§ 1. Living and Not-living. § 2. The Essential Characteristics of Living Organisms. § 3. Persistence of a Complex Specific Metabolism and of a Corresponding Specific Organisation. § 4. The Capacity of Growth, Reproduction, and Development. § 5. Effective Behaviour, Registration of Experience, and Variability.
§ 1. Living and Not-living.
IF we are to reach a coherent view of Nature, such as could be included in a philosophy, we must arrive at some discernment of the characteristics which mark off living organisms from their not-living surroundings. In the present state of science a definition of the organism cannot be more than tentative, but it must be continually attempted.
When we pass from watching a flowing stream or the wind-swept clouds, to look at the bees visiting the flowers, or the swallows building their nest, we feel that we are facing something newliving. What we see is not, indeed, in every respect new as compared with the inorganic, for gravity acts on animals just as on drops of rain, and living creatures never disobey, so far as we know, the ordinary laws of physics and chemistry which sum up the routine of our analytic experience of the not-living. On the whole, however, especially if we look at animals rather than plants, the differences impress us more than the resemblances, we feel rightly that we are in the presence of something new. Organisms show characteristics which mark them off from their non-living environment. What are these characteristics? What are the criteria of living organisms? What is essential in the admitted contrast between the living and the not-living?
§ 2. The Essential Characteristics of Living Organisms.
In the most general way what we see is plain enough. We see organisms acting on their environmentdisplacing it, changing it, eating it, and so on; and again we see that the environment acts upon the organismdisplacing it, changing it, stimulating it, oxidising part of it, and so on. So that living is a twofold relation between organisms and their environmenta twofold relation of action, and reaction, of thrust and parry, of doing and suffering. At one moment the organism is relatively the more active, at another the environment. Living is a continual adjustment between these two relations.
When we look at the facts a little more closely we see that all living creaturesplants as well as animalsare active towards two main results, their own self-maintenance and the continuance of their race. Organisms have in their living just two main businessescaring for themselves and caring for their offspring. But all this is living rather than life; we are only hiding the problem behind the word organism. What are the marks of a living creature?that is the question. What is the best answer we can give for the time being? Many answers have been given, but none has found wide acceptance, which doubtless means that biologists have not yet seen the insignia of organisms in their entirety, or in proper perspective.
One of the best statements is that of Roux, who recognises five elementary functions:
II. Self-preservation, including assimilation, growth, movement, feeding, etc.
V. Self-regulation in the exercise of all functions, including self-differentiation, self-adjustment, self-adaptation, and in many organisms distinctly recognisable psychical functions.
It is very interesting to notice how this hard-headed founder of what he calls developmental mechanics speaks deliberately of self-preservation, self-increase, self-differentiation, self-regulation, and so on.
The statement we propose differs a little from this and from others, being an attempt at a logical grouping of the fundamental characteristics.
§ 3. Persistence of a Complex Specific Metabolism and of a Corresponding Specific Organisation.
The image of the organism is the burning bush of old; it is all afire, yet it is not consumed. Nec tamen consumebatur. Or it is like the sunlit top of a fountain rising in the air; its component elements are restlessly changing on their way up or on their way down, yet the form remains approximately the same. The peculiarity is not that the organism is in continual flux, for chemical change is the rule of the world; the characteristic feature is, that the changes in the organism are so regulated and balanced that the integrity of the creature is retained. The great English physiologist, Sir Michael Foster, used to say that A living body is a vortex of chemical and molecular change; and the image of a vortex expresses the fundamental fact of persistence in spite of ceaseless change.
A vivid statement of this characteristic feature of life was given by Huxley in his Crayfish (1880, p. 84):The parallel between a whirlpool in a stream and a living being, which has often been drawn, is as just as it is striking. The whirlpool is permanent, but the particles of water which constitute it are incessantly changing. Those which enter it, on the one side, are whirled around and temporarily constitute a part of its individuality; and as they leave it on the other side, their places are made good by new comers.
Those who have seen the wonderful whirlpool, three miles below the Falls of Niagara, will not have forgotten the heaped-up wave which tumbles and tosses, a very embodiment of restless energy, where the swift stream hurrying from the Falls is compelled to make a sudden turn towards Lake Ontario. However changeful in the contour of its crest, this wave has been visible, approximately in the same place, and with the same general form, for centuries past. Seen from a mile off, it would appear to be a stationary hillock of water. Viewed closely, it is a typical expression of the conflicting impulses generated by a swift rush of material particles.
Now, with all our appliances, we cannot get within a good many miles, so to speak, of the crayfish. If we could, we should see that it was nothing but the constant form of a similar turmoil of material molecules which are constantly flowing into the animal on the one side, and streaming out on the other.
Without accepting the view that the organism is exhaustively described by calling it nothing but the constant form of a turmoil of material molecules, without forgetting that the organism-whirlpool acts on the stream, and gives rise to other whirlpools, we welcome the metaphor as vividly true within its limits. But the image is too general to be adequate; we must inquire into the changeful integrity of the organism more carefully. Three points are of outstanding importance: (a) that the changes in the organism are very complex, having essentially to do with protein substances in a colloid state; (b) that they are specific for each kind of creature, and (c) that they are correlated in such a way that they go on, and the specific structure likewise persists. Let us take each of these points in turn.
(a) Metabolism of Proteins.
According to some physiologists the only absolute difference between living organisms and inorganic bodies is, that proteins are universally present in the former and absent in the latter. Verworn writes: Since it is known that the nitrogenous proteids, with their allies, which in part are derived from the proteids and in part are necessary to their formation, are the sole organic compounds that are never wanting in living substance, that everywhere they constitute its chief mass and alone are sufficient for its formation, it can be said that all living organisms are characterised by the metabolism of proteids (1899, p. 136). These protein compounds, such as white of egg or the gluten of bread, are peculiarly intricate, with a large number of atoms or atom-groups in their molecules; they diffuse very slowly and do not readily pass through membranes; they occur in a colloid state, and although some, e.g., hæmoglobin, are crystallisable, they are not known in a crystalloid state in the living organism; they are relatively stable bodies, yet they are continually breaking down and being built up again within the body, partly under the direct influence of ferments or enzymes. The constructive, synthetic, upbuilding, winding-up processes are summed up in the term anabolism; the disruptive, analytic, down-breaking, running-down processes are summed up in the term katabolism, both sets of processes being included in the term metabolism, for which we have, unfortunately, no English equivalentlike the German word Stoffwechsel, change of stuff. But when Verworn says The life-process consists in the metabolism of proteids, he, like Huxley, is summing up too simply; it would be more correct to say that living always involves the metabolism of proteids or proteins.
(b) Specificity or Individuality of Metabolism.
A second feature is that each organism has its chemical individuality, and associated with this a specific structural collocation. There is a chemical specificity in the milk of nearly related mammals, and in the grape-juice of nearly related vines. A stain due to the blood of a rabbit can be readily distinguished from a stain due to the blood of a mana fact that has been used with effect in some modern murder trials. Nay more, the blood of a horse can be distinguished from that of an ass. The crystals of the red blood pigment of a dog differ from those of a wolf; indeed, those of a domestic dog differ from those of the wild or feral Australian dingo. The familiar fact that there are individuals who cannot eat particular kinds of food, such as eggs, or oysters, without more or less serious symptoms is another illustration of specificity which is actually individual. It looks as if a man were individual not merely as to his finger-prints, but as to his chemical molecules. Even the sexes differ in their metabolism, as is diagrammatically shown in one or two cases where the colour of the blood is actually different. We are here in contact again with what we have already alluded to as one of the remarkable differences between the organic and the inorganicIndividuality. We come back to what was said of old:All flesh is not the same flesh: but there is one kind of flesh of men, another flesh of beasts, another of fishes, and another of birds.
Prof. Charles Richet and other physiologists have of recent years devoted much attention to the phenomenon that dosing an animal with certain poisons may bring about, if the animal survives, a peculiar physiological condition, called anaphylactic, which make the creature hyper-sensitive to subsequent doses. An extract of sea-anemone's tentacles is very poisonous to dogs, but, when the dog recovers, a very minute second dose a month afterwards may be rapidly fatal. The phenomenon of anaphylaxis is extraordinarily subtle; thus a man to whom shrimp flesh is poisonous may be unaffected by lobster. He is violently poisoned if he eats a single shrimp, and yet he is able to enjoy a whole lobster; straining at a gnat, he swallows a camel with ease. The importance of this is that it points towards the conception of the chemical individuality of the living creature. There is a specific chemical constitution which is on the whole best for the species in question, which makes for stability. Those that survive the introduction of a poison, it may be the result of digesting a particular kind of food, do not necessarily mark the surviving type, for they may be killed by the anaphylactic violence following a second dose. So much the worse for the individual, but so much the better, possibly, for the species, which cannot safely admit of any compromise with poison. Thus, speaking of man, Richet says: Anaphylaxis appears to be an efficacious and energetic method of maintaining the chemical stability of our bodies by provoking an immediate and violent reactional response to the introduction of any substance which might change it.
(c) Persistence in Spite of Change.
In the ordinary chemical changes in the inorganic domain, as in the weathering of rocks, one substance changes into another. Iron becomes rust. So is it also in the living body, but there we encounter a new and characteristic featurecontinual restitution or recuperation. The reactions are not self-destructive. Repair counteracts waste ceaselessly. There is a continual balancing of accounts so that debts are more or less effectively avoided. Without metaphor, the specific organisation is continuously repaired so that the specific activity continues, and if organismsafter they once got griphad been content to remain relatively simple they need never have dieda natural death.
We regard this characteristic as fundamental,the capacity of retaining integrity in spite of ceaseless specific change,one may almost say through change. For the energy liberated in katabolism is used to promote compensating anabolism. The more it changes, the more it remains the same thing; the most intensely living animals have the most persistent integrity of form. In any case, an organism was not worthy of the name until it showed, for a time at least, not merely activity, but persistent activitya power of balancing accounts. Like a clock the organism is always running down and always needing to be wound up; but unlike a clock it can wind itself up, if it gets food and rest. In green plants, as every one knows, there is usually a quite unnecessary amount of winding upwith the interesting far-off result that animals, utilising already manufactured food, have time for agency, and that we have time for thinking about it all.
We are familiar with the self-preservative devices and reactions of higher animals and with the self-preservative way in which the various organs of the body work into each other's hands; and it is a remarkable fact that a specific activity in a nervous system may be restored after the destruction of the particular nerve-elements on which the activity previously depended. This vicarious functioning is all the more remarkable inasmuch as there is not in higher animals any regeneration or replacement of nerve-cells after birth. But deeper than all this is the correlation of chemical processes in the individual units, so that down-breaking leads to up-building, so that up-building makes further down-breaking possible, the pluses balance the minuses, and the creature goes on. The unicellular organism spends its substance and yet has it, through its fundamental capacity for self-renewal. If the living creature is a machine, it is a self-stoking, self-repairing machine, and it can take a rest betimes.
Several saving-clauses must be appended:
(1) The organism shows persistent functionality, but it is not known to offer any exception to the law of the conservation of energy. In living it expends energy, and suffers wear and tear; it cannot continue unless it captures more energy and is able to repair its structure. Fatigue and the dying of parts, such as leaves, not to speak of senescence and death itself, show that the fundamental capacity for self-maintenance is not perfect. But the broad fact is that the capacity has for a variable time a very considerable degree of perfection. The organism's chemical activities (and repair-processes) are so correlated that it remains for a considerable time a going concern. As we shall afterwards see, some investigators claim for the organism a unique power of retarding the universal tendency of energy to sink into unavailable form, in other words, of evading, in some measure, the second law of thermodynamics.
(2) If a piece of organism be ground up in a mortar and the expressed juice poured into a vessel, a process of metabolism is sometimes observable similar to that which occurs in the living body. Every one knows that pepsin may be bought at the chemist's, and used to digest a shred of beef in a test-tube. It is true that neither the ferment nor the proteid can as yet be synthesised artificially, but this may be only a question of time and ingenuity. We cannot dogmatise as to the limits of mimicking in a test-tube what occurs normally in an organism, and if the reaction be mimicked, then there is nothing characteristically vital about it, any more than there is about organic substances like sugar and indigo which used to be regarded as producible in organisms only. But the point is that in the living organism the process in question is a link in a concatenated series which makes for self-repair and continuance. The essential secret of living is in the correlation which secures persistence amid change.
(3) If the whole of a living organism, say a spinach plant, were to be minced up quickly, no change of chemical composition would necessarily occur for some little time, but what exhibition would there be of the alleged fundamental characteristic of self-repair? It may be answered that the mincing has destroyed the make-up of the organism, that the living units of the body are in most cases adapted for self-repair only in particular conditions, such as an environment of other cells, in the collocation which has been abolished by the mincing. But while the power of self-repair cannot operate except under certain conditions, it is an extraordinary fact that some creatures can be re-made even after mincing. If a sponge be minced up and forced through a cloth filter, little drops of the débris, placed in appropriate environment, will at once proceed to build themselves up into new sponges. The characteristic metabolism is retained, re-differentiation sets in, the tiny mass begins to feed and grow, the normal organisation is restored, the sponge is once more a going concern. The restoration of the sponge from a drop of débris is as different from the re-building of a crystal from a fragment, as the highly differentiated sponge from the very homogeneous crystal, or as the intensely metabolic living sponge from the self-contained, though certainly not inert, crystal.
(4) If living implies persistent metabolism, we must admit a saving-clause to the effect that the metabolism may sink at times to a minimum. Further investigation will make things clearer, but there is difficulty at present in regard to the familiar facts that dried seeds may retain their power of germinating for as long as a man lives, or that desiccated animals and germs of animals (as in the case of some thread-worms, rotifers, bear-animalcules, and small crustaceans) may remain in a state of so-called suspended animation for, it may be, a dozen years. Small Nematode worms have been, known to revive after being fourteen years dryalive rather than living. It has not been satisfactorily proved that mummy wheat germinates, but Becquerel got seedlings from seeds which had lain for eighty-seven years in a herbariuma hortus siccus indeed.
Becquerel took seeds of wheat, mustard, and lucerne, and perforated their air-tight seed coats; dried them in a vacuum at 40° C. for six months; sealed them up in an almost exhausted tube for a year; submitted them to the temperature of liquid air (190°) for three weeks, and of liquid hydrogen (250°) for three days; and then put them on moist cotton wool, where they germinated. We are forced by such experiments to realise that life is not an entity but a relation between organism and environment, but we must have more facts before we deal effectively with the difficulties which the facts raise. Does the process of living suffer complete interruption, and recommence when water soaks in, and oxygen after it, as Becquerel seems to think; or does the metabolism sink to a minimum, like the combustion of a sleeping fire? Very interesting, in this connection, is Professor Waller's observation that as long as a tissue is living, or an egg capable of development, or a seed able to germinate, there is a particular electrical reactionthe blaze reaction which disappears when living has irrecoverably ceased.
(5) The criterion of an organism to which we have given prominence is that of persistence, which is obviously relative. Some organisms can keep agoing for a hundred years, some for only a hundred days, and some for only a hundred hours. The question arises as to the limit. Is it possible that there were primeval organisms which lived for only a hundred seconds? If so, how would these hypothetical creatures differ from the pill of potassium which flares itself out, rushing about on the surface of the basin of water on which it has been thrown? The answer must be, that it is not the length of life that counts; the criterion is whether, alongside of disruptive processes associated with protein substances, there were also correlated constructive processes, making for repair and self-maintenance. Some Infusorians divide more than once every day, some Bacteria divide more than once every hour, and these may be near the limit of the duration of individual life at the one extreme. The Big Trees living for two thousand years may be near the limit in the other direction.
§ 4. The Capacity of Growth, Reproduction, and Development.
One can readily conceive of an organism which balanced its accounts from hour to hour, but never had much margin. There are such delicately-poised ephemeral organisms, which live, to use a homely expression, from hand to mouth. They are going concerns, but they are trading on a very restricted capital, and cannot survive a crisis. So we see at once that there is a commanding advantage in being able to store energy in potential form, and this is fundamentally characteristic of organismsespecially of plants. As regards the ratio between the income of energy and the work done, living organisms are far ahead of any engine, but there is also the power of accumulating energy which can be used later. Thus we are led to recognise the power of growth as one of the characteristics of organisms. A surplus of income over expenditure is the primal condition of organic growth. It has further to be noted that the growth of living creatures, as contrasted with that of crystals, is at the expense of materials different from those which compose the organism; it implies active assimilation, not passive accretion; and it is very definitely a regulated process. An organism does not grow like a snowball.
But growth leads on to multiplication. As Haeckel clearly indicated in his Generelle Morphologie (1866), reproduction is discontinuous growth. How impossible it is to draw any hard and fast line between a fragmentation which separates off overgrowths, and the more specialised modes of reproduction! Perhaps we are looking back to near the beginning of organic life when we see the fragmentation of a protoplasmic corpuscle which has grown too large to be a successful unity. It cannot be gainsaid that the division of a cell remains one of the mysteries of the world. Professor Bateson writes (1913, p. 39): I know nothing which to a man well trained in scientific knowledge and method brings so vivid a realisation of our ignorance of the nature of life as the mystery of cell-division.
It is this power of spontaneous division which most sharply distinguishes the living from the non-living.
The greatest advance I can conceive in biology would be the discovery of the instability which leads to the continual division of the cell. When I look at a dividing cell I feel as an astronomer might do if he beheld the formation of a double star: that an original act of creation is taking place before me.
In most cases the cell divides into two precisely similar daughter-cells, this being associated with an exceedingly complicated division of the nucleus, which secures that each of the two daughter-cells gets a meticulously precise half of the chromatin material of the original nucleus. But the difficulty of the problem is increased by the fact that a cell may also divide into two dissimilar halves, as appears to happen in certain modes of inheritance. In exceptional cases among multicellular organisms the process of cell-division is simpler and more direct, and in some unicellular organisms it is very simple. It is probable that the complicated methods of cell-division which are now the rule are the results of a long process of evolution, and that the fundamental characteristic is simply division. But why should the protoplasmic unit divide? Spencer, Leuckart, and James pointed out independently that, as a cell of regular shape increases in volume, it does not proportionately increase in surface. If it be a sphere, the volume of material to be kept alive increases as the cube of the radius, while the surface, through which the keeping alive is effected, increases only as the square. Thus there tends to be a hazardous disproportion between volume and surface, which may set up instability. The disturbed balance may be restored by the emission of processes from the surface of the cell, making it like a country with a big coast-line, as in Rhizopod Protozoa or in the amboid cells found in most multicellular animals. But the disturbed balance is normally restored by the cell dividing into two cells. This view indicates the advantage of cell-division, but beyond the hint that a disproportion between volume and surface may induce physiological instability, perhaps a cell-solution or cytolysis, it does not tell us what brings the process about.
It is an interesting fact that if a non-nucleated fragment of cell-substance be cut off from a large Protozoon, it can move about for a time, but it cannot feed or grow, and sooner or later it dies. But a nucleated fragment does not die. There are other facts which point to the same conclusionthat the nucleus is a sort of dynamic centre to the cell (especially a trophic centre), and that stability depends on keeping up a certain proportion or relation between the nucleoplasm and the cytoplasm. It follows, therefore, that if growth imply an increase of cell-substance out of proportion to nuclear substance, a state of physiological instability may set in, which cell-division may counteract. In many large Protozoa there are numerous nuclei.
It has also been suggested that a period of growth is automatically followed by a process of autokatalysis, or self-fermentation, but precise data are awanting. What we wish to indicate, however, is that the correlation of chemical processes which makes continued self-maintenance possible, naturally leads on to growth, and that growth naturally leads on to division or reproduction. This remains true though our ignorance of the physiology of cell-division is confessed.
It is possible, however, to take another step. It is characteristic of organisms to multiply, and they multiply by division, separating off a fragment, a group of cells, or a single cell. This brings us face to face with developmentthe power that a part has of growing and differentiating until it has literally reproduced the whole. Development is the making visible of the latent potentialitiesthe intrinsic manifoldnessof the liberated fragment, or sample, or cell; and while the development of a fertilised egg-cell into an organism remains to us one of the wonders of the world, we venture to suggest that the development may be profitably thought of as a continuation of the processes which are always going on to preserve the specific organisation in good repair. Every gradation between the two may be found in the phenomena of regrowth or regeneration of lost parts. But when we associate this capacity of development with growth and multiplying we see that we may unite them all in the conception of cyclical development, which Huxley was wont to emphasise in his discussions of the characteristics of living creatures.
From a microscopic egg-cell an embryo plant develops; the ovule becomes a seed, the seed a seedling; by insensible steps there is fashioned a large and varied fabric of root and stem, leaves and flowers. But no sooner has the edifice attained completeness than it begins to crumble. The grass withereth and the flower thereof fadeth, and soon there is nothing left but the seeds, which begin the cycle anew. It is Huxley said, a Sisyphean process, in the course of which the living and growing plant passes from the relative simplicity and latent potentiality of the seed to the full epiphany of a highly differentiated type, thence to fall back to simplicity and potentiality again. So is it also among animals. The microscopic egg-cell divides and re-divides, and there is built up an embryo. This may develop steadily and directly into the likeness of its kind, or it may give rise to a divergent larval phase such as we are familiar with in caterpillars and tadpoles. Through more or less critical phases of adolescence the adult stage is reached, and it is a not infrequent achievement to lengthen out this period of full epiphany and freedom. But whether the creature's life is counted in days or in months, years or centuries, there is for most an ascending and a descending curve from the vita minima of the egg-cell (which often dies in a few hours if it be not fertilised) to the vita minima of senescence or to the not less frequent terminus of violent death.
In reference to Sir Michael Foster's definition, A living thing is a vortex of chemical and molecular change, Professor Bateson points out that the living vortex differs from all others in the fact that it can divide and throw off other vortices, through which again matter continually swirls (1913, p. 40). The parallel, he says, may be carried even further, for a simple vortex, like a smoke-ring, if projected in a suitable way, will writhe into two rings. If each loop as it is formed could grow and then twist again to form more loops, we should have a model representing several of the essential features of living things (1913, p. 40). It has to be added, as we have seen, that the living vortex is the seat of complex and specific chemical changes which are correlated in such a way that the creature lasts.
This power of persisting on its own patha sort of protoplasmic inertiais very fundamental. It has received remarkable illustration in the astounding facts established in regard to the continued life of excised or explanted fragments or even cells. Pieces of skin, drops of blood, fragments of embryo may with proper precautions be kept alive for months.
Is there any unifying concept behind these extraordinary powers of growing, multiplying, developing, and growing again? The well-known physicist, Professor Joly of Dublin, made many years ago (1891) the very interesting suggestion that the living creature has a unique power of accumulating energy acceleratively. The organism is a configuration of matter which absorbs energy acceleratively, without limit, when unconstrained (p. 79). If we heat a piece of iron or charge a Leyden jar, the process becomes more and more difficult as we go on. The transfer of energy into any inanimate material system is attended by effects retardative to the transfer and conducive to dissipation. But the young leaf growing in the sunlight utilises the solar energy acceleratively; the more it gets, the more it grows, and the more it can take. The transfer of energy into any animate material system is attended by effects conducive to the transfer, and retardative of dissipation. On what this peculiar power depends Professor Joly does not tell usthat would be the secret of life; but it is very interesting to get from a physicist a clear statement of the dynamic contrast between animate and inanimate material systems. The animate system is aggressive on the energy available to it, spends it with economy, and invests it with interest, till death finally deprives it of all.
§ 5. Effective Behaviour, Registration of Experience, and Variability.
So far we have sought to arrange in a logical way certain insignia of organisms. Absolutely fundamental is the power of persistent individuality in spite of ceaseless change. There is a unifying idea of persistence or of functional inertia. This led us to consider growth, multiplication, and cyclical development. Here, perhaps, there is a unifying idea of accumulating potentialities. We have now to recognise that living creatures are characterised by effective behaviour, registration of experience, and variability. The common note in this triad of qualities may not be obvious, but is it not agency, self-expression, creativeness?
(a) Life is a kind of activity which comes to its own in effective behaviour, that is to say, in an organically determined correlated series of acts which converge towards a definite result. Behaviour is seen at many levels and in diverse modes, which will be discussed later, but its common features are correlation, concatenation, individuality, and purposiveness. Big words, indeed, for the Amba gliding along on the mud of the duck-pond. And yet, if we take this Amba, and lay aside the contempt which superficial familiarity breeds, we find that we are only beginning to make its acquaintance.
Professor Jennings describes a large Amba, a, which had imperfectly swallowed a smaller one, b. The prisoner moved as if trying to escape, the swallower moved as if trying to prevent it. Finally the small one did get completely out again, whereupon the large Amba, a, reversed its course, overtook b, engulfed it completely, and started away. The small Amba, again imprisoned, lay still until through the movements of a there happened to be but a thin layer of protoplasm between it and freedom. It then broke loose, escaped completely, and was not further molested. If this behaviour had been described and even drawn by a tyro, we might have distrusted it entirely, but when we have it from a master in the difficult art of observing Protozoa, we must give it careful consideration. Without saying anything just now about the Amba's mind, must we not agree that this concatenation of following, catching, losing, chasing, re-capturing, and losing again is either behaviour or magic?
Most living creatures show more behaviour than is generally supposed, but many of them, plants especially, have little. We often complain that they do not show any interesting habits when we are watching them. This may be admitted, however, without affecting the general truth of the statement that organisms are characterised by a capacity for effective behaviour. That many men run their lives, or have to run their lives with a minimum of thinking, does not affect the general truth of the statement that men are characterised by a capacity for rational discourse.
(b) The effectiveness which characterises the behaviour of those organisms that show enough to be profitable subjects of study, appears to depend on profiting by experience in the individual lifetime, or on the entailed results of ancestral experiments (chiefly, perhaps, in the form of germinal variations), or, usually, on both. The registration of experience and experiments is one of the insignia of organisms, but we must include under the term organism the germ-cell, which is an implicit organism, a microcosm corresponding to the macrocosm which develops from it. We must include the germ-cells because, so far as we can judge at present, many if not most new departures of importance have had their origin as germinal variations. If the word experiment be inadmissible, some other will serve. We refer to the permutations and combinations, the adjustments and compromises, the subtractions and additions that seem to occur in the history of the germ-cells.
As W. K. Clifford said, It is the peculiarity of living things not merely that they change under the influence of surrounding circumstances, but that any change which takes place in them is not lost, but retained, and, as it were, built into the organism to serve as the foundation for future actions. As Bergson puts it, Its past, in its entirety, is prolonged into its present, and abides there, actual and acting. As Jennings says, from the physiological point of view, in discussing the behaviour of the brainless starfish, The precise way each part shall act under the influence of the stimulus must be determined by the past history of that part; by the stimuli that have acted upon it, by the reactions which it has given, by the results which these reactions have produced (as well as by the present relations of this part to other parts, and by the immediate effects of its present action). We know as solidly as we know anything in physiology that the history of an organism does modify it and its actionsin ways not yet thoroughly understood, doubtless, yet none the less real.
(c) The crowning attribute of lifeand the most elusiveis variability, the organism's power of producing something distinctively new. At present we must take it as given. The capacity most like it is Man's power of mental experiment, the secret of the artist, the musician, the poet, the inventor, the thinker, and the true statesman.
A discussion of this innermost secret of life must be postponed till we come to consider the factors in evolution, but two points may be noticed in the meantime. There is variation and variation. There is a change wrought on the body by some peculiarity of nurture, environment, or habit. That is a modification, and, so far as we are aware, it is not transmissible in itself or in any representative degree. So this does not help us. There are also variations which consist in the loss of some ancestral character, such as horns or a tail, and we know that there are opportunities in the history of the germ-cells for the dropping out of hereditary items. There are also variations which consist in new arrangements of ancestral characters, as when the progeny of black and yellow rabbits are grey. Many apparently novel features are just old characters in new guise. This again is not difficult to understand in a general way. But the kind of variation before which we are dumb is the brusque origin of something distinctively novel, a new pattern, an originality. And unless one is to make the assumption that every character was given in the first organisms and that evolution is only unrolling, time counting for nothing, we are bound to assume that these momentous new departures have been of frequent occurrence all down the ages. Our suggestion meanwhile is simply an assumption that organisms are essentially creative. Even the inorganic has a tendency to complexify; a fortiori the organic. The chemist is always turning out new carbon-compounds, the organism is an unconsciously inventive chemist. The same chemical substance can sometimes crystallise in more than one waywe know the variety of snow crystalsso, but with infinitely more subtlety, may the germ-cell experiment with its own architecture, or trade with its environment in adventurous differentiation. Just as an intact organism from the Amba to the Elephant tries experiments, so the germ-cell, which is no ordinary cell, but an implicit organism, a condensed individuality, may make experiments in self-expression, which we call variations or mutations. Such, at least, is our present view of a great mystery.
What has all this to do with Natural Theology? Little, perhaps, directly; but much indirectly. For a superficial or flimsy conception of the essential characteristics of living creatures means putting a bushel over one of the great wonders of the world. A commonplace view of Animate Nature is an impiety, and a mechanical view is a gratuitous complication of the problems of existence. Geniuses like Nietzsche of yesterday and D'Annunzio of to-day have admitted the darkening of their eyes by a mechanical view of life, accepted as scientific. We seek to show that it need not be accepted.
But there are three concluding remarks that we wish to make:(a) The subject is not yet a matter of exact science, and we do not say that ours is the true or the truest way of stating the criteria of organisms. It is the best answer we personally can give for the time being. Some would state, more definitely than we have done, that all organisms are psycho-physical beings. And others would reject, erroneously, we think, all such categories as individuality, behaviour, experience, experiment, and self-expression.
(b) Secondly, when we say that an organism has the capacity of retaining its integrity in spite of ceaseless metabolism, we do not explain this capacity. If we could we should know the secret of life, which remains hidden from us.
(c) Thirdly, our description of the general characteristics of living creatures remains too cold-blooded. Like every analytical and formal treatment it falls far short of giving an adequate idea of life in its concrete fulness. No one who did not know plants and animals would gather from our statement any idea of their sparkle and subtlety and surprises. For that requires more than science. We must use our everyday and our red-letter day experience of livingness both in ourselves and in other organisms, wherewith to enliven sympathetically all that biology can give. We need not be in the least afraid of engendering an exaggerated idea of the wonder of life!
No one can tell us wherein a living organism essentially differs from a not-living thing. The one is alive, the other is not. Perhaps we err in speaking too much about the unread riddle of life. For this seems to imply the expectation that we shall be able some day to explain life in terms of something elsean expectation which is not likely to meet with anything but disappointment. The materialists look forward to explaining or re-describing the activity we call living in terms of matter and motion. The animists look forward to doing the same in terms of soul. But it is not at all evident why we should be so very desirous to explain life in terms of anything else, or why we should be sanguine in making the attempt. Life is an aspect of reality which found expression when there were evolved those particular collocations of matter and energy which we call organisms, just as Mind is an aspect of reality which found expression when nervous systems of considerable degree of complexity were established. We mean by Life and Mindthe capacity for certain kinds of activity and behaviour and internal experimenting with ideas, and it may well be that Life and Mind are alike irreducible, and that they are not very different from one another. But this is mere speculation. What is practically more important is to appreciate the characteristics of living creatures. Hence this inquiry into the criteria of livingness. The bearing of this on modern Natural Theology is that an easy-going concept of organism is a dead fly that may spoil many an ointment.
If we are to reach a coherent view of Nature, such as could be included in a philosophy, we must arrive at some definition of the characteristics which mark off living organisms from their not-living surroundings. In the present state of science this definition cannot be more than tentative, but it must be continually attempted.
Living may be described as a twofold relation of action and reaction between organisms and their environment, and Living creatures are always active towards two main results, self-maintenance and the continuance of their race. But the difficult question is: What are the insignia of living creatures?
The first is the power of persisting in a complex specific metabolism, and in a corresponding specific organisation. (a) The essential metabolism of life has to do with the up-building and down-breaking of protein substances in a colloid state. (b) Each living creature has its own chemical individuality and its own specific microscopic and ultra-microscopic architecture. (c) Part of the secret of life is a correlation of chemical processes so that in spite of ceaseless change the organism persists in its integrity for days or years or centuries. It is always burning away; but it is not consumed.
Secondly there are the capacities of (a) growth, of (b) reproduction, and of (c) developmenta triad of qualities. (a) Organic growth, an increase in the amount of organised living-matter, is at the expense of materials different from those which compose the growing substance; it implies active assimilation rather than passive accretion; it is very definitely a regulated process. (b) The power of spontaneous divisionleading on, directly or indirectly, to the origin of new individualitiesis one of the momentous distinctions between the living and the not-living. (c) Development is the actualisation of the intrinsic manifoldness of the liberated fragment, sample, or cell, and may he brought into line with the process of repairing the specific organisation.
Thirdly, there is another triad of qualities(a) effective behaviour, (b) registration of experiences and experiments, and (c) variability. The common note here is agency, self-expression, creativeness. (a) Behaviour, exhibited at many levels and in diverse modes, is an organically determined concatenated series of acts converging towards a definite result. Its common features are correlation, individuality, and purposiveness. (b) The effectiveness which characterises organic behaviour depends on the organism's power of profiting by experience in the individual lifetime, or on the entailed results of ancestral experiments (chiefly perhaps germinal variations), or, usually, on both. (e) The crowning attributeand the most elusiveis variability, the organism's powerbut, more accurately perhaps, the germ-cell's powerof giving rise to something distinctively new.