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SOCIETAS SciENTIARTJM FeNNICA COMMENTATIONES BlOLOGICAE XXII. 7
Charles Darwin and Ethology
The Expression of the Emotions in Man and Animals reconsidered
Lars von Haartman
EJNAR MUNKSGAARDS FOKLAG K0BENHAVN
NORTHERN ACADEMIC BOOKSTORE ANTIQUARIAN BOOKSTORE
SOCIETAS SCIENTIARTTM FENNICA COMMENTATIONES BlOLOGICAE XXII. 7
Charles Darwin and Ethology
The Expression of the Emotions in Man and Animals reconsidered
Lars von Haartman
Communicated March 21st 1960
CENTRALTRYCKERIET HELSINGFORS 1960
In the history of biology three great personages stand out: Aristotle, Linnaeus, and Darwin. In part, their greatness consisted in versatility. As far as Darwin is concerned, his stature is only fully appreciated when we remember that, besides his major achievement, the doctrine of evolution, he wrote on such disparate subjects as volcanic islands, the origin of coral reefs, the formation of vegetable mould through the action of earth-worms, insectivorous plants, movement in plants, fertilization of orchids, the anatomy of the Cirripedes, and the expression of the emotions in man and animals. His work »The Expression of the Emotions in Man and Animals» (1872)1, and to a certain extent also »The Origin of Species* (1859) and »The Descent of Man and Selection in Relation to Sex» (1871) entitle us to link Darwin's name with the science of ethology.
Darwin once referred to his mind as »a kind of machine for grinding general laws out of large collections of facts» (Darwin's Autobiography, the Dover Edition 1958, p. 54, see also Lindroth, p. 172). Proof of this ability to discern what is common to seemingly disconnected phenomena was afforded by his treatment of the behaviour of man and animals from the same angle of approach. Here, wTe already find the nucleus of that biological approach to man which seeks the beast in man, and man in the beast.2 For want of information on animal behaviour, Darwin, it is true, had to concern himself mainly with man.
Nowadays, Darwin's »Expression of the Emotions* is half forgotten. In fourteen large volumes of »Behaviour» there are only three papers containing even a passing reference to it. Marler's monograph on the Chaffinch (Behaviour, Suppl. 5) forms the only exception, especially in respect to the antithetic or reversed movements. A paper by Barnett published on the occasion of the Darwin Centenary gives an interesting survey of ethological problems, but hardly does justice to »The Expression
1 Unless otherwise stated, all quotations from Darwin in the following text are taken from the first edition of this book.
2 As an example of the latter goal, the studies of Koehlbr on counting without words in animals deserves special mention.
of the Emotions*. Quite a different picture of its significance is given by Marler (1959) and by Poulsen (1959). Among students of human psychology and related sciences, opinions concerning »The Expression of the Emotions» likewise diverge. Worner (1940) pointed out nearly all the shortcomings of the book but none of its merits, whereas Landqxjist (1959) praises it as one of Darwin's most eminent achievements.
It would, of course, be a blunder not to realize the errors and weaknesses of »The Expression of the Emotions*. But it would be unfair to blame its author for not having anticipated the whole science of ethology, or for being a child of his time in respect to his knowledge of genetics and neurophysiology. In particular, Darwin's attitude to the doctrine of the inheritance of acquired characteristics deserves some comment. It is, as Lorenz (1956) has pointed out, remarkable that Darwin realized so clearly that complicated behaviour patterns may evolve through natural selection. On the other hand, his attitude towards )>Darwinism», i.e. the doctrine of evolution through natural selection of superior genes, vacillated as he aged. In »The Descent of Man» and in »The Expression of the Emotions)) he appears to some degree a Lamarckist. The relations of the Secretary Bird, the Mungo, and other snake-eating animals to their prey is, it is true, spoken of in purely »Darwinistic» terms (1872, p. Ill):
»beneficial variations, supposing the characters in question to vary, would commonly have been preserved through the survival of the fittest)).
In other places Darwinian and Lamarckian ideas are expressed side by side:
»although some instincts have been developed simply through long-continued and inherited habit, other highly complex ones have been developed through the preservation of variations of pre-existing instincts — that is, through natural selection* (p. 41). »Such attitudes and utterances (become) after a time . . . through habit instinctive* . . . »Nor must we overlook the part which variation and natural selection may have played; for the males which succeeded in making themselves appear the most terrible to their rivals, or to their other enemies, if not of overwhelming power, will on the average have left more offspring to inherit their characteristic qualities ... than have other males.» (Pp. 103—104.)
In still other instances, Darwin seems completely to have adopted the theory of Lamarck, for instance when discussing blushing:
»This tendency will have been much strengthened, if frequent attention has been paid during many generations to the same part, owing to nerve-force readily flowing along accustomed channels, and by the power of inheritance.* (P. 339.)
More generally: »The tendency to such movements will be strengthened or increased by their being thus voluntarily and repeatedly performed; and the effects may be inherited.» (P. 356.) »The fact of gestures being now innate, would be no valid objection to the belief that they were at first intentional; for if practised during many generations, they would probably at last be inherited.)) (P. 61.)
Thus, when reading Darwin's later works, we have always to remember how little was known about »the power of inheritance*) at his time. Mendel was unknown to his contemporaries, and the rest was silence.
THE ETHOGRAM OF MAN
Darwin set himself to describe, as fully as possible, the expression of emotions in man, or, to use a more recent term, to give an ethogram (Makkink) of man. Such ethograms nowadays belong to the routine study of animal behaviour. Again and again, when the same species has been studied repeatedly, it has become evident that such an ethogram is never complete. This also applies to Darwin's human ethogram. Nonetheless, it is imposing. It is based on five main sources: observations on adults (including lunatics), observations on children, especially Darwin's own, observations on foreign races, some gleaned from the literature, some obtained from a number of correspondents, Dr. Duchenne's experiments on the function of mimic muscles, and finally paintings and sculptures.
The works of art obviously disappointed the great naturalist. He remarks, for instance, that the expression of suffering on the faces of Laocoon and his sons is wrong: the wrinkles on their foreheads ought to be horseshoe-shaped, rather than parallel. The giant Alcyoneus on the Pergamon altar, which was discovered only a year after the publication of »The Expression of the Emotions*), shows the expression intended somewhat more correctly.1
Of greater importance were the experiments of Duchenne. Through galvanization of certain muscles in the face of an insensitive person, Duchenne was able to mimic the expression of different emotions. Darwin held the results to be somewhat oversimplified, but nevertheless attached great importance to them. Recently, Baerends has complained that so little is known about the part played by single muscles in producing the instinct movements. The forgotten experiments of Duchenne seem to be
1 »About suffering they were never wrong, the Old Masters)) (W. H. Auden: Musee des Beaux Arts).
Fig. 1. The giant Alcyoneus from the Pergamon altar, showing the expression of
grief or pain.
unique of their kind; it would be worth while to repeat them, possibly with dogs or other mimically expressive animals as subjects.
The observations about foreign races included in Darwin's book have been criticized as partly consisting of anecdotical stuff. Unfortunately, we still know comparatively little about this subject, despite anthropologists, sociologists and UNESCO; at any rate, we lack a survey of the problem.
Finally, as far as Darwin's own observations are concerned, they bear testimony to his talent. To give details is impossible, as it would demand a review of large parts of the book.1
1 One example may suffice. Both Pavlov (see Wintersteist) and ethologists have pointed out that, in higher vertebrates, there is a certain tendency to become
THE SIGNAL FUNCTION OF THE EXPRESSION MOVEMENTS
Taking into consideration the general functionalism of living beings, we have, a priori, reasons to assume that the expression movements have a function. It might, perhaps, be suggested that they serve as an outlet. van Iersel has shown that not only does the consummatory act of a drive lower its level, but so also, at least to a certain extent, do other behaviour patterns belonging to the same drive. In other cases the effect of the expression movements may be self-stimulating.
In many animals, however, it has been experimentally shown that the expression movements have a communicatory function (summary by Tinbergen 1948). Darwin himself used a simple experimental method, in checking whether a number of experimentees were able to recognize different expressions from pictures. He clearly realized the signal function of the expression movements, for instance when stating:
»The power of communication between the members of the same tribe by means of language has been of paramount importance in the development of man; and the force of language is much aided by the expressive movements of the face and body.* (P. 355.)
»With social animals, the power of intercommunication between the members of the same community, — and with other species, between the opposite sexes, as well as between the young and the old, — is of the highest importance to them. This is generally effected by means of the voice, but it is certain that gestures and expressions are to a certain extent mutually intelligible.* (P. 60.)
It is a matter of dispute among students of psychology whether instinct movements, of which expression movements form the most spectacular group, are influenced by experience or not. Through isolation (»Kaspar Hauser») experiments we know that even very complex instinct movements, such as the song of different birds, may develop normally independently or partly independently of learning (Satjer, Messmer; Thorpe). Darwin held that many of the expression movements are »inborn»:
sleepy in critical situations. Tinbbkcen (1951) considers sleep in such situations a displacement reaction, and draws the conclusion that sleep is an instinct like other instincts, whereas Pavlov suggests that sleep is general thwarting. This strange behaviour occurs in man, too (Palmgeen). It is well known from fiction: in R. C. Sheriff's Journey's End the soldiers sleep in before the attack, and the hero in Barnaby Conrad's novel »The Matador» yawns when he enters the bull-ring. The phenomenon had already been mentioned in Darwin's classical book (p. 291).
»That the chief expressive actions, exhibited by man and by the lower animals, are now innate or inherited, — that is, have not been learnt by the individual, — is admitted by every one.» (P. 351.)
He also remarks (p. 359) that: »Their recognition would likewise have become instinctive.»
With human beings Kaspar Hauser experiments are excluded and we are, therefore, in many cases thrown exclusively upon assumptions or analogies. A person who is born blind is, however, in many respects completely isolated from his surroundings (a »Kaspar Hauser of zero order»). Darwin noticed that a person blind from birth, for instance, blushes from shame, which he could not possibly have learnt to do. He stresses, however, that:
»Certain other gestures . . . apparently have been learnt like the words of a language ... So it is with kissing as a mark of affection; but this is innate, in so far as it depends on the pleasure derived from the contact with a beloved person.» (P. 353.)
THE DERIVED MOVEMENTS
It is difficult to imagine that the expression movements generally originated as signals, as this would presuppose that other individuals of the same species immediately recognized them. The problem of the evolution of signal movements would be greatly simplified if one could find evidence that they originally had another function, and that the recognition mechanism evolved secondarily.
If a phenomenon without signal function (s—) regularly precedes a phenomenon (X) of biological relevance for a certain species, it will often turn out to be advantageous for the individuals of this species if they react at the moment of perceiving s— instead of only at X. An innate releasing mechanism will thus in many cases evolve, converting the neutral s— into a signal s-\- that releases a certain effect.1 As soon as a movement has acquired a signal function it will be exposed to a completely changed selection pressure, and will tend, on analogy to the signals used in human society, to become conspicuous and distinctive (Lorenz 1935, 1943). Further, it must be given at the appropriate moment. Using the above symbols, one may say that s+ (the original movement) evolves into a
1 This change of significance from s— to s+ may also develop in the individual as a »conditioned reflexi).
derived1 movement (*S-f-). The process whereby s— is transformed to s+ may appropriately be called signalization.2 The transformation of s-\- to S-\- has been called ritualization (Huxley). Morphologically, too, there are »derived» structures, such as the facial musculature in the quadrupeds. The problem of ritualization was not clearly discerned by Darwin, but he raised the question of the origin of expression movements, and answered it in a way which anticipates the findings of modern ethology:
»There are no grounds, as far as I can discover, for believing that any muscle has been developed or even modified exclusively for the sake of expression.* (P. 355.)
»Every true or inherited movement of expression seems to have had some natural and independent origin.»
»Some expressive movements may have arisen spontaneously, in association with certain states of the mind . . . and afterwards been inherited. But I know of no evidence rendering this view probable.* (P. 355.)
Only on the subject of sound production did Darwin hold a different view. It is, however, likely that sound signals are derived breathing responses (Spurway and Haldane, Morris 1956).
Darwin advanced three main principles to explain the expression movements, i.e.:
1. The principle of serviceable associated habits.
2. The principle of antithesis.
3. The principle of the direct action of the excited nervous system on the body, independently of the will and.in part of habit.
According to these »or closely analogous principles*) Darwin hoped to explain all expression movements. Below, a summary is given of the
1 This term was coined by Tinbebgeh (1952). A terminological question which need not bother us here is where to draw the line between derived and nonderived movements.
2 Signalization is not identical with ritualization. Signalization without ritualization is common in the habitat selection of higher animals. Klomp found that Lapwings in Holland prefer to settle down, in spring, on meadows with yellowish grass. The colour as such has no significance, but where the grass early exhibits a green shade, it will grow too high during the nesting season and so make locomotion difficult when the young are hatched. Similarly, terns on the Finnish coasts avoid nesting in the vicinity of trees. Even a single tree may serve the crows as a base of attack on their marauding trips, whereas they have great difficulty in breaking through the air defence of the terns without an intermediate place to alight. Green grass and trees (or the lack of these features) have acquired signal value in the umwelt of Lapwings and of terns respectively.
recent findings of ethologists on the evolution of signal movements, in order to examine to what extent Darwin's views agree with them.
1. Displacement reactions. These are (Tinbergen 1940) seemingly irrelevant in the situation where performed, for instance preening movements occurring in courtship display or in territorial fighting, van Iersel and Bol found that a carefully studied displacement reaction was not »allochtonous» but »autochtonous»: when two drives blocked each other, their inhibitive influence on a third drive was removed, so that this discharged. Displacement reactions often evolve into signal movements, becoming ritualized, sometimes to such an extent that their origin is more or less obscured. Darwin failed to recognize the displacement reactions, although a few reactions of this kind may have been included in his treatment of his third principle.1
2 a. Intention movements. These are (Hinde and Tinbergen) prepatory and incomplete2 (low intensity) movements which reveal the >>intentions» of the animal. A bird which is going to fly up crouches before taking off, almost as one compresses a steel spring before one lets it jump away. As changes of place very often precede instinct actions, the intention movements of locomotion (flying, walking, swimming) form an important source of derived movements (Daanje, Andrew).
b. Balance movements. Locomotion without balance is impossible. It is therefore probable, although a physiological analysis has not yet been undertaken, that some elements of the posture adopted, for instance, by a bird about to take wing, are balance movements. A passerine bird kept in the hand and rotated around its transverse axis will spread its tail and move it up and down compensatorily in a way which resembles the tail flicking displayed by many birds (for a few examples: v. Haartman 1958, Morris 1957, Braestrup).
1 Recent motivational analysis (Tinbergen, van Iersel, Hinde, and others) has shown that signal movements do not necessarily appear in a »pure» form. Two (e.g. aggression and escape) or even three (sex, aggression and escape) drives may be activated simultaneously. This may result (1) in one drive blocking the other, occurrence of (2) displacement or (3) redirection activities, (4) alternate dominance of the rival drives, or (5) (simultaneous) superposition of expressions of the different drives involved. Compound movements of types (4) and (5) may evolve into independent signal movements, as seems, for instance, to be the case with the famous zigzag dance of the Three-spined Stickleback (Lorenz 1941, p. 212). The process is, in some respects, imperfectly understood (Lorenz 1951).
2 The group called ointention movements* is obviously physiologically heterogeneous. Preparatory movements are not necessarily incomplete.
c. Anticipatory movements. No sharp distinction can be drawn between these and some of the intention movements. Anticipatory movements may be exemplified by the precopulatory display of female birds of many species, which consists, basically, of an anticipation of the attitude necessary for copulation.
Darwin's principle of serviceable associated habits is up to a point identical with the above-mentioned types (2 a, b, e) of signal movements. Thus, he mentions the crouching attitude of carnivores, which is obviously the intention movement of attack:
»Many carnivorous animals, as they crawl towards their prey and prepare to rush or spring on it, lower their heads and crouch, partly, as it would appear, to hide themselves, and partly to get ready for their rush; and this habit in an exaggerated1 form has become hereditary in our pointers and setters. Now I have noticed scores of times that when two strange dogs meet on an open road, the one which first sees the other, though at the distance of one or two hundred yards, after the first glance always lowers its head, generally crouches a little, or even lies down; that is, he takes the proper attitude for concealing himself and for making a rush or spring, although the road is quite open and the distance great. Again, dogs of all kinds when intently watching and slowly approaching their prey, frequently keep one of their fore-legs doubled up for a long time, ready for the next cautious step; and this is eminently characteristic of the pointer.)) (P. 43.)
Other cases discussed by Darwin under this principle may, perhaps, best be characterized as »anticipatory», as, for instance, when a horse »depresses his ears, so as to protect them from being bitten, as if he were fighting with another horse» (p. 45). There are other examples of Darwin's which cannot easily be identified with any of the principles established so far by modern ethology. Some of these examples are not convincing. For instance, his physiological explanation for the grimaces adopted in crying does not seem to rest on an adequate groundwork of fact, but his basic intention, to search for the origin of the derived movements, is beyond critisism.
3. Autonomic responses. In situations of »emotional disturbance*), i.e. according to Morris (1956), situations characterized by thwarting, the animal shows responses caused by the function of the autonomic nervous system. These responses prepare the animal for action (see e.g. Cannon). Both sympathetic and parasympathetic responses may serve as sources of signal movements, e.g. defaecation, urination, extreme pallor and blushing, accelerated or retarded breathing, gaping, sighing, panting,
1 Here, Darwin, without using the term, is speaking about ritualization.
weeping, sweating, and above all, pilomotoric responses, i.e. erection or sleeking of feathers or hairs (Morris). From such responses have evolved the urination of male dogs on posts, the raising of the hairs in hostile dogs and other mammals, including man (concerning Darwin's observations, see p. 20), and numerous acoustic signals which may be interpreted as ritualized inspiration and expiration movements (Eibl-Eibesfeld, Morris 1956). Some of these autonomous responses were known to Darwin, although he held that »our present subject is very obscure» (p. 66). He also failed, throughout, to distinguish between ritualized and unritualized movements.
THE ANTITHETIC MOVEMENTS
A good example of antithetic movements is provided by Darwin's own description of a dog approaching a strange dog or man »in a savage or hostile frame of mind» as compared with a friendly dog. A short summary of the dog's behaviour in these situations reveals how completely it is reversed:
savage or hostile friendly
walks upright body sinks downwards or crouches
very stiff thrown into flexuous movements
head slightly raised or not much lowered
tail erect, quite rigid tail lowered, wagged
hairs bristle, esp. along neck and back hairs smooth
ears forward ears depressed, drawn backwards, but not
as closely to head as in attack eye round and staring eyelids elongate
when close: shows teeth lips hang loosely
According to Darwin a dog, when approaching an enemy, prepares to attack. Its posture is therefore intelligible according to the principle of serviceable associated habits. On the other hand, he thought that none of the expressions of a friendly dog are of any direct service to it: »they are explicable, as far as I can see, solely from being in complete opposition or antithesis to the attitude and movements which, from intelligible causes, are assumed when a dog intends to fight» (p. 51). With reference to a dog throwing itself on the ground, Darwin remarks: »This is a movement as completely opposite as is possible to any show of resistance* (p. 120). An analogous example of antithetic behaviour he found in a hostile and a friendly cat.
Darwin held that if a certain movement is connected with a certain mood, the nervous system will more or less automatically produce an opposite movement in the opposite mood. I do not think this explanation is convincing. Antithetic movements are rather the outcome of selection for distinctiveness, whatever their origin may be.1
The antithetic movements seem to have been completely forgotten,2 until in 1952 Tinbergen and Moynihan (see also Tinbergen 1959) detected a movement in the Black-headed Gull which they called head flagging (later also facing away). The Black-headed Gull has an aggressive posture called the forward posture which consists of stretching the head forwards, whereby the weapon of attack, the bill, shows in a conspicuous way, enhanced by the dark hood. This is a typical associated serviceable habit in Darwin's sense. Head flagging occurs (Tinbergen 1959) as appeasement behaviour in hostile encounters and may be connected with different postures; when it takes place between members of a pair it is always connected with an erect posture. In head flagging the gulls face away from each other in such a way that the partner cannot see the bill and the dark mask of the other gull. Moynihan (1955) has suggested that the movement is derived from an escape intention movement and selected for because of its antithetic nature.
Similar appeasement reactions occur in other gull species (Tinbergen 1959). The feature common to all of them is that the bill, which is the gull's chief weapon, is either hidden or withdrawn. Likewise appeasement behaviour in dogs (Lorenz 1943) has been interpreted by Tinbergen as a hiding of their weapon, the teeth.
Lind has described an appeasement reaction in the Lapwing. Two individuals approach at a territorial encounter, then suddenly turn around, the bill being hidden from the antagonist. The posture is enhanced by the rusty colour of the under tail-coverts. In courtship display a
1 The same opinion has been expressed by Marlbb (1959) and Ckaig. The existence of interspecifically antithetic movements is evidence against Darwin's explanation.
2 An example of antithetic behaviour was, however, incidentally mentioned by Lorenz in 1941 (p. 218). The behaviour in question is the round-head posture (Kopfrundstellung, Weidmans) of the male Mallard: he swims high on the water Dwahrend das Riickengefieder in 'gewolltem' Gegensatz zur gewohnlichen Ruhe-stellung sehr glatt angelegt wird>>.
3 There may be still other appeasement reactions in man, such as for instance »turning the other cheeko.
similar posture is frequent, whereby the male turns away from the female, showing her his under tail-coverts and moving the tail up and down.
Marler (1956) has given a detailed analysis of antithetic behaviour in the Chaffinch. It is common in the courtship postures of the male, and in submissive behaviour. Thus, the avoidance behaviour of a submissive Chaffinch consists of components of the relaxed posture together with (1) avoidance of looking directly at the opponent, (2) avoidance of frontal presentation, and (3) avoidance of sudden movement near the aggressor. These components contrast with both aggressive and escape postures which encourage immediate attack. (Cp. also Hinde concerning the Great Tit and Morris 1954 concerning the Zebra Finch.)
Many of the reversed movements consist solely of hiding a weapon. This we may, in a way, regard as presentation — although in an odd way — of a biologically significant feature. In other cases, the appeasement behaviour is more complex, the whole posture being antithetic to a certain aggressive posture. A good example of this is the courtship display of the female Three-spined Stickleback (Tinbergen 1953). In reaction to the zigzag dance of the male, a ripe female turns obliquely upwards, which seems to be the nearest possible antithesis of the male's vertical threat posture.
According to Darwin, man has two antithetic appeasement postures, shown by a humble man as contrasted with an arrogant one, and a helpless (or one might rather say submissive) man as contrasted with an aggressive or indignant one. The latter case may serve as an example:
squared shoulders shrugs shoulders
expanded chest volume of chest reduced
clenched fists, one or both arms with bends elbows showing palms with ex-rigid muscles placed in the proper tended and spread fingers position for attack
head erect throws head a little on one side
closed mouth mouth open (lower jaw drops)
frowns raises eyebrows
Darwin remarks that none of the gestures of the helpless man are serviceable, but that all of them are completely opposite to aggressive behaviour. The extended and spread fingers may evidently be interpreted as a reduction of armaments quite as complete as the facing away in the gulls. Darwin maintains that the submissive posture is very much rarer in the restrained English than in the French. It is said to be especially
common among Jews. Against the background of their tragic history, this may be seen as a pathetic correlation between behaviour and biological need.
It was a great merit of Darwin's to have realized how common the antithetic movements are. An example which, perhaps, in the spirit of Darwin could be interpreted as antithetic behaviour is the approval through nodding and disapproval through shaking the head (in some races also the hand, or just a finger). Darwin thought head shaking to have originated from the small childrens habit of refusing food by moving the head to right and left. In most languages the letter n, pronounced with closed teeth, according to Darwin's relative Wedgwood, is included in the word for »no», e.g. »njet». Nodding is the complete antithesis of the lateral shaking, whatever its origin may be.
The problem of the distinctiveness of signals is a twofold one: intra-and interspecific distinctiveness. All the antithetic movements described by Darwin are intraspecifically distinctive. The interspecifically antithetic signals throw some light on the general problem of antithesis, however, and will therefore be briefly considered here.
It is a well known fact that closely related bird species often have very distinct songs. Examples of such species are afforded by the Pied and the Collared Flycatchers, the Willow Warbler and the Chiffchaff, the Chaffinch and the Brambling. Most of the sounds of the black and white flycatchers are similar, but the territorial song and the contact-and-warning sound diverge. In the Collared Flycatcher this sound has partly assumed the role of a song (v. Haartman and Lohrl). The song of the Chiffchaff is very unlike that of the Willow Warbler (although composed of homologous elements (Faber)) except in Spain, where the Chiffchaff sings relatively like a Willow Warbler and the latter species is lacking (Ticehurst). The phenomenon that the differences between closely related species are accentuated in the zone of geographical overlap has been called »character displacement* (Brown and Wilson). The interspecific antithesis is more marked in males than in females (Sibley). Marler has pointed out that the tendency to interspecifically antithetic behaviour is more marked in the precopulatory than in the post-copulatory behaviour (when it may be too late, anyway!).
In the Brambling and the Chaffinch the song antithesis (Marler) is very striking and, moreover, enhanced by the different postures of the singing males (Bergman 1952). This difference is the more noteworthy as the North American House Finch (Carpodacus mexicanus), without being
closely related to the Fringilla species, has a song which resembles that of the Chaffinch.
In other animals, too, (e.g. Orthoptera, Perdeck), there are examples of interspecifically antithetic songs among closely related species. It should be pointed out, however, that the rule is not always valid; for instance, members of the genus Acrocephalus may be difficult to recognize by their voices. This is the more striking since they look comparatively similar and live in dense thickets, being at least partly nocturnal.
In species which are isolated geographically, ecologically or temporally, a striking convergence of sound signals may develop. This is the case with some of the members of the northern bird fauna, e.g. the Snow Bunting and the Crested Tit, the Wood Lark and the Wood Sandpiper, the English Sparrow and Richard's Pipit.
One may ask whether there is any evidence that signals may be misunderstood owing to lack of distinctiveness. In the case of intraspecifically distinct signals few examples are known to me, except in man himself. It struck Darwin and many of the students of expression after him,1 that man's ability to recognize expressions on photographs is comparatively poor. This may partly be so, because the face of man, that rather restricted area, is »overloaded» with duties in respect to signalling. No wonder if the selection for antithesis has been exceptionally strong in man. Among birds, the precopulatory behaviour of the female often seems so undistinctive and, moreover, mixed with asexual behaviour elements that mistakes are possible. In the Pied Flycatcher, I saw a male trying to copulate with a warning female which sat motionless close to the nest. A certain lack of motion belongs to the copulatory behaviour of the female, whereas the warning sound, if not very frequent, has but little communicatory value. Kttusisto (1940, p. 23) observed an analogous case in the Willow Warbler. In this species the female solicits copulation with spread wings. A female which had been scared out from the nest showed distraction display with spread wings, which released copulatory behaviour in the male. In the Sandwich Tern and in the Skylark, Ritting-haus observed that food begging of fledged young may release sexual behaviour in the male.
There are more numerous examples of interspecifically inadequately distinctive signals. Two Australian passerines, Pachycephala rufiventris and Lalage tricolor, have songs sufficiently similar to cause duels to start
1 See Fbois-Wittmann 1930.
Fig. 2. Yen Lo, Decider of Life in Hades. Glazed stoneware, Ming Dynasty.
Courtesy: Royal Ontario Museum. Expression of the fighting drive with uncovering
of the teeth (»snarling»). Note the »ritualized» enormous canine teeth, an intuitive
achievement of the unknown artist.
between males, but these cease when they approach each other, presumably because of mutual identification by plumage differences (Robinson). Lorenz (1943) mentions that juveniles of Cairina moschata followed Alpochen aegyptiacus, which has a wing-patch of the same colour as adult Cairinas. The Turnstone has a tendency temporarily to join other birds with some black in their plumage, such as the Dunlin, and even Starlings (Bergman 1946). According to Moynihan (1960), the colours of some Central American Finches have converged instead of diverging, facilitating the formation of mixed flocks.
Fig. 3. Sneering. From Rejlander's photo in Darwin's »The Expression of Emo-tions». The expression is faked, but seems to be accurate.
THE SEAL OF THE PAST
The number of species whose behaviour was known, even to a very moderate degree, in Darwin's time was too small to allow much in the way of comparative ethology. It was not until the study of pigeons by Whitman and of swimming ducks by Heinroth and Lorenz that the foundations of this branch of ethology were laid. Evidently, comparative ethology is impossible without a knowledge of evolution, or it could only exist without realizing its own aims, as did comparative anatomy before Darwin's day. Darwin clearly realized the usefulness of behaviour studies in establishing phyletic relationships. He says, for instance (p. 367):
»the study of the theory of expression confirms to a certain limited extent the conclusion that man is derived from some lower animal form, and supports the belief of the specific or subspecific unity of the several races; but as far as my judgement serves, such confirmation was hardly needed.d1
Paradoxically, Darwin's comparative ethology was mainly based on a single species, man. Above all the vestiges of behaviour proved useful in reconstructing man's ancestry. One has to remember that in Darwin's time vestiges were a much more convincing argument for evolution than
1 The contrast between the restrained tone of Darwin's writing and its revolutionary content deserves special notice.
Fig. 4. Adult male Gorilla showing canine tooth. In the absence of a fuller description no conclusion can be drawn about possible homology with sneering in man.
(From Svensk Uppslagsbok.)
more regular kinds of homology which could more easily be brought into line with the orthodox theory of creation. This may be one of the reasons why rudiments were popular subjects of study in the early days of the study of evolution, whereas nowadays they are virtually ignored. Darwin's attitude towards vestiges is shown, for instance, by the following quotation (p. 351):
»Slight movements, such as . . . the . . .drawing down of the corners of the mouth, are the last remnants or rudiments of strongly marked and intelligible movements. They are as full of significance to us in regard to expression, as are ordinary rudiments to the naturalist in the classification and genealogy of organic beings.*
On erection of the hairs in man, Darwin states (p. 308—309):
»It is certainly a remarkable fact, that the minute unstriped muscles, by which the hairs thinly scattered over man's almost naked body are erected, should have been preserved to the present day; and that they should still contract under the same emotions, namely, terror and rage, which cause the hairs to stand on end in the lower members of the Order to which man belongs.*
Darwin's skill as an observer and his inductive method reach one of their high points in his analysis of vestigial aggressive behaviour in man (p. 244):
»This retraction of the lips and uncovering of the teeth during paroxysms of rage, as if to bite the offender, is so remarkable, considering how seldom the teeth are used by men in fighting . . .»
He also calls this behaviour (p. 243):
»a remnant of a habit acquired during primeval times when our semi-human progenitors fought together with their teeth, like gorillas and orangs at the present day.»
From this intention movement of fighting Darwin derives the sneering of man. He describes it in the following way (p. 249—250):
»The expression . . . differs but little from that already described, when the lips are retracted and the grinning teeth exposed. The difference consists solely in the upper lip being retracted in such a manner that the canine tooth on one side of the face alone is shown; the face itself being generally a little upturned and half averted from the person causing offence. The other signs of rage are not necessarily present.*
(p. 250) »The expression of a half-playful sneer graduates into one of great ferocity when, together with a heavily frowning brow and fierce eye, the canine tooth is exposed.*
Discussing a young man who showed this reaction with rare distinctiveness, he writes:
(p. 250) »When this was exhibited, »the corner of the lip over the eye-tooth, which happened in this case to be large and projecting, was raised on the side of his accuser, a strong frown being still retained on the brow*.
(p. 251) »The action is the same as that of a snarling dog; and a dog when pretending to fight often draws up the lip on one side alone, namely that facing his antagonist.*
Darwin draws the following conclusion (p. 253):
»The expression here considered, whether that of a playful sneer or ferocious snarl, is one of the most curious which occurs in man. It reveals his animal descent; for no one, even if rolling on the ground in a deadly grapple with an enemy, and attempting to bite him, would try to use his canine teeth more than his other teeth. We may readily believe from our affinity to the anthropomorphous apes that our
male semi-human progenitors possessed great canine teeth, and men are now occasionally born having them of unusually large size, with interspaces in the opposite jaw for their reception.»
No wonder that Victorian England was a bit upset. »Is man an ape or an angel. My Lord, I am on the side of the angels» stated Disraeli in a speech after the publication of »The Origin of Species». Paleontology has been more on the side of the apes, but there are still large gaps in our knowledge of the prehistory of man. Proconsul, an unspecialized early Miocene great ape which may have been the ancestor of man, had large, protruding canines, reminiscent of those of the now living apes (Romer). Some other Miocene and Pliocene genera of apes had far smaller canines (Le Gros Clark). In Australopithecus, the man-ape from South Africa, the canines were large, but at an early stage of attrition did not protrude beyond the general level of the tooth row. It is, however, possible that Australopithecus was only a blindly ending branch of the human family tree, in which case few conclusions can be drawn from his dentition. In Pithecanthropus erectus, living about 500 000 years ago, the canines were large and protruding, in some individuals (Le Gros Clark) a diastema in
Fig. 5. Diagrams illustrating A, the relatively long and robust root of the upper canine tooth in Homo sapiens; B, the occlusal relationships of the canines and a sectorial first lower premolar tooth in a cercopithecoid monkey (1), and the occlusal relationship of the canines and first lower premolar tooth in Homo sapiens before attrition (2), and at an early stage of attrition (3) (after Remane). From Le Gros
Clark 1955, p. 166.
the tooth row of the upper jaw corresponding to the lower canines, as in the apes. The replacement of the canines was late, as in the Pongids. The males probably had larger canines than the females, which is not the case in any other Hominids, but is typical of Pongids. The form of the canines was rather scapulate, however, as in modern man, than conical as in apes.
In the Heidelberg and Neanderthal men the canines did not project. In recent man, however, they still retain what one might call the seal of the past, having unusually large roots which by no means correspond to their moderate size. In the milk teeth, especially, the canine may be relatively pointed and projecting, although at an early stage of attrition it is worn down to the height of its neighbours. The permanent canines erupt comparatively late, in some modern races even later than the second molars.
It has been argued that the projecting conical canines of the Pongid type of dentition known from Miocene and Pliocene apes are specializations which could not have found a place in Hominid ancestry. Lb Gros Clark regards this suggestion as improbable, but admits that the paleon-tological data are too scanty to allow of confident conclusions. The snarling and sneering described by Darwin support the theory that man is descended from forms with large canines which could be used as weapons in fighting.
Thus, paleontology, anatomy, and ethology leave a consistent picture of our descent. Darwinism has evolved into neo-Darwinism, also known as the synthetic (Htjxley) or eclectic (Mayr) theory of evolution, which builds its conclusions on facts from all branches of biology.
Darwin's observations on vestigial behaviour in dogs are generally known. A dog, before lying down, turns round repeatedly as if to trample down grass. This is (as far as my experience with a German retriever goes) especially true with a dog which is sleepy; in the day-time this behaviour is rarely seen.
After defaecation dogs scratch backwards a few times with their feet, without, however, ever covering their excreta. Wolves and jackals also behave in this way. Obviously, a remote ancestor of theirs must have shown this behaviour more completely.
There are comparatively few recent studies on vestigial behaviour. Poulsen has shown that secondary ground-nesting passerines have retained the habit of building bowl-shaped nests, and have not acquired the egg-rolling behaviour typical of primary ground-nesters. Wickler has studied »yesterday's adaptations)) or the »burden of history» in fish.
The males of Noemacheilus kuiperi have retained a way of fighting, namely »parallel swimming*, which is typical of fish living in running streams, the habitat of the ancestors of this species.
It has sometimes been assumed that fixed patterns are more conservative than bodily structures in general, and that they may therefore survive for enormous lengths of time after becoming purposeless. Heinroth's observations on »indirect» head scratching in many birds, especially passerines and their relatives, and Krtjmbiegel's on the vestigial flying motor pattern in the Ostrich are the best examples.
The »indirect» head scratching, whereby the wing is drooped and the leg brought up over it, is thought to be homologous to the scratching posture probably adopted by the four-legged avian ancestor.1 This character has been said to be very rigid, occurring in the same way in all members of the same family. Nice and Schantz have shown, however, that the scratching movement may vary even in one and the same individual. This makes its alleged homology questionable.
A vestigial flying pattern was said to occur in an Ostrich under special test conditions. If Gltttz von Blotzheim's recent theory on the evolution of the Ratites from flightless forms is valid, the interpretation of the experiment must have been incorrect.
In this connection, attention should be drawn to the criticism levelled by Wallace Craig at Darwin's conception of vestigial movements. Craig (p. 362) is probably right in stressing that the baring of the canine tooth in man is not devoid of any meaning, but has persisted »to this day because of its utility as a piece of emotional behaviour*. This does not disprove its vestigial nature, however. From the facts known, it seems likely that the communicatory value of sneering has diminished during the evolution of man, and that it will continue to do so in the future. That it has survived at least half a million years — the time since Pithecanthropus — depends on the preserving influence of the corresponding innate releasing mechanism (seeLo-RENZ 1943). Without entering further into the philosophical aspects of vestigialism, I do not think it necessary to postulate complete lack of function as a characteristic of vestiges; it seems that the reduction of a movement or structure generally goes hand in hand with reduced function.2
1 It should be noted that Heinkoth himself never drew this conclusion.
2 Although, for instance, in the famous case of the vermiform appendix the function has deteriorated more rapidly than the structure.
As an example of a vestige in Darwin's sense, Craig mentions the billing of pigeons, which looks as if the male were feeding his mate, although no food is passed. This case is hardly analogous to sneering in man. The billing is rather a symbolic (Antontus) or »degraded» (Schenkel) movement. So also is the demonstration of the nest-site in some birds nesting in holes and niches (v. Haartman 1957). The male Spotted Flycatcher, for instance, demonstrates a nest-site to females at places which would not do for this purpose. The billing and the symbolic nest-demonstration have become dissociated from their original subjects, resembling in this respect the vestigial demonstration of the canines, but there is, at the same time, a clear-cut difference. The evolutionary fate of an animal's teeth is almost entirely dependent on factors other than their releasing value, i.e. on the general ecology of the animal. A reduction in the size of the canines will almost certainly cause a reduction in the effect of showing them, whereas the emancipation of the nest-demonstration from real nest-sites is, so to say, a »voluntary» step in the evolution of the organism which will cause enhancement of the display (for instance, higher frequency and independence of the locality), instead of deterioration.
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Citation: John van Wyhe, editor. 2002-. The Complete Work of Charles Darwin Online. (http://darwin-online.org.uk/)
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