position of initiative in evolution. Professor Sherrington says at the end of his book, speaking of the adjustments of nervous reactions in the lifetime of the individual: “These adjustments though not transmitted to the offspring yet in higher animals form the most potent internal condition for enabling the species to maintain and increase in sum its dominance over the environment in which it is immersed.” A little care in reading the foregoing chapters will show that this in no way contradicts the views expressed.

Facilitation.

From Professor Starling’s Principles of Human Physiology I may again quote part of his account of Facilita­tion or “Bahnung.” “When an impulse has passed 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 is the laying down of nerve-channels in the central nervous system, while still plastic, by the process of ‘Bahnung’ along fit paths combined with inhibi­tion (by pain) in the other unfit paths. Memory itself has the process of facilita­tion for its neural basis,” again, “stimula­tion of one anterior root produces no definite movement of a group of muscles, but partial contrac­tion of a number of muscles which do not normally contract simultaneously. Thus, stimula­tion of a sensory nerve may provoke either flexion or extension of a limb, not both simultaneously. Stimula­tion of the motor roots will cause simultaneous contrac­tion of both flexor and extensor muscles. It is this subordina­tion of morphological to physiological arrangements in the limbs which has necessitated the founda­tion of limb-plexuses.” (Italics not in the original). Professor Graham Kerr in his work on Embryology before mentioned says: “In early stages of Evolution, whether phylogenetic or ontogenetic, we may take it that vital impulses flitted hither and thither in an indefinite manner within the living substance and that one of the features of progressive evolution has been the gradual more and more precise defini­tion of the pathways of particular types of impulse, as well as the transmitting and receiving centres between which they pass. We may then regard the appearance of neuro-fibrils within the protoplasmic rudiment of the nerve-trunk as the coming into view of tracks, along which, owing to their high conductivity, nerve-impulses are repeatedly passing. It may be that as each successive passer-by causes a jungle-pathway to become more clearly defined so each passing impulse makes the way easier for its successors and makes it less likely for them to stray into the surrounding substance” (p. 112).

Professor Macdonald, in the Portsmouth address referred to, speaking of the states of the cells under excita­tion, rest, and inhibi­tion, says “excita­tion is associated with an increase in pressure of certain particles within the cells; in rest these particles are in their normal quantity and have their normal number. During inhibi­tion they are decreased in number or have a retarded motion. Thus it happens that the excited cell tends to grow in size, on the other hand the inhibited cell tends to diminish, and the resting cell to remain unaltered in the nervous system. Structure is everywhere the outcome of function.” Speaking of the relationship of parts within the nervous system, “In so far as it is fixed, it is a sign of the orderly action of circumstance upon the structures of the body, and the result rather than the cause of the monotony of existence. I hold it as probable that all the individual structures of the nervous system, and so in the brain, have just so much difference from one another in size and shape and in function as is the outcome of that measure of physical experience to which each one of them has been subjected; and that the physiological function of each one of them is of the simplest kind. The magnificent utility of the whole system, where the individual units have such simplicity, is due to the physically developed peculiarities of their arrangement in relation to one another, and to the receptive surfaces and motor-organs of the body.” As to the lens-system of the eyeball he remarks, “Surely there is no escape from the statement that either external agency cognisant of light, or light itself has formed and developed to such a state of perfec­tion this purely optical mechanism, and that natural selection can have done no more than assist in this process.” He applies the same conclusion to the formation of the sound-conducting and resonant portion of the ear as well as the semi-circular canals and to the cerebellum. These statements are not strictly associated with this chapter but bear by analogy very strongly on the matter at issue. Indeed the whole of this address might be utilised by a junior counsel for Lamarck if he rested alone on the authority of a leading physiologist. The same may be said of the anatomist whose Arboreal Man has attracted so much attention. Speaking of the arboreal habit in the phylogenetic history of mammals he asks the question, “How did this factor enable that particular stock to acquire supremacy?” and says that it will be answered as far as it is possible, by the study of the influence of the arboreal habit upon the animal body; which may be put in another way as the produc­tion of reflex-arcs suited thereto (p. 3.) Of the muscle groups of fore and hind limbs he says, “With a simple arrangement of anatomical parts a slight shifting of muscular origins has turned a perfectly mobile second segment into a supporting segment constructed upon very simple lines: that these changes are those produced by the demands of support from the hind-limbs in tree-climbing seems obvious” (p. 6); of the position of uprightness upon a flexed thigh of an arboreal man, “It is tree-climbing which makes this posture a possibility” (p. 63). “But it is not to be doubted that the underlying principle is clear enough, that the arboreal habit develops the specialised and opposable thumb and big toe” (p. 71). “Even before the power of grasp is developed, we may imagine the dawn stages of educational advances initiated by hand-touch” (p. 159). “Tactile impressions gained through the hand are therefore perpetually streaming into the brain of an arboreal animal and new avenues of learning about its surroundings are being opened up as additions to the olfactory and snout-tactile routes” (p. 160). He asks also the pertinent question, and says at least a partial answer to it can be given, “Did the cerebral advance create the physical adaptations, or did the physical adaptations make possible a cerebral advance?” (p. 196). Two more statements from this chapter show what the answer to this question from the anatomist would be—“and again in the evolutionary story we are forced back to consider a combina­tion of seemingly trivial, and apparently chance associations: in this case the dawning possibilities of neo-pallial developments combined with the physical adaptations due directly to environmental influences” (p. 198). I have ventured to underline this passage.

I regret the necessary length of these quotations but, on account of them, can the better be suffered to finish this study, when I briefly consider certain well-known nervous reactions in the cat and dog as to their probable origin. It would be a highly interesting thing to hear an exposi­tion by an expert of all the reflexes and reflex-arcs of such a system as those which in a cat, dog, ape, or man are concerned with the passage of a morsel of food from the mouth through all its chequered and varied career till it undergoes metabolism and excretion, but I could not do it if I would, and would not here if I could, because of their fundamental fixed and innate character, and I think it simpler and safer to refer to such minor reflex-arcs as those which govern the scratch-reflex in a dog, the pinna reflexes in a cat, and a few smaller ones, on the principle of ex uno disce omnes. Such minor nerve-mechanisms as these in a pair of well-known domesticated animals will suffice for evidence on behalf of initiative in evolution.

The Scratch Reflex.

The scratch-reflex in the dog, which like the tendon-reflex in man was in my youth a subject for schoolboy tricks, has received a vast amount of attention and research from physiologists to whom it has brought valuable fruit. It is a familiar phenomenon in a familiar friend of man. There is a saddle-shaped area on the back of the dog over which it was found empirically that even a light stimulus when applied rhythmically, produces the “scalptor-reflex” or a reflex rhythmical action of the flexor muscles of the leg on the same side, calculated to remove the irritating causes of the stimulus. This includes a series of receptors in the skin leading to a spinal segment in the region of the shoulder, a long neurone in the cord, then a motor neurone, the axon from which activates the flexor muscles of the leg and produces scratching. It is described as an efferent arc from receptor to the motor neurone, from which the Final Common Path supplies the motor apparatus or effector. Professor Sherrington says that in this reflex a single stimulus which is far below threshold intensity is found on its fortieth repeti­tion and nearly four seconds after its first applica­tion to become effective and provoke the reflex and that its frequency is about 4.5 per second. The reflex movement remains rhythmic and clonic under the strongest as under weaker stimula­tion. When it is easily elicitable the scratch-reflex can be evoked by various forms of electrical as well as mechanical stimula­tion, but, when not easily elicitable, electrical stimula­tion fails whereas rubbing or other mechanical forms of stimuli still evoke it, though less vigorously than usual. This reflex can also be set aside by the “nociceptive arc from the homonymous foot” or, in other words, a nocuous stimulus to the leg of that side produces “interferences which amounts to inhibi­tion.” Empirically it is easy to notice also that if the “scalptor-reflex” can be elicited on both sides of the body, the dog when standing will momentarily lose the power in the hind legs.

Note.—The rhythm of this reflex act is so special even to the layman that lately I had a singular confirma­tion of its stereotyped character, when lying awake at night and being puzzled by a curious rhythmical scratching sound coming from my next door neighbour’s back yard. It might have been taken by a wakeful person for some mechanical work on the part of a burglar, but after listening repeatedly to the apparently familiar sound I found that it came from the kennel of a fox terrier kept by my neighbour.

Purposes of Reflexes.

All reflexes being purposive this particular innate reflex is acknowledged to have for its purpose the grooming or cleaning of the skin over its hereditary territory. This introduces its connec­tion with initiative here propounded, and the justifica­tion for its introduc­tion is contained in Professor Sherrington’s statement that “In the analysis of the animal’s life as a machine in action there can be split off from its total behaviour fractional pieces which may be treated conveniently, though artificially, apart, and among these are the reflexes we have been attempting to decipher”—scratch-reflexes and others. There seems to be no reason for the existence and stereotyped character of this reflex except the need or rather the desire (if one may use a convenient but inaccurate term) on the part of the dog to remove an irritant which disturbs its comfort when at rest. Some “minor horrors,” probably fleas moving across the skin-receptive field of its shoulder and back, must be assumed to be the irritant in question. This touches the great question of the initiative of this remarkable reflex, which seems more fixed and powerful in the dog as we know him than that other reflex which leads him to turn tail and flee immediately he sees a boy stoop down as if to pick up a stone. I dare say a clever advocate on the opposite side might impress a jury by building up a case under which an adapta­tion to a protective need would be conceived as responsible for the rapid flight at the sight of the threatening attitude of the boy. Such a reconstruc­tion is not required, for it is perfectly clear that in the history of the domesticated dog the selection of such an adapted reflex could have no place. The survival-value of this reflex would be nil, for the number of dogs killed by a stone or maimed for life would be so negligible that the produc­tion of a specialised reflex for the purpose by selection or survival of the fittest would not arise. Obviously the danger would be intermittent and rare; and dead dogs tell no tales. On the other hand it would be highly unpleasant for dogs to be hit by stones and educability would lead them to avoid the stooping attitude associated with missiles.

We are told on high authority that not education but educability is transmissible, and yet this humble reflex appears in very young dogs that could hardly if ever have known the impact of a stone. Incidentally we are compelled to remember how in past battles of our youth the aim both of “ourselves and the enemy” was deplorably poor, and not from want of practice. This school-boy-stone reflex is either an example of educational effects transmitted or of a minute bit of the unpacking of an original complexity which it would require the brain of a de Quincey to work out. But if we suppose the initial stages of such a stimulus as the occasional impact of a stone in many generations to be slowly ingrained in the skin-receptors, reflex-arcs and receptors we do not need opium either for the acceptance of orthodox dogma or to aid us in the Mendelian alternative to a very simple ideal construc­tion.

This digression bears on the initiative of the more important scratch-reflex, and it is profitable to ask “are not both of these reflexes in dogs examples of Evolution of the Indifferent?” Is it possible to imagine that from its inception to its fully-formed state, with a specialised territory of skin-receptors accurately mapped out, with receptor neurones, reflex-arcs and adapted effectors, this scratch-reflex can have arisen through Germinal Selection or selective processes within the germ? At no stage can anything more than a contribu­tion to more or less comfort to the animal be held to result from its operation. It is strangely reminiscent of the proceedings of an elderly man after lunch on a hot day when he protects his head against house-flies with a handkerchief. I am aware that it is but one of a large number of reflexes produced for the purpose of grooming the trunk head or limbs of animals as low down in the scale as the house-fly or grasshopper, many of which were beautifully described a few years ago by Miss Frances Pitt in the National Review in an article dealing with small mammals, chiefly rodents. But I have availed myself here as elsewhere, of the liberty of doing what Professor Sherrington says we may do, and consider this scratch-reflex as split off from the rest of the animal’s behaviour for the purpose of analysis. He also says in discussing the subject of parasites moving across the receptive surface of the skin that the ulterior purpose may be the removal of what “would confuse its function as a receptive surface to more significant environmental stimuli.” This statement is hypothetical and the problem obscure; but at any rate we know this that the removal of the parasite must conduce to the greater comfort of the dog without any more recondite purpose. The one suggested by Professor Sherrington would in some possible but very vague manner be referable to selection, but, whether the sugges­tion be valid or not, it is almost impossible to suppose that a saddle-shaped area of the kind described could be under the guidance of selection. The law of Parcimony forbids. There is a close similarity between this saddle-shaped area in the dog and that on the cow’s trunk described in Chapter X. It is difficult to believe that from man downwards to grasshoppers relief from mild irritating causes such as this is not enjoyable to the particular animal, and yet indifferent altogether as to its survival in the struggles of life for food and mates. The “scalptor-reflex” only reaches the limits of the receptive field of the scratch-reflex and it is contrary to observed facts that parasites confine their depredations just to the region where the formidable scalptor-reflex can reach. The wicked flea knows better than that. The initiative of this reflex can well be pictured as taking place in domesticated dogs and their wild ancestors whose habitats in prehistoric times were probably infested with these irritants to such a degree that no modern mind can conceive, and the adequate stimuli, leading to receptors after ages of impact and consequent hammering out pathways through certain reflex-arcs until the required weapons of offence or effectors were organised into a defensive-offensive system—were there in profusion. But a great and fundamental principle of the evolutionary process such as Selection is not honoured by being dragged in, even for forensic purposes, to account for results which owe to the search for comfort their perfec­tion of organisa­tion. I have personally seen in some professional invalids of the softer sex nearly as perfect adaptations to their comfort which in no way contributed to their length of life. This may be put aside as irrelevant but it is at least suggestive.

I submit the statement as to the scratch-reflex in the dog that from beginning to end it is an indifferent mechanism and the probability is immense that its initial stages were governed alone by repeated stimuli from parasites which produced receptors, conducting fibres afferent neurones and efferent neurones, leading into the Final Common Path controlling the flexors of the hind limb. It would then come under the Law of Subjective or Hedonic Selection formulated by Professor Stout in the words: “Lines of action, if and so far as they are unsuccessful, tend to be discontinued or varied; and those which prove successful to be maintained. There is a constant tending to persist in those movements and motor attitudes which yield satisfactory experiences, and to renew them when similar conditions recur; on the other hand those movements and attitudes which yield unsatisfactory experiences tend to be discontinued at the time of their occurrence, and to be suppressed on subsequent similar occasions.”

In this connection a statement from Professor McDougall’s work may be advantageously quoted. He says that “It is characteristic of those (arcs) of the higher or third level that their organisa­tion, their interconnections, by means of which the simpler neural systems of great complexity, is congenitally determined in a very partial degree only, and is principally determined in each individual by the course of its experience. The arcs of the higher level thus constitute the physiological basis or condition of docility, the power of learning by experience.”88 (My italics)

Scratch Reflex of the Cat.

There is a notable difference between the scratch-reflex of the dog and that of the cat, especially as to the site of its receptive-field. That of the dog has been referred to, but it appears to be generally accepted that the cat has no such saddle-shaped or indeed other area of skin receptive-field on its back or flanks. I have repeatedly tried by various mechanical stimuli, applied both irregularly and rhythmically, to evoke a scratch-reflex in a cat, young or adult, on the surface corresponding to that of the dog, and have found no response. This has been tried both when the animal was awake and when asleep. But the receptive field of the cat’s scratch-reflex has received careful and elaborate attention, which is described in a paper by Professor Sherrington in the Journal of Physiology, Vol. LI. No. 6. By means of delicate stimuli, mechanical and electrical in a decerebrate cat, the receptive-field of the scratch-reflex has been accurately delineated in the pinna, and several other pure reflexes have been obtained. These are protective of the pinna; some, the retrac­tion and folding reflexes seem directed against irritant touches, e.g. the settling of fleas—or against exposure to injury in fighting; others, the cover and head-shake and scratch-reflexes against the ingress of foreign matter, such as dust, water, insects, into the meatus and ampulla. The threshold for their elicita­tion is extremely low, that is to say, they require very gentle stimuli to evoke them, while with the exception of the scratch-reflex they are elicited with difficulty and uncertainty by electrical stimuli (My italics) to which the animal has been subjected in the course of its total experience. He adds that the pinnal reflexes are readily obtained in the normal animal, and I may allude here to some small observations I made on a normal young cat during profound sleep, recorded in Nature, Vol. 106, Sept. 2, 1920. Light mechanical stimuli, applied during this state of deep sleep to the internal surface of the pinna, especially close to the meatus, produced first, twitching of the facial muscles on the same side; second, as this ceased the fore foot was moved irregularly towards the ear, and third, as this ceased a rhythmical scratching action of the hind foot took its place, the rate of which seemed to be exactly the same as that of the scratch-reflex in the dog evoked from stimula­tion of the flank and back. I had not then, unfortunately read more than an abstract of the above paper, but if the full account be followed it will be seen that the various “territories” belonging to all the former-reflexes are now known as well as the frontiers of a European Kingdom. All I was able to do with this unusual opportunity of a heavy sleep in a normal young cat was to verify more roughly Professor Sherrington’s observations and slightly to extend them in respect of a sleeping animal.

In the course of these observations on a young cat I examined the various regions of the back and flanks with mechanical stimuli of different degrees of strength. These were applied during sleep and I found that it was more often during a moderate than a light or deep sleep that the following results were shown—chiefly under the stronger stimuli the tail was raised sharply and swept in a circular way, and this would be repeated according as the stimulus was applied; but at the same time there was shown a strong, irregular twitching along the flank, extending forwards to a point near the level of the shoulder. This latter reflex would appear to be a reaction on the part of the panniculus carnosus. Both the reflex of the muscles of the tail and this of the flanks appear to be connected in their origin with movements of parasites in their respective territories.

In considering the scratch-reflex in the cat a subtle bit of adjustment is found. That coarse and simple scratching of its ear, which we see so often in the cat, must have often astonished us for its vigour and yet its bloodless character. This action is of course a purposeful one, for it goes on when the animal is awake. Here if anywhere this profoundly hedonistic animal shows that for it the laws of comfort are its laws of conduct. It is clear that there may be two processes or conditions involved in its bloodless violence. On the one hand the reflex retractile mechanism of the claws may be kept in abeyance by another reaction which is pre-potent; on the other, it is a fact that the hind foot in the cat is furnished with claws which are much blunter than those of the fore foot. As far as I have been able to examine cats of different ages I have found the claws of the hind foot more like the blunt claws of a dog than the familiar sharp claws of the Felidæ. So in the violent scratching referred to there may be a double reason associated in the process. As to the difference in the sharpness of the fore and hind claws it would appear to be remarkably like a transmitted bit of adapta­tion initiated and kept in being by use and habit in progression, for the hind foot in such animals as the cat has a larger share in this action than the fore foot. But here it is difficult as so often to assign to selection its possible share of the adjustment.

Certain minor but persistent reflexes may be briefly mentioned in support of this side of the evolutionary process. In the dog and cat, as we know them, the action of the muscles of the tail by which it is elevated during the act of defæca­tion is very suggestive of a reflex acquired by a very small degree of physical comfort and repeated in countless individuals, wild and domesticated. I have seen not only this but a few small scratches made by a cat before defæca­tion in a kitten as young as three weeks old. It is also mentioned in illustra­tion of a vestigial character that a horse will paw the ground with no immediate apparent object, the act being derived from ancestors which thus cleared away snow from the ground. This is claimed, doubtfully I think, as a vestige of a formerly useful habit but seems more probably to be one of these indifferent reflexes connected with comfort than with survival-value.

It will be observed that in this branch of the case for Lamarck v. Weismann the indirect evidence from inference far exceeds in amount that of direct experimental evidence, but from the nature of the problem under considera­tion this could not be otherwise.

If we may again look back in thought over the long series of animals, from man downwards, we shall picture those of the spinal level striving (with apologies for the use of an anthropomorphic word) to reach the sensory level and finding out the fact that few there be that enter therein. Again we see in vision the higher creatures of the sensory level reaching forwards to the strait paths of primate existence, and again finding the difficulty of self-advancement that their predecessors found. We see the elect few of these, by a happy combina­tion of nature and nurture, uprearing to glory and honour the primate stock with its culmina­tion in man. A long vista indeed and a vision, but assuredly no mere figment of the imagina­tion, as some of the slender facts and arguments here would seem to show. With Professor Bateson we personify Nature in the story, with her wonted coyness betraying the fact that though she is stern she has her tolerant moods; that she allows her children, even that “insurgent son” who calls himself Homo Sapiens, a genial liberty to frame new reflex-arcs which make for his enjoyment of life in indifferent fields, and that the great neural process of Facilita­tion is the leading factor in their constructions and probably also in more deeply-based systems of sensori-motor arcs.

SUMMARY.

Though it be true that dolus latet in generalibus, it is a more important truth that “without premature generalisations the true generalisa­tion would never be arrived at.”89

Therefore I conclude:—

INDEX.