Physiological Foundations of Behavior

It seems that something more than this is necessary to account for the facts. In Planaria, as in many other forms, cells at all levels of the body are capable of giving rise to heads, posterior ends or any other region of the body, but in any particular planarian the cells of each level actually give rise only to a certain region. Evidently it is not the hereditary mechanism of those cells, but their environment, i. e., their relations to other cells or parts, or to the external world, which determines what they shall do in any particular case. Consequently, although they are all primarily alike as regards hereditary constitution, they give rise to different regions and organs in the individual, and in isolated pieces they react to the altered environment by altering their behavior. Moreover, it has been shown in earlier chapters that physiological axes of polarity and symmetry may be experimentally altered and obliterated and that new axes may be determined in many different ways. Preformistic theory has usually

endeavored to account for such facts as these by the assumption that polarity and symmetry are inherent in protoplasm, but can be affected or altered by external factors. At present, however, there is no convincing evidence in support of this view and much against it (pp. 25- Again, the preformist maintains that the high degree of constancy of axiate pattern in each species cannot be accounted for, if polarity and symmetry are not inherent, but determined by environment. The development of the experimental method is showing us that this “constancy” is itself related to the conditions under which development of the individual occurs. As soon as we alter these beyond a certain limit, the constancy disappears. Apparently this relative constancy in development under normal conditions results chiefly from two factors: in the first place, the protoplasmic systems are products of very long periods of evolution and have attained a dynamic equilibrium or condition which under the range of conditions standardized as normal is relatively constant; and second, in the course of evolution the conditions under which the gametes arise and under

which the individual develops have become increasingly constant, 7. e., have undergone progressive standardization (see pp. 222, 223). In the excitatory reaction of protoplasm an external factor initiates, but the nature of the protoplasm is the primary factor in determining the character and further course of the reaction. In the case of a nerve fiber we know that the same effect may be determined by electrical, chemical, thermal, or mechanical energy and over a wide range of quantity or intensity for each form of energy. And as regards protoplasm in general we know that excitation is not dependent on any specific action of an external factor, but rather on a sufficient intensity, or perhaps in some cases, amount, of energy transfer. As regards the axial gradient we have seen that as soon as the external factor has brought its development to a certain point, the protoplasmic constitution becomes the chief factor in determining its further development. In a particular protoplasm similar gradients may result from widely different environmental relations, because, as in other reactions, so here the external factor merely initiates and the protoplasmic constitution determines the further course of events. As a matter of fact, the relative constancy and uniformity of so-called normal development and form present no difficulties to the conception of the individual as a reaction, a behavior pattern, in a specific protoplasm. On the other hand, the ease with which axial relations may be altered, obliterated or determined anew, does constitute a real difficulty for the preformistic conception. If a particular protoplasm possesses an inherent fundamentally bilateral “intimate” or molecular structure, the fact that such structure can be, so far as we can determine, completely obliterated by simply exposing the egg or embryo to certain concentrations of many different inhibiting agents (pp. 83, 104) is certainly remarkable and inexplicable.

We should expect such inherent structure to be one of the most stable and persistent characteristics of protoplasm, but as a matter of fact polarity and symmetry are readily altered, obliterated or determined in the simpler organisms and the earlier stages of development. Leaving out of account the speculative assumptions of preformistic theory and considering the evidence as it stands, the only possible conclusion seems to be that the individual organism as a pattern, an order, a physiological whole, originates in a reaction of a specific protoplasm to certain environmental factors. There is no conflict between this conception and modern theories of heredity, except in so far as some of those theories attempt to interpret the individual in terms of heredity alone. But when we recognize the fact that he-

-redity has to do with potentialities and the individual pattern with realization of come of those potentialities under certain conditions, the theories of heredity and the gradient conception are not in conflict, but supplement each other. Even the interpretation of inheritance in Mendelian terms does not account for the individual. It accounts merely for the distribution _ of certain differences in different individuals. For the realization of

the different potentialities segregated into different germ cells, environmental factors are always necessary. Here as elsewhere, the individual represents the behavior of a specific protoplasm in reaction to certain environmental factors. The gradient is merely the most generalized, the most primitive form of organismic behavior of a living protoplasm and if it persists long enough, it becomes the basis of later changes, some more or less permanent, others evanescent. Such changes constitute development, function, behavior of the individual. The gradient pattern constitutes the pattern, the order, the individuality in which the realization of the heredity potentialities occurs. That the gradients persist and so are hereditary in certain processes of agamic reproduction means merely that environmental relations are not such as to alter or obliterate them, but such persistence is in no sense Lamarckian inheritance.

The conception of the individual as a behavior pattern in a specific protoplasm is, in short, a purely physiological conception having to do with the realization of hereditary potentialities in the form of individuals. It is not in conflict with the facts of inheritance nor with the essential points of current theories of heredity, but accepts the hereditary potentialities as given in some form and attempts to account for the development of individuals from them. It is a theory of development and is therefore not primarily concerned with the problems of heredity, though the light which it throws on development may at some time be reflected to some extent upon those problems.

Regulation of function. — Investigation of the functional activities of organisms, particularly the higher animals and man, could not proceed very far without becoming aware of the existence of various mechanisms and processes which serve to control, order and adjust the various activities to varying conditions in such manner as to maintain the physiological unity and harmony of the organism in the changing environment to which it is subjected. Through such mechanisms and processes the activities of organisms are “regulated” within certain limits, and physiologists have very naturally come to call them regulatory mechanisms and processes. We know more or less concerning many such mechanisms in organisms, e. g., the mechanism of the regulation of heat production and heat loss in the warmblooded animals, of respiration, of blood flow and blood volume, of neutrality in the blood and tissues, of blood sugar, of the heart beat, of various digestive functions, of various internal secretions, of the transport of water, salts and carbohydrates in plants, and so on.

Our knowledge of even the simplest of such mechanisms is far from complete, but it is evident that with the progress of evolution their number and variety and the complexity of interrelation between them have increased, until in the higher animals and man they are far beyond the present range of scientific analysis. These mechanisms of functional regulation are mechanisms of physiological correlation, involving the transmission of excitation, or in some cases, of purely mechanical effects, or the mass transportation of substance, or in many cases, all of these factors. In general terms these mechanisms may be said to represent the rdéle of physiological correlation in maintaining the organism as a functional whole.

Regulation of form and structure. — With the development of the experimental method and its application to the phenomena of individual development, it became evident that the capacity for regulation or adjustment appears, not only in the special functional activities of organisms, but in the development of form and structure. The ability of the plant body to react to altered conditions by the development of new individuals or parts from other parts has long been known and it was demonstrated some fifty years ago that in certain of the simpler plants, every cell, or almost every cell, even though normally giving rise to only a small part of an individual plant, is nevertheless capable of giving rise to a complete new individual.

The systematic and analytic application of experimental methods to the development of animals occurred somewhat later, but as investigation along these lines developed, it was soon discovered that in the normal development of an individual only a part, often a small part of the hereditary potentialities inherent in any cell or cell group was realized. When the cell or cell group was subjected to conditions different from those which acted upon it in the normal or usual course of development, the reaction often showed that it possessed potentialities which did not appear at all under the normal conditions. It was discovered, for example, that in many species the two cells resulting from the first division of the egg, and in some forms even the first four or eight cells, or even smaller portions, were each capable when isolated from each other of giving rise to a complete embryo or larva. Moreover, although it has long been known that many animals were capable of regenerating missing parts, more extended investigation along these lines brought to light potentialities of isolated pieces, particularly in the simpler animals, which had been hitherto unsuspected. It was found that in many forms, e. g., hydroids, various turbellaria, ete., even small pieces of the body from any, or almost any region were able by a process of reconstitution to give rise to complete individuals.

The earlier workers in these fields, particularly the zodlogists, were much impressed by the fact that although the course of events in the reconstitution of a new whole from a part was in many respects different from the course of events in embryonic development, the final result was, nevertheless, within a wide range of experimental conditions, an individual essentially identical with the individuals of the species developing in the usual way. In such cases, then, although the course of developmental events was “abnormal,” the result as regards form and structure was “normal.’”” The only possible inference from such facts is that reaction and adjustment of some sort to altered conditions may occur in the development of form and structure as well as in the special functional activities of

fully developed individuals. On this basis developed the general biological conception of regulation. Definition of regulation. — In the development and formulation of this conception Roux and Driesch have perhaps played the most important parts.'' According to Roux regulation has a physicochemical basis and is dependent upon physiological correlation, but his interpretation is in terms of a preformistic theory of heredity and is to a large extent formal, rather than directly physiological. Driesch, on the other hand, postulates a non-mechanistic principle, to which he applies the Aristotelian term “entelechy,” as the basis of regulation and regards it as involving a purpose or end to be attained. In the conception of regulation as defined by these authors the idea of the normal plays an important part. For example, according to Driesch “regulation is a process or a change in a process occurring in the living organism by means of which a disturbance of any sort of its preéxisting ‘normal’ condition is wholly or in part, directly or indirectly compensated and the ‘normal’ condition, or at least an approximation to it, reéstablished” (Driesch, ’01, p. 92). Again, according to Roux, ‘regulation is the complete or incomplete compensation of disturbances, that is, the return or approach of the disturbed organism to the type or norm” (Roux, fI2 339).

In both these definitions it is implied that the “normal” condition is internally determined and independent of external disturbances. This conception of the normal is the logical consequence of the views of these authors. For Roux the normal organism is determined solely by heredity, although he is forced to recognize certain environmental factors as playing a part in the realization of hereditary potentialities. For Driesch the entelechy is the determining factor and physico-chemical constitution and conditions are merely means which it uses. For both, the action of external factors, except those essential to life, is always “disturbance” or alteration of the norm and regulation is the return or approach to it. Although Roux emphatically rejects the vitalistic viewpoint, his conception like other predeterministic conceptions of the organism involves a vitalistic or dualistic implication in that the hereditary mechanism is conceived as fundamentally autonomous in its relation to the individual organism.

From the strictly physiological viewpoint it appears impossible to maintain any such distinction between normal and abnormal, disturbed, or altered organisms. At all stages of its existence the organism is in relation to external factors of some sort and these factors are always subject to change. Life apparently consists in a succession of disturbances and alterations by external factors and in the reactions to them, and there is abundant reason to believe that in the absence of such disturbances and alterations life would soon cease and static equilibrium would sooner or later supervene.

It is evident, however, that protoplasms and organisms are within certain limits complex dynamic equilibrating systems. We mean by this that more or less complex internal alterations, compensations, reversals of former processes, etc., occur in relation to each other, in the living system following action upon it of an external factor, with the result that the system either approaches more or less closely its previous condition or progresses toward an altered equilibrium. Within certain limits the changes are such that life continues, and the order and integration which constitute the individual persist either with or without appreciable alteration. This capacity for equilibration depends primarily on the physiological interrelation or correlation of the various activities. In consequence of this correlation the effect of disturbance by an external factor is not limited

~ to the part directly affected, but is determined to a greater or less extent by the whole. Through physiological correlation with other parts, the change in the part directly affected may be more or less completely inhibited, compensated, neutralized, or otherwise obliterated and the organism may approach, or practically attain its previous condition, or the disturbance may modify the whole organism so that, instead of approaching its previous condition, it attains a new condition. Evidently in all cases in which life continues after such disturbance some sort and degree of equilibration must occur in the living system. Physiological equilibrium does not necessarily consist in return or approach to a preéxisting or normal condition, but may involve persistent alteration of the living system. In fact, it is at least a pertinent question whether the condition of a living organism is ever exactly the same after the action upon it of an external factor as it was before. It is impossible to answer the question on the basis of evidence, but it becomes more and more evident, as our knowledge of organisms advances, that the reactions to ex-

ternal factors very commonly consist in more or less permanent alteration of the organism in some way, rather than in a return to the preéxisting condition. Moreover, if we regard the organism as a physico-chemical system, it seems certain that we must answer the question in the negative. From this physiological standpoint the normal condition appears, not as a condition independent of external factors, but rather as the range of conditions determined in a particular organism, species or group by the range of quantity, intensity and kind of external actions to which it is ordinarily subjected in its natural environment. In other words, the normal is nothing more than the usual, as standardized in the course of evolution. Normal individuals of the same species, variety, or race may differ from each other, both as regards hereditary potentialities and the alterations determined by external factors, and as a matter of fact no two of them are alike.

What then becomes of the conception of regulation as a return or approach to the normal? It seems clear that the regulatory mechanisms are mechanisms of dynamic equilibration and that regulation is in general dynamic equilibration of some degree and some sort, in reaction to a disturbance. But if it is true that an organism is never the same after action of an external factor as it was before, every equilibration is, strictly speaking, an alteration, and every regulation is to some extent a modification, rather than a return to a preexisting condition.

The point of chief importance in this general discussion is that the conception of the normal and that of regulation, like any other abstractions, merely serve the purpose of calling attention to certain similarities, while ignoring certain differences in a number of individual cases viewed from a certain standpoint. The persistence and continuity of the individual organism in a changing environment is unquestionably a fact of great interest and significance and, observing that in general organisms of the same Species are much alike, we reach the conception of the normal. Similarly, when we investigate the physiological conditions on which their maintenance and persistence is based, we see that when these are disturbed by external factors they commonly react in a way that appears to be useful in that it makes maintenance possible. The reaction may be a compensation of the disturbance, an escape from it by locomotion, or some other reaction, but the effect in general is some sort and degree of equilibration of the system as a whole. On this basis we attain the idea of regulation as a useful reaction. Both

these conceptions are convenient and valuable, but when we view living organisms in certain other aspects, we see variation instead of a normal, and equilibration and modification instead of regulation as a return to normal (Cf. Herrick, ’24, chap. XX). The broader conception of regulation as equilibration is more satisfactory from the physiological standpoint, because it does away with the difficulties inherent in the conception of regulation as fundamentally a useful and apparently purposive process, involving an approach or return to normal. Much stress has been laid upon the apparently useful or purposive character of regulatory processes. In the mutilated animal, for example, missing parts may be replaced or at least healing of the wound occurs. In the mutilated plant removal of a part may be followed by development of new, or modification of old parts in other regions of the body. In the sea urchin and various other forms isolated blastomeres or portions of the embryo, within certain limits of size and region, develop into complete larvee. In all such cases the regulatory process appears to be useful.

Functional regulations, 7. e., regulations of special function in mature organisms, show similar characteristics. In the mammal a rise in internal temperature brings into play mechanisms which tend to decrease the internal temperature; life in high altitudes brings about increased production of red blood corpuscles; similarly in motor reactions, the organism encountering unfavorable or injurious conditions commonly moves away, and the useful reflexes, such as the withdrawal of a part from painful stimulation, the closure of the eyelid in excessive light, etc., are familiar to all.

The wide range, great variety and remarkable delicacy of the useful and apparently purposive regulatory or equilibratory mechanisms in organisms has often tended to obscure the fact that there is also a great group of reactions to disturbance which do not tend toward restoration of the normal and which are neither useful nor purposive. Many interesting cases of this sort are found in the developmental reactions of isolated pieces. Under certain conditions isolated pieces of hydroids, planarians, etc., give rise to partial individuals, biaxial heads, headless forms, ete. Pieces which give these “abnormal” results are not necessarily any smaller or otherwise different from pieces which give rise to “normal” animals. In fact, it can often be determined experimentally whether a piece shall give a

normal or an abnormal result. Many of these abnormal forms are incapable of continued existence because of absence of essential parts, such as mouth, certain sense organs, organs of attachment, etc. It is also possible to alter and control by means of experimental conditions the proportions and relations of organs and parts and so to produce forms which are extremely abnormal in various respects and often incapable of continued development, or even of continued existence.!

Similarly the special functional regulatory mechanisms, under conditions outside the normal range, may work in such a way as to alter, injure, or even destroy the organism. A case in point is the ability of the organism to acquire tolerance to drugs or other toxic substances. The development of tolerance may lead to habit-formation and the desire for larger and larger quantities. Shelford (’18) has shown that fishes rapidly establish a preference for water containing certain toxic substances, e. g., alcohol, cocaine, ete., but to carbon dioxide, which apparently has physiological action resembling in certain respects that of alcohol and cocaine, they are persistently negative (Shelford and Allee, ’14). The interpretation suggested is that since fishes may be exposed more or less frequently within the range of “normal” environment to carbon dioxide in toxic concentration, evolution has had time to act by natural selection or otherwise in developing the negative useful reaction. Alcohol and cocaine, on the other hand, being outside the range of the normal environment, the reaction of the fishes to them occurs independently of useful or injurious results. Similarly the moth singes its wings or even kills itself in the flame to which it is attracted. The mechanisms of heat regulation, neutrality regulation, blood sugar regulation, etc., in man may work under certain conditions of disease or experiment in very different manner from the normal and injury or death may result.

All these cases obviously involve equilibration in the organism, but they are equilibrations to unusual or abnormal conditions, 7. e., conditions more or less outside the range standardized by evolution. The point which I wish to emphasize is that the useful, apparently purposive regulations are not a fundamentally different category of reactions from these injurious or destructive reactions, but that both belong physiologically in the same category of equilibration processes. The useful regulation is an equilibration process of significance to the

organism in its relations to environment. Once present as a potentiality of a particular protoplasm, such a reaction may of course become a factor in evolution, 7. e., the protoplasm possessing it may be maintained or favored by natural selection and so the reaction may in time be regarded as an adaption, but the equilibration process itself is a matter of the physico-chemical constitution of the protoplasm and its reaction to a certain range of environment.

The useless, injurious, or non-adaptive equilibrations are usually, if not always, reaction to conditions outside the standardized range of the normal, e. g., the reaction to habit-forming drugs, the reaction of the moth to the flame, the development of biaxial or partial forms from isolated pieces and of abnormal forms under experimental conditions. Physiologically these are as truly equilibrations as the useful reactions, but whether we call them regulatory or not depends on whether we regard regulation as simply equilibration or as equilibration which is useful to the organism.

Normal development and heredity. — It may appear, and in fact has often been asserted that.the course of development in its earlier stages is, so far as its “typical” or “normal” features are concerned, independent of external factors and determined by heredity (pp. 215- 219). That is to say, up toa certain point at which functional relation to the external world begins, the individual organism represents primarily the working out of a scheme, order, or pattern predetermined by heredity. This typical hereditary course of events may be modified by external factors which transcend the normal range, but within the normal range the external factors play no essential part, except in making possible the continuation of life. This typical or normal course of development unmodified by external factors results in the normal individual and regulation represents the return or approach to normal when modification does occur. According to this preformistic conception, the development of the individual represents primarily the construction of certain mechanisms through internal factors, and only when this construction is completed, or has attained a certain stage, does function begin. Regulation is a sort of repair process, through which the hereditary mechanism obliterates or compensates more or less completely the accidental action of external factors. The biologists of the Roux-Weismann school, and particularly Roux, have made much of this distinction between the typical or normal as predetermined and the regulatory

as essentially the result of accident, and have attempted in various ways to reconcile it with the facts of developmental physiology. Actually, however, it becomes more and more evident that life is largely, if not wholly made up of accidents. The constancy and uniformity of normal development in nature, results, as already noted, from the fact that a certain degree of standardization has occurred in the course of evolution as regards the range of such accidents to which the developing individual is likely to be exposed. This has been accomplished in various ways, e. g., through position of the gonads, through conditions under which fertilization occurs, through the formation of enveloping membranes, jelly, or capsules about the developing eggs, through the selection of certain localities for egg deposition, through care of the young, viviparity, etc. But these various provisions do not eliminate external factors; they merely tend to limit the variation in range, in other words, to standardize their action.