Cooperative Phenomena PDF
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COOPERATIVE PHENOMENA Edited by H. Haken and M. Wagner With 86 Figures Springer -Verlag Berlin Heidelberg New Yark 1973 Prof. Dr. HERMANN HAKEN Prof. Dr. MAX WAGNER Institut fur Theoretische Physik, Universitat Stuttgart ISBN 978-3-642-86005-8 ISBN 978-3-642-86003-4 (eBook) DOl 10.1007/978-3-642-86003-4 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks. Under § 54 of the German Copyright Law where copies are made for other than private use, a fee is payable to the publisher, the amount of the fee to be determined by agreement with the publisher. © by Springer-Verlag Berlin Heidelberg 1973. Library of Congress Catalog Card Number 73-79119. Softcover reprint ofthe hardcover 1st edition 1973 The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Tbis Book is Dedicated to Herbert Friiblicb, F. R. S. on the Occasion of his Retirement from the Chair of Theoretical Physics, Liverpool University HERBERT FROHLICH Life as a Collective Phenomenon "Chance is a cause, but it is inscrutable to human intelligence." * Democritus By F. FROHLICH If one thinks without preconceptions of collective phenomena in which the discrete constitutive individuals are modified in their behaviour and indeed in their constituting a large collective group, and the whole is more than and different from a simple addition of its parts, living organisms would seem to be the ideal example. (" The universe is an animal", as Plato said.) Most of the contributions to this book are about physics where the collectivity seems a priori less obvious. The billiard-ball model of physics states that if one knows what every independent particle will do, then one can calculate the whole universe past and future; this is the perfect example of a non-collective phenomenon. As FROHLICH has frequent ly pointed out, it would be practically impossible to calculate all of the paths of all of the particles of a gas. The gas laws would be hidden in this mass of informa tion, but one could not pick out the relevant pieces of information to yield their simple relations. At this degree of apparent complication, relevance becomes an essential cognitive property and some sort of overall insight into the whole situation becomes necessary in order to reveal the comprehensible simplicity amid this mind-stunning complexity. So even here, in what at first sight seems the most auspicious field for explaining the whole in terms of its essentially independ ent parts, there is a practical impossibility in understanding the whole situation in terms of the movements and activities of the parts. In contrast, let us take the case which is farthest from the random movements and collisions of the essentially homogeneous particles of the ideal gas: the func tioning of an organic unit whose parts are essentially differentiated and interact specifically when performing their different functions-the living cell. Here the movements are no longer random but precisely correlated and specific-for example, meiosis which has been poetically called" the dance of the chromosomes", or the meeting of a specific enzyme with its own substrate. In this case there is a whole level of overall organization and specificity which is not to be found in the gas laws. Such specific and precise movements within a non-equilibrium but metastable system would seem to render plausible some form of collective explana tion. However, the forms of explanation actually preferred-indeed, considered to be the only" scientific" form of explanation-by today's most popular group of * Quoted in Aristotle's Physics, Book II, Chapter 4. VIII F. FROHLICH: biologists, the molecular biologists, are more analogous to those of the homoge neous, independent particles in a gas. This is a fact so implausible that it can perhaps best be understood in a historical context as a reverberation of the old controversy between the mechanists and the vitalists. Vitalism in the nineteenth century and in its modified form at the beginning of the twentieth century asserted that there must be laws other than those of physics to explain the extra ordinarily complex phenomena of life. Such an assumption seemed mystical and unscientific, in direct opposition to the scientific belief or assumption that the laws of physics were adequate to explain everything (especially in the nineteenth century before physics itself became so mysterious that it was forced to take cognizance of its own internal contradic tions). While physics provided the model of clarity in explanation, it seemed an insult to logical thought to say that living organisms required a different form of explanation. It seemed almost animistic. The opposing view, that all living proc esses could be understood in terms of the laws of physics, was called mechanism. Vitalists said there must be laws for organic systems which surpass those of in organic systems, which perhaps contradict the laws of physics. Mechanists said: "N0 ; everything that happens to living organisms can be explained solely by the laws of physics. " This almost temperamental as well as methodological opposition between vitalism and mechanism became historically entangled with the reduc tionist programme of logical positivism. The aspect seen as particularly anti thetical to scientific (positivistic) explanation was any attribution of purpose and significance to living organisms. However, it seems that this drive to go on looking for explanations of both organic and inorganic phenomena in terms of the fundamental laws of physics had bifurcated into two directions. The one was a purely methodological pro gramme which exhorted those studying living organisms to go on looking for explanations in terms of the laws of physics without having recourse to any special murky or mystical concepts such as entelechy, meaning and purpose. This says nothing about what facts should actually be found. The other fork of the bifurca tion concerned the content of the possible, or acceptable, laws of biology. It pro jected both the content and the "Weltanschauung" of current nineteenth-century physics onto any possible future development of biology. It predicted that the laws of biology, when finally understood, would be essentially the same as those of chemistry, making use of local interactions and of transport by diffusion as visualized in nineteenth-century physics. (JOHN LOCKE had already in the seven teenth century theoretically or philosophically planned such a project for ex plaining the organic phenomena of sensation-perception of sounds, colours, etc., i.e. the secondary qualities-in terms of purely mechanical properties.) This predictive picture of the necessary form of explanation of biological phenomena was covertly made respectable by being entangled with positivistic methodology. It illegitimately borrowed the authority of the scientific method from the other fork of the bifurcation. From this confusion biological research acquired apparent necessary synthetic knowledge about the ultimate forms of biological explanation. It thus asserted as self-evident that, if we find the appropriate independent biological molecules moving by diffusion and interacting by chemical laws, then we have found a complete explanation. This hypothesis, which under- Life as a Collective Phenomenon IX lies much of the thinking of molecular biology, has of course been enormously fruitful. But it can limit the type of questions asked and the forms of explanation considered and thus inhibit new directions of thinking. It blocks certain lines of enquiry which might provide facts of a different order, more relevant to treatment by modern physics or to explanations on a higher level of the hierarchy. Thus the paradigm of explanation in molecular biology, the enzyme, might be described in this form: "There are particles, enzymes and other proteins, moving independent lyand at random within an enclosed area (a cell). All of their movements are to be accounted for by diffusion. On collision, they interact to form chemical bonds, but there are no long-range forces which regulate and direct the overall situation". Whenever there is a problem, a process which is not understood, an enzyme is sought to account for it and very frequently one is found. But how is the finding of a particular enzyme a sufficient explanation of everything that goes on? It is a complete explanation in the sense that it answers the question: What substances are present before and after the interaction? Once a biochemist has found the sub stance and identified it, he feels he has found the sufficient as well as the necessary cause. But is this identification of substances a sufficient cause or does it merely create satisfaction (a "There-are-no-more-problems" attitude) within an arti ficially restricted range of problems? A result of this attitude is that, when one attempts to introduce into biology different forms of explanation, or even to reformulate problems in terms of collective phenomena, the approach is dismissed as superfluous, or even felt to be mysterious and vitalistic. There may be here a certain distant echo of the opposition to NEWTON'S "mystical" forces. Thus paradoxically (by a certain inertia in the change of "Weltanschauung") there has arisen from the programme to apply the scientific method to the explanation of biological phenomena by means of the laws of physics the contrary result that modern physics in its role of possible overall coordinating explanation of biological systems is rendered suspect as being vitalistic. This prejudice inhibits such potential ly illuminating methods of enquiry of a dynamic nature as measurements of the rate of various processes; furthermore, it blurs the perhaps essential differences between multicellular, differentiated organisms in which movements over long distances must take place relatively rapidly and in a highly coordinated fashion, and very much smaller monocellular organisms where diffusion could plausibly serve as an adequate mechanism of movement. It neglects qualitative differences which might arise from di.fferent orders of magnitude in size. For instance, a cell of a higher or ganism may be one thousand times as large as that of a bacterium so that movement by diffusion across it would take one million times longer, even assuming that the final position is not exactly specified. This is a significant order of magnitude, perhaps requiring the introduction of different kinds of forces. Such physically and dynamically essential differences are disregarded as superfluous. The tacit assumption is that identification is explanation (cherchez l'enzyme). The biological molecule is seen as a mysterious agent whose activities explain everything once its name is known. Thus in present-day molecular biology life is treated, not as a collective phenomenon, but as an aggregate of individual particles travelling over long distances by diffusion and interacting strongly and specifically only on con tact. In cases where diffusion quite obviously cannot apply another name, active transport, has introduced (e.g. the "sodium pump" in membranes). Now 'dif- x F. FROHLICH: fusion' is a familiar, but in biology unexamined, physical concept; it requires a certain analysis to reveal the different levels lumped together in it. Diffusion as applied to long-range movements is the physical equivalent of chance. "Chance" itself is a much wider concept which melts together many epistemological distinc tions. Deomocritus' statement: "Chance is a cause, but it is inscructable to human intelligence", placed at the head of this paper, applies aptly to the acceptance of diffusion as a means of long-range movement. There are two points of view here: The inside one-the point of view of the moving particle (e.g. enzyme)-and the out side one-the point of view of an observer interested only in the average movement of many such molecules. These might be called the microscopic and the macroscopic points of view. Macroscopically, diffusion is regarded as motion of a particle over a certain distance without reference to its specific final position. Microscopically, ho wever, unless the molecule, say a specific enzyme, meets its specific substrate the required reaction does not take place. Moreover, unless there is a fairly improbable three-cornered meeting between transfer RNA, the appropriate nucleic acid and the enzyme which unites them, and subsequently between this complex and the ribo some and the mRNA, the process of protein formation cannot proceed. It is a wide, complex story with a plot, like history, and it has to have well-defined characters meeting amid the mass of irrelevant molecules, not just random move ments of masses of non-differentiated particles. The kings and generals must somehow meet each other at the right time among the milling, nameless armies. To achieve this by diffusion is not impossible in principle, though on investigation it might well turn out to require quite unrealistically long times. In fact, uncritical acceptance of diffusion indicates a lack of interest in the differences between individuals, whereas in biology the differences in types of molecules are vital. Thus it would seem that present-day biology comprises two logically dif ferent forms of explanation: 1. the individual molecule as a highly differentiated, active agent (the" leave it to the enzyme" type of explanation) and 2. the diffusion model of overall movement which tends to ignore the differences between indivi duals. Used simultaneously, they seem to yield more than they actually do-in deed, everything. This engenders the attitude that everything in biology is now in principle explicable-it is only necessary to find more enzymes, proteins, etc., etc. and mix them together in a diffusing soup and everything will be made plain. This attitude discourages the asking of questions answerable only in terms other than those currently in use. As an example, let us consider enquiring into the speed of reactions. Biologists are now inclined to assume that size makes no essentially qualitative difference i.e. that collective phenomena are either not present or are only rarely relevant. As mentioned above, however, given that cells of higher organisms can be one thousand times larger than those of the bacteria tacitly assumed to be an adequate model for all living processes, it would take a molecule one million times longer to move across the cell by diffusion, even without a final specific location. This suggests that a range of empirical observations enabling actual speeds of reaction in vivo to be compared with those calculated according to the rate of diffusion alone might be relevant. If we were to make such comparisons between the actual in-vivo rates of processes and those calculated on the assumption that diffusion is the only Life as a Collective Phenomenon XI moving force and there is no directing force at all, and if we should find a discre pancy of several orders of magnitude, this might provide evidence that some theory of long-range collective forces was required. Then again, let us consider the apparently unnecessarily large size of some biological molecules. To quote FRANCIS CRICK [1]: "It appears to be a general rule that intricate three-dimensio nal biological structures are always bigger than one might naively expect. The examples of globular proteins, transfer RNA and ribosomes spring to mind." In these cases the economy of biological structures might suggest that this apparently excessive size has some functional role, and we might again be encouraged to look for new forces arising from the very size of biological molecules themselves considered as collective phenomena. Finally, a comparison of the speed of the processes occurring in a metabolizing organism (in terms of physics, a non-equilib rium state being fed with energy) with those taking place among the same materials when the system is not metabolizing might suggest that there is some physical force which is operative only when the system is being fed with energy. An example of this difference is the one-way transport of auxin when the system is respiring, in contrast to its non-directional movement when the system is not respiring. Such a hypothesis of biological explanation was originally suggested by FROH LICH in terms of long-range coherence at the first meeting of L'Institute de la Vie in 1967 [2, 3]. Epistemologically, it has the advantage of unifying the types of explanation from the point of view of the particles and from the point of view of the observer by formulating the microscopic and macroscopic situations in the same field-theoretical terms. Heuristically, it opens up new ranges of dynamic phenomena to be investigated and brings many seemingly unconnected observa tions within one potential frame of explanation. A case in which specific long-range forces are obviously required is the pairing of homologous chromosomes in meiosis. This has been interpreted by HOLLAND [4] in terms of these novel concepts to show that coherent oscillations are excited, leading to selective long-range forces [5]. The specific attraction of mRNA to particular sites on the ribosomes might require a similar interpretation. It would be highly interesting, to attempt to impose the necessary oscillations by external means in the hope of influencing biological developments. Thus, in auxin transport, one might attempt to effect directional transport by induced interactions rather than by respiration. Another possibility would be to try to influence the cambrium, which differentiates differently depending on its posi tion-hence environment-within the plant. Thus, cambrium cells produced by division on the inside of the cambrium become xylem and those produced on the outside become phloem. Let us try to induce such differe~ces in differentiation by growing cambrium in solutions in which appropriate ostillations are imposed from outside. Or let us attempt similarly to influence cell differentiation in small groups of cells of meristem grown in fluids with superimposed vibrational fields. Plant cells grown artificially in a nutrient normally do not differentiate so long as they remain separate or in small groups, but differentiation begins as soon as a mass of cells is formed. This is strongly indicative of a collective phenomenon. Observations by HELLER [6] could point to influences of imposed fields (micro wave region) on biological behaviour. Clearly, extensive experimentation is required
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