Individuality in Organisms

And finally there remains the process of sexual or gametic reproduction in which the union of two cells, the gametes or their nuclei, is followed by a series of developmental changes. In most cases of gametic reproduction the two gametes are sexually differentiated as parts of two different individuals or in different organs of the same individual before they come together. Moreover, they are themselves individuals, and their union results in a new individuation. In the higher animals this form of reproduction is, with very rare exceptions, the only process which gives rise to organisms.

Apparently gametic and agamic reproduction are very different processes, but we must at least raise the question whether they are similar in any way, or, if they are different, what the difference may signify. It is in those parts of pre-existing individuals which become new whole individuals that the process of individuation goes on before our very eyes, and it is there that we have the opportunity to determine something "of its nature. It is by no means necessary for us to wait for the occurrence of reproduction in nature. In many of the simpler organisms we can bring about the occurrence of reproduction at will, simply by cutting out pieces of the body and so isolating them from their physiological relations with other parts. Such pieces may become new organisms or parts of organisms more or less like those from which they were taken. These experimental reproductions constitute, as I shall show, invaluable material for the study of the organic individual and of the process of individuation, although their value for this purpose has not heretofore been generally recognized.

The living organism consists of a substance, or more properly a complex mixture of substances, in which the series of chemical reactions known as metabolism occurs. The fundamental constituents of protoplasm occur in what is known as the colloid condition, i.e., they do not form a true molecular solution, but exist as suspended particles larger than molecules in the fluid medium, which in the case of protoplasm is water. Living protoplasm may range in its physical condition from a semi-fluid to a stiff jelly-like substance according to the aggregate condition of its particles. This mixture of substances, protoplasm, is the visible substratum of the living form , and in it the changes which constitute hfe occur. Changes in its aggregate condition and in the chemical constitution of one or more of its parts form the basis of specialization and differentiation and so of structure and form, and the energy of the organism originates from certain of the chemical reactions which occur in it.

Metabolism consists in a complex series of interrelated chemical reactions in protoplasm. On the one hand, nutritive substances are transformed and built up into protoplasm or into other substances characteristic of living organisms, and, on the other hand, portions of the protoplasm and of these other substances are broken down and oxidized, setting free energy, which appears in the various activities of life. What we know of metabolism indicates that the oxidations are in general of fundamental importance in the whole reaction system. Apparently life cannot continue without them, and the other reactions are to a greater or less extent associated with and dependent upon them. In a given organism, under given external conditions the rate of oxidation is in some degree a measure of metabolic activity and of life. Objection is sometimes made to the term "metabolism" because of its vagueness. It is of course true that we do not know all the various reactions and their relations to each other and to other conditions, but we

do know that for a given organism metabolism is in general a definite and characteristic system of reactions subject to variation with change in conditions but nevertheless maintaining in the long run a certain rate and character. In general terms, protoplasm is the foundation of structure and form, and metabolism, of function, in the organism. The relation between structure and function has been the subject of much discussion. For some the organism possesses a certain structural organization which arises in some way or other quite independent of function and w^hich makes function possible, just as a man-made machine possesses a certain structure which makes its function possible. Such an organism must be constructed before it can begin to function, and hypotheses of this character are chiefly concerned with the supposed method of construction. This conception of the organism ignores the fact that it is always functioning while it is alive: life is function. In no case does the organism begin to function only after its construction is completed; it always functions from the beginning; it constructs itself by functioning, and the character of its functional activity changes as its structural development progresses. Structure and function are mutually related. Function produces structure and structure modifies and determines the character of function.

Here it is possible to refer only very briefly to a conception of the relation between structure and function which I have discussed more at length elsewhere.' According to this view protoplasm and structure represent primarily those products of metabolism which are relatively stable under the ordinary physiological conditions and in such physical condition that they cannot escape from the organism without change. Therefore they accumulate, and their accumulation constitutes growth, and their differences in different parts constitute the morphological structure of the organism. The less stable products appear only temporarily or not at all as structural features, for they are decomposed and eliminated. These differences in stability are of course only relative and between extremes numerous intermediate degrees occur. Moreover, a structure which is stable under certain conditions may, under altered conditions, become unstable and be broken down and replaced by other structures. In general, structural stability increases both during the development of the individual and the course of evolution. The evolutionary increase in structural stability is in fact what makes possible the structural permanency and complexity of the higher as compared with the lower organisms.

If the organic individual is a physico-chemical entity of this kind the foundation of its unity and orderly character must be present somewhere and somehow in this metabolic-protoplasmic system. Definite relations in both space and time must exist among the reactions occurring in the protoplasm, and the problem of individuality resolves itself into the problem of the nature, origin, and maintenance of these relations. It is with the problem in this form that this book is chiefly concerned.

In order to avoid confustion and for the sake of convenience and brevity it is necessary to fix upon and define certain terms to be used. The individual which forms the starting-point of a developmental, reproductive, or life-history I shall call the primary individual. This primary individual may give rise by reproduction to secondary individuals^ or, by the individuation of certain organs within itself, to partial or organ-individuals. When such secondary, partial, or organ-individuals continue to constitute parts of the unity of the primary individual it is the dominant individual and they are subordinate individuals. The segments of the earthworm body or the leaves of a plant are such subordinate individuals. When the primary and secondary individuals each constitute a more or less distinct unity though still organically connected they are co-ordinate individuals. In many trees and in some branching colonial animals various branches approach or attain the condition of co-ordinate individuals. Between strictly co-ordinate and the extremes of dominant and subordinate individuals there are of course various intermediate degrees. A common or general individuality resulting from the physiological combination of a number of more or less co-ordinate individuals, either similar or of different kinds, is a composite individual. Strictly speaking, all organisms except perhaps some of the simplest unicellular or monoplastic forms are to some extent composite individuals for different cells, and even different parts of a cell may possess a physiological unity and order of their own, but ^nce the following chapters are chiefly concerned with the larger, more general, features of organic individuality rather than wdth its more minute details, the term will be used primarily for the more extreme cases in which a number

of morphologically and physiologically well-defined and usually multicellular individuals make up a relatively persistent composite individual. Most plants and the so-called colonial animal forms are good examples. The individuals which make up a composite individual are constituent individuals. These may be either parts of a cell, different cells, or cell groups composing organs. As regards the various axes of the axiate individual, uniformity of designation is also highly desirable. The polar, longitudinal, apico-basal, or antero-posterior axis, as it is variously called, represents the primary or major order when such an order is present in the individual. In cases where the axes of the individual arise de novo and are not simply carried over from preexisting individuals, this axis is apparently the first to arise and other axes arise in relation to it. It is often convenient, therefore, to call this axis the major axis of the individual and the other axes minor axes.

With reference to particular axes, we are accustomed to distinguish position and direction according to the general plan of the individual, the relation of certain axes to others, the characteristic position, behavior, or direction of movement of the organism. The following terms are commonly used for this purpose: apical and basal, distal and proximal, anterior and posterior, peripheral and central, median and lateral, dorsal and ventral, besides various others which refer to particular regions, such as cephalic and caudal, oral and aboral, etc. All these terms are useful in particular cases, but greater uniformity and simplicity are desirable for purposes of general consideration.

As following chapters will show, there is reason for believing that what we call an axis in the organism represents the general course and direction of a gradient in rate of metabolic reactions, the rate of reaction being highest at one end, or in a certain region, and decreasing from this point in the direction in which we conceive the axis to extend. Moreover, the physiological and structural order along any axis is definitely related to this gradient. If all organic axes are fundamentally metabolic gradients we may call the region of highest rate in any axis the apical region or end, the region of lowest rate the basal region or end, while other intermediate regions may be distinguished as more or less apical or basal, and opposite directions in the axis as respectively apical and basal directions. From this point of view apical and basal regions of radially symmetrical whole organisms are merely the apical and basal regions of the major axis of such organisms and so the most conspicuous or most widely separated apical and basal regions of the body, but not fundamentally different in their dynamic significance from the corresponding regions of other axes. In the following pages it will often be convenient to use these terms, "apical" and "basal," in this general way for bilaterally as well as for radially symmetrical forms.

Having formulated the problem, it is necessary to in.quire what progress has already been made toward its solution. The first section of this chapter is a very summary consideration of this question. Since the experimental and observational data upon which my own conclusions are based are so varied and their relations to the problem in many cases so complex, the inductive method of procedure is impossible within the limits of the present book. It has seemed necessary, therefore, to state my conclusions briefly in categorical form as a working hypothesis before attempting to review and interpret the various lines of evidence. This I have attempted to do in the second section of the chapter.

The organic individual has very often been compared to a human society or state with orderly division of labor and correlation among its component parts. The fundamental feature of the human state, that which distinguishes it from a mere aggregation of human beings and makes it an individual, is some kind and degree of law and order, of co-ordination and control of the activities of its constituent units; in short, some degree and kind of government. If the organism is a cell-state or organ-state some degree and kind of government must exist in it, but in making such comparisons biologists have often ignored or failed to recognize

the importance of this fundamental point. There has been much discussion of "formative substances" and their distribution and role, and the magic word "organization" has served as the all-sufficient answer to many questions, while the fundamental problem of unity and order involved in the origin and action of the so-called formative substances and in the nature of organization has too often been completely neglected. Various theories of the organism, which may be called corpuscular theories, have been advanced and have met with more or less general acceptance. Among these Weismann's germ-plasm hypothesis is most familiar and has played the most important role in biological thought. These theories postulate in one form or another a multitude of specific material entities, each of v/hich represents in some way some characteristic of the organism. The organism as we know it is the product of their combined and harmonious activity. Examination of these theories shows that these hypothetical entities, gemmules, determinants, physiological units, pangenes, specific accumulators, or whatever we prefer to call them, are themselves endowed, ex hypothesi, with the essential characteristics of individuals and that the organism as a whole is merely a composite of their orderly activities. Neither the problem of the individuality of the hypothetical units nor that of their orderly combination and unification in the organism receives any adequate consideration in those theories. They merely translate the problem into hypothetical terms which are beyond the reach of scientific method. The combination of these units into the individual is assumed to occur as the facts demand, and although the problem of the control

and ordering of millions of such units through all the changes involved in the development of a complex organism, say the human being, is one which staggers human intelligence, it is practically ignored. Even some of our present-day speculations which attempt to assign actual topographic positions in the chromosomes to particular factors in heredity ignore completely the problem of the ordering and control of these factors which is involved in their assumptions. In fact, if we subject this group of theories to logical analysis we soon reach the point where it is necessary to assume the existence of something very like a superhuman intelligence as the underlying principle in all of them. They leave the essential problem unsolved, but their implications are anthropomorphic and teleological.

Dualistic or ^'vitalistic" theories of the individual recognize the real problem more or less clearly, but assume the existence of a non-mechanistic ordering and controlling principle. Before the development of the experimental method in biology the doctrine of vital force as something peculiar to the organism and fundamentally different from the forces acting in the inorganic world was very generally accepted, but as evidence for the validity of physico-chemical laws in the activities of living things accumulated, the hypothesis of vital force was discarded by most biologists. Within recent years, however, various attempts have been made to show the inadequacy of mechanistic conceptions of life. Driesch, at present the chief exponent of this line of thought, has postulated the existence of a controlling and ordering principle which he calls entelechy, following Aristotle. Entelechy is independent of and superior

to physico-chemical laws, and controls and orders the physico-chemical factors in the organism to a definite end or purpose. It constructs the organism as a man constructs a machine. In many respects it resembles human intelligence, but seems to be far superior to it. Other neo-vitalistic theories are more or less similar in their general conceptions, but differ in detail. In certain respects these theories constitute a real advance over the corpuscular theories, for they recognize and state more or less clearly, instead of ignoring, the essential problem. For the present, however, most of us find little intellectual satisfaction in the solution which they offer, and they are either frankly speculative or involve unwarranted or premature assumptions, and, like the corpuscular theories, they place the problem beyond the bounds of science.

Various attempts at solution or progress toward solution of the problem of organic individuality have been made along physico-chemical lines. The evident unity and order, the individuality of the inorganic crystal, together with the discovery of the existence of fluid crystals, have led to comparisons of the organism with the crystal and so to hypotheses which postulate an essentially crystalline character for organic unity and order. According to these hypotheses the laws underlying this unity and order are essentially those governing the aggregation and arrangement of molecules. The construction of the orderly framework of the organism is the expression of such laws, and its activities represent the chemical changes which go on in this framework.

These hypotheses are open to various objections. The crystal consists primarily of hke molecules though under certain conditions some crystals may show differences in constitution at the two poles resulting from the presence of other substances besides the primary constituent of the crystal. The organism, on the other hand, is a complex of many different kinds of molecules, some of which are undergoing breakdown and being built up anew during life, and, moreover, there is no optical or other evidence that protoplasm in general is fundamentally crystalline in structure. The unity of the crystal is a static unity, a unity of form and arrangement, and disappears or is replaced by another unity when chemical change occurs, while the unity of the organic individual is a dynamic unity dependent primarily for its existence on chemical activity and disappearing when such activity ceases. To believe that metabolism results from structure and ''organization" as the activity of the man-made machine results from its structure is to ignore the fact that metabolism is the formative agent in the organism. Undoubtedly crystals or crystalloid individuals are present in at least many organisms, but their individuality is quite distinct from that of the organism.

Some biologists, while not admitting that the organism is fundamentally crystalline, assume that its constituent molecules possess unknown properties which determine its unity and order. These hypotheses are open to the same objections as the crystal hypotheses. All such hypotheses in fact proceed on the assumption that a certain more or less complex "organization" is necessary as a starting-point; the machine must somehow be constructed before it can run. Actually, however, the organism runs throughout its construction from the condition of amorphous protoplasm to that of a complex anatomical system.

Modern investigation of the chemistry of the organism has demonstrated that the chemical correlations, as they are commonly called, which exist between its parts are most various and complex and often highly specific in character. Certain parts produce substances which are essential to the normal activity or structure of other parts, and the statement is frequently made that every organ in the body is an organ of chemical correlation, which means merely that it produces something which plays a role in making other parts what they are.

On the basis of these facts the hypothesis has been advanced, and is at present widely current, that the unity and order in the organism consist primarily in such chemical correlations. These chemical correlations depend upon the production and transportation within the organism of more or less specific substances, and it is evident that parts more or less specifically different must be present in order to produce such substances. These hypotheses provide no solution of the real problem of individuality, for they all involve the assumption of an underlying order or ''organization" which makes orderly chemical correlation possible. To return to the analogy between the organism and the state, exchange between human beings arises from the existence of different individuals with different needs. In order that the exchange may be orderly and specific in character some degree of unity and order must exist in the activities of the parties to the exchange. This order may result

from the authority of one person and its transmission to others, or from that of consensus of opinion, but in either case it is not the act of exchange nor its character which determines this order but the order that determines the exchange and its character. The orderly union of human beings to form an individuahty which shows the most various degrees of individuation from the family through the clan and tribe, etc., to the highly developed modern state is based primarily on authority of some kind and its transmission, not upon the material relation of the production and transportation of substances. When this union of men exists, no matter how primitive its character, the substances which it receives in exchange may play a very important part in determining the character and course of its further development. If the unity of the organic individual is in any way comparable with that of these composite social individuals, it is evident that it must originate in some ordering or controlling factor which makes possible the existence and orderly and definite arrangement of specific parts. These two types of relation — authority or dominance of some sort and its transmission to subordinate parts and the production and transportation of substances — represent the two kinds of relation possible between persons, organs, cells or parts of a cell, so far as direct mechanical relations of contact, pressure, or tension are not concerned. The unity of the social individual evidently depends primarily upon the transmissive rather than the transportative kind of relation. If the organic individual is in any way comparable to it we might reasonably expect to find the same thing true there.

Various biological theories have concerned themselves primarily with that particular aspect of unity and order which appears in the geometrical relations of parts. These are commonly known as theories of polarity and symmetry, but since polarity and symmetry are fundamental features of organic individuality, these theories must be regarded as theories of the organic individual. It is unnecessary to discuss these theories particularly, for they fall into the same groups as those already considered, and are open to the same objections. They either assume the existence of some kind of structural order or ''organization," physical or chemical, or some sort of pre-existent plan or pre-established harmony, or they ignore or fail to recognize the real problem and postulate migrations or distributions of formative substances, differences in tension, permeability, or other properties, as if such factors could behave in an orderly and constant way without a constant underlying order of some sort.

Some few biologists have attempted to deny the existence of individuality in the sense of a definite determining and controlling unity and order. The basis of such denials is usually the fact that organisms behave differently under different external conditions, while the more important fact that a definite unity and order exists in these different reactions is completely overlooked. This brief consideration of the various lines of biological thought concerned with the problem of the individual is sufficient to show that the problem is by no means solved. The remainder of the present book is an attempt to make some progress toward a solution of the

problem along somewhat different lines from those already considered. My own investigations in this field, extending over some fifteen years, together with the facts already at hand, as I see them, have forced me to the conclusion that the organic individual is fundamentally neither a structural system, whether physical or "vitalistic" in character, nor a system of chemical reactions, but rather a system of relations between a physical substratum or structure and chemical reactions. These relations, I believe, constitute the fundamental problem of life, so far as it is a biological problem, and as one aspect of it the problem of biological individuality. This is the point of view which underlies the conception of the individual presented in the following pages. Since the relations between protoplasmic substratum and chemical reactions, whatever their physical or chemical character in particular cases, are essentially dynamic, I have called it a dynamic conception.

The foundation of unity and order in the organic individual is the transmission of dynamic change, '' stimulus," ''excitation," from one point to another in the protoplasm. In the course of such transmission the transmitted change undergoes a decrement in intensity or energy so that finally at a greater or less distance from its point of origin it becomes inappreciable or ineffective. In the simplest case such a transmitted change originates in a region of high metabolic rate, and transmission occurs to regions of lower rate. The region of high metabolic rate results in the final analysis from

the action of factors external to the mass acted upon, whether part of a cell or a cell mass. A simple schematic consideration will serve to make these points clear. Let us assume a spherical mass of living protoplasm (Fig. i) which is morphologically and physiologically homogeneous except as regards the essential features of protoplasm or cells. Such a mass, whether consisting Fig. I. — Diagram illustrating the origin of a single axial gradient in protoplasm: a, the point of action of the external factor.

of a single or of many cells, possesses no axis, is undifferentiated, and is not a physiological individual. Now let us suppose some external factor which increases metabolic rate, a ''stimulus," to act on this mass in the region a of its surface. The first result of such action is an increase in the rate of metabolic or of certain metabolic reactions in the region a. This is followed by a spreading or irradiation of a dynamic change, either over the surface of the mass or through it from the region a.

This change is fundamentally a transmission, not a transportation, for it consists in the passage of a certain energetic change and not in the bodily transportation of substance.' Such a process of transmission may be compared to the spreading of waves in a pond from the point where a stone is thrown into the water, although it probably does not always or necessarily consist of a series of rhythmical changes like the water waves. The question of the nature of the transmitted or conducted excitation has been the subject of much investigation and discussion, and many different attempts to answer it have been made. Recent investigation indicates, however, that whatever its exact nature, it involves an increase in metabolic activity. It seems in fact to be a wave of increased chemical activity spreading from the point of origin much as a wave spreads in a pond. The question of the relation of the electrical and chemical changes observed in the transmission of excitation in protoplasm does not concern us here. The fact of transmission and the increase in metabolic activity in connection with it are the important points for the present purpose.