Architecture in Living Structure Edited by G.A. Zweers and P. Dullemeijer Reprinted from Acta Biotheoretica Volume 34, Nos. 2-4 1985 MARTINUS NIJHOFF/DR W. JUNK PUBLISHERS ,L a member of the KLUWER ACADEMIC PUBLISHERS GROUP II DORDRECHT I BOSTON I LANCASTER 'liliiii Distributors for the United States and Canada: Kluwer Academic Publishers, 190 Old Derby Street, Hingham, MA 02043, USA for the UK and Ireland: Kluwer Academic Publishers, MTP Press Limited, Falcon House, Queen Square, Lancaster LA1 1RN, UK for all other countries: Kluwer Academic Publishers Group, Distribution Center, P.O. Box 322, 3300 AH Dordrecht, The Netherlands Library of Congress Cataloging In Publication Data Main entry under title: Architecture 1n living structure. Proceedings of • symposium held 3/15-17/84 in LochmUhle, AU5senste lIe der Senckenbergischen Naturforschenden Gesellschaft, Frankfurt am Main. lncludes bibliographies. 1. Morphology (Animals)--Congresses. L Zweers. G. A. II. Dullemeijer, P. III. Senckenbergische Naturforschende Gesellschaft. Aussenstelle LochmUhle. QL799.A73 1985 591.4 85-21492 ISBN-13: 978-94-010-8787-2 ISBN-13: 978-94-010-8787-2 e-ISBN-13: 978-94-009-5169-3 001: 10.1007/978-94-009-5169-3 Copyright © 1985 by Martinus Nijhoff/Dr W. Junk Publishers, Dordrecht. Softcover reprint of the hardcover 1s t edition 1985 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, mechanical, photocopying, recording, or otherwise, without the prior writ- ten permission of the publishers, Martinus NijhofflDr W. Junk Publishers, P.O. Box 163, 3300 AD Dordrecht, The Netherlands. [3] 109 Proceedings of a symposium on Architecture in Living Structure The primary goal of the symposium was to arrive at a comparative analysis of various methodological pathways. The symposium was organized by W.F. Gutmann, P. Dullemeijer and G.A. Zweers and was held from March 15-17, 1984 in the Lochmuhle, Aussenstelle der Senckenbergischen Naturforschenden Gesellschaft, Frankfurt am Main. This issue is edited by G.A. Zweers and P. Dullemeijer. Contributions to the symposium R. McNeill Alexander: The legs of ostriches (Struthio) and moas [59] 165 (Pachyornis) . J. Bereiter-Hahn: Architecture of tissue ce11s. The structural basis [33] 139 which determines shape and locomotion of cells. Tj. de Cock Buning: Qualitative and quantitative explanation of the [87] 193 forms of heat sensitive organs in snakes. Tj. de Cock Buning, E. Otten & P. Dullemeijer: Some methodological [171] 227 remarks. P. Du11emeijer: Diversity of functional morphological explanation. [5] III M. Grasshoff: On the reconstruction of phylogenetic transformations: [43] 149 The origin of the arthropods. U. An der Heiden, G. Roth & H. Schwegler: Principles of self- [19] 125 generation and self-maintenance. J.W.M. Osse: Jaw protrusion, an optimization of the feeding apparatus [113] 119 of Teleosts? E. Otten: Proportions of the jaw mechanism of cichlid fishes: changes [101] 107 and their meaning. D. S. Peters: Mechanical constraints canalizing the evolutionary [51] 157 transformation of tetrapod limbs. W.E. Reif, R.D.K. Thomas & M.S. Fischer: Constructional morphology: [127] 233 the analysis of contraints in evolution. G. Roth & D.B. Wake: Trends in the functional morphology and sensori- [69] 175 motor control of feeding behavior in salamanders: an example of the role of internal dynamics in evolution. G.A. Zweers: Greek classicism in living structure? Some deductive [143] 249 pathways in animal morphology. Additional symposium presentations W.J. Bock: Parts and wholes in morphology: a reductionistic and inte- grative approach to holism. W.J. Bock: Adaptations and other structural components to fitness. W.F. Gutmann: Organisms as energy converting systems. Symposium participants R. McNeill Alexander, J. Bereiter-Hahn, J.C. Vanden Berge, W.J. Bock, Tj. de Cock Buning, P. Dullemeijer, A. Grosse-Lohmann, M. Grasshoff, W.F. Gutmann, U. An der Heiden, W. Maier, J.W.M. Osse, E. Otten, D.S. Peters, G. Rehkamper, W.E. Reif, E. Reisinger, G. Roth, K. Vogel, M. Weingarten, E. Zeiske, U. Zeller, G.A. Zweers. Page numbers in breckets refer to pagination of book edition DIVERSITY OF FUNCTIONAL MORPHOLOGICAL EXPLANATION PIETER DULLEMEIJER Zoologisch Laboratorium, Rijksuniversiteit Leiden, The Netherlands An introduction to the 19th Lochmuhle conference on 'Architecture in living structure', organized by P. Dullemeijer, W.F. Gutmann and G.A. Zweers, held from March 15-17, 1984 in the Aussenstelle des Forschungs- instituts Senckenberg der Senckenbergischen Naturforschenden Gesellschaft, Frankfurt am Main. 1. INTRODUCTION Although functional morphologists form a minority group amongst biologists, there is, among them, a wide diversity of opinion in approach, aim, attitude and procedure, resulting in controversial questions and answers. This Lochmuhle conference was organized to elucidate these differences with the aim to obtain a soil for a mutual understanding. A first pre- requisite to reach this aim is an analysis of the various motives to do functional morphology and the applied methodologies. Therefore the participants were asked to emphasize the following aspects: 1. to indicate the aspects intended to be explained in a functional morphological case study; 2. to clarify the type of explanation; 3. to describe the subsequent methodological steps; 4. to focus on the following questions: a. how the conclusion depends on the first step of abstraction; b. how the conclusion changes if the selected part is considered a member of an integrated wider system; c. how the conclusion and the procedure changes when temporal aspects, such as ontogeny and evolution, are introduced. 112 [6] .-:-~-,7 ....,: ,, ,, ,- ------- \ ............ " ',,- ,- ---'-., ::.---- - ---"- ;;? " ". Figure 1. Diagram of the bony elements in a viperid snake. Drawn lines: opened mouth; stippled lines: closed mouth. be, braincase; ec, ectopterygoid; lj, lower jaw; m, maxilla; pf, poison fang; pt, pterygoid; vc, vertebral column. 1.1. An example As an introduction I shall demonstrate the various possibilities of explanations on a very simple, almost classical example, rather than present an abstract discourse on philosophy, procedure and science theory [5]. There is a small bone in the upper jaw of a viperid snake (viper, rattlesnake), the ectopterygoid, which transfers the force and movement of the protractor and levator pterygoid muscles to the maxilla (fig. 1). As a result the latter is rotated so that the poison fang is erected. The ectopterygoid is retracted by the adductor pterygoideus muscle. This mediation of protractor and retractor movement during strike and swallowing is its function, its biological role, in a total chain and pattern of structures and movements. To fulfil this role the bone has to perform certain activities; one of them is to resist the strain put on it. Evenly distributed strain resistance of a specified bone is obtained by a specific shape, given the kind of material. This statement is reasonable in view of general experience from engineering science, but it needs of course an accurate analysis in each particular case. This analysis is provided by the deductive method, by which the shape is deduced from the functional [7) 113 FORCES IN A HORIZONTAL. PLANE • r===~:: u _____ - -j 1 FORCES IN A VERTICAL PLANE ----.-~ + ~- -----~ \;______ .-====\=---,_/=::::::::::::::J ~ ~L:=-==---:=---=-==----, \ / 7~~' ~~ J:,~ Figure 2. Mechanical model for the explanation of the shape of the ecto- pterygoid in Vipera berus. Left row the construction of the model for the activities of the muscles in retraction (a) and protraction (b) in the horizontal plane. In (c) the necessary shape for resisting the bending and compression for the retractor (m.adductor pterygoideus), in (d) that for the protractors (m.protractor et levator). As both systems work alternately, in the addition both figures can overlap (d). In (f), (g) and (h) the same in the vertical plane. Combining (e) and (h) results in the three-dimensional model (i), which is compared to the actual shape represented by cross-sections. demands by means of a general theory (fig.2). In this deduction the following steps are taken (6). I. Of all functional demands the resistance against muscle force is qelected. 2. The position and the length of the ectopterygoid in the construction is taken as a given feature. 3. The type of construction is determined. 4. It is supposed that the elasticity of bone is known and that the material is evenly distributed. 5. It is supposed that the laws of static mechanics are applicable. 6. A model of the shape is made by applying the principle of optimal design. 7. The model of the shape is compared to the actual shape; the model is accepted or refuted. 8. If accepted it is concluded that the shape is explained from the functional demand (i.e., the activity of the bone) by means of the theory of statics under the mentioned boundary conditions. In formula S = f(A) in which S = shape, A = activity and f the explaining theory. This is the general deductive-nomological formula of Hempel and [8] 114 others [9]. In Popper's system the falsification of the models is emphasized [12] , whereas in other systems confirmation is accepted, as is common in the majority of natural sciences. 2. TYPES OF EXPLANATION If we now generalize this formula in Hempel's sense as y = f(x), in which y is the phenomenon to be explained (the explanandum) and f(x), the explanans, of which f is the explaining theory and x, the explaining phenomenon, we can use it to demonstrate the differences in morphological exp lana tion. As morphologists we shall always take for y a morphological feature. However, for x we have many options: the activity, another form feature, a completely different phenomenon, e.g. an ecological factor or a behav- ioural aspect [14]. As the latter two pose the demands for the whole animal, we recently have divided functional morphology into ethological and ecological morphology. We also distinguish a 'bauplan' morphology, be it that this term does not cover the original idealistic 'bauplan' concept but the concept of totality composed of interrelated functional components, i.e., constructional morphology [3,7]. For f we can also introduce different factors. In the example I used a mechanical theory, but other physical theories (such as optics) as well as other theories from biology itself such as selection theory, evolutionary theory, morphogenetic theories, can be used. Whether we still want to call it functional morphology is a matter of taste, as long as form features are explained and the various explaining formulae are not mixed. If activity and shape are reversed in position we generally are dealing with a physiological explanation. However, the reversal is also met in morphology to analyse the biological meaning of a structure. The conclusion reads then that one understands the form feature because it fulfils an essential activity. So, although in practice the reversed order is used, the ultimate logical formula is the same. Although there are striking examples of confusing explanatory principles in biology, within the theme of our conference other aspects of the procedures are more important for the understanding of the differences in opinion. In the example we observed a functional explanation of the shape by means of a mechanical theory and we can ask now whether other explanations of the shape are possible. In addition to the functional explanation we may try a causal and a 115 historical explanation. If we do so we see a peculiar shift in the choice of the parameters. A morphogenetic or causal explanation of the shape means that we try to find the factors influencing the origin or the change of shape. In the latter case the known phenomenon should also be a shape, be it at an earlier stage, and f must be the theory describing the process of influence. So we lose the activity of the bony element, whereas the forces of the muscles appear as causal factors in the theory instead of structure-demanding factors. Notwithstanding the fact that the statement: 'the shape of the bone can be derived from the demands put on it by the muscle forces' seems almost identical to the statement: 'the shape of the bone is influenced by the muscle forces', both explanatory formulae are quite different. It is therefore not allowed to equalize both explanations, but only permissible to transpose one into the other with additional information, i.e. bone is sensitive to force influences in such and such a way, so that the parameters in the explanatory formula shift. We observe a comparable shift when we go from a functional explanation to a historical one. However, the historical explanation has more aspects. There is first the historical sequence, obtained by comparing various ectopterygoids. Then x is the first member in the sequence, y the follow- ing, and f the theory of comparison. This sequence can be set up as a purely morphological, e.g. in idealistic comparative or formal morphology. Another, more appropriate way for us, would be to construct a sequence of functional components. If combined to muscle force we get a combination of the functional explanation with the sequence explanation. The functional complex, i.e. the result of the functional explanation, is described in x as the first member, and y as the second member, and f is the theory of comparison. In other words, the change of the demands is related to the change in shape with the same explanatory theory. A particularly interesting situation is the scale effect [1]. In most constructions the proportions of demands and shapes are non-linear and the shape has a limited size increase due to the boundary conditions. The result is that sudden changes in shape can occur with a linear increase of the demand. This phenomenon is even more apparent when more than one demand has to be met, because even with linearity of each demand they do not have the same linearity. The sequence of demands and shapes is often recognized immediately and taken as the beginning of an investigation. We are dealing then with an inductive methodology, in which primarily a 116 [10) relation or correlation between demand and shape is described and, there- after, a theoretical explanation is suggested. Such a sequence does not (yet) give any insight in the causes of the changes. Another step is therefore to, introduce causality, as in morphogenesis, but then placed in its historical context, in other words, the change of the developmental process and result during history and, last but not least, causality as formulated in evolutionary theory in terms of mutation and selection. The latter two steps need further exposition. Here I like to add a few words on the concept of adaptation in order to prevent confusion. This term is used for all the connections of y and x, so that we have a means to distinguish the various meanings of this concept. It is used for the connection activity-shape, for function-shape, for environment-shape (in the case of the example of the bony element, the environment is the muscles), for morphogenetic change, for the measure of selective value, for evolutionary change. 3. FURTHER METHODOLOGY Returning now to the example we can ask a number of questions relating to the methodology. First, why did I choose this bone and focus only on the shape. For this presentation I used it as the simplest case in which I can demonstrate easily the methodology. However, more important is that this bone is a member in a chain of elements assembled in a complicated construction, a totality. This, in principle, holistic point of view is the most important starting idea for functional morphology. Structures, components, elements, or whatever they may be called, must fit together to form a meaningful construction, a system, symbolically a pattern or net- work, and frequently bound to a specific space. In this view an element cannot be understood without taking into account its membership in the totality. Whether this totality concept is the same as the machine concept [8) depends on the definition of the machine concept. If the latter is taken very broadly inCluding not only kinematic and chemical processing, but also production and reproduction, and if the machine parts are con- sidered changeable, then an analogy is possible. However, it is doubtful whether the machine concept needs to be used instead of the organismic, structuralistic or holistic concept which seems to encompass the machine concept (cf. [4). The fitting together of the structures, components and elements can [Ill 117 also be formulated as a mutual demand although it is different from the functional demand. The former relates mainly to space, position and size features, whereas the functional demands require generally position, form and structure features. The theories in the explanatory formula are the rules recognized in architecture and construction sciences (constructional morphology!) and contain various aspects as functional, behavioural, ecological components. Whether all these aspects should be called functional is a matter of how wide one wants to define function. Although some of us are working on these aspects, little is still worked out theoretically (the idea of capsular matrix of Moss [Ill; the simple concept of mutual exclusion in space; the positions in a chain of rigid elements; the positional aspects of muscular attachments). In Roux's idea [13] space occupation was morphogenetically a matter of mutual force and strength (Kampf der Teile); a struggle between the elements. This seems to be so in cases of diseases, but in general there is a rather strict programming of the space occupation with an order in dominance. Particularly interesting is the combination of the two types of demands, shortly called the functional and the spatial demand (including topography, size), leading to systems showing all kinds of compromises, integrations and additions, which can shift under the influence of minor changes in the demands and their proportions. 4. THE SELECTION AND ABSTRACTION It is evident that a totality cannot be explained at once. At best we can say that we understand (verstehen) the totality, that we have an intuitive comprehension but not (yet) an explanation in the deductive sense. Therefore a selection of features is made using this intuitive understanding by selecting what one 'believes' is the dominant feature. There is no proof of the relevance of this selection except for the a posteriori conclusion that it works. From thereon the relationships between the members in the totality can be established. I want to stress the point that the members are distinguished for analytical purposes, but that they are not separated from the totality. Various investigators will have different opinions on what they think are the dominant features; it depends on the problems they are interested in, their personal taste and the criteria they use for the selection. For us the totality consists of a number of more or less dominant components,