Physiological Foundations of Behavior

1 See for example, Pfeffer, 97, p. 70, gives references to the more important some other fibrillar structures, it appears predominantly in dead secretions and inclosures rather than in the living protoplasm. It has been pointed out repeatedly that the appearance of anisotropy, particularly in various fibrillar structures, may be the result of mechanical tension. Very generally the axes indicated by such anisotropy have reference to local conditions, single cells, fibrils, etc., but in some of the unicellular organisms the anisotropy of the ectoplasm of its outer layers indicates a close relation between the axis of the organism and the structural system underlying anisotropy. In all the eyidence, however, there is nothing to justify the assumption that anisotropy is a primary, inherent property of protoplasm. Apparently it arises secondarily, either because of the crystalline character of the substance in which it appears, in consequence of mechanical tension, or possibly of other local conditions. These investigations then afford no support to the theory of molecular or micellar polarity and symmetry.

And finally, the supporters of the stereochemical theories have not been able to show in any convincing way how the molecular structure and orientation determine the differences in rate of metabolism and of growth and the course of differentiation in different cells or cell groups. Harrison’s recent stereochemical interpretation of the symmetry relations of amphibian appendages in his transplantation experiments (Harrison, ’21) may be cited as a case in point. Here, as in so many other cases, the stereochemical structure is simply assumed, apparently without evidence and without consideration of-the difficulties involved in the assumptions (see pp. 126-129).

As a matter of fact polarity and symmetry appear to be largely if not wholly independent of the specific constitution, whether molecular or molar, of different protoplasms. Different axes, different axial combinations and different symmetries may appear in nature or be experimentally determined in a particular protoplasm and similar polarities and symmetries may exist in very different protoplasms (see pp. 33, 41). In axiate organisms, then, as in simpler forms, the factor which determines the order and unity of the individual is apparently a non-specific factor, while the specific hereditary constitution of the particular protoplasm determines the specific characteristics of the individual.

It may also be noted in passing that the conception of formative substances advanced by Sachs and its various modifications in the hands of Loeb, Conklin, Morgan and others, do not afford a solution of the problem of polarity and symmetry, for the movement of the formative substances to the proper regions or their gradation or segregation in the proper order, must depend either upon a preéxistent underlying polarity or be in some way directly determined by external factors. In either case the nature of polarity and symmetry remains to be determined. Moreover, it seems to be true that thus far no one has really demonstrated the existence of a formative substance in organisms, or has even shown how any particular substance may exert a really formative action.

The fundamental difficulty of the predeterministic conception as regards the organism as a whole lies in the assumption that the unity and order, the “‘wholeness”’ of the individual organism, as well as the hereditary potentialities of the individual, are inherent in the protoplasm. No theory of heredity can account wholly for the individual organism. The individual represents heredity plus environment, in other words, behavior of a particular kind of protoplasm with certain hereditary potentialities, genes, or factors, in a particular environment. This behavior is the factor which orders and unifies the hereditary machinery and constitutes the starting point of the organism as a whole. The problem of the individual is then the problem of the environmental factors initiating this behavior, the nature of the behavior itself and of its action in realizing the hereditary potentialities.

This conception falls of course into the category epigenesis, but it differs somewhat from the earlier epigenetic theories. It does not necessarily conflict with, nor replace modern theories of heredity, except as they attempt to interpret the individual as “the collective action of the genes’’ alone, but merely supplements them by providing a physiological basis for the orderly realization of the hereditary potentialities in the form of an individual organism. The interpretation of the order and control of hereditary potentialities in the individual organism has alway constituted a stumbling block for predeterministic theories of heredity. They must either deny it or ignore it, or they must postulate a supergene which controls and orders all the others, or a predetermined harmony among the genes. There is no evidence for a supergene, and predetermined harmony among the genes can scarcely be accounted for in other than dualistic or vitalistic terms. If, however, it can be shown that simple reactions to environment, to which every germ is exposed, are concerned in the orderly and harmonious realization of the hereditary potentialities, all the difficulties concerning the organism as a whole disappear. Then the organism as a whole represents, 10% heredity

alone, but heredity plus environment, in other words, it is primarily the reaction to environmental factors of a protoplasm with a certain hereditary constitution. The organism is inexplicable without environment. Every characteristic of it has some relation to environmental factors. And particularly the organism as a whole, 7. e., the unity and order, the physiological differences, relations and harmonies between its parts, are entirely meaningless except in relation to an external world. Nevertheless predeterministic theories have maintained that the organism as a unity and order is primarily independent of an external world and enters into relation with it only secondarily. This viewpoint has resulted in confusion and sterility in various fields of biological thought, and, as Dewey has pointed out, a similar viewpoint has had much the same effect in philosophy (Dewey and others, 17).

It may be pointed out that the recognition of the significance of environmental factors in determining the unity and order of the organism does not, as often wrongly assumed, involve us in La- marckian assumptions, or hypotheses. The action of environment is primarily a matter of the developmental physiology of the individual. If the effect of such action persists through more than one cell generation this persistence involves no transmission of effects from body to germ cell, but the effect persists merely as a physiological condition in the protoplasm which arises by cell division and growth from the protoplasm originally affected. In pieces isolated by section from the stems of certain hydroids the polarity of the original individual may persist in the piece and the new individual, therefore, inherits its polarity. On the other hand, it is possible to determine experimentally a new polarity in pieces and such pieces may give rise to new individuals and these may again be cut into pieces which inherit their polarity. Similarly an egg may conceivably inherit its polarity from earlier cell generations and somewhere in the course of these generations this polarity may have been determined by environmental factors. It is obvious, however, that such cases involve no Lamarckian assumptions concerning inheritance of “acquired” or somatic characters, but represent simply the persistence of direct physiological effect of environment upon the germ cell or other reproductive unit. Moreover, the general conception illustrated by such cases may provide a simple physiological interpretation of certain facts which have seemed to favor La- marckian hypotheses.

Vitalism as a biological form of dualistic theory is simply the assumption of a metaphysical ordering and controlling principle of some sort as the basis of unity and order in the individual organism. The older vitalism was essentially the inference drawn from the uncritical observation of the behavior of living, as contrasted with nonliving things and from introspection, and needs no comment here. The so-called neo-vitalism, however, is based to a considerable extent on the data of modern experimental biology, and is concerned primarily with the question of order and unity in the organism, 7. e., the question of the organism as a whole. Driesch’s entelechy, for example, is the ordering and controlling principle which brings order and unity out of the physico-chemical complex (Driesch ’08, and earlier papers).

This neo-vitalism unquestionably represents in some degree a reaction from the predeterministic conception of the organism. The neo-vitalist sees clearly the ditficulties involved in the conception of organismic unity and order in predeterministic physico-chemical terms, but at the same time he fails to recognize the significance of environmental factors in relation to unity and order. Consequently the only way out for him is the assumption of a metaphysical ordering and unifying principle. to which he gives a name. The chief service of neo-vitalistic theory to biological thought is perhaps its clear recognition of the difficulties involved in physico-chemical predeterministic conceptions of the organism, but it fails to take account of environment. Driesch’s arguments against the “machine theory”’ of the organism are valid only against predeterministic conceptions of the “machine” as consisting of specific or qualitatively different localized parts, and fall to the ground at once when it is conceived as a quantitative dynamic machine related in its action to environmental factors. Driesch used for example, the argument that ‘a machine cannot remain whole when separated into its parts #3 to prove, as he says, that a mechanistic interpretation of the reconstitution of new individuals from the various isolated parts of a preexisting individual is impossible. The argument holds only of the “machine” as specifically or qualitatively different in its different parts. If it is fundamentally a dynamic “‘machine,”’ e. g., an eXx- citation-transmission process, or the record in protoplasm of such a process, it may remain whole when separated into parts just as truly as two flowing streams resulting from the division of one are

wholes to the same extent as the original stream. In short, the physiological gradient (Child, ’15b, ’21 a) is a “machine” for which Driesch’s arguments do not hold. In general, the vitalistic or dualistic viewpoint with its negation, explicit or implicit, of the value of scientific method, does not provide a solution of the problem of the organism which is intellectually satisfying to the inquiring mind, and real “ proofs of the autonomy of vital processes”’ are at present non-existent. Only when all physico-chemical possibilities of experiment and interpretation shall have been exhausted without providing a satisfactory solution will a vitalistic formulation of the problem be scientifically justified.

If we admit that environmental factors play some part in ordering and unifying the process of realization of hereditary potentialities in the development of the individucl organism we avoid the difficulties of predeterminism and do not require vitalism. We do not hesitate to say that certain potentialities given in the hereditary constitution of the protoplasm are realized only in relation to the action of an external factor. The pecking reaction of the newly hatched chick, for example, represents a high degree of integration of behavior, but although the machinery for it is present, the integration itself occurs in relation to an environmental factor. Similarly the hereditary constitution of the particular protoplasm, the genes, factors or whatever we may call the hereditary potentialities, constitutes, so to speak, the machinery for the development of the organism as a whole. The integration of this machinery into an orderly working unit, however, does not occur autonomously any more than the integration of motor behavior in later stages of development, but in the first instance only in response to the action of an environmental factor. From this viewpoint the organism as a whole represents an integration of behavior just as truly as do the complex motor reactions of later stages. Moreover, the organism as an order and unity in protoplasm is the primary behavior integration on an organismie scale, and on it all others are based. Following chapters are devoted to the further development of this conception.

In Chapter II it was pointed out that the organism stands in relation to environment at all points and that all of its characteristics re referable in one way or another to this relation. If this is true, it follows that the pattern of the organism in its more general features must constitute a physiological basis underlying the whole complex of reaction patterns and mechanisms, 7. e., the behavior in the broadest sense of the individual. As we pass from the general to the special features, the details of organismic pattern, we find that the more highly specialized and specific these features, the more directly are they concerned in some particular reaction pattern or mechanism of a particular species or group. We may say then that the general features of organismic pattern constitute the basis of physiological integration of the organism and so make it possible for it to react in one way or another as a whole, while the special mechanisms of reaction depend not merely upon the presence of an organismic pattern but upon the material, the kind of protoplasm in which the pattern exists.

When we compare different organisms we find that the most general features of organismic pattern are much alike for many different forms. B For example, the same general plan of Fia. Poe VIAcTA ROBES ee “ ari ‘ symmetr < . polar-bilateral plant and animal: (4) a polarity and s metry EB) oe liverwort; (B) Planaria, a flatworm. in protoplasms of very different con- The dominant region 3 the trowing stitution but as we progress from the ae ne eels) in the fla

pattern the part played by the specific constitution of the protoplasm becomes more and more conspicuous. The special mechanisms and structures which arise along a polar axis or a plane of symmetry in different species and groups depend not merely upon the existence of a polarity but upon the nature of the protoplasm in which the polarity or symmetry exists. For example, the liverwort Marchantia, the flatworm Planaria (Fig. 1) show certain resemblances as regards the general plan of organization, but differ as regards the particular reaction mechanisms. Both forms possess polarity and bilaterality, that is, a longitudinal and a ventrodorsal direction of order: the planarian possesses a head region, the Marchantia a growing tip and these regions dominate or control in some way and to some degree other regions of the body within a certain range. But in spite of these general resemblances the two organisms are very different in structure and behavior because the protoplasms are different in constitution. The general organismic pattern merely determines a general plan or order of integration, but the sorts of parts, organs, mechanisms, etc., which are integrated depend upon the constitution of the protoplasmic material. As a preliminary to further analysis along these lines it is necessary to determine if possible what the most general characteristics of organismic pattern are.

So far as the actual physiological relations which integrate the regions, parts or organs of an organism into an orderly whole are concerned, the fundamental characteristic of organismic pattern appears to be a relation of dominance and subordination of control and being controlled. The physiological relations between different regions or parts of an organism may be collectively called physiological or organismic correlation. Like the relations between organisms and the external world, they may be, on the one hand, material, 2. €., chemical or transportative, consisting in the mass transportation of substance, or, on the other, dynamic, consisting in energy transfer, and the dynamic relations may be either mechanical or excitatory (see Chap. V).

In material or chemical correlation between parts, the part producing a substance which influences another part controls the latter to some extent. This is also true in cases in which chemical relations between the two parts are more or less mutual. Such cases are in some degree analogous to the social reaction system consisting of two groups of human beings between which mutual commercial relations exist. To take a rather primitive social system of this sort, one group for example inhabits the coast, the other an inland region. The first group exchanges fish, shell, salt, for skins, game, or perhaps

_ for metal articles. The articles received constitute a factor in deter- - mining the further activities of the group in each case. In purely mechanical correlation the part in which the mechanical change is initiated dominates other parts, e. g., in the muscleskeleton correlation, the muscle is dominant. In the mechanical correlation involved in circulation of the blood the heart is dominant, but as regards particular regions vaso-motor factors exercise a certain degree of control. In other forms of mechanical correlation dominance and subordination are also concerned in some way.

The relation of dominance and subordination appears most clearly, * and is most important in excitation and its transmission. The point of primary excitation is the region of primary dominance, and as each adjoining region is excited in the course of transmission it becomes dominant over regions still unexcited. If a decrement occurs in transmission so that an excitation-transmission gradient appear, (see pp. 186, 195) the region of primary excitation dominates the whole gradient because it is the chief factor in determining its existence. This sort of dominance and subordination is most highly developed in the nervous system of higher animals and its relations ~ to other parts, but is a general feature of organismic pattern, since all protoplasm is excitable and to some degree capable of transmission.

The harmonious activity of different parts or organs, particularly in the motor reactions of organisms, we call codrdination. It is this coordination which gives organismic behavior its orderly and definite character. The complexity of codrdination increases with the complexity of mechanism and in the higher animals and man muscular coordination, for example, is almost inconceivably complex. We know that the acts of walking, flying, swimming, necessitate the harmonious activity of many different muscles and muscle groups and that the acquirement of skill in highly specialized motor reactions, such as writing with pen or typewriter, or playing the piano or violin, really consists in the development of a greater delicacy and refinement in coérdination.

The conspicuous character and importance of this harmony or coérdination in reaction has perhaps tended to obscure the fact that the codrdination pattern represents physiologically a system of re- Jations of dominance and subordination. In playing the piano, for example, a relation of dominance and subordination exists, first between the sensory cells, the receptors of the eye which receive the elements of the sense impression of the notes on the printed page, and their nerve fibers which transmit the excitation; second, between the

ends of these fibers and other nerve cells stimulated by them, and so on, through various parts of the central nervous system until the motor neurons, leading to the effectors, in this case the muscles, and dominating them are reached. The codrdination of parts in the reaction actually consists of relations of dominance and subordination, of control and being controlled. The order of these relations depends in any case upon the mechanisms concerned, that is, upon the manner in which the series of relations of dominance work out in that particular organism at that particular time. Differences in physiological state of different neurons resulting from previous relations may determine that one is dominated by a certain nerve impulse reaching it, while another is not so dominated. In this way the ' further path of the imif c 2 : : ;

of relations of physiological dominance and subordination, from the receptor, the sense organ, through the conductor to the central organ the adjustor, from this again through the efferent neuron to the effector, e. g., the muscle. According to this brief analysis, the physiological factor primarily concerned in the integration of the regions or parts of an organism in organismic reaction is a relation of dominance and subordination. _ This dominance and subordination may be determined in one of \ three possible ways, 7. e., by mechanical correlation, by material, chemical or transportative correlation, or by excitation and its transmission. The question of the rdle which these different sorts of

dominance and subordination play in the origin of organismic pattern is considered in later chapters. The fundamental spatial factors in organismic pattern are those which determine the localization and arrangement of organs and parts, and so the form of the whole. Whatever their nature, they constitute the general spatial plan of organization which underlies development and differentiation. The most general characteristics of spatial pattern in organisms are physiological polarity and symmetry.

Since polarity and symmetry of some gort are of wide, if not of universal occurrence among anisorgms, they must be in large meas- - ure independent of the differences in specific constitution of the different protoplasms, or else they must differ in nature in different protoplasms. In relation to polarity and symmetry there are in fact only three components of pattern in all organisms (see p. 26, Chap. VI). These are the radiate, the polar or longitudinal and the bilateral or dorsoventral. In the radiate pattern the arrangement of parts is geometrically about a point, in the polar pattern it is referable to a line and in the bilateral pattern to a plane, the so-called plane of symmetry. It is important, however, to note that physiologically a bilateral pattern may result from ventrodorsality or dorsoventrality, that is, the general direction of the order or pattern may be either ventrodorsal or dorsoventral, in other words neurohaemal, so far as animals are concerned, but since the organism is tridimensional, dorsoventral difference involves also a difference between \ median and lateral, and right and left sides are mirror images of each | other, hence the term “bilaterality.” In other words, as regards the right and left sides of the body, the primarily ventrodorsal or dorsoventral order consists of two similar components in opposite directions from the median plane, but viewed as a whole it represents only the one order.

The botanists have apparently recognized this fact more clearly than the zodlogists, perhaps because of the direct relation of the dorsoventral order in many plants to an environmental differential in one direction. In the present book the terms “ bilaterality” and “bilateral symmetry”’ are employed in conformity with general z0é- logical usage, but it is important from the physiological viewpoint to recognize the fact that bilateral pattern may be an incidental feature of a single order at right angles to the polar axis and determining primarily ventrodorsality or dorsoventrality. We very commonly refer bilateral symmetry to both a transverse and a dorsoventral axis, but though our knowledge of the physiological conditions underlying bilaterality is still far from complete, it seems to be true that the bilaterality of whole organisms is usually the result of a physiological order in one direction, a direction different from that determining the polar pattern. Obviously, however, the origin of bilaterality is possible by a direct determination of a physiological order in two opposite directions independently of, and preceding determination of a dorsoventral order. This possibility may be realized in various cases. And finally the asymmetric modifications of bilaterality result from differences in the two sides which must be determined by special conditions. These conditions may be different

in different cases, but concerning them we know as yet practically nothing. : Polarity and symmetry constitute in some way the basis of the geometric order or plan of the organism. They represent, so to speak, Fies. 3-5.—Various types of radiate organismic pattern: Fig. 3, diagram representing surface-interior pattern. All radii (AC), (EC), (KC), ete., are alike and the only regional differences are along the radii from surface to interior; Fig. 4, diagrammatic outline of a hydromedusa. The two radii of each diameter represent similar orders, but in opposite directions: Fig. 5, diagrammatic outline of a starfish. The two radii of each diameter represent dissimilar orders and indications of bilaterality are present in the position of the madreporite (m), and of certain internal organs. In Figs. 4 and 5 general plan of central nervous system, (ns) is indicated.

a system of coérdinates to which we refer organismic pattern. The simplest conceivable organisms are those in which differences exist merely between surface and interior (Fig. 3). Such organisms are completely or spherically symmetrical, that is to say, the geometric plan of the pattern is represented by the radii of a sphere. Most organisms, however, show some degree and kind of axiate pattern (Figs. 4-9), 7. e., some combination of polarity and symmetry. As ‘regards the chief axis, axiate organisms are heteropolar, 7. e., the polar axis represents the direction of an order, arrangement and relation in which each level differs from all others (Figs. 4-9). The

Fias. 6-9.—Bilateral patterns and spiral modifications: Fig. 6, diagrammatic figure of Planaria as example of bilateral pattern, (ms) central nervous system (from Child, ’15 c);. Fig. 7, diagrammatic transverse section of Planaria (ns), longitudinal nerve cords; Fig. 8, Paramecium showing spiral course of oral groove; Fig. 9, 6 a rotifer, Diuwrella tigris, showing the spiral ridge along body (from Jennings, ’03). axes of symmetry, 7. ¢., the directions in which the order constituting symmetry appears, may be either homopolar or heteropolar. They are homopolar in certain radiate forms (Fig. 4) in which the two radii of a diameter represent similar orders, but in opposite directions, 7. ¢., are mirror images of each other, and in bilateral forms in which the medio-lateral orders are likewise in mirrored relation, 7. e., similar, but in opposite directions (Figs. 6, 7). In certain other radiate forms the syminetry axes are heteropolar, e. g.,

in starfish and sea urchin (Fig. 5), and the two radii of a diameter represent more or less dissimilar orders, opposite in direction. Again, the dorsoventral axis in bilateral forms is heteropolar, 7. e., a single order, each level differing from others (Fig. 7). And finally, there are spiral modifications of radial and bilateral pattern (Figs. 8, 9) and left and right lateral asymmetries of many different parts occur in many forms, e. g., the visceral asymmetry in mammals and man.