Elements of Physical Biology

° For a discussion of the Atmosphere considered as an engine see Sir Napier Shav’s Rede Lecture, published in Nature, 1921, p. 653. This author arrives at the estimate that ‘‘the best you can expect from the steam-laden air of the equatorial region working between the surface and the stratosphere, under favorable conditions, is a brake-horsepower efficiency of 25 per cent.”’ 13 Power, its significance and needs; Smithsonian Institution Bulletin 102, Part 5.

14 For a comprehensive survey of power development actual and potential see F. G. Baum, U.S. A. Power Industry. Also W. 8. Murray, A Superpower System for the Region between Boston and Washington. United States Relation of Transformer Cycle to Circulation of the Elements. The circulation of substance in the organic world and its inorganic background, which was considered in an earlier chapter in its purely material relations, now acquires a new significance. We recognize in it now a typical characteristic of the great world engine which, for continued operation, must of necessity work thus in cycles. The picture presented to our minds is that of a gigantic overshot mill wheel, receiving from above the stream of sunlight with its two hundred twenty-seven million gross horsepower—though much of this is spilt without effect—and discharging below its dissipated energy in the form of heat at the general temperature level. The

Sunlight Green Plants ————> Her. bivorous Animals eve, Animals Heot main outstanding features of the wheel are represented diagrammatically in figure 68. But in detail the engine is infinitely complex, and the main cycle contains within itself a maze of subsidiary cycles. And, since the parts of the engine are all interrelated it may happen that the output of the great wheel is limited, or a least hampered, by the performance of one or more of the wheels within the wheel. For it must be remembered that the output of each transformer is determined both by its mass and by its rate of revolution. Hence if the working substance, or any ingredient of the working substance of any of the subsidiary transformers, reaches its limits, a limit may at the same time be set for the performance of the great transformer as a whole. Conversely, if any one of the subsidi-

ary transformers develops new activity, either by acquiring new resources of working substance, or by accelerating its rate of revolution, the output of the entire system may be reflexly stimulated. As to the significance of this for the evolution of the system as a whole more will be said later, in the discussion of certain phases of the evolution of the human species in particular; for it is hardly necessary to remark that the case of man presents features of so remarkable character that it calls for special consideration, quite aside from the pardonable excess of interest which we personally feel in the creature.

Evolution of the World Engine: The picture we must keep before us, then, is that of a great world engine or energy transformer composed of a multitude of subsidiary units, each separately, and all together as a whole, working in a cycle. It seems, in a way, a singularly futile engine, which, with a seriousness strangely out of keeping with the absurdity of the performance, carefully and thoroughly churns up all the energy gathered from the source. It spends all its work feeding itself and keeping itself in repair, so that no balance is left over for any imaginable residual purpose. Still, it accomplishes one very remarkable thing; it improves itself as it goes along, if we may employ this term to describe those progressive changes in its composition and construction which constitute the evolution of the system. For—the statement will bear reiteration and emphasis— this is the conception we must form of organic evolution: the evolution of the great world engine as a whole, not merely that of any single species of organisms considered separately. What is the trend of this development? Toward what end does the great transformer shape and reshape itself? A provisional answer to the question will be suggested in due course. For a time we must now abandon our broad viewpoint, and turn from the consideration of the great transformer as a whole, to a discussion of certain of its subsidiary engines which present points of special interest and importance.

As an enterprise, mathematics is characterized by its aim, and its aim is to think rigorously whatever is rigorously thinkable or whatever may become rigorously thinkable in course of the approved striving and refining evolution of ideas.—C. J. Keyser. Distributed and Localized Sources of Energy. In Carnot’s classical analysis of the operation of a heat engine the source of energy is taken for granted as one of the fundamental data of the problem.

In nature sources of energy are not thus supplied unconditionally, and for our present purposes it becomes necessary to extend the analysis of transformer operation so as to take into its scope also some of the significant characteristics of the sources from which the engines of nature derive their supplies. And here a fundamental distinction is to be made between two kinds of sources, namely, (1) evenly, or at least continuously distributed sources, and (2) localized sources, heterogeneously distributed.

If the transformer draws its energy supply from a source uniformly distributed over a region R, at any point of which it can make contact with the source, then, evidently, within the region R the performance of the transformer is independent of its location. So, for example, plants derive their energy from sunlight falling upon them gratuitously, and draw their supplies of material partly from atmospheric carbon dioxide and oxygen diffusing to them by a spontaneous process, and partly from dissolved salts seeping to their roots automatically, that is to say, by a process essentially independent of any intervention on the part of the plant. And quite in accord with this general distribution of plant food, the typical plant is a sessile, passive organism.

If, on the contrary, the transformer draws its supply from discontinuous, heterogeneously distributed sources, then continued operation demands at least some degree of relative motion between the transformer and the sources, so that the occasional collisions may occur between the transformer and a source. Random and Aimed Collisions. Purely random collisions, such as those contemplated in the kinetic theory of gases, may suffice to bring an adequate supply to the transformer.! But evidently the output of the transformer will be enhanced if, instead of relying upon a precarious supply gleaned in fortuitous encounters, a suitable correlation is established between the motion of the transformer and the location of the sources. This may be accomplished in two ways, as follows:

1. There may be actual mechanical union? positively connecting transformer and source, so that there is a functional relation (in the mathematical sense) between the motion of the transformer and the topography of the source. A simple instance in point is a trolley car. Here there is a definite relation between the topography of the system (track), the reaction of the transformer up it, and the distribution of the source. The car is not free to move except along the track and along the trolley wire.

2. Contact with the source may not be positively secured, but merely rendered more probably than in purely random collisions, by the occurrence of more or less accurately aimed collisions. Source and transformer are in this case mechanically independent, the motion of the source is not fully determined when the topography of the system is given; a certain freedom remains, There is, in this case, not functional relation, but only correlation between the motion of the transformer and the topography of the system: no specific motion is determined, only certain motions are rendered more probable than others.

Negative Correlation. It is to be noted, of course, that such correlation between the motion of a transformer and the location of features 1 For an experimental investigation of the movements of lower organisms (Paramecium, Colpidium, Trachelomonas) see Przibram, Pfliigers Archiv, 1913, vol. 153, pp. 401405. The movements were found to follow the law deduced by Einstein and Smoluchowski for Brownian movement (which, of course is random), namely that the mean square of the displacements of a particle in any direction in equal intervals of time tis proportional to ¢. The order of magnitude of the movements of the organisms, however, and the influence of temperature, were quite different in the case of Brownian movement. (For an account of the Hinstein-Smoluchowski law see, for example, C. Schaefer, Einfiihrung in die theoretische Physik, 1921, vol. 2, p. 487.)

2 Compare L. T. y Quevedo, Essai sur Vautomatique, Revue Générale des of its environment is competent to bring other benefits aside from a a supply of energy and material (food). All transformers are more or less vulnerable. Exposed to an environment varying from point to point and from instant to instant, a transformer will in general sooner or later meet with an injurious stress, that is to say, a stress that will change its structure or constitution to a point where effective operation is impaired or altogether abolished. If it is desirable, in the interest of increased output, that collisions with suitable energy sources be rendered more probable than in purely random motion, it is evidently equally desirable, in the interest of continued operation of the transformer, that collision with harmful features in the environment be rendered less probable. In other words, in addition to apparatus establishing a positive correlation between the motion of the transformer and the location of sources, it is desirable that there be also provided apparatus establishing negative correlation between such motion and the location of injurious features of the environment. Collisions should, as far as possible, be aimed toward sources, and away from points of danger. The fate, the success of the transformer, will evidently depend both on the versatility of the aim, and on its accuracy; on the number and character of targets picked out for aim, and on the closeness with which the hits upon the target cluster around the bull’s eye.

The Correlating Apparatus. It is on the general plan indicated in the preceding paragraph that nature’s mobile transformers, especially the typical animal organisms, operate. In the competition among these, for food and for safety, the accuracy and the versatility of aim characteristic of each species will evidently be most important determinants of relative success or failure, and hence of the trend of evolution. The dynamics of evolution thus appears essentially as the statistical dynamics of a system of energy transformers, each having a characteristic vulnerability, a charasteristic versatility and accuracy of aim. It is here that the method of thermodynamics is inadequate. Its austere virtue of impartiality toward different mechanisms becomes a vice when information is sought regarding systems in which mechanism plays a leading réle. The mechanism, or, touse a somewhat broader term free from mechanistic implications, in apparatus, by which the correlation is established between motion and environment, by which behavior is adapted to circumstances, is here not an incidental detail to be lightly dismissed as of secondary

importance, but must occupy the very center of attention. To a somewhat detailed consideration of this apparatus we now proceed; in the interest of vivid, realistic presentation of the subject it will, however, be desirable to abandon from this point on the very general treatment and, to speak now specifically in terms of biological units, organisms, rather than in terms of the broader physical concept of energy transformers. It should be constantly borne in mind, however, that this change in attitude, or, it were better to say, in terminology, is chiefly a matter of convenience and effectiveness of presentation, and the fundamental physical principles involved, as set forth in the more general terms, should never be allowed to sink far below the surface of our immediate thought.

The Component Elements of the correlating Apparatus. The continued existence of the organism, toward which his actions are aimed, demands that he shall direct his energies, his activities in accordance with the state of his environment, of the external world, avoiding unfavorable conditions, and seeking out those favorable or necessary to his maintenance. This includes the locating and seizing of food. But as a material, physical system, his actions are primarily determined by his own state. Hence, in order that his actions, determined immediately by the state of the organism himself, may be mediately determined by the state of the external world, apparatus must be provided whereby the state of the organism becomes in a certain suitable manner a function of the state of the external world. The external world is depicted in the organism by a certain apparatus, a set of organs and faculties, which we may appropriately term the Depictors.

The depictors include first the Receptors or Organs of Special Sense (eyes, ears, nose, etc.); and second the Elaborators, whose function is to combine and further elaborate the crude information furnished by the senses. The physical location and structure and mode of operation of the elaborators is much less obvious than that of the receptors. In fact, we ordinarily recognize them rather as faculties (Memory, Reason) than as organs. Another set of organs and faculties, the Adjustors, determine the particular reactions, the behavior of the organism, in the light of the information brought in by the receptors and further elaborated by the elaborators. So the hungry bird, sighting a worm on the lawn, flies

down to the spot from the tree on which it is perched, and secures its prey. The sight of the worm, together perhaps with the memory of earlier meals collected near the same spot, acts as a stimulus or Drive to responsive action. This last step, action, commonly involves the use of members, or motor organs, /ffectors, such as wings, feet, hands, etc. In complicated cases, as in human behavior, the elaborators may also play an important réle in the effector step of the process by which motion is correlated to environment, behavior adapted to circumstance. So, for example, the traveller, before setting out on a journey, plans his itinerary, perhaps months or years in advance.

Receptor-Effector Circuit Begins and Endsin Environment. It is a noteworthy fact that this process of correlating action to conditions is essentially cyclic in character: It has its origin in the external world, which becomes depicted in the organism, provokes a response, the terminal step of which is usually, if not always, a reaction upon the external world. The net result is, in a sense, that the external world has reacted upon itself. The organism has acted as an intermediary. There is something more than a mere surface significance in this fact. For it is true generally that animals function essentially as catalysers, as agents assisting in a change that is “trying” to take place on its own account. So the green grass is, in a sense, hungry for oxygen, namely in the sense that its oxidation is accompanied by a diminution of free energy. The animal consuming the grass and deriving from its oxidation the requisite energy for further activity has not initiated any revolutionary process, but has merely helped nature in its course, has merely rolled the ball downhill, so to speak. This is all that the animal organism is competent to do, and man is not exempt from this restriction: In all our doings, whether we will it or not, we are assisting in a fundamental natural process, we are obeying an inevitable law of energetics.

Correlating Apparatus Not Peculiar to Living Organisms. It must not be supposed that the typical elements of the correlating apparatus, the receptors, adjustors and effectors, are wholly peculiar to living organisms. They can be very clearly recognized also in certain mechanisms of human construction. In fact, owing to the circumstance that the operation of such man-made mechanism is fully known to us, that they harbor no mysterious‘‘vital’’ principle or ill-understood element of consciousness, such purely mechanical

contrivances furnish particularly apt illustrations of the principles involved in the operation of the correlating apparatus. It is therefore well worth while to consider here a simple example of this kind. Some time ago there appeared on the market an ingenious toy, primarily designed, no doubt, merely to amuse; but, in point of fact, highly instructive. Its general appearance and simple mechanism are illustrated in figure 69. The beetle ‘“‘walks’” on two toothed wheels, of which one is an idler, while the other is rotated by a spring whose gradual release is ensured by a simple escapement device. At its forward end reckoning in the direction of motion (at the “head’’) the toy is provided with a pair of antennae, of which one is a dummy, and rises clear of the table upon which the beetle is placed to exhibit its talents. The other antenna is operative and is so bent downward as to glide along the table top, in contact with it. A little

Fig. 69. MecuanicaL WALKING Brrtiz, EXHIBITING THE SEVERAL CHARAC- in advance of the propelling wheel is another smaller toothed wheel, running idle, and disposed transversely to the direction of the driving wheel. This transverse wheel clears the table without contact in the normal working position of the beetle. The animal, if placed somewhere near the center of the table, makes a straight track, apparently intent upon reaching the edge and seeking destruction in a species of mechanical suicide. But the moment the operative antenna clears the edge of the table, the body of the toy, till then held up by the contact of the antenna with the table surface, sinks down a fraction of an inch, and the transverse wheel now contacts with the table. In consequence the toy rotates until the running wheel is parallel with the table edge, and the insect continues its peregrinations with the operative antenna hugging the side of the table top.

Clearly here the antenna is a receptor, which “apprises’”’ the insect of certain features in its environment, which depicts, in a crude but sufficient manner the environment in the toy. The law of depiction is here extremely simple; a depression in the external world (table top) is translated into a downward tilt in the angle of repose of the toy. The adjustor, in this case, is the transverse wheel, about as simple an example of an adjustor as can well be imagined. It “construes” the information furnished by the receptor antenna, and modifies in accordance with this information the law of motion of the toy, in such manner as to preserve the beetle from a fall which might destroy that stability of form on which the continued operation, according to schedule, of the mechanism depends.

It would be easy to cite a number of other examples of devices constructed either as toys, scientific curiosities, or for actual technical use, which exhibit more or less prominently the typical correlating apparatus, with receptor, adjustor and effector. By far the most highly perfected of such automatic devices is the modern machineswitching apparatus for telephones, which eliminates the ‘“operator” at the central offices. This device, which fulfills an amazing multiplicity of functions, will be found briefly described in non-technical language in the April number 1923 of The Bell System Technical Journal.

Perhaps more directly in line with our present interest here is a mechanical chess player that was designed some years ago by L. Torres y Quevedo;’ this device successfully counters any move (with a limited number of pieces, merely as a matter of simplicity) that a living opponent may choose to make upon the board. The game of chess itself is so well conceived a conventionalization of the battle of life’ that it is well worth the while to make a seeming digression to analyze the fundamental elements of this remarkable game. The bearing of this analysis upon certain problems of biological evolution will then become apparent.

* A description will be found in the Scientific American Supplement, November 6, 1915, p. 296. ‘The aptness of this illustration has no doubt been remarked by many. I have recently noted the following pertinent references: F. L. Wells, Mental Adjustments, 1917, p. 6. Eddington, Time Space and Gravitation, 1920, p. 184; T. H. Huxley, A Liberal Education and Where to Find it. Collected Hssays, 1894, vol. 3, p. 81. A bibliography of the mathematical treatment of chess will be found in W. W. R. Ball, Mathematical Recreations, T91T, Chapter VI, p. 109.

Chess as a Conventional Model of the Battlefield of Life. A game of chess is a succession of physical events. How is its course determined? 1. A topographic map, a chart of geometric constraints, the chess board. 2. Movable upon this chart, a number of movable points (chessmen), each the center of a field of influence, defined for each movable point in relation to the geometric constraints. So, for example, the field of influence of a pawn extends to the two squares diagonally in front of the pawn.

3. A law restricting the time-rate of advance of each moving point (moves alternate from white to black). 4, A law defining the influence upon each other of two points in collision, i.e., two points whose fields of influence have interpenetrated to a prescribed extent. An example of this is the rule that a chessman arriving upon a square occupied by a hostile piece, throws the latter off the board. 5. A law restricting the movements of the points when not in collision, i.e., when outside one another’s field of influence. So, for example, a bishop may move only diagonally.

6. The elements enumerated so far place restrictions upon permissible changes (moves). These elements alone cannot, evidently, determine any occurrence of any kind: Absolute immobility, for example, or any random move that did not violate the rules of the game, would equally satisfy the conditions enumerated. 7. In addition to the elements, 1, 2, 3, 4, 5, there must therefore be in operation some positive principle (tropism) which not merely restricts possible occurrences, but which determines actual events. In chess this principle is furnished by the effort of each player to bring about checkmate. Each move is so aimed (with greater or less accuracy and breadth of view, versatility, according to the skill of the player) as ultimately to force a checkmate.

From the battlefield of chess we now turn our eyes on the scene of the great biological contest: Before us is a topographic map, over which move those organisms that are by nature gifted with motion. We may think of each such organism as a moving point, the center of a field of influence. As the chessplayer must accustom his mind’s eye to see, radiating out from each chessman, its field of influence upon the board, so we, in envisaging the battleground of organic evolution, must see each organism carrying around with it, as if rigidly attached to its body, a field, or a target, of zones, of the following character.