ESSAY: On tangentiality in behaviour of animals and humans. (translation and update of an earlier series on this blog in Dutch).

by Koenraad Kortmulder                                       k.kortmulder@kpnplanet.nl

I. Lateral Display.

My late friend and colleague Jaap L. Dubbeldam suggested that I wrote together the concepts that I have contributed to the biological theory of behaviour. 

“But all of it has been published at least once,” I objected. 

“No harm in presenting a review of it,” he replied, “and probably most people haven’t seen your papers in Acta Biotheoretica, because the latter didn’t immediately relate to their specialties.”

Looking for a common theme to connect the concepts, diverse as they are, I decided on ‘tangentiality’, because I had not specifically published about it before. It had played a role in the development of those concepts, and could thus serve as a clue in a chronological reconstruction.

Jan van Iersel was my first teacher in ethology; a very gifted man, whose life would be worth a biography. Physics was his ideal of science, and he strived to shape his specialty along those lines (1). Physics, to him, meant precision, accurate measurement, careful definition of concepts and compelling conclusions. He held to me that a concept like Force, originally derived from human experience, had been refined until it could be unequivocally defined. Similarly with energy, warmth etc. He expected that, in analogy, ethology would grow beyond such vague concepts as ‘aggression’ or ‘motivation’ and free them from their anthropomorphic connotations.

My eager young mind resonated with these ideas, but with a different emphasis. From high school I had brought an interest in mechanics and geometry rather than in comparative epistemology. My first exercises in measuring behaviour I got at the Hulshorst field station as a helper of Kees Groot who studied a tiny, ground-living grasshopper of barely 2 cm length, Myrmeleotettix maculatus. This chirping, dancing and jumping animal offered many opportunities to assess distances and angles in the movements of its many appendages and to record the ‘chirpsongs’ of which it had many.

1.1 Myrmeleotettix male, en face

1.3 Observing a grasshopper

1.2 female left, courting male right

The ideas on tangentiality came later, when I studied barbs in the lab. Barbs are carp-like fishes, native to tropical Asia, and popular with aquarium fanciers because of their gaudy and diverse colours and lively demeanour. Their displays are mainly visual (and tactile).

In addition to straight attacks, and fleeing in the opposite direction, their social repertoire embraces a lateral display, characterised by a tense body and tautly spread fins, while they turn one side towards a conspecific, apparently a rival. Because the displaying fish looks as large as possible to the opponent in this orientation, and shows off to him his contrasting markings and colours to best advantage, its posture has been called Lateral Display. Since it often seems to intimidate or discourage the other fish, the display is also called Threat Posture. However, instead of being intimidated the other fish may sometimes adopt the same display or even attack; so let us be cautious and use the term Lateral Display.

We have thus three possible, preferred orientations: towards, away from, and lateral. It was probably Konrad Lorenz who first suggested that the lateral stance is intermediate between the other two and might represent a compromise or conflict between the tendencies to attack and to flee.

Lorenz’ idea was taken up and extended by others to encompass other behaviour elements with a lateral orientation, as in courtship and in other animals: chickens and cats. Ambivalence was the key-word for the two (or more) conflicting motivations, and many other behaviour categories came to be explained in the same way: redirected attack, displacement behaviour, responses of the autonomic nerve system, etc. Van Iersel played an active role in the development of the theory and quite understandably hugged it. Some ethologists even explained animal play behaviour along the same lines (Meyer-Holzapfel, 1956), and Gerard Baerends suggested ambivalence as an explanation for teder (2) behaviour (tenderness). Legitimate, of course; one has to probe the limits of a new theory. But somewhere it stops.

Full of zeal, I applied the theory to the behaviour of the barbs. What about their lateral display? Did it represent a conflict between attack and flight, as Lorenz had suggested? Starting from the lateral orientation, I could pin-point diverse elements that fitted in (3). For instance, if turning left was effectuated by the muscles at the left side of the body, and conversely for turning right, the simultaneous intentions to turn towards and away from the opponent might produce the stiff condition of the whole body; fin-raising could be a braking movement counteracting the propulsive tail movements; strenuous pivoting around a vertical axis: hesitations between attack and escape; C or S curves along the body axis: balances between the two forces different in front and at the rear of the body; etc. So far so good, until I realised that it was the very lateral orientation itself that was the problem. Of course this position (call it 90 degrees) would be passed every time the animal wavered between approach and fleeing (say between 0 and 180); but there is no reason why exactly 90o would be preferred; 100, 80 or 110 would be passed just as well. A barb in lateral display, however, actively seeks the perpendicular stance specifically, and strives to maintain it as long as the display lasts (4). With this, also the other items in the interpretation lost much of their cogency. Apparently, there is a third factor, of which the lateral orientation is the Leitmotiv.

Ethology did not stop with form analysis. Quantitative data were needed to test the conclusions. If a lateral display was motivated by simultaneous aggression and fear , one might expect that the display occurred most frequently when, in the same observation period, also attacks and flights were most common. Similarly, immediately following or preceding the display, the probability of attacking and fleeing would be at a maximum. Some such analyses had been done with other species of fish, and had supported the hypothesis. But not in all cases. In some, there was nothing to indicate the expected effect, and my data on barbs were rather complicated.

Now, ethologists had already found a reason for the negative results. A display posture might have been motivated by conflicting motivations at an earlier stage of its evolution, but have become emancipated from its original motivation. One  said: the display has become ritualised in the course of evolution. There was some evidence from comparative studies of closely related species, where a certain display was ritualised in some, but still under the original motivation in others.

However, I began to doubt this interpretation seriously, when I saw the responses that Erich von Holst (1934; 1935) had elicited from preparations of some species of fish in which the connection between brain and dorsal chord had been severed (fig 1.4). These body curves were similar to those I had observed as C and S curves in intact, displaying barbs. In von Holst’s preparations they could be evoked by mild touch on the lateral skin. In my barbs I could elicit them at will, in a displaying fish, by almost touching it on its side as indicated in figure 1.5.

1.4 Von Holst's schematic representation of experiment. Top view.
Arrows: touch stimulus. I: caudal half of eel. II: each half subdivided.

   1.5 Tactile stimulation of live fish

with small bulb. Compare fig 1.4

Even more curious is that in a long fish such as an eel, one-half or one-quarter of the body was sufficient to produce the same stimulus-response result as in a whole fish! (figure 1.4). Von Holst presumed that these reflexes, along with others (tailbeats as in pivoting, see above, strong propulsive movements) were parts of the natural spinal locomotory rhythms. Certainly, ambivalence between attack and fleeing tendencies could have nothing to do with them, because the neural circuits responsible for them are in the brain, and the connection between brain and neural chord had been severed! Good-bye then to the  ambivalent interpretation of barb lateral display. It never was ambivalent.

This led me to the ‘spinal reflex hypothesis’ according to which the entire lateral display was built out of spinal reflexes that originally belonged to normal locomotion, but were arranged in a different manner (Kortmulder, 1972) (5). I had no independent proof for this, but it solved the problems of my earlier interpretation and also shed light on some vexing questions as to tail-beating, a side-ways wallop that sparring fish can exchange, or another manoeuvre which is particularly clear in some Anabantids, where one of two contesting males swims backward so as to move the side of its tail in front of the opponent’s face (fig. 1.6). Tail-beating (Rumpfschlagreflex), by the way, did occur in von Holst’s preparations too, as well as strong and regular locomotory movements.

1.7 relative positions of males in duel (top view).

1.6 Paradise fish, top view, lateral display.

The importance of the lateral orientation can be appreciated to its full extent when the fishes get moving. They may go in circles, or their trajectories may not  be along the straight line that connects them, but perpendicular to it or in other words parallel to the other’s skin, Examples can be taken from the figures of contest, such as carousel and parallel threat swimming (fig. 1.7). Later, we shall see that this orientation is not confined to contest, but occurs also in Courtship, and in higher vertebrates also in Play and Teder behaviour.

For an appropriate name for these lateral components, I turned to geometry. (fig. 1.8). Let each of two interacting fishes be the centre of a circle. If the one to the left moves towards or away from the other, he follows the radius of the other one’s circle: his trajectory is radial. Movements as in lateral display follow the periphery of the same circle, that is tangentially. Tangential is the word I’ll use (6).

NOTES:

(1) Not as in Biophysics. It wasn't the kind of object he meant, but the methods.

(2) Tederheid. Adj.: teder. Social interaction characterised by toning down of force and/or amplitude, tangential movement patterns and/or introverted attenbtion. Often involves subtle tactile stimulations of the skin and unusual stances of body and/or head in space. The term has been borrowed from Dutch, because English 'tender' and 'tenderness' do not distinguish the qualities included in our definition from the softness of meat or the vulnerability of a baby. See for instance the first 5 pages on 'Tenderness' at Google Scholar: the great majority deals with the chewability of meat, and how to enhance it.

(3) Form analysis this was called: you tried to interpret little parts of an act as representatives of major behaviour categories (attack, flee, sex, feeding, preening etc.). Classical ethology had scored some significant successes with it.

(4) See Kortmulder & Robbers, 2011, p. 22 and end-note nr 9.

(5) The locomotory movements of a fish may be pictured as two alternating waves of muscle contractions running backwards along the two sides of the body. A likely by-product of this arrangement is that the two sides get synchronised, thus blocking the system - a small reorganisation which might first have happened by way of accident, but which was favoured by natural selection because it could function as a display. Ritualisation, in fact, but from a different point of departure.

(6) The following is about analogies, but it seems worthwhile to note that tangentialities occur in nature in diverse forms. How comparatively dull the world would be if electrical and magnetic forces did not act perpendicularly to each other's direction of movement. There would be no electromagnetic waves, for instance. Without its helicity, the Weak Nuclear Force would be of a different nature, and quantum phenomena would be hardly distinguishable from their classical counterparts if the quantum potential - the imaginary part of the Schrödinger equation - did not act at 90 degrees on the path of a moving particle.                                                                                                                                                      Much more likely to be related to the lateral displays of fish, cats or deer, are human rituals, art and show. All show is extended perpendicularly to the line that connects it and the beholder. That might be a significant similarity to the biological display with which this essay started off. I find it fascinating to look at art from this side.                                                                                                                              As already implicit in this discussion, the terms 'tangential' and 'tangentiality' are not unique to the spatial orientations of animal and human behaviour. The currently most common use, as testified by pages on Google Scholar, refers to a certain psychiatric disorder of speech: people who cannot stick with one subject, but repeatedly "fly off at a tangent". Other uses of the terms are, like ours, more directly related to their plane-geometric origin, such as for instance forces in materials under physical stress or orientations of anatomical sections (transversal, longitudinal, tangential, etc.).

1.8 Top view of possible trajectories of fish (left), relative to conspecific (right): radial or tangential.

II. Courtship.

The fore-going chapter was mainly about fighting. Another complex of behaviour is courtship: the introduction to the mating of a male and a female. With barbs, the male is, as so often, the more conspicuous party in both colour and movement. For the interpretation of the male’s courtship moves, the ambivalence hypothesis again looks promising. Besides a tendency towards mating, one may discern one to swim away from the female - dubbed leading - and a third to butt the female, mostly gently with a slight sideways movement, but in some species with full force, all without interrupting the typical courting posture. At first sight it is tempting to view the whole as a combination of fleeing, aggressive and sexual tendencies, which together make the dance. Moreover, much of the courtship dance is done in a tangential orientation to the female - but not in the same posture as in Lateral Display - the male circling, standing perpendicularly in front or stroking along her skin with the tip of his mouth.

Great, but if a careful analysis showed this interpretation to be inconsistent in the Lateral Display, it is legitimate to doubt its being sound in the case of courtship. Not without reason, for, as in the lateral display, the whole sequence of courtship is performed in a characteristic posture: relatively relaxed body muscles, adducted fins and a swift trembling over the whole length of the fish. Unlike neutral swimming around, where moves are alternated with abrupt stops and turns, the trajectory of the courting male is continuous. The leading and touching actions are as it were superimposed on this rhythm, just like tiny approach and withdraw moves were superimposed on the continuous tension of the lateral display. Lateral display has its own, specific stimulus: mild touch or turbulence on the flank. Similarly, courtship is elicited by one specific cue: a chemical substance exuded by a willing female. When the female of a courting pair is caught and returned in a glass jar, the male immediately stops courting; if anything he may fight her. When the original situation is restored, the male resumes his courtship.

On the basis of these similarities between lateral display and courtship, it is not far-fetched to consider the male courtship of barbs as a relatively stable state, which allows, or even regulates, the occurrence of quasi-aggressive and quasi-fearful moves, rather than being created by the three motivations together (7).

Two individuals engage in either the lateral display or courtship preferably under conditions of relative security. Once in one of these states, however, they are hard to divert (8), their attention being bound by their mutual interaction. Doesn’t that remind us of other sorts of activities in which animals seem to forget their surroundings? Not so much in fish, but certainly in higher vertebrates, young (and adult) mammals may engage in play with that same abandon; and a similar concentration of attention may be observed in teder behaviour in both animals and humans. Conversely, barb courtship and lateral display do look like play, while courtship of Paradise fish (Macropodus) resembles teder behaviour. Only, in fish, these behaviours still serve immediate reproductive functions (9), while in birds and even more so in mammals, play and tederheid have become behaviour categories in their own right, performed for their own sake, and only indirectly relevant to reproductive success (10).

Examples of teder behaviour:

2.1 (Photo Sasha Meyer)

2.2 (Photo Sasha Meyer)

2.3 (Photo Sasha Meyer)

Il Correggio (Antonio Allegri). La Madonna del S Gerolamo (detail).

fig. 2.4 Correggio (Antonio Allegri) La Madonna del S Gerolamo (Detail).

NOTES:

(7) An objection sometimes made is that the specific stimulus elicits fear, aggression and sex in fixed relative strengths - aggression and fear in the lateral display - but that amounts to begging the question: this fixed relationship is then the third factor.

(8) Which makes understandable, from a functional point of view, that they are keen on safe circumstances to begin with.

(9) Fishes do also exhibit some true play, for instance by letting themselves be carried upwards by turbulences, such as the stream of air bubbles in an aquarium. Barbs then change colour and roll through unusual stances in space. Like playing mammals, they can't stop.

(10) I do not mean to say that play and tederheid have no functions in mammals. All behaviour that arises in evolution and maintains itself through generations does acquire function(s). That does not exclude the possibility that at first it just happened, just because it was possible.

III. Tederheid and teder behaviour (11) .

As a result of my considerations on the tangential component in lateral display and courtship, I was susceptible for some new concepts that came floating into the world of the ethologists, in particular the concept of tederheid, and the two modes of social relationship: hedonic and agonic.

Johannes J. Groen (1903 - 1990) was a specialist in internal and psychosomatic medicine, and a proponent of the multi-disciplinary approach. When he struggled with a scientific problem, he used to consult psychologists, medical specialists and biologists. One such problem was teder behaviour in humans, and the possible adverse effects of a  tederheid-deficit in childhood. He convened a symposium on the subject in the winter of 1987. There, he addressed the ethologists in his usual charming manner. First, he buttered them up: “you are the true scientists, our masters,” and so on. Next he asked what they thought of the concept of tederheid, and whether something of the sort did occur in animals. It wasn’t, of course, out of a sheer scientific interest in animals and their development. He hoped that experiments with animals could be done such as are not allowed with humans. In general, the responses of the ethologists were negative. Some found that tederheid was not a behaviour, but a sentiment; and feelings were not among their competences. In so far as some others meant that any behaviours of their experimental animals could be called teder, they were convinced that these were not a coherent class of behaviour, let alone that there would exist a unitary motivation that governed it. The experiments they did on the effects of juvenile experiences, were not specifically concerned with possibly teder behaviour and, all in all, they weren’t happy with the importance that Groen seemed to attach to the early experience of tederheid. The vestiges of this part of the discussions are visible in the contributions by Jaap Kruijt and Otto Adang to the book titled ‘Tederheid’ that originated from the conference: De Groot & Kruijt (eds.) 1991.

Now, these negative responses were not unexpected. For Groen’s attempts at a definition of tederheid did not use the sort of language that ethologists are used to; and some of the same terminology had been irritating the classic ethologists since the days that Konrad Lorenz and Niko Tinbergen protested against the ideas of influential animal psychologists Bierens de Haan, Portielje, Alverdes, Portmann and others. In Groen’s latest version, printed in the book, he had already formulated as descriptively and objectively as he could, but even with this version it is difficult to assess whether (some) animals have teder behaviour or not (12).

Nevertheless, as already indicated, I was attracted by the concept, particularly because in tederheid in humans there were several tangential elements. In Groen’s extended definition: soft touch and stroking of the other’s skin with the hands, kissing, embracing, taking on the lap, pressing and hugging, all actions in which skin-to-skin contacts and transfer of warmth are prominent. Apparently, the tangential extension of the contact and the tangential movements are essential. It was here that Baerends made his suggestion about lateral orientation as a compromise between attacking and fleeing. In this context his suggestion sounded to me like over-stretched (13).

A film on disturbed maternal behaviour of some Rhesus monkeys was shown during the symposium. Clearly aberrant were the ways in which these handicapped mothers picked up and laid down their babies, not just  roughly, but also directly: ‘bang’ onto the floor; ‘here’ at her body. That is radially, in the terminology of part I of this essay. By contrast, the healthy mothers, also in the film, ‘scooped up’ their young with a flowing movement of arm and hand, which ran almost parallel to the skin of the young one and thus touched it mildly. The tangential component again.

So, teder behaviour does occur in animals? Or shall we first state that Groen’s definition, apart from its subjective psychological terminology, is geared all too specifically to humans? Even other primates, for instance, do not stroke but groom at one another’s skin. That means: they ‘saunter’ slowly through the other’s fur with their hands, and pick out edible particles. Judging from the relaxed postures of the groomed party (fig. 3.1) and the eloquent invitations to be groomed, it produces a skin-centered sensation comparable to being stroked in humans. Birds ‘preen’ their own feathers, and in many species they preen each others’ too, at least between friendly partners. In contrast, many species of mammals lick one another’s fur or skin. Stroking, grooming, preening or licking, but all directed at stimulating the skin.

3.1 Grooming Rhesus monkeys (Photo: Sasha Meyer) 

Let us discuss a few more details in Groen’s extended definition: how generally applicable are they? As primatologists have noted, certain behaviour classes are accompanied by specific facial expressions. In humans, the facial expression typically accompanying tederheid is the smile. Rhesus monkeys and other macaques, however, smack with protruded lips in comparable situations. So, signals differ according to the species or larger taxonomic group. Sitting or lying in contact occurs in a wide variety of vertebrate animals, but whether poikilothermous reptiles in that position experience any transfer of warmth is questionable. Even with many birds and mammals, one may wonder whether the fur or feathers do not prevent sharing of warmth in spite of physical contact. Few animal species are as naked as Homo sapiens, where transfer of warmth is easy. The vocalisations mentioned by Groen need not be restricted to humans, but verbal signals occur in no other animal. Finally, there are a number of qualifications in Groen’s text, such as affective, experience, meaning, intention that one may better avoid when talking about animals, because they cannot be assessed in any objective sense.

In order to circumvent these objections, I distilled 4 criteria from Groen’s definition which can be used to decide whether a certain behaviour of an animal may be qualified as teder (Kortmulder, 1991; 1994). 1. Toning-down: reduction of force and/or amplitude of movement; 2. Tangentiality; 3. Inwardness: withdrawing of attention from the surroundings towards the pair or small group that interacts (photo below); 4. Mutuality. None of these criteria alone suffices (or is necessary) to distinguish teder behaviour from all other. For example, the lateral display of duelling barbs is tangential, but far too powerful to be dubbed ‘teder’. A cat defecating turns its attention inwards, but none of the other criteria is applicable to it. Two or three criteria taken together, however, give quite convincing results. An example is the courtship of Paradise Fish (Macropodus opercularis). The initial, hostile, lateral display of the male towards a female changes gradually into a more relaxed and mobile variant (toning-down). Finally, the partners get nearer, the female hugs up to the male’s flank with her ventral surface (tangentiality). Next he wraps himself around her (tangentiality and mutuality). Together they roll over until the female’s belly is turned upwards. In this position, they release ova and sperm.

3.2 Attention inward. (Photo: Sasha Meyer)

The ‘play’ of fishes in a stream of air bubbles combines characteristics of tederheid with those of play.

John S. Price (pers. comm.) once suggested that the tangentiality of teder behaviour may be interpreted as a contrast to the radiality of aggression, according to Darwin’s Principle of Antithesis. Darwin observed that appeasing signals are often the opposite of hostile postures (14). A similar suggestion was made by Groen (1990: 11) in connection with diverse characteristics of tederheid. From a communication point of view, this is correct: if a signal is to convey peaceful intentions, it has to be easily distinguishable from hostile ones. This explains how appeasing signals could evolve, but not the current motivation of the appeasing behaviour (15). Consider, for instance, that also sexual behaviour may act as peace-maker: in the act of ‘presenting’ by a monkey (female or male) towards a dominant group-mate, or by the female of the African Black Duck towards its mate outside the breeding season (Anas sparsa) (16). This phenomenon does not disqualify sexual behaviour as a behavioural category in its own right. The same applies to tederheid as appeasement.

3.3 Sitting in contact. (Photo: Sasha Meyer)

Judging from the responses of colleagues, the concept of tederheid is to-day well accepted in ethology. There are also connections to American studies, where ‘touch’ is the key-word. Jaap Dubbeldam’s neurological considerations (17) have contributed to our understanding of what happens within the receiver of tederheid. The side of the donor of tederheid, however, needs some further study, both as to its motivation and the underlying neurology. Certainly, Harrison’s opinion (1965) on the motivations of allopreening in birds is outdated. To me, it seems highly improbable that tederheid  towards a partner might be reducible to a distorted form of aggression. That would ignore the inviting signals from the receiver and the pleasure the latter derives from it.  Another observation that speaks against Harrison’s view is that self- and allopreening in birds may smoothly merge one into the other.

Tapia (18) emphasises the importance of oxytocin in the physiology of tederheid in mammals. There are many older and more recent studies on tederheid in human psychology, most of them not directly relevant to the present comparative discussion. Kalawski (19) concludes that tederheid is a basic emotion in humans, and independent of joy. Similarly, according to Lishner et al., (2011) and Niezink et al. (2012), tederheid and sympathy are mutually independent variables, as well as sexual urgency and tederheid towards infants (Beall & Schaller, 2014).             

So far, I have discussed tangentiality as an aspect of social behaviour. Some other contexts may be noted which may or may not have common phylogenetic roots. One is the position taken by fishes that invite specialised ‘preening fish’ or ditto shrimps. These ‘clients’ turn or roll to turn their flanks maximally towards the preener; and stretch their fins. This attitude has much in common with the lateral display, but it serves a different function. Another example is in ‘sunning stances’ adopted by birds, but also by a variety of insects, where they expose a maximal surface to the sun. You may well have found blackbirds or thrushes indulging in this in your garden or in a park, too saturated with warmth to immediately fly off at your approach. The grasshoppers mentioned in the first chapter arrange their hind-legs, wings and abdomen to form a broad fan and lean over to let the sunshine fall perpendicularly on it. The neurology of the fish and bird examples will have to be studied to find out whether they are homologous. Those of the insects probably are convergencies.

NOTES:

(11) See footnote nr 2 in chapter I.

(12) The main part of Groen's definition (my translation): "'Tederheid' I define as a complex of affective-communicative behaviour, ritualised or not, consisting of the one-sided or mutual administration of signals or stimuli, with the intention (anticipation) that these will be experienced as pleasant by the partner, or (and) that the latter will respond with actions that will be experienced as pleasant by the first actor." Next, he enumerates examples and categories.

(13) With deep respect to Baerends who, to me, was the 'Old Dutch Master' of ethology.

(14) The postures of the submissive and the threatening dogs (Darwin, 1872) and Tinbergen's head-flagging vs threatening gulls have been reproduced too often to be necessary here.

(15) This would imply a rational understanding of Darwin's principle by the animal, which is absurd.

(16) McKinney et al., 1978..

(17) Dubbeldam & Kortmulder, 2009.

(18) Tapia, 2013.

(19) Kalawski, 2010.

IV. The Two Modes according to Michael R.A. Chance.

Both teder behaviour and play may be considered as sub-regions of a broader category of behaviour: the hedonic mode. The latter was signalised first by Michael R.A. Chance in the social interactions of Chimpanzees. I quote from the first publication (Chance & Jolly, 1978): “Chimpanzee attention structure is based upon attention-demanding behaviour or display, practised competitively between males of the colony, and is distinct from the pattern of aggression between the same individuals. This display behaviour leads not to submission or appeasement by a subordinate, but is a form of social solicitation as it leads on to forms of associative behaviour in which there is a continuing interaction between individuals, such as grooming, play, sexual or mothering behaviour with the displayer.

“Aggression has to be opposed by counter-aggression, appeased or avoided, all forms of behaviour designed to eliminate the intensity and continuity of social contact. [The above-mentioned] display behaviour, responded to by greeting, stimulates and enhances the tendency of individuals to develop many forms of contact behaviour at close quarters. Manipulation, both of the individual’s own body or that of the companion, not only by grooming but also by holding and investigation, is jointly engaged in. Their attention may also switch to the environment or to other objects and give rise to manipulation of objects and tools.

“Such varied and flexible behaviour, both social and non-social in form, but often involving the combined attention of the two companions towards each other and towards a physical object, is clearly of a different nature from the rigid, fixed pattern of agonistic behaviour, and should be regarded as constituting a separate mode for which the term hedonic is proposed, without the subjective connotation associated with ‘hedonistic’ but suggesting an affinity with pleasant human feelings.”

The difference with the social forms of, for instance, Rhesus Macaques (Macaca mulatta), says Chance, is striking. Their group structure is reigned by tension - both social and physical - contrasting with the more relaxed ways of Chimpanzees. The stability of a Rhesus group depends on threat and fear instead of attention-soliciting display as in Chimpanzees. The hierarchy, the order of who is boss over whom, is an important factor in Macaque life; the dominant males control it and the subordinates have to spend much time and energy to keep on the right side of their ‘chiefs’, and in maintaining a precarious balance between approach and avoidance, all at a respectful distance. In order to give a name to this way of staying together, different from the Chimapanzee manners, Chance (1984. 1988) proposed the term agonic mode for the Macaque system.

Both modes are stable social networks: they further group cohesion, lend predictability to interactions between members, and enable them to respond group-wise to outside dangers or opportunities. In this respect both modes differ from agonistic behaviour, which consists of free-for-all fighting (20).

No mistaking: chimpanzees are not sweet; they are not even hedonic all the time. Under stress, for instance between top-males shuffling for power, they adopt the agonic, if not the agonistic mode. Chimps on a raid in foreign territory are just as bad as humans at war. On the other hand, not all Macaca species are as strictly hierarchical as the Rhesus (21). That humans can operate in either of the two modes, is known by any of us who has served under an authoritarian boss or alternatively under one who knows how to inspire his personnel to the common cause. On how humans behave in war, nobody can be ignorant to-day.

One might believe that the explication above would suffice to define the nature of the two modes. Yet, the members of the Social Systems Institute (SSI) - a group of people  from diverse scientific disciplines that had gathered around Chance out of interest in the two modes theory - could never agree on a definition. Together, they developed a fair number of criteria that distinguished between the modes, but there was no unanimity on the relative weights of these. It is not the place here to list them all (22). A sample may do. John Price (1995) defined the two modes as alternative forms of competition among the members of a group; competition through intimidation (threat and aggression) in the agonic, and competition through the attraction of attention from all group members in the hedonic mode. The prize of agonic competition is power, won in one-to-one confrontations, while hedonic competition strives to get prestige, granted by thirds (the group). Later (2000), Price suggested to dub any relationship hedonic, as long as it is not challenged, the key-word being consent (of both parties). Frank Cawson, in his turn, found that a relationship is hedonic, as long as the partners emphasise their similarities; agonic when differences are stressed. David Stevens (1993; 1997) introduced several new criteria, for instance (in)egality, flexibility and respect. He also enquired thoroughly into the position of the theory of the two modes in the context of more or less similar dichotomies suggested by other authors (1997). He was the first of the SSI group to use “droodles”, diagrammatic sketches representing diverse relationships between group members à la Kurt Lewin. His initiative to analyse relationships within human organisations (army; mafia) in this way, was leading for my own contribution (23). 

From my personal input (24), I would like to mention the balance trust/distrust as a dynamic switch between the hedonic and agonic modes. This entailed the following definitions (25):

Hedonic refers to styles of social interaction governed by mutual trust. Trust allows a free flow of energy and information (in the group and in the individual). Because trust involves the expectation of trust, it tends to reinforce or maintain itself, and lead social interaction towards relaxed and creative states.

Agonic refers to styles of social interaction governed by distrust. Distrust counteracts the free flow of energy and information (in the group and in the individual). Because distrust involves the expectation of distrust, it tends to reinforce or maintain itself, and lead social interaction towards stressful, rigidly ordered states.

Trust is the anticipation of security, and ..... of trust.

Distrust is the anticipation of unpredictable threat, and ..... of distrust.

These definitions introduced the concept of free-flowing vs stagnating energy. With energy I mean tension and motion in the interactions between group members. 

Another criterium I contributed was tangentiality. The hedonic mode embraces more tangential elements than the agonic. That is evident in teder behaviour, that obviously is at home in the hedonic mode (26). In play behaviour tangentiality is present in more subtle ways, for instance in a tendency to not go for the partner or play object immediately, but rather go round it in circles; in a more figurative sense in the unlimited repetitions of the same manoeuvres. In a still more abstract form, tangentiality may be recognised in the metaphor that partners in hedonic relationships stand rather more ‘besides’ one another, than above, below or opposite, as in the agonic mode.

From 1994, I joined the SSI. The book  “The agonic and hedonic styles of social behaviour” (Kortmulder & Robbers, 2005) offers a wide zoological perspective on the theory of the ‘two modes’. While the discussions in the group and in their written pages had dealt only with Chimpanzees, humans and two Macaque species, our book explores the roots and the biological significances of the bimodal organisation through other Vertebrate classes, down to fishes. It also offers a dynamic and a statistical model of the workings of the agonic and the hedonic modes, and of the transitions between the two.

The concept of modes, the game rules according to which individuals can interact, reaches much wider than Michael Chance’s  two modes. I have already mentioned agôn. Some others are: the dominant-submissive mode (a sub-mode of the agonic), the sexual, and the collective mode. The latter consists of schooling, herding or flocking behaviour (according to which class of vertebrate animals is described). Play and tederheid may be identified as sub-modes of the hedonic. In a paper: ‘On sustainable Peace’ on this blog (19  November 2012), I have indicated how the concept of modes may help to define 'Peace' and suggested some ways to sustain the state of peace among peoples.

The two modes have been suggested as models for human psychological disorders, notably depression and mania. Price et al., (27) sketch the history of the idea, which started with the observation of similarities between depressed persons and monkeys that had lost a confrontation with another group member. Later, in response to some criticism, the theory was further specified by reference to MacLean’s views on the ‘triune brain’ (basal ganglia, limbic systems, neocortex (28)). Price and Gardner (29) indicate how depression may have evolved as an adaptation to life in organised groups of animals in steps: submission, hedonic mode, reconciliation and depression. Their idea that submission and depression are adaptations to the benefit of both loser and dominant, is no doubt too simple. Submission and depressed states following a lost fight occur all over the Vertebrate subphylum including fishes such as barbs which have no organised groups, and beyond.  Their function thus seems to be the escape and recuperation of the losing party and nothing else.

Amos et al., (30) apply the theory of the two modes to diagnosis and treatment of disturbed mother-child relationships. Their approach is thoughtful, and profited from the revised definitions of the modes by Kortmulder & Robbers (2005) and the latters’ introduction of the concept of tension as a product of insecurity and uncertainty.

Other applications may be found in the interpretation of non-verbal expressiveness in TV debates by American presidential candidates (‘Happy Warriors’(31)), in studies of innovativeness of nations, i.c. China (32), and studies on peer harassment (33).

4.1  Simple diagram of an anatomy of Peace. AGO = Agonic; HEDO = Hedonic.

IV bis. Coping styles.

A different, but probably related, field of research is concerned with ‘behavioural syndromes’, also called ‘personalities’ or ‘coping styles’ of individuals of a species. House mice, rats and Great Tits have been the best studied models. Intraspecific differences in aggressiveness between male mice  tend to fall in two modes in tests measuring the latency before they attack a male intruder in their territory. Short Attack Latency (SAL) males score higher on all other parameters of aggression than Long Attack Latency (LAL) ones. They also respond more actively to non-social disturbances such as an electrically charged object or forced swimming. ‘Proactive’ is the general characterisation of their behaviour, as opposed to ‘reactive’ for the LAL males. Besides behaviour, a variety of physiological parameters co-vary with these syndromes: the activity of the Hypothalamus - Pituitary - Adrenocortical (HPA) axis, the sympathetic and parasympathetic nervous system, testosteron secretion and others. Essential is the combination of a large number of parameters occurring together to form these ‘personalities’; studies monitoring only one parameter do not justify the use of the term (Koolhaas et al., 1999) (34). The name ‘coping styles’ refers to the advantage that either one style lends in natural environments, (Koolhaas et al., 2010; Dingemanse  et al.,) (35) .

Koolhaas et al. 2010 and Coppens et al. (36) agree that the physiological characters mentioned above are not to be considered as directly causal to the behavioural part of the syndrome. It is probably different for a circuitry consisting of the PreFrontal Cortex (PFC) and its dopaminergic and serotonergic input from the ‘emotional’ parts of the brain. The PFC is  responsible for the inhibition of impulsive behaviour (such as immediate attack) and the resulting flexibility of behaviour. Such flexibility is, according to Coppens et al. characteristic of LAL-type individuals. With flexibility they mean the ready adaptation of the individual to unexpected changes in the environment - not creativity! - without adhering to fixed routines.

These syndromes have a strong genetic component, relatively independent of prenatal and mothering influences (Sluyter et al., for mice; Wigger et al., for rats) (37). Selected lines have been bred for SAL and LAL mice. Rats have been selected for high and low anxiety, resulting in HAB (High Anxiety-related Behaviour) and LAB lines. LAB rats display proactive behaviour, similarly to SAL mice (Veenema & Neumann,) (38). LAL mice and HAB rat lines have been proposed as models for human depressive and anxiety disorders (Landgraf & Wigger,) (39) and SAL and LAB rats for excessive aggressive disorders in humans (Veenema & Neumann).

Similar coping styles have been found in Great Tits (Parus major). Individuals of both sexes that are ‘fast’ in exploring a new environment, are also ‘bold’ towards novel objects that are put into their familiar surroundings. Fast explorers (FE) explore superficially, while slow explorers (SE) are more thorough in learning about new surroundings. In social encounters, FE are more aggressive and they win more contests, but they suffer more when defeated. They are quicker at forming habits, but relatively rigid under changing conditions (Drent et al., 2003, and references therein) (40). These syndromes have been proven to have a genetic component (Drent et al., 2003), though also epigenetic effects - mainly due to the degree of competitiveness of nest siblings - have been shown to be important (Groothuis et al,) (41). The two personalities differ in their dispersal after fledging: the fast explorers, as well as the off-spring of fast explorers, disperse further (Dingemanse et al.) (42).  [cf Chitty 1967?]

In later years, understanding the nature of the syndromes has been further refined (especially Sih et al.) (43) and more species are being included (Dammhahn & Almeling; Kralj-Fiser & Schuett,) (44) .

Synthesis?

It is tempting to equate the two theories of bimodal behaviour. Shall we call SAL agonic and LAL hedonic? But that is too quick. Firstly, the behavioural syndromes called coping styles are properties of individuals, whereas the agonic and hedonic modes are primarily about structures of groups. Chance did insist, however, that the characteristics of the modes could be applied to individuals as well. Moreover, at least some of the criteria, such as behavioural flexibility and varied positive social interactions are in common between the LAL-type animals and the hedonic. Secondly, the hedonic/agonic dichotomy is about species and not on co-occurring individuals of one population. Where the hedonic and agonic modes meet within one species (or individual) - as they often do -  they are more or less separated in time or dependent on the kind of social relationship (Kortmulder & Robbers, 2005). Nevertheless, a further analysis of similarities and differences between the theories looks promising.

For the comparison, the coping styles as they occur in natural populations seem to be better candidates for elements in hedonic or agonic groupings than those of selected lines. The SAL mice from selected lines, as described by Veenema & Neumann (2007) are belligerent little brutes, fitting in the ‘free-for-all’ of the agonistic mode at best. Similarly, LAL from selected lines having been proposed as a model of human depression (see above), doesn’t suggest them as members of a hedonically structured group. Of primary importance would be to look for coping styles in animals with highly structured group life, for instance in comparative studies of macaques, of ducks or of barbs (Kortmulder & Robbers, 2005).

Finally, I might draw attention to the paper by David Stevens in the ASCAP Bulletin: ‘Bimodal theory in context’ (45) where he discusses a large number of bimodal theories in relation to the hedonic-agonic dichotomy. As this paper is not accessible to everyone, I shall reproduce it on this blog. 

NOTES:

(20) The term agonistic is also used for the entire complex of hostile behaviour. In Chance's terminology the agonic mode is excepted. In my paper  on peace (19th Nov 2012 on this blog), I did the same with agôn. The diagram of modes accompanying that paper, is reproduced here as fig. 4.1.

(21) Kortmulder & Robbers, 2005, chapter 3.

(22) Kortmulder in prep.

(23) Kortmulder & Robbers, 2005, chapter 1.

(24) Kortmulder, 1996, 1998; Kortmulder & Robbers, 2005

(25) Kortmulder & Robbers, 2005, pp. 27, 147, 151.

(26) See also Chance's definition cited at the beginning of this chapter for elements of the hedonic mode.

(27) Price et al., 2007.

(28) MacLean, 1989.

(29) Price & Gardner, 2009.

(30) Amos et al., 2015; see also: Amos & Segal, 2018; Goran, 2020.

(31) Bucy & Grabe, 2008; See also: Bucy, 2010.

(32) Redding & Drew, 2016.

(33) Hawkes & Boulton, 2001.

(34) Koolhaas et al., 1999.

(35) Koolhaas et al., 2010; Dingemanse et al., 2004.

(36) Coppens et al., 2010.

(37) Sluyter et al., 1996.

(38) Veenema & Neumann, 2007.

(39) landgraf & Wigger, 2002.

(40) Drent et al., 2003.

(41) Groothuis et al., 2005.

(42) Dingemanse et al., 2003.

(43) Sih et al., 2015.

(44) Dammhahn & Almeling, 2012; Kralj-Fiser & Schuett, 2014.

(45) Stevens, 1997.

V. The cognition of Congener.

This chapter does not offer further examples of tangentiality. Instead, it explores the context: the cognitive world of the animal. Let me again begin with a long citation (46):

“ ‘Nobody has ever seen a visual impression’, wrote E.H. Gombrich in Art and Illusion, meaning that it is a far cry from the image on the retina or from the vibrations of the Corti membrane in the inner ear, to perception. The German philosopher W. Schapp (47) said it differently: We are “In Geschichten verstrickt” (entangled in stories). We cannot avoid interpreting any signal or sound in terms of what we know or what we assume. It is similar with [higher] animals. They filter, process and interpret stimuli before they perceive, and it is perception, not the bare stimuli that determine the behavioural response, both in animals and in humans.

“For convenience, we may call everything that comes between stimulus and perception: cognition. It is on cognition that I focus in this chapter, particularly on an aspect which I think is of paramount importance: the cognition of a congener. Briefly, this means that any individual, whether human or animal, has a preconceived image of ‘another one, like self’, which may be ‘recognised’ when another individual is encountered in the real world. This real partner may be a conspecific, but quite often ‘recognition’ is restricted to certain classes of conspecifics only, such as juveniles of the right age, or same-sex or opposite-sex adults. This is what Lorenz called ‘companions’ (Kumpane) (48). Sometimes, on the other hand, the image of the congener is wider than conspecifics, as when animals engage in play with members of other species (e.g. Loizos, 1967; Fagen, 1981) .

“The notion of a cognition of a congener is a postulate. It cannot be observed directly, but there are some arguments that make its existence very likely. First, meeting another individual of the ‘right’ kind, may alter the behaviour of an animal drastically. Social play, courtship or agôn differ very much from what an animal does when alone. Some of the behaviour elements that compose these interactions are never shown in the absence of a companion. Moreover, in many species, the presence of and interaction with the right kind of conspecific during a sensitive period in early life, is essential to the normal development of behaviour. The developing young animal is ready to perceive a congener, so to speak, and if the latter does not appear, its development is curtailed. For instance, Jungle Fowl missing that opportunity in early life, will never be able to sustain normal sexual and social relationships, as Jaap Kruijt demonstrated in the sixties (49).

“Second, if an animal cannot for a while find a partner with whom to play or court, it may act as if a virtual partner is there. Kittens will stalk and pounce upon an arbitrary object in the absence of a play-mate. Male Three-spined Sticklebacks may court air bubbles when no female has presented itself for a long time. This means that the animal’s cognition is more or less independent from actual physical stimuli. A congener may be imagined in the absence of the appropriate sensory stimulation.

“Third, many natural behaviour patterns in which animals interact require perfect coordination in order to be performed (even if the ultimate outcome of the interaction may be competitive). A very beautiful example was described by D.W. Snow in the Blue-backed Manakin (50). Typically, two males of this bird species perform a display called ‘Cartwheel’ in perfect coordination, even following the movements of a third bird (usually a female) “as one bird”. Other striking cases are to be found in duet and antiphonal singing in birds, as studied by W.H. Thorpe and others (51). For instance, two birds would have a tune consisting of seven notes on their repertoire, one of them singing the first four, the other supplementing the other three. In the absence of the second bird, the first would do the whole song. This shows that each bird knows the whole, but ‘respects’ the role of the other.

“This point was demonstrated in more detail in the study on territorial behaviour of fish (Puntius oligolepis). We described the interactions of two neighbouring males as one integrated pattern built up by the two together. Such a thing is possible only if the animals acknowledge some sort of equivalence of self and the other. On the face of it, such a description may seem arbitrary. However, we derived some specific predictions from it, which were subsequently verified by precise measurement (52).

“One may well ask what are the structural grounds of a universal cognition like self-and-congener. I have gone into this question pretty thoroughly in two papers, one together with Tom Spreij in which we went well beyond the mechanistic order (53), (without finding a definitive answer, by the way). For the present it may suffice to state that life has a strong tendency for recurrence, to repeat and even reproduce itself from a heterogeneous environment. The image of the congener may be considered as another aspect of this tendency at the cognitive level.”

In short, there is reason to assume that every individual animal is tuned to interact with another one, even before it had the experience of such interaction (54). The terminology ‘self-and-congener’ means to say that a cognition of ‘the other’ cannot exist without a notion, however vague, of ‘self’, irrespective of the degree to which the two are cognitively distinct (individuation) or fused (cognitive integration).

This may be somewhat speculative, but important it is, because through such cognitive equivalence animals may be enabled to act “as one machine”. The example of the Manakins is telling in this respect, but comparable activities do occur in the ‘daily life’ of other animal species. For instance the lightning speed carousel of barbs, in particular Puntius nigrofasciatus, a ‘pas de deux’ of competitive nature, but one that requires considerable mutual consent to be performed. Such ‘ritualised’ contests are common in animals. It is as with two humans juggling together, except that the latter do it without the competitive element. Even though...

Some contemporary ethologists might remark that such ‘ritualised’ contests are governed by optimal functional advantage to each individual, and that they have  in that way been evolved under natural selection. It may be clear, however, that the two explanations do not exclude one another: a question of ultimate vs proximate causation.

For those who want more tangible evidence for the concept of congeners, there are the mirror neurons, known since 1996 (55). These cortical cells respond to the performance of a certain behaviour by another individual as well as during the same behaviour by the animal itself. So far, the animals in which these neurons have been found, Primates and a few bird species, are a rather select group. However, in Science of Dec. 2011, Jaak Panksepp explicates his thoughts re an experiment on empathetic behaviour in rats (56). He hypothesises that a tendency to empathetic behaviour might find its source in the emotional brain, far below the cortex, also in the lower mammals such as rats. Still theory, but Panksepp is a important person in the field of neurophysiology. In the same paper, he also refers to a shift in thinking among scientists about empathy and related gifts in animals, which up till recently were generally considered to be a privilege of human beings and perhaps one or two talented chimpanzees.

The name ‘mirror neurons’ is thus inspired by their specific role, not by their structure or functioning. I would speculate that the activity of these cell groups takes a form like: response upon response upon response, analogous to the images in tailor’s mirrors: a series of images of images of....images (57). A comparable structure of reverberating signals might be at the base of consciousness. It seems even possible, that the two phenomena of consciousness and self-and-congener depend on partly the same neuronal circuits. Intuitively, they are mutually connected. Specialists in diverse disciplines believe they may contribute to the understanding of consciousness. So this was my bit. Let us get back to the cognition of congener.

The concept of congener must not be confused with ‘friend’ or ‘chummy’. The opponent in agôn is an enemy, but also a congener, as is the partner in courtship, play or tederheid. The cognition of the congener is a source of empathy, not necessarily of sympathy. With this in mind, we may also untie the apparent paradox that agôn may be simultaneously cooperative and competitive. In a carousel, two rivals engage in a common behavioural mode, which in essence is hostile. The whole theory of modes of behaviour, play, tederheid or agôn, which was the subject of the fore-going chapter, is based on this ability to engage-in.

The sub-mode of play takes us to Gregory Bateson’s concept of metacommunication (58). In play, animals perform actions that, when done in earnest, would be responded to as hostile: chasing, fleeing, pouncing and sham biting. However, when engaged in play, the receiver interprets it as just play. How does this come about? By each of the participants giving specific signals meaning: ‘this is play’. It is this message behind the message that Bateson calls metacommunication.  Apart from style of  performance, the meta-message is conveyed by specific signals. Many mammals, for instance, put the fore-feet forward and lower the thorax as an invitation to play; monkeys use a facial expression: relaxed-open-mouth (which by the way is related to laughing in our own species). Perhaps we may interpret the diverse colour musters of barbs in the same sense (59). Male ‘Black Rubies’, for instance, are black all over with a red head during agôn, in courtship in the absence of rivals all pale, and barred black and white in the collective mode. In related species where these modi are less strictly separated in time, also the colour patterns are less specific.

If each mode corresponds to a specific image of the congener, what then is the difference between these images? The most likely answer would be that one image includes another. In Barbelenverhalen (60), I explained how play embraces many other kinds of behaviour such as courtship and agôn. Courtship, in its turn, embraces agôn, and agôn attack and flight. With the congener images it may be similar: images of the congener in play and tederheid being relatively open to detail, whereas the images at the hostile end of the spectrum are more rigidly defined in the shape of key stimuli. Thus, partners in play and tederheid may learn more about their partners than rivals, and get ‘nearer to each other’.

The inward trend of attention that is typical for the modes of agôn, courtship, tederheid and play may be related to the interaction of the partners’ congener images. Here we touch on the concept that I have called the behavioural field (61). Should such a behavioural field be a real option, it would certainly be a self-and-congener field.

This chapter implies all groups of vertebrate animals. Panksepp’s paper reached out as far as all mammals, but I see no reasons in the behaviour of birds or fishes to exclude them from the theory of self-and-congener.

NOTES:

(46) Kortmulder, 1998, pp. 20-22.

(47) Schapp, 1985.

(48) Lorenz, 1935.

(49) Kruijt, 1964.

(50) Snow, 1963.

(51) Thorpe, 1972.

(52) Kortmulder & Feuth-de Bruijn, 1993.

(53) Kortmulder, 1986; Kortmulder & Spreij, 1990.

(54) I must be careful to not get entangled in the nature-nurture controversy. I assume the animal is thus tuned and that there is a structural base for that. The tuning may be destroyd or mutilated, for instance through lack of social interaction during sensitive periods of the developing individual.

(55) e.g. Rizolatti et al., 1996.

(56) Panksepp, 2011.

(57) Artist Wil van Blokland expressed this idea concisely with two oblong capsules, their hemispherical ends, covered with shining white metal, facing vis-à-vis. Each mirrors the other, including itself being mirrorred in the other, including.... and so forth, in a sheer endless series, limited only by the speed of light and the quantum-mechanical minimum size (since at each step the image becomes reduced). The title was: 'Love reflects Love'; and the explanatory text ran: "you reflect yourself in the other and the other in you." (Zomerexpo Liefde, 2012, Den Haag, W-Books). Also on the web.

(58) Bateson. 1956.

(59) That would be an interesting additional function of these patterns, besides the functions of intimidation at short range and inconspicuousness from a distance, as suggested earlier (Kortmulder, 1972; Kortmulder & Robbers, 2011).

(60) Part 1: Kortmulder & Robbers, 2011.

(61) Kortmulder, 1994; Kortmulder & Feuth-de Bruijn, 1993

VI. Tension and Symmetry.

When two barbs engage in agôn, they create a concentration of physical tension, in their bodies through the contraction of antagonistic muscles, and in the space between and around them through the pressure their actions exert upon each other via the water. The pressures within the ‘system’ of the two interacting animals tend to be continued, because in their turn they act as a stimulus for the lateral display in both combatants. Technically, it may not be easy to measure those pressures generated by such small fish, but it is possible in principle. With animals which duel at the water surface, for instance coots or moor-hens, the pressures are visible and measurable from the centrifugal waves emanating from them. With terrestrial animals, different techniques are needed. They exert forces not on the surrounding air, but rather on the solid substrate, again requiring a different experimental set-up.

Barb species differ in how much tension they can build up. On the basis of arguments described in my Ph.D. thesis (62) and in ‘Barbelenverhalen part 1 (63)’, Puntius nigrofasciatus males build up substantially more tension in their spawning groups than P. conchonius, and P. tetrazona more than P. stoliczkanus. In a diagram:

6.1 Four Barb species; differences in build-up of tension in spawning group. Abscissa: more tension build-up from left to right.

So far about how tension is generated. Are there also ways to reduce it? Yes, there are several, and they are diverse. The most evident one is to wait till the end of the spawning period, a few hours at most. Fighting dwindles then with the sexual activities. More interesting is the possibility that a male in agôn lets himself be diverted by a passing willing female and starts courting her. A courting pair creates much less local concentration of tension than duelling males: the male’s posture is much more relaxed, and the couple moves around instead of sticking to one spot.

More interesting in the present context is the reduction of tension through symmetry breaking. Let us observe the duelling males. Their ‘dance’ consists of some stereotyped ‘steps’: carousel, swimming in parallel threat, regular alternation of charges and broadsides and, in some species, vis-à-vis mouth-biting. What these patterns have in common is that the partners are equally waged and take similar positions. From the viewpoint of either partner, the spatial patterns are the same. That is a form of symmetry. In technical terms: the system is invariant under translation. In the course of the duel, the males get more and more limited to one spot and, finally, the interaction has only one exit: surrender of either one or the other. Submission is signalled by the male who lowers his fins, relaxes his body and rolls over to present the narrow surface of either the back or the belly to the other. This is an appeasement gesture - the already mentioned antithesis to lateral display. At the same moment the two males are no longer symmetric in their behaviour and the tension goes steeply down. It is tempting to think that it is the decrease in symmetry - or symmetry breaking - that causes the decrease in tension.

There is another, more subtle, form of symmetry breaking that is also accompanied by tension reduction: establishing territories. To explain this let us consider two equally strong males introduced into an empty aquarium space. They have just begun to challenge one another. They swim around in lateral display, both covering the whole available space, though only rarely together in the same region of the tank. From time to time, A may approach B, or B A, and withdraw from his vicinity. This situation again is symmetric. Irrespective of which of the two we observe, the pattern is the same: the same spatial pattern, and the same pattern of approaches and avoidances. Similarly, there are no differences in their responses to the approaches and avoidances of the other. Until...each of them begins to show a preference for part of the space, say A in the left and B in the right half of the tank, and each begins to defend its half against intrusions by the other. From this moment their visiting of certain locations is asymmetric, and suddenly A responds differently to B’s presence in the left as compared to the right half; and vice versa. At the same time, there enters a form of relaxation in their respective demeanors. They abandon the lateral display, apart from short episodes. In between, they are free to quietly swim around, feed, chafe, and so on.

Note that their relationship has retained some degree of symmetry. What A does in the left compartment, B does in the other. Both respond similarly to the actions of the other, as in a mirror. This demonstrates an important aspect of symmetry; a system need not always change from some degree of symmetry to none in one stride; there are steps, and systems tend to change in steps rather than all the way down (65).

It is also clear that there are sorts of symmetry. In the situation above, before the formation of territories, the system looks the same, from whatever point in space it is viewed. That is symmetry of translation. After the territories are established, the situation is mirror symmetric. The symmetry of the duelling males is again translation symmetric, but in the carousel it is also rotation symmetric. All symmetries break with the capitulation of one male.

Let us get back to the four species of figure 1: as we have seen, in each horizontal line, the species to the right differs from its neighbour to the left in that during spawning, the males build up more tension. Now, in the vertical dimension, they differ in the ability to lower tension by symmetry breaking; that is to say the ways of symmetry breaking that I have mentioned above, and some more. For these four species, the tendency to break symmetry is consistent through all elements of reproductive behaviour of a species (66). The diagram of figure 1 may now be redrawn as:

6.2 Abscissa: tension build-up; Ordinate (downwards): breaking symmetry.

The two species of the lower row are more apt to break symmetry. They are, for instance, territorial during spawning; the top two are not. Their agôn mode breaks up more easily in attack resp. flight, that is: mode agôn is reduced to mode dominant-inferior; and their courtship changes more easily into fighting. Of these four species, P. tetrazona combines the highest tension with the strongest tendency to break symmetry. This lends the behaviour of this species an explosiveness and high unpredictability. Konrad Lorenz (67) noted their “springgiftige Aggression.”

Figures 1 and 2 might suggest that species on the same vertical line generate equal amounts of tension.  That is misleading. As a result of the very differences in symmetry, for instance territorial vs group, there are no identical contexts in which tensions can be compared. Thus, as for tension, only species on the same line can be compared. In practice, for instance in the propensity of dominants to subdue and/or damage their submissive partners in groups of the same size, one may consider the two species to the right as great producers of tension, and the other two as more relaxed. Only, we have no method to express this in a single arithmetic figure.

If it is interesting that one may describe the differences between four related species with only two dimensions, tension and symmetry, it is certainly striking that the same can be done with as many as 21 species (68). Apparently, these are the two lines along which these species evolved. In evolutionary biology, such ‘channels’ for evolution are called constraints: limitations or stream beds for evolutionary change through natural selection. In experiments on the effects of selection, constraints appear as disturbing factors, but it is also interesting to investigate the nature of the constraints themselves. Why did barbs evolve preferentially or exclusively according to these channels? Possibly because the corresponding structures in the brain are easily disturbed by changes in their organisation, except in these  two directions.

For some biologists, this discussion about tension and symmetry may be unusual, but it will be different for physicists. Reduction of potential energy through symmetry breaking is a well-known property of dynamical systems. The reason why the present system of two interacting fish would belong to the same universality class is still unclear. Possibly, the nature of the self-and-congener cognition in both partners has to do with it. In the fore-going chapter I pictured the self-and-congener of each partner as a system of two mirrors reflecting each other. I wonder what happens if two such systems interact.

In all cases of symmetry breaking here described, the attention of the partners shifts from self-and-congener towards self. That is what I called individuation in chapter V. The same happens, briefly, when a partner performs a displacement act. When two birds, roosters or male starlings for instance, are engaged in agôn, one of them may quickly peck at the soil or preen its (own) feathers. That too has a tension relaxing effect on the performer, as Ciska Feekes demonstrated for ground-pecking in Junglefowl (69). In ‘Play and Evolution’ (70), I argued that the same may not  apply to displacement behaviour alone, but to many other so-called conflict behaviours, such as redirected attack, cut-off, etcetera. This would bring together many sorts of behaviour under the heading of tension relaxation, an interesting result worth further research.

There are still more ways to reduce tension. An interesting one is the de-escalation. One might be inclined to believe that this is a privilege of some higher mammals, at the level of at least dogs or cats. However, also barbs are able to mutually withdraw out of an already begun exchange of lateral displays. They do so gradually, alert if the other one continues doing the same (71). Speaking of self and congener.... Of course one does not have to assume that these fish consciously plan the manoeuvre, but some notion, however vague, of the comparability of self and the other is implied.

A very different way to relaxation of tension may be seen when a hostile interaction merges into a playful or teder one. In the fore-going chapter, I mentioned the greater flexibility of the congener image in the latter two situations. Something similar happens in visible behaviour. Play embraces more  sorts of behaviour, borrowed from diverse social and non-social contexts than for instance agôn. In tederheid, it is the sensorial rather than the motor window that is wide open. Courtship may take an intermediate position between agôn on the one hand and play and tederheid on the other. When watching courtship in a species that one doesn’t know, it is easy to confuse it with play or with tederheid. For this process of opening-up to more varied behaviour, I have suggested the term behavioural expansion; for the reverse behavioural constriction (72).

The essential difference between relaxation by behavioural expansion and by symmetry breaking becomes apparent when one asks what happens to the tension. As we have seen, the relaxation by way of a displacement act is very short-lived; tension is back immediately afterwards. The same as a result of subordination or territory formation is of longer duration, but also here the tension only becomes latent. It is immediately revived when a territorial neighbour crosses the boundary or when a subordinate rebels. The resident male, respectively the dominant, responds and in no time the tension is again manifest. (It was for this reason that we needed the notion of ‘potential’ besides  ‘tension’, in the comparison of barb species) (73).

Even when agôn is replaced by play or tederheid, this need not mean the immediate ending of hostilities. While engaged in play, one partner may be alarmed by an unexpected move and a relapse may take place. In general, however, play enhances trust between the partners, and tension becomes definitively extinguished.

In a sense, the effects of symmetry breaking and expansion are each other’s opposite. While in the former case the symmetry of the system as a whole is decreased, it is increased in the other. In play, more sorts of behaviour are accessible, and the transitions between them are easy; (a translational symmetry). Something similar is the case in teder gedrag, but then in the sensory region. While symmetry breaking can remove unbearable tension by ‘parking’ it in forms that are in principle temporary, behavioural expansion can truly dispose of it, though the latter procedure usually takes some time.

During the decades following the second world war, the study of aggressive behaviour in animals and humans was a hot topic. Understandable, both from an emotional point of view, and because funding was good. Many people hoped that war could be abolished for ever; and if science could contribute to that purpose by studying the nature of aggression, that was worth some costs. Particularly in the sixties a veritable clash of opinions developed in ethology about the dynamics of aggression: was there an, innate, aggressive drive, which arose spontaneously and increased with time, and could it be controlled to an extent through football matches and other competitive sports; or was aggressive behaviour reactive, conditioned, a response to stress or even pathological? Perhaps the fierceness of the battle was enhanced by both parties focussing on aggressive behaviour and destruction as such, isolated in vitro so to speak, instead of considering attacking as one element in a network of social interactions of many forms. Who knows whether considering social tension as the most important parameter instead of aggression, wouldn’t have taken much of the heat out of the argument.

At the end of this essay, I note how many of the new ideas originated from my work with those tropical barbs. That I came to study these fish anyway, was an initiative of Jan van Iersel. His first instruction was relatively limited: investigate the function of the black bars and spots on their bodies in the context of their differences in aggressive tendencies, in particular in the two species P. nigrofasciatus and P. tetrazona. “If you do this in the manner of a comparative study...,” he added. I soon extended the project to a few more species, because the first-mentioned differed relatively little in the number of those markings: 3 vs 4, and too much in many other characters, both behavioural and in colours; but as to the comparative method, I did stick to the instruction. These wonderful fish continued to fascinate me throughout my scientific life, lively and handsome as they are, extravert little creatures, and it looks like they have inspired me to some new and promising ideas.

NOTES:

(62) Kortmulder, 1972.

(63) Kortmulder & Robbers, 2011.

(64) Quite functional too, for both males, particularly in species that spawn in dense aggregations with many willing females, such as P. nigrofasciatus, but that is another story.

(65) Stewart, 1993; Stewart & Golubitsky, 1992.

(66) Kortmulder, 1998, p. 110.

(67) Lorenz, 1961.

(68) Kortmulder & Robbers, 2017, p. 83.

(69) Feekes, 1972.

(70) Kortmulder, 1998, pp. 93-4

(71) They may even fool the other by retreating, relaxing, looking back, and suddenly attack, when the other is off guard.

(72) Kortmulder, 1974.

(73) Kortmulder, 1998, pp. 106; Kortmulder & Robbers, 2011, p. 48.

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