Individuality in Organisms

Further analytic investigation along these lines is greatly needed to enable us to determine the part played by the various factors in different cases of reproduction, but the mere observation of various reproductive processes — such, for example, as the production of a newplant by a strawberry runner, after it has attained a certain length — will enable us to learn much concerning the range of dominance and its changes under different conditions.

The reduplication of parts in an organism, such as leaves and roots in the plant and segments and various other parts in the animal, belongs in the same category with the reproductive processes which give rise to new whole organisms. In such cases physiological isolation may be partial or with reference to a specialized constituent individual of the organism. The localization of reproduction in the individual may be determined by various other factors besides distance from the dominant region. Some parts less distant than others may be physiologically isolated earlier because of lower conductivity of paths, or because of other correlative conditions within the organism, or because of certain external conditions. In isolated parts the least differentiated cells or regions, or those with the highest metabolic rate, are likely to react earher tnan others and so determine the localization of the reproductive process. Sometimes, particularly among plants, in reproductions which occur with advancing age or under depressing conditions, it is the original dominant region which separates from other parts as a smaller individual and so becomes the reproductive body, spore, or whatever it may be called.

Special unrecognized factors may play a part in certain cases, but it seems impossible to doubt that, in general, agamic reproduction in organisms results from physiological isolation of parts of the individual. Individuation is a physiological integration depending primarily on the dominance and subordination of part's in relation to an axial gradient or gradients, and agamic reproduction is a physiological disintegration of this unity which makes possible new integrations.

The fundamental similarity in individuation and reproduction in the lower animals and plants is well illustrated by a comparison of certain corals with tlie plants. Wood- Jones' has recently found from a study of living animals under natural conditions that in the staghorn corals there is a radially symmetrical, apical zooid at the tip of the stem which gives rise by budding to the bilaterally symmetrical, lateral zooids, while these do not reproduce as long as the apical zooid is present and active. At a certain distance from the apical zooid one of the bilaterally symmetrical zooids may become radially symmetrical and begin to reproduce new zooids and so become the apical zooid of a branch. If the apical stem-region with the apical zooid is removed, several branches may arise by the transformation of bilateral into radial, reproducing zooids. Moreover, the apical zooid of stem and branches remains young indefinitely, while the lateral zooids which do not reproduce undergo senescence and die. In other corals various degrees of composite individuation are found to exist. The relation of the dominant apical zooid to other parts in the staghorn corals is very evidently essentially the same as that between the growing tip and other parts in plants, and it is impossible to doubt that the same fundamental principle underlies and determines the relation, not only in these two cases, but in organisms in general.

Sexual or gametic reproduction, with rare exceptions the only reproductive process giving rise to whole new organisms among the higher animals, is commonly regarded as very different from the agamic reproductive processes. Actually, however, there are certain fundamental similarities between the two processes. I have discussed this matter at some length elsewhere/ and need only review certain important points here. The evidence indicates that the gametes, the two cells which unite in sexual reproduction and which in their more highly specialized forms we call egg and spermatozoon, are physiologically subordinate parts of the body and undergo differentiation with other parts, instead of being composed of a mysterious, independent substance, the germ plasm, as Weismann and many others have believed. Gametic maturity occurs at a relatively advanced physiological age in the organism, and the gametes, like other parts of the body, are physiologically old cells with a low metabolic rate and are evidently approaching death. Their isolation from other parts of the body in those multicellular forms in which complete isolation occurs has apparently no relation to the range of dominance, but seems rather to be associated with the completion of their period of growth and differentiation. So far as the parent organism is physiologically concerned, the isolation of the sex cells may be compared with the casting off of other old cells which have played their part and are approaching death. In many cases, however, the egg remains in the parent body until an earlier or later stage of embryonic development is reached, but even in such cases the egg, after completing its developmental period, seems to have little physiological relation to other parts of the parent body.

Except in the case of parthenogcnic eggs, which develop without fertiHzation, neither of the gametes undergoes dedifferentiation and a new development Ijy itself, but in some way their union, or conditions associated wdth it, or in various cases certain experimental conditions (''artificial parthenogenesis"), initiates the process of dedifferentiation and rejuvenescence which makes possible the development of a new individual and a new period of differentiation and senescence. The increasing metabolic rate and the loss of differentiation in the early stages of embryonic development indicate clearly that rejuvenescence is occurring, but sooner or later the intake of nutrition results in renewed accumulation of substratal substance and senescence begins again. The period of dedifferentiation and rejuvenescence is short, and during most of its development the sexually produced organism is growing old.

As I have endeavored to show, the development of the individual in gametic reproduction is fundamentally the same process as in agamic and experimental reproduction. In most cases the polarity, i.e., the major axial gradient, and in some cases the minor gradients, are determined in the eggs before embryonic development begins, usually, so far as observation permits definite conclusions, by their relations to the parent body, but in some of the lower plants the major axis is apparently determined after the egg leaves the plantbody by the direction or differential action of light or other external factors. The point of entrance of the sperm seems in many cases among animals to be a factor in determining the symmetry gradients, where they are not already determined. In at least many

plants, however, and doubtless in some animals, the symmetry gradients are determined in later stages. From this point of view the chief difference between agamic and gametic reproduction is that in the latter the mere isolation of the reproductive body from the parent individual is not sufficient to start the process of dedifferentiation and new development. The gametes do not react except under special conditions, because they have become so highly specialized and differentiated as parts of the parent individual that they are incapable of such reaction. But when the special conditions are present, dedifferentiation begins and development proceeds. Certain eggs develop parthenogenically, and these in many cases are very evidently less highly differentiated than eggs which require fertilization. It is probable that they or some of them represent a stage in gametic development in which the egg is still capable of reacting to isolation like the physiologically or physically isolated part of the body of Tuhidaria or Planaria by undergoing dedifferentiation and a new course of development. If this conclusion is correct, these parthenogenic eggs represent a condition intermediate between the parts of the body of lower forms which undergo agamic reproduction when isolated and the more highly specialized gametes for which fertilization is a necessary condition of further activity. At least many of the eggs in which development can be initiated experimentally by other means than fertilization are apparently almost capable of natural parthenogenesis, and so are probably less highly specialized than eggs which are not susceptible to experimental treatment.

If we accept this view, we must regard gametic reproduction merely as a more highly spcciaHzed form of reproduction which occurs in more advanced life or in more highly differentiated individuals than agamic reproduction, but which involves essentially the same cycle of differentiation and senescence, followed by dedifferentiation and rejuvenescence, the production of a new individual, and another period of differentiation and senescence. From this standpoint the egg and the embryo are in general the most unfavorable material that could be found for the investigation and analysis of the processes of reproduction and individuation, for in most cases the gametes are formed in the parent organism under C(jnditions which do not permit of extensive and exact experimental control. Moreover, they consist of single cells, and so cannot be divided experimentally before development begins, and the egg has usually attained a certain, often a very high, degree of individuation before it is isolated. The agamic and experimental reproductions afford a much wider range of control, and we can analyze the beginnings of individuation there as we cannot in the egg. The only logical procedure is, in my opinion, to interpret gametic reproduction, as 1 have attempted to do, on the basis of our knowlerlge of the experimental and agamic processes, and not vice versa. Our slow progress toward an adequate conception of organic individuality has undoubtedly been due in considerable part to the fact that we have confined our attentioTi so largely to gametic reproduction, and have neglected the simpler processes in which, if anywhere, the key to the problem is to be found.

If the organism is fundamentally a specific reaction system in which quantitative differences initiate physiological individuation, development, and differentiation, nothing can be more certain than that it acts essentially as a unit in inheritance. It is the fundamental reaction system which is inherited, not a multitude of distinct, qualitatively different substances or other entities with a definite spatial localization. Development is not a distribution of the different qualities to different regions, but simply the realization of possibilities, of capacities of the reaction system. The process of realization differs in different regions because the conditions are different. Neither characters nor factors as distinct entities are inherited, but rather possibilities, which are given in the physico-chemical constitution of the fundamental reaction system, but not necessarily localized in this or that part of it.

The fact that in the past investigation of inheritance has been almost entirely limited to the special aspects of heredity and development connected with gametic reproduction has contributed very largely to delay our progress and limit and distort our conceptions of the processes cf inheritance. This, the most highly specialized form of reproduction, is the most unfavorable point of attack upon the problems involved, for the possibilities of control of the earlier stages of individuation are narrowly limited, and many factors which are not really essential to reproduction and development are characteristically present in this reproductive process.

The process of inheritance is involved to exactly the same extent in the reconstitutional development of a new individual from a piece of Tuhularia stem or of the planarian body, or in the formation of a new growing tip from the differentiated cells of a leaf (Figs. 38, 39), from callus tissue (Fig. 40), or from any other part of the plant, as it is in the reproduction of a new individual from the egg, with or without fertilization, in any of these forms. The simple agamic and experimental reproductions, moreover, afford very much greater possibilities for the analysis and control of the processes and mechanism of inheritance and develoj^ment than gametic reproduction. Any adequate conception of inheritance and development must be based upon analytic investigation of these simple reproductions and synthesis of the results, and it must interpret inheritance in gametic reproduction in terms of the simpler processes. Continued sexual breeding and hybridization under controlled conditions and with pedigreed individuals has contributed much and undoubtedly will contribute further toward the solution of certain special problems of inheritance, and also affords results which possess a statistical value, but this method of procedure alone can never carry us very far toward the solution of the fundamental problem of inheritance. The key to this problem also will be found in the simpler reproductive processes.

If the organism is a unit in inheritance and development we must expect to find that so-called "acquired characters" may be impressed on the organism to such a degree that sooner or later the reaction system may give rise to these characters without the action of the particular external factor which originally produced them. The reaction of the organism to a sufficient local excitation is not simply a local reaction, but a reaction more or less of the whole organism, and we know that in the case of many physiological reactions the repetition of the reaction in response to repeated external excitation alters the reaction system so that response occurs more readily or more rapidly or with a lower intensity of stimulus. We say that the irritability of the protoplasm is increased, its "threshold" for stimulation is lowered, etc. If this change goes far enough the reaction may occur in the absence of the external factor which first produced it, simply because the condition or constitution of the protoplasm has been so altered by the repetition of the reaction that it occurs automatically when any condition determines a sufficiently high metabolic rate in the reaction system. The "inheritance of acquired characters" then belongs in the same general category as the increase in irritability resulting from repeated excitation, but it may in many cases require thousai>ds or hundreds of thousands of generations before a condition approaching automaticity in its production is attained. In the face of the physiological facts it is difficult to understand how biologists can continue to maintain the distinction between soma and germ plasm, and to content themselves with the assertion that natural selection is adequate to account for adaptation in the organic world. If the organism is in any sense a dynamic entity, then its evolution must be a reaction determined, on the on^. hand, by its physico-chemical constitution, and on the other, by its relation with the external world,

and its adaptations are simply special features of this relation. Evolution is not directly concerned with morphological characters, but with the physico-chemical constitution of the reaction system, and so with the rate and character of its reactions and the conditions under which they occur. I have called attention elsewhere' to the resemblance between the progress of evolution and the progress of senescence and development in the individual, and have suggested that evolution, like senescence and other processes in nature, may be essentially a change from a less stable to a more stable condition in the dynamic reaction system which constitutes the organism.

The significance of this dynamic conception of the organism for various other biological problems will be apparent without further discussion, and I beheve it may possess a certain significance for certain problems of comparative psychology and sociology. It is at least a matter of some interest to be able to trace the fundamental identity in individuation from the simple unicellular organism to the highest plants in the one direction and to conscious man in the other, and to showthat the growing tip of the plant and the brain of man have something in common. Moreover, to find the same principle of individuation in the egg and in the adult organism and again in the single nerve cell and its fiber is at least highly suggestive. The recognition of the fact that individuation in the organism is a relation of dominance and subordination of parts removes much of the difficulty in accounting for the high degree

of definiteness and the constancy of character of the developmental processes and other activities of living things. It also has a certain bearing upon the problem of the origin of individuations whose component parts are human beings or groups of human beings. Between the organic individual and the state there is, from this point of view, a real analogy, for control or government is tjie essential feature in the individuation in both, and the relations are in certain respects similar in both cases. It is not a mere fanciful analogy to conceive the organism as a state or the state as an organism, since both are dynamic individuals and some degree of dominance or government exists in both. These suggestions are an indication of some of the broader bearings of the dynamic conception of the organic individual, but discussion along these lines must be postponed.

In conclusion it is perhaps permissible to call attention to the simplification and unification of viewpoint which this conception accomplishes. The separation of morphological from physiological investigation and thought, particularly in zoology, which followed the acceptance of the theory of evolution, and the fact that the morphologists, rather than the physiologists or biochemists, have chiefly concerned themselves with the great problems of heredity, development, and evolution, have brought it about that biological theory in these fields has been to some extent a world apart. While proclaiming their acceptance of the mechanistic or physico-chemical conception of life, the theorists of this group and their followers have not only made but few attempts to apply physico-chemical conceptions to

the organism, but have often decried the value of such attempts. It is still true, therefore, to a large extent that to grasp these theories we must enter a new world of symbols, which only too often appear to have no resemblance or relation to any other symbols commonly in use in scientific thought. When we have become famihar with our new world, we can perform marvelous feats with its symbols and fill our pages with fonnulae of gametic constitution or what not, but so far as any real connection between this world and the other world of science is concerned, such theories and their symbols leave us, at least in most cases, eaxctly where we were at the beginning. We can discuss the topographic location of hereditary factors in the chromosome, and we can arrange them in any way necessary to account for the observed facts. In fact, we can invent symbols to describe development or any other process in the organism. But some of the discussions which have to do with these static, morphological symbols remind us irresistibly of that old problem of the angels and the needle point.

Being entirely unable to find any degree of intellectual satisfaction in those static conceptions of the organism which seem to have no relation to anything else in the world and which raise many questions but answer none, and being forced by my own experimental investigations to conclusions very different from these, I have attempted to apply dynamic conceptions to certain biological problems, with the results which have been considered in the preceding pages. Whatever other value the dynamic viewpoint may i)ossess, it serves as a basis for the synthesis and ordering of many

facts in various fields whi -h heretofore have seemed to have little or nothing in common, and I think we maysay that it aids in bringing certain aspects of biology at least within hailing-distance of physico-chemical conceptions. Note. — References give the number of the page on which the matter referred to begins. Axis, organic: occurrence of, 8; apical and basal ends of, 10; terminology of, 19; simplest form of, 35; susceptibility gradients in relation to, 53, 60; independence of apical region of, 96, 113; dominance of apical region of, 102; control of space relations in, 128; experimental obliteration and determination of, 142; as resultant of two pre-existent axes, 164; quantitative character of, 167, 185; time of determination of in egg and embryo, 199. 5ee a/50 Dominance; Gra- ■ dients; Individual; Polarity; Symmetry

Biaxial forms: in Tubular ia, 97, 133; in Planaria, 99, 117; experimental transformation of, in Corymorpha, 144; experimental determination of, in Planaria, 149. See also Axis; Gradients; Intlividual Conductivity: in relation to transmission, 40; increase in, during development, 150; in relation to physiological isolation, 194. See also Transmission Corals, individuation in, 197 Correlation, physiological: different kinds of, 4, 27; occurrence of transportative, 26, 44, 170; conditions determining transportative, 26, 170, 172. Sec also Axis; Dominance; Gradients; Individual; Transmission; Transportation

Corymorpha: dcscri[)tion of, 92; metabolic gradients in, 132; obliteration and determination of gradients in, 142 Cyclamen persicum, dominance and subordination in leaf of, 1 56 Dedifferentiation: in agamic reproduction, 7, 9, 91 ; in formation of adventitious indi\iduaI.^ in plants, 83; in reconstitution of Planaria, 109; capacity for, in lower and higher animals, 120; in embryonic development, 199. See also DitTerentiation Differentiation: occurrence of, 6; orderly character of, 7; different degrees of, in eggs and embryos, 121; in relation to metabolic gradient, 171; in relation to metabolic rate, 183, 190. See also Dedifferentiation

Evolution: increasing stability of order in, 6; in relation to environment, 204; as an equilibration process, 205 Ginkgo: developmental gradient in embryo of, 73; formation of growing tip of, 77 Gradients, developmental: in relation to metabolic gradients, 65; in early embryo of frog, 66; in flatworm, 67; in chick embryo, 69; in relation to rate of growth, 72; in embryo of moss, 73; in embryo of Ginkgo, 73; in plant axes, 73; in bilaterally symmetrical plants, 77; in agamic reproduction of Pennaria, 79; in reconstitution of Planaria, 81; in Metzgeria, 83; in adventitious buds of Begonia, 83; in buds on callus, 86. See also Gradients, metabolic

egg, 56; in parts and organs, 57; demonstration of, by differential inhibition, 58; in relation to axes, 60; in plants, 61; as gradients in carbon-dioxide production, 62; in neuron, 62, 151, 173; in relation to differences in electrical potential, 63; demonstration of, by differential staining, 64; in relation to developmental gradients, 65, 79; in experimental reproduction in Marchantia, 86, 165; in Tubularia, 91; in agamic reproduction of Planaria, 93; independence of apical regions of, 96; in reconstitution of Tubular ia, 130; control of length of, in Planaria, 140; experimental obliteration and determination of, 142; localization as resultant of different, 164; problem of different kinds of, 178; relation of, to inhibition, 178, See also Axis; Dominance; Individual

Growling tip: as feature of plant individual, 73; in relation to developmental gradients, 74; in adventitious individuals, 83; in relation to range of dominance, 150; dominance of, in plants, 152; localization of, as resultant of different axes, 165; selfdetermination in, 189; conditions determining character of, Head-frequency: in pieces of Planaria, 108; experimental alteration of, 108; interpretation of, 119; relation of, to metabolic rate, 184

Individual, organk: fundamental characteristics of, 2; nature of unity in, 3, 48, 175; various theories of, 3, 22; character of order in, 8, 17, 35; reproduction in relation to, 12; terminology of, 18; comparison of, with social individual, 21, 26, 206; formulation of the problem of the, 29; dynamic conception of the, 29, 88, 172; as one or more metabolic gradients, 40, 170; limitation of size of, 45, 47, 151; as result of relation between protoplasm and environment, 49; origin of adventitious, in plants, Ss, 154, 194; size of, in relation to range of dominance, 151; fundamental reaction system of, 188; difference between plant and animal, 189; in relation to inheritance, 202; significance of dynamic conception of, 205, See also Axis; Dominance; Individuality; Individuation Individuahty : different kinds of, 48; superficial origin of organic, 49. See also Axis; Dominance; Individual; Individuation Individuation: in Amoeba protoplasm, 6; in experimental reproduction, 14; nature of, 41, 48; in "rings" in Harenactis, 146; conditions determining low degree of, in plants, 189; in corals, 197; degree of, in egg, 201; fundamental identity of, in organisms, 205. See also Axis; Dominance; Individual; Individuality Inheritance: of metabolic gradients, 41, 182; in relation to organic individual, 202; in relation to different reproductive processes, 202; of "acquired characters," 204

Inhibition: of head-formation in Flanaria, 112, 141; in reconstitution of Tiibulana, 135; of growing shoots in plants, 153; in apical direction in plants, Isolation, physiological: conditions determining, 45; effect of, 46; infrequency of, in higher forms, 47; in agamic reproduction in Tubular ia, 92; in agamic reproduction in Flanaria, 94, experimental, in Tubular ia, 155; experimental, in Flanaria, 141; experimental, in plants, 152; as the basis of agamic reproduction, 192; diff'erent conditions determining, 193; in relation to repudiation of parts, 195. Su also Dominance

Marcliantia: experimental reproduction in, 86; localization in, as resultant of different axes, Metabolism: characteristics ot, 15; relation of, to protoplasm, 16; susceptibility in relation to, 51 ; increase in rate of, after section in Flanaria, no; rate of, in relation to differentiation, 183, 190; rate of, in relation to stabihty of structure, 191. See also Gradients; Individual; Ir- ritability Nervous system; in relation to metabolic gradients, 40, Oi, 175; superficial origin of, 4(); metabolic gradient in cells of, O2, i sr, 173; independent fc.rmation of, in reconstitution, 114; supposed

formative influence of, 119, 176; self-determniation, of, in development, 120, 188; extension of dominance in, 151; dominant region of, 175; Tunctional dominance of, 176; possible nature of inhibition in, 180; in relation to fundamental reaction system, 188; animal organism in relation to, i8g; possibility of dedifferentiation in, 191. See also Conductivity; Transmission Organization: theories of, 22; as a condition of chemical correlation, 26; not the basis of organic individuality, 41; in relation to minimal size in reconstitution, 124; in relation to experimental conditions, 1S4

Pennaria, developmental gradients in agamic reproduction of, 79 Flanaria dorotocephala: susceptibility gradients in, 52; developmental gradients in experimental reproduction of, 81; agamic reproduction of, 92; experimental reproduction in short pieces of, 99; dominance and subordination in, 102; reconstitution in, 105; different forms of head in, 106; head-frequency in experimental reproduction of, 108; experimental control of headfrequency in, 108; control of range of dominance in, 138; determination of biaxial forms in, 149; extension of dominance in, 149; localization as resultant of diffei»unt axes in, 164