Facial Expression in Primates with Remarks on a Parallel Development in Certain Carnivores (A...

Facial Expression in Primates with Remarks on a Parallel Development in Certain Carnivores(A Preliminary Report on Work in Progress)Author(s): Niels BolwigSource: Behaviour, Vol. 22, No. 3/4 (1964), pp. 167-192Published by: BRILLStable URL: http://www.jstor.org/stable/4533071 .

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FACIAL EXPRESSION IN PRIMATES WITH REMARKS ON A PARALLEL DEVELOPMENT IN CERTAIN CARNIVORES (A PRELIMINARY REPORT ON WORK IN PROGRESS)

by

NIELS BOLWIG1)

(University of Ibadan, Nigeria, former of Makerere University College, Kampala, Uganda.)

(With 8 Plates and 13 Figures)

(Rec. 3-IX-1962)

C ontent s. Page

Introduction ... .......... 168 Material and Technique ............... 69 The facial musculature ................ 170 The approach to the live material . . .......... 78 Description of facial expressions . . .179

A: Expression of happiness and joy . I79 B: Unhappiness . . .183

I: Fear and horror ............. . 183 2: Sadness ............... 185

C: Anger ................... 86 D: Love and affection . . .187 E: Concentration . . .88

Conclusion and discussion.. I88 Summary .................... 191 References.... 191 Zusammenfassung . . .192

I) The author wishes to thank the many people and institutions who have made this study possible. He is indebted to all who have presented him with animal material or assisted in obtaining it; also to the various Zoological Gardens, listed in this paper, for allowing access to the animals for observation and handling.

During the Author's stay in Madagascar he was granted facilities for his work by the Institut Scientifique de Madagascar and he warmly thanks Professor MILLOT and Dr R. PAULIAN, both formerly of the Institut.

In addition the author extends his thanks to the Medical School in Johannesburg for its help with material for dissection, to Professor GALLOWAY of Makerere College who allowed the author to spend several days in the company of his chimpanzee Napoleon and to Dr DESMOND MORRIS of the London Zoo for the useful discussions which drew the author's attention to various features. Finally he must thank the University of the Witwatersrand and Makerere University College for their financial support. Behaviour XXII 13



i68 N. BOLWIG

INTRODUCTION

In the past there have been various attempts to describe and to find rules

governing the facial expressions of animals and man.

The first thorough study was that of DARWIN (1872) who based his conclusions mainly on direct observations made by himself and others on humans and on animals. His hypothesis of an antithesis in facial movements can no longer be fully accepted, but his book still makes inspiring reading. A similar analysis based on pictures was made by KRUKENBERG (1920). Like DARWIN he concluded that certain rules govern the facial expressions. A confirmation of most of KRUKENBERG'S ideas is given by BOVING and TIT-

CHENER (I923) who made models for the demonstration of facial expressions in man.

In a thorough experimental study of emotional reactions LANDIS (I925) came to the conclusion that in humans no rules can be given for the facial

expressions of emotions. The negative result he obtained may be explained from the very complex emotions he created in his subject and they do not

necessarily contradict the results obtained by previous workers.

Besides humans DARWIN also included various animals in his study. He

discussed, for example, the expressions of dogs and cats. The erection of the "mane", ears and tail and the baring of the teeth which is characteristic of an aggressive, threatening dog is almost completely a reverse picture of the submissive animal. In this case the hair is sleeked, the ears laid back, the tail lowered and legs and neck bend into a cringing posture. The corners of the mouth are drawn back and the teeth are covered. It was observations such as these which gave DARWIN support for his principle of antithesis. DARWIN'S observations were in many ways confirmed by SCHENKEL (I948) who made an excellent detailed study of the behaviour of wolves.

Various authors have dealt with the facial and other modes of expression in primates. Thus ZUCKERMAN (I932 and I933) has given a general account

of his observations on a great number of animals. The faces of lemurs he found to be "notoriously blank", apart from flinching movements of the eyes and upper eyelids in the case of fear which could be accompanied by slight movements of forehead and ears. An attempt to give a more detailed description was made by BOLWIG (I959b and I96I) but he also failed to notice much activity and ascribed the major part of their intercommunication to the production of scent. ZUCKERMAN found that higher monkeys showed such great similarities to man in their facial expressions that man can easily interpret their significance. Exhibiting of teeth in dominance he found pre- ceded fights and therefore was to be considered a threat. In one monkey



FACIAL EXPRESSION IN PRIMATES, ETC. I69

(Cercopithecus leucampyx) he observed an extrusion of the lips which he

interpreted as a friendly gesture. A more detailed description of facial ex-

pression in baboons was given by BOLWIG (I959a) and discussed further in

comparison with other primates in his following paper (I959b). He found similarities between the facial expression of catarrhine monkeys and man.

In contrast to these claims are the experimental results of W6RNER

(I940). He deduces from his study of rhesus monkeys that some of the animal's moods are indicated by the rhythm with which it moves its eyebrows up and down. His experiments, however, were so designed as to make it impossible to pass a fair judgement on the animal's state of emotion.

The most important description of facial expression in apes was given by KOHTS (I935). She brought up a chimpanzee in her home and later on

compared her observations with those she could make on her own child. The description she gave has in many ways been confirmed by KELLOGG

and KELLOGG (1933), and YERKES and YERKES (I945). Her observations

support the idea of basic similarities in the facial expressions of emotions in higher primates.

A comparative study of the facial muscles of primates was made by HUBER

(193I). Besides giving an account of the facial anatomy he also passed various remarks on the function of the muscles.

MATERIAL AND TECHNIQUE Most observations were made on animals belonging to the author. During

his daily handling of the animals observations were made and noted and

photographs taken so that the features of the facial postures could be studied in detail and at leisure. When it was thought advisable situations were created which induced the desired emotions in the animals. This was done to check

previously made observations and they were also checked when possible on wild animals and on animals in a number of Zoological Gardens. The list on page I70 shows the animals observed and indicates the conditions under which the observations were made.

It is natural that the animals in the author's possession were those on which the most intensive work was done. In the case of the Lemurs much time has also been spent on them in the Zoo of Tananarive and in the wild.

Similarly much time was spent on some privately owned monkeys and apes, such as the chimpanzee Napoleon, which belonged to Professor Galloway, Makerere University College.

The Zoological Gardens visited were: Johannesburg, Pretoria, Tananarive, Entebbe, Khartoum, Cairo, Munich, London, Chester, Copenhagen.

Wild animals have been observed in various parts of South Africa, in East



170 N. BOLWIG

Name of animal Author's Privately Public Wild

menagerie owned Zoo

Suricata suricatta + + Canis familiaris + +

Tupaia glis + Odorlemur catta + + Lemur mungoz +

variegata + macaco + +

Leontocebus rosalia +

Hapale jacchus + Saimire sciurea + Cebus sp. + Cercopithecus aethiops + + + +

ascanius -+ + + hloesti + + mona + +

Cercocebus torquatus +

albigena + +

aethiops + + ,, galertus + +-

Silenus silenus +

Erythrocebus patas -+ + + Mandrillus spinx +

,, leucophaews + Papio ursinus + + +

,, doguera + + +

abyssinicus + Pan styrus + + + Gorilla gorilla +

, beringei -+ + Homo sapiens, whenever possible.

Africa, particularly in Uganda, in Eastern Congo and on Nossy-be Island of Northern Madagascar.

Besides watching the live animals the author has dissected a number of animals. This was found desirable because it can be very difficult to under- stand the often very small movements of the face without at least a super- ficial knowledge of the underlying structures.

THE FACIAL MUSCULATURE

In order to assess the movements of the primate face and its expressions of emotion a study of the mimic muscles has been carried out.



FACIAL EXPRESSION IN PRIMATES, ETC.

The material used for dissection was mainly made available by the Depart- ment of Anatomy in the Medical School, University of the Witwatersrand, Johannesburg. Some of the material was the author's private property. The animals dissected or observed while being dissected were: Lemur pulvus, Cercopithecus aethiops, Papio ursinus, Pan satyrus and Homo sapiens of various races. Among the carnivores Suricata suricatta was dissected.

Unfortunately most of the material suffered from having been stored in formalin over a great number of years. The dissections were therefore not as perfect as could have been wished for. It is mainly for this reason that the brief account given here follows closely that of HUBER (I93I).

The mimic muscles of the primates have, as could be expected, undergone great evolutionary changes from the most primitive to the highest members of the Class, thus making possible the evolution of an elaborate facial mimic, which has reached its highest development in man. The original "primitive sphincter colli" gave rise to two separate muscle sheaths; the sphincter colli

superficialis and the sphincter colli profundus. The platysma developed from the former while all the many other facial muscles, which in man form a most intricate system seem to have developed from the latter.

^-^^ f,^^I^ /^ M. auriculo-labialis

_M. naso-labialis

M. levator labii superioris

" M. buccinator

]Platysma

Fig. I. Facial muscles of lemur.

In primitive primates, such as lemurs (Fig. I) the platysma forms a broad sheath of muscle fibres which runs from the neck below the ear to the lower corner of the mouth. Above, and almost continuous with the platysma is another smaller sheath stretching from the ear to the upper ,corner of the mouth. This is the m. auriculo-labialis which in higher primates becomes shortened to form the m. zygomaticus. Of the same origin as the m. auriculo- labialis are some fibres extending from the maxilla to the area of the vibris- sae of the upper lip. They form the m. maxillo-naso-labialis. These muscles act as antagonists to the m. orbicularis oris and, when contracting, draw the corners of the mouth backwards. Another sheath of muscle fibres, the

I7I



172 N. BOLWIG

m. naso-labialis, extends from the nasals down to the upper lip. When con-

tracting it lifts the lip so that the teeth become exposed. Finally, a thin sheath of fibres fans out from the top of the ear over the temporal region where part of it interlaces with upward bending fibres from the m. auriculo labialis.

In the marmoset, Hapale jacchus, the face has become shortened. The m. auriculo-labialis (now m. zygomaticus) no longer reaches the ear but extends from the zygomatic arch to the upper corner of the mouth. Its upper part is in broad connection with the m. orbicularis oculi. At its lower border it no longer forms a continuation of the platysma which it meets at an obtuse

angle at the corer of the mouth. The m. naso-labialis fans out from the nasals to the upper lip as it did in the lemur. None of these muscles permit movements of the face which are appreciably different from those of the lemurs. An advance over the lemur is the well developed m. frontalis which makes it possible for the animal to lift its brows.

In the higher platyrrhines (Fig. 2) there is a further development from the marmosets. The muscles of the temporal region have been re-arranged so as to make more varied movements possible, and the zygomatic muscle is less integrated with the orbicularis oculis than was the case in Hapale. Moreover, the frontal muscles are well developed allowing for a lifting of

MI naso-labialis

M. zygomaticus

M. trinagularis

" Platysma

Fig. 2. Facial muscles of platyrrhine monkey (HUBER).

the eyebrows. The brows are lowered by a strong m. depressor supercilii. Of particular interest is the development of a m. triangularis which can affect



FACIAL EXPRESSION IN PRIMATES, ETC. 173

M. zygomaticus

M. naso-labialis

M. caninus

iM. triangularis

Fig. 3. Facial muscles of catarrhine monkey, Cercopithecus.

the corners of the mouth. The orbicularis oris is better developed than in the marmoset and gives a greater mobility to the lips.

The mimic muscles of the catarrhine monkeys (Figs 3 and 4) are similar to those of the platyrrhines. The m. frontalis is, however, more regularly arranged than in, for example, Ateles making possible a forceful lifting of the eyebrows but not permitting the curious vertical contraction of the scalp

M. depressor superioris.

M. naso-labialis

M. levator labii _~~ ~superioris

- M. caninus

iMI. triangularis

M. buccinator

' M. zygomaticus

Fig. 4. Facial muscles of catarrhine, Papio.

in the region of the temple such as may be observed in some platyrrhines when they become excited. A m. caninus extends downwards across the maxilla to the corner of the mouth where it meets the upper end of the m. triangularis. Another remarkable feature is the formation of a buccal

pouch which is covered by the buccinator muscle. This pouch forms a hernia in the platysma. Below the jaw the platysma sheaths of the two sides of



174 N. BOLWIG

\ M. zygomaticus

,Mv. risorius

M. triangularis

Fig. 5. Facial muscles of chimpanzee (HUBER).

the face meet and interlace. There is a tendency for the muscles to split into minor sections and it is possible that each section of a muscle may act inde-

pendently or partly independently of the rest, thus permitting the development of a more elaborate mimic.

M. naso-labialis

M. zygomaticus

M. risorius

., M. triangularis

Fig. 6. Facial muscles of gorilla (HUBER).

The face of the chimpanzee (Fig. 5), the gorilla (Fig. 6), and man (Fig. 7) have very similar mimic muscles although there is a clear progress in evolution from chimpanzee to man with the gorilla as an intermediate




form. Where the platysma passes over the mandibular border into the m.

quadratus labii inferioris deep bundles of fibres attach themselves to the mandible. In man this attachment is more extensive than in apes. Some muscle bundles which have split off from the muscles lowering or lifting the lower and upper lip respectively traverse the lips in the region of the

lip red and play an important part in shaping these borders.

,.

M. levator labii superioris

M. zygomaticus

-- M. risorius

M. triangularis

Fig. 7. Facial muscles of human child (HUBER).

In the chimpanzee the m. zygomaticus is wider and less differentiated than in the gorilla and in man, and its upper portion is broadly connected with the m. orbicularis oculi. In all three, but more so in man than in the chimpanzee or gorilla, many of the fibres have been attached to the zygomatic arch.

The most complicated of all the mimic muscles of the chimpanzee, the

gorilla and man is probably the orbicularis-triangularis system. The m. trian-

gularis has given rise to the m. risorius Santorini and the m. transversus menti. Where the m. triangularis joins the orbicularis oris it covers the m. buccinator. It continues upwards into the m. orbicularis oris of the upper lip and into the m. caninus. All these muscles form a functional entity. It is most complicated in man but there is no reason in this report to go into further details in this direction.

In the Cercopithecidae the m. maxillo-naso-labialis has its origin higher up on the maxilla than in the case of the lemurs. In the chimpanzee, the

gorilla and in man this muscle has become the m. levator labii superioris proprius. In man it has obtained new secondary association with the neigh-



176 N. BOLWIG

bouring muscles, namely the m. levator labii superioris et alae nasi and a derivate of the m. zygomaticus - the m. zygomaticus minor.

The muscles of the nose have differentiated and they become progressively more elaborate as one passes from the chimpanzee through the gorilla to

man, a fact which may partly be explained by the development of a pro- minent nose in humans.

In contrast to the catarrhine monkeys, the chimpanzee, the gorilla and man all have a well-developed m. corrugator supercilii with a firm origin on the frontal bone. A m. proceres nasi continues above into the muscular

portion of the m. frontalis. All these muscles are better developed in man than in the two big apes.

It is interesting to note the similar primitive pattern of facial muscles of the suricate (Suricata suricatta) (Fig. 8a) to that of the lemur. A broad sheath of platysma fibres attach themselves to the lips around the corers of the mouth. Continuous with the upper edge of the platysma is the m. auriculo-labialis (zygomaticus) which tends to divide into sections not unlike what is found in the case of the primates. The lower part extends from the ear to the upper lip, with an attachment to the skin in the zygomatic region.

The upper part extends from the outer corer of the eye, where it is

broadly connected with the m. orbicularis oculi. Two bundles of muscle fibres extend from the eyebrow towards the ear. Almost covered by the m. auriculo- labialis is the m. lavator labii superioris proprius which extends from the maxilla to the upper lip. Another muscle to the upper lip is the m. levator naso-labialis. Its major part extends from the frontals to the lip where it interlaces with the m. auriculo-labialis. A minor part extends from the nasals to the tip of the snout.

In the dog (Fig. 8b) the muscular arrangement is very different from that of suricata and primates. There is no continuous sheath of platysma as in the primates. A m. cutaneus spreads out from the upper part of the ear across the sides of the face to the lower eyelid where it blends with the orbicularis oculi. Other fibres go to the nasal region and those best developed extend to the upper lip and the angle of the mouth. A narrow m. auriculo- labialis (zygomaticus) also extends from the upper ear to the corer of the mouth. The m. buccinator forms two thin sheaths the fibres of which cross one another at right angles. The outer sheath serves to pull the upper lip down and draws the corner of the mouth forwards. The upper lip and the nose are provided with two parallel muscles, the m. levator labii superioris proprius and the m. dilatator naris lateralis. Both have their origin on the maxilla behind the infraorbital foramen. These muscles draw back the upper




M. auriculo-labialis

ii II M. levator labii superioris

proprius

M. levator naso-labialis

r ,

\Platysma

Fig. 8a. Facial muscles of suricate.

lip and the angles of the nose. Another muscle, the m. levator nasolabialis, extends from the frontal and nasal bones downwards, in the form of a broad sheath, to the wings of the nose and to the upper lip. It lifts the lip into a

NM. cutancus

\ 4,a' Mi. h auriculo-labialis

xv 'x

M. levator naso-labialis

M I. dilatator naris lateralis

\' NL levator labii superioris

A M. buccinator

Fig. 8b. Facial muscles of dog (based on drawing by SISSON & GROSSMAN).

snarl and is probably also responsible for the drawing of the eyebrows into a frown. Finally a m. frontalis (scutularis) stretches over the crown of the head and, among other movements, causes the lifting of the eyebrows.

In comparison with the faces of primates it will be noticed that the lemur



178 N. BOLWIG

and the suricate are very similar in facial anatomy, indicating common an- cestral pattern. The dog, on the other hand, has deviated greatly from the

original pattern and has become very specialised. One recognises, however, the basic pattern of the muscles which move the snout and the upper lip. At the corner of the mouth the m. buccinator has taken on a position and a function similar to, but not indentical with that of the m. triangularis in the

higher primates.

THE APPROACH TO THE LIVE MATERIAL

The present account of observations on a number of primates does not claim to be a completed study, but a report on the observations made to date

by the author. This report may be criticised as being basically subjective. Nobody knows

what thoughts and feelings an animal may have. However, those who are familiar with primates, and accustomed to handling them daily will undoub-

tedly agree that certain deductions regarding their moods, in the sense of

psychological or physiological conditions are permissible. Unless the person who looks after the animals allows himself to make such deductions he will soon find that he has no success in handling them.

The animal-keeper who talks about a happy, a sad, a frightened or an

angry animal is in reality less subjective than appears at first sight. His deductions are based on numerous small observations which unconsciously have been sorted out and classified in his own brain. When he says an animal is angry he draws his conclusion from the observations that an animal which behaves in a particular way will attack and put strength into the attack unless curbed. In other words, experience has taught him that an animal behaving in a particular way is in a c o n d i t i o n which motivates a certain sequence of actions. With this consideration in mind it should therefore be possible to give some basic rules for the judgement passed by the keeper. The fol-

lowing is a brief survey of the author's own criteria for the animal's mood:

J oy: A condition which motivates increased activities. The stimulus in-

ducing the condition may be external or internal. If attack is a result, force is not put into the organs of aggression (except when feeding) and retreat is only a passing phase. Postures of aggression and retreat never become

complete, and non-aggressive movements are frequently exaggerated. In other words, joy is a condition which induces play-actions, or a symbolic play-action. (For the definition of play see below.)

A m u s e m e n t: A type of joy which in animals may have a slightly aggressive motivation. The animal shows amusement by teasing.




U n h a p p i n e s s: A condition of fear, sadness or a combination of the two: the opposite of joy.

F e a r: A condition which motivates r e t r e a t. If checked or if retreat becomes impossible the observed reaction becomes s u b m i s s i o n.

S a d n e s s: A condition caused by drives of either joy, love or affection which cannot find a release. The postures tend to be submissive and the activities are slowed down. It seems easily changed into anger.

Anger: A condition which induces attack into which the animal

puts force. R a g e: Anger with very high motivation. If anger and fear occur simultaneously they induce t h r e a t. The

character of the threat is dependent on the proportion and the load of the two conflicting motivations.

L o v e and a f f e c t i o n: Conditions during which the animal focuses its attention on an animate or inanimate object and attempts to be close to it, preferably in bodily contact with it. It will resist separation from the object and if separated from it, it may fret and show sadness. Love is affection with a strong motivation which may be sexual.

DESCRIPTION OF FACIAL EXPRESSIONS

A: EXPRESSION OF HAPPINESS AND JOY

Most, if not all, mammals will particularly while young show various activities which in popular language are termed play. What can be observed is an outlet of surplus energy during which the animal exercises its

bodily as well as its mental structures, so that they may develop and grow and shape in a manner which is the most advantageous to the individual in its particular ecological niche. During its play the animal explored its sur-

roundings and its own abilities, and thereby it gains in experience and it learns. Animals playing together seek one another's company and by their actions they induce one another to act and react. When playing with an inanimate object they actively seek stimulations from the object. The motivating condition for play is termed joy. The play may be symbolic only.

To many animals, particularly the carnivores and primates, fighting and

biting form essential parts of the play. Biting, however, is never hard and often gentle.

When lower mammals such as insectivores play, the observer notices

nothing or almost nothing in the way of facial activities which indicates the mood or the intentions of the animal. He notices the mouth being opened, the animal apparently intending to bite, but there is no indication of whether it



ISo N. BOLWIG

is seriously meant or not; whether the bite is going to be hard or gentle. Similar observations are made in the case of the prosimians (Plate XV, Fig. I), the animals rolling about with open mouths biting one another. Only the relaxed gaze gives some indication of their mood. It is rather the whole attitude of the animal, and its vocalisation, which makes it possible for a human to enter into a game with a young lemur.

The author has made very few observations on western monkeys. Some

time, however, was spent in I959 with a family of marmosets (Hapale jaccu- lus) in the Copenhagen Zoo. It was interesting to notice how closely these animals resembled lemurs in much of their behaviour1). The young animal was

very playful and irritated the parents by attacking and biting, and it attacked

my hands in a similar way without hurting. The parents regularly rebuked it and drove it off. The difference in attitude of parents and child was never visible in their faces but in the whole attitude of the animals. The playful and the angry animal each opened its mouth so that the teeth became visible, but

apart perhaps from a slight difference in their gaze, their faces remained the same. As with the lemurs the attitude and intentions were reflected in the

postures and movements of the body as a whole.

Among the carnivores, the mongoose and the suricate (Suricata suricatta) behave in a manner which reminds the observer of the lemur and marmoset 2). Whether playful or angry they show very little difference in their facial ex-

pression. Only in cases of frenzy do they tend to draw their lips back more than in play. A glance at Fig. I and Fig. 7 will be sufficient to convince the reader that the facial muscles of the lemur and the suricate are not fit for

expressing any emotions. Their function can only be to bare the teeth before the animal bites.

In higher primates observed by the author, such as the American Cebus and all the monkeys of the Old World much progress has been noticed. When

playing (Fig. 9, a and b) the mouth is opened and its corners are drawn backwards and slightly upwards by the zygomatic muscle. It is possible that the m. triangularis also exerts a slight pull. The result is that the upper lip becomes tight. Usually it covers the upper incisors and bends in beneath them (Plate XV, Figs 2 and 3). Only in forms with very large front teeth such as Cercocebus, Silenus and Papio does the lip frequently or normally slide up. Otherwise this only happens at higher motivations of play. The

gaze of the animal is always relaxed before and during the play-bite. The

I) The marmosets mark their territory and examine the scent tracks in a manner similar to that employed by lemurs.

2) The suricate also marks its territory with its anogenital region.




eyelids may be somewhat drawn together; the lower lid is lifted more than the

upper is lowered. The outer corners of the eyes are always slightly lifted due to a pressure from the zygomatic muscle. How much the corner is lifted

depends on the tension of the muscle. The eyebrows may be raised or de-

pressed. There seem to be individual as well as specific differences on this

point.

a b Fig. ga & b. Laughter.

In the playing dog one always notices a pull backwards of the corners of the mouth similar to that observed in monkeys. Its gaze is relaxed, its lower lids lifted.

When observing playing monkeys, particularly if the observer himself

plays with one, it will be noticed that the grimace preceding a play-bite does not invariably lead to a bite. Sometimes it is obvious that the animal has no drive whatsoever to bite but merely expresses its joy (Plate XV, Fig. 7). There are all grades from a definite drive to bite (Plate XV, Figs 2 and 3) through a slight drive (Plate XV, Figs 4 and 5) to no drive at all (Plate XV, Fig. 7, and Plate XVI, Fig. 6). It is often impossible to decide whether or not

any biting drive is present but there are cases, however, in which it is obvious that it is absent. In such cases the biting posture has become ritualised to

express the animal's psychological and nervous condition. The animal laughs in the human sense of the word.

Sometimes when the animal has a drive to tease (not necessarily by biting), or its attention is taken by something it likes, small pulls at the corers of the mouth may be noticed, accompanied by a slight upwards pull of the corners of the eyes. The lips may or may not be slightly parted (Plate XVII, Fig. 8 and 9). Such a grimace very much resembles the smile as known in humans and should undoubtedly be classified as such. The smile is particularly noticeable



182 N. BOLWIG

in the author's baboon, Maco, just before she launches a teasing campaign on her companion of smacking, stealing or leaping on top of him from her tree. Her mouth widens without her lips parting and the skin around its corners wrinkles. Moreover, the lifting of the outer eye corners gives her an unmistakably amused appearance. It thus seems obvious that smile and laughter have evolved from the play-bite or from the preparation for the play-bite. They seem to express joy and anticipation of play. How far they also express affection is uncertain. The moderate laughter of the baboon Jenny pictured on Plate XVI, Fig. 6 expressed joy over the author's approach and may have indicated affection as well.

The drill and mandrill appear to form an exception to the facial expressions of joy described above. These exhibit a peculiar squaring of the comers of the mouth which, to those unfamiliar with these animals, gives the impression of an angry snarl. What happens here is that the backwards pull of the corner of the mouth by m. zygomaticus combined with what looks like a downwards pull by m. triangularis and a tightening of m. orbicularis oris produces the squaring effect referred to above.

Similar to the higher monkeys the happy dog pulls a face which cannot be distinguished from that preceding a play-bite. Here again it is not possible in most cases to decide whether the animals has any motivation to bite or not and all one can say for certain is that the animal does not intend to hurt.

The similarity in facial expressions is best seen when a dog and a monkey play together. A small patas monkey, Fredrik, was introduced to a dachshund puppy. After a few cautious approaches the two animals began to play and were soon engaged in a rough and tumble without, however, hurting each other. The interesting part was the completeness of understanding between the two animals from the outset, the way in which they reacted to each other and how, in their facial and bodily movements they resembled each other. Both wore what, to the observer, amounted to a broad smile.

The apes observed by the author approached man in their facial expression. Chimpanzee, with its large mobile lips, gorilla and man follow one another in a natural succession. The m. zygomaticus and probably m. risorius San- torini draw the corners of the mouth back in preparation for a play-bite. In the chimpanzee it results in a complete covering of the upper teeth (Plate XVII, Fig. Io). It is only in cases of the strongest motivation that the chimpanzee exposes its front teeth. When this happens the face becomes so distorted that it is impossible to decide whether the animal expresses fury or joy. The gorilla show similar features but great individual differences exist. The small mountain gorilla Reuben in the London Zoo exposes its upper teeth much more readily than does for example Guy, the great lowland gorilla.



BEHAVIOUR XXII

1 2

i .. _w qIN

4

j

5

Fig. I. Playing ringtailed lemurs. - 2. Play-bite, Vervet. - 3. Play-bite, Young patas. 4 & 5. Laughter with slight motivation to bite. Olive baboon. - 7. Laughter without

motivation to bite. Olive baboon.

PELATE XV



BEHAVIOUR XXII

Fig. 6. Expression of joy, possibly affectionate. Chacma baboon.

PLATE XVI



BEHAVIOUR XXII

8

9

11 _ - --4 ssW-

12

Fig. 8 & 9. "Smile", Patas. - Fig. IO. Laughter. Chimpanzee. - Fig. 1. Mischievous smile. Gorilla. -- I2 & 13. Smile.

PLATE XVII



BEHAVIOUR XXII

15

14

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Fig. 14. Laughter. - 15. Horror. Young patas. - I6. Horror caused by earthworm. Chimpanzee. - I7 & I8. Sadness. - I9. Angry, inhibited lemur.

PLATE XVIII



BEHAVIOUR XXII

20 21

22

23

24 25 26

Fig. 20. Anger. Young patas. - 21. Anger (high intensity). Chimpanzee (photograph by Dr D. MORRIS). - 22. Infuriated African child. - 23. Sucking for comfort. Young

patas. - 24. Love-bite. Olive baboon. - 25 & 26. Concentration. Young patas.

PLATE XIX



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28 27 .Fig. ,z7- Concentration with some disapproval. Chimpanzee. -28. Concentration. Chimpanzee.X

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BEHAVIOUR XXII PLATE XXI

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BEHAVIOUR XXII PLATE XXII

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The contraction of the zygomatic muscle always results in a lifting of the outer corner of the eye which becomes accentuated by the slightly lifted lower

eyelid. To those who have observed chimpanzees play ball or engaged in other

games in which play-biting is not involved it is obvious that the grimace described as an introduction to the play-bite is the same as that noticed during the non-biting games. As was the case with the higher monkeys the grimace has, in the chimpanzee and the gorilla, also become a ritualised expression for

joy. In its lowest degree it is no more than a slight pulling of the comers of the mouth and a similar lifting of the outer corners of the eyes as in a human smile. The smile frequently precedes a mischievous action but not necessarily. Plate XVII, Fig. II shows a young gorilla in the Copenhagen Zoo before it tried to snatch the author's camera. Unfortunately, the pulling of the outer corner of the eye is not clearly visible in the photograph but that at the corner of the mouth can be seen.

In man, play-bite is rarely seen but the grimace of the play-bite remains and has become fully ritualised as smile or laughter. In smile and laughter the

zygomatic muscle causes the same distortions of the face as in the higher monkeys and in the apes, but due to the relative shortness of the upper lip the teeth tend to be exposed. The upper lid usually forms a straight line above the curved lower lip. The lower eyelids are normally lifted and their outer corners pressed upwards. It seems as if the whole infraorbital complex of muscles may also contract and take part in lifting and tightening of the lid. Plate XV, Fig. 5 shows clearly the similarity in the expressions of the baboon Maco and the author. Figs I2 and 13 in Plate XVII, and Fig. 14 in Plate XVIII illustrate smile and laughter in African children. All the pictures show the distortions around the eyes particularly well.

B: UNHAPPINESS

Unhappiness may occur in various forms which have much in common in their means of expression. The most important forms are fear and horror, and sadness.

I: F e a r a n d h o r r o r find very little expression in the face of lower

primates, but in the catarrhine monkeys observed the emotional condition of an animal is frequently clearly expressed in its face. Fear is shown mainly by a lifting of the eyebrows, a gaze that is shifting from the danger to the

escape and a downwards pull of the corners of the mouth by the m. triangularis. Most observations were ma(le on the young patas, Fredrik, and on various baboons.

As fear intensifies, culminating in horror, more muscles come into action.

Behaviour XXII 14



184 N. BOLWIG

In this condition (Fig. IO a and b and Plate XVIII, Fig. 15) the animal lowers the outer end of its eyebrows, probably by contracting the m. depressor supercilii. Possibly, however, contraction of the upper section of the m. zygo-

/ /09 V_ /

a b Fig. Ioa & b. Horror.

maticus also plays a part. The consequence of this downwards pull acting against the strong upward pull of the frontal muscle is a curious slanting position of the eyebrows. When the highest degree of fear or horror has been reached the gaze becomes less flickering and more steadily fixed on the

object inspiring the emotion. The mouth becomes wide open and by action of all the muscles radiating

out from it the teeth are exposed. The strong downward pull by the platysma and m. triangularis is particularly noticeable.

Very few observations have been made on apes, but on the whole the same rules seem to apply except for the lip movements of the chimpanzee (Plate XVIII, Fig. I6). When very upset the chimpanzee tends to pouch its lips into a long funnel or tube. This posture of the mouth is accompanied by a loud ho-ho-ho.

The movements and postures of the faces of frightened humans seem to follow the same basic rules as do the faces of monkeys. The lifting of the

eyebrows at low intensities is, however, less pronounced than in these. At

high intensities the brows become slanting as they do in monkeys, but in addition they are drawn closer together by the well developed m. corrugator supercilii, so that a frown develops. Whether or not a slight frown develops in monkeys cannot easily be determined. There seem to be a few muscle fibres which may be able to draw the brows a little closer together, but the movements can only be slight compared with the other movements and therefore are not very noticeable. Another feature is that in man, the gaze seems less

flickering than in monkeys and there is a tendency to open the eyes wide.




The frightened dog shows a curious similarity to the frightened monkey. The brows are lifted and the corners of the mouth are pulled down by the m. buccinator.

2: S a d n e s s in monkeys, apes and man, is characterised by a much calmer facial appearance. The gaze is steady, not darting from one place to another as in fear, and the tension around the mouth which so often is noticed in fear never occurs except in adult man who tries to hide his feelings. The corners of the mouth, however, are always pulled down by the m. triangularis and (Plate XVIII, Figs 17 and I8) the lips are often

a b Fig. I Ia & b. Despair.

slightly pouched. In monkeys they part a little at higher intensities (Fig. I Ia and b) to form a rounded opening and the animal gives out soft small cries. The same curious slanting of the eyebrows as mentioned under "Fear" is also noticed in monkeys at the higher intensities.

The author has made very few observations on apes but they seem closely to resemble man in higher intensities of sadness. The unrestrained human child will at these levels open its mouth slightly and emit loud sounds. In doing so the lower teeth may be exposed. The tension of the eyebrows is similar to that in monkeys except for a frowning caused by the now well developed m. corrugator supercilii. The chimpanzee, when unhappy after being scolded, seems to expose its teeth, but it is possible that on such occasions sadness is mingled with fear. Another reaction observed which also may be partly due to fear is a protrusion of the lips as described under that heading.

In dogs, the expression of the sad animal seems identical to that of the frightened one.



i86 N. BOLWIG

C: ANGER

Unlike the joyful animal, the angry animal probably always anticipates the possibility of giving a hard bite. As mentioned earlier on the faces of

primitive carnivores and primates reveals very little or nothing about the mood of the animal whether it is playful or angry. In lemurs a rounding of the eyes becomes visible in fury. In all the species of lemurs observed the lower eyelid becomes lifted if the animal for some reason is prevented from attacking and its gaze becomes evasive (Plate XVIII, Fig. I9).

The angry Cebus, Cercopithecus, Cercocebus, Erythrocebus and Papio always look straight at their opponent with a stiff gaze and frequently with rounded eyes. The mouth is usually tightly closed and the lips are drawn inwards. Snarling is not frequent. The teeth are bitten hard together and the platysma is tight. If no antagonistic drive, such as a drive to flee, interferes, the eyebrows become lowered and probably drawn somewhat

together into a frown (Fig. 12 a and b, Plate XIX, Fig. 20). Whenever the drive to flee interferes with the drive to attack threat postures appear. Al-

though there seem to be great specific variations in the appearance of threat, a rounding of the eyes, lifting of the brows, opening of the mouth and a

lowering of the head seem to be common features (Fig. 13 a and b). How

a b Fig. I2a & b. Anger.

threat has developed in each case is not clear, but it is possible that all threat postures, facial and otherwise, show elements of submission, as for

example laying back the ears, lifting the eyebrows, ducking and readiness to flee.

In apes and man anger and aggressiveness seem to be indicated by a

frowning, stiffening of the gaze and tightening of the lips while the mouth is pulled downwards by the platysma. At higher intensities more muscles come




into action and at extreme levels every muscle which can participate in

opening the mouth and baring the teeth contracts (Plate XIX, Fig. 21). At this level the face is completely distorted into a grimace similar to that of laughter at its highest intensity. Usually, so it seems, the teeth are exposed more readily by the angry ape than they are by an infuriated man (Plate XIX, Fig. 22).

a b Fig. I3a & b. Threat.

In angry dogs a frown similar to that in man will be noticed. The gaze becomes stiffly fixed on the opponent; the upper lip is lifted and tightened by the m. naso-labialis and m. levator labii superioris proprius and the nose lifted by the m. dilatator naris lateralis. Finally, the corners of the mouth are drawn forwards by the m. buccinator.

D: LOVE AND AFFECTION

Judging from numerous observations, the author has come to the conclusion that love and affection are emotions which find expression in various

ways through facial postures, movements and approaches. Lipsmacking which is particularly pronounced in baboons and far less noticeable in other

monkeys is a friendly gesture probably with a slight sexual motivation and connected with grooming. Zuckerman interpreted the extrusion of the lips in Cercopithecus leucampyx as a friendly gesture. The author has often noticed a similar extrusion accompanied by a blowing out of the cheeks in his female patas. In these monkeys also it seems to be a friendly attitude.

Gentle biting (Plate XIX, Fig. 24), sucking and licking are common signs of affection in monkeys and apes which the author on several occasions



188 N. BOLWIG

has been able to follow from their earliest beginnings, i.e. sucking for comfort (Plate XIX, Fig. 23). They may vary in form but basically it is always the same. The human kiss, the caressing of the beloved with the most sensitive

parts of the body, the lips, is only one of many variations of the loving suck or bite.

Similarly in dogs. They lick their master's face and hands and bite him

gently to show their affection.

E: CONCENTRATION

Concentration is not to be classified as an emotional condition which motivates action. It is a receptive condition during which the senses are directed towards a single object or phenomenon. During the reception the animal's central nervous system is stimulated and emotional conditions are created.

In higher primates and in man there is a considerable similarity between the expression of anger and that of concentration. In all of them can be noticed a frowning and a tightening and inwards bending of the lips mainly due to a tightening of orbicularis oris. It seems as if other muscles around the mouth may also contract, particularly the platysma (Plate XIX, Figs 25 and 26, and Plate XXII, Fig. 31). The expression shown by apes and man is

basically the same as in higher monkeys but the play of emotional conditions

may find a far more obvious expression in the former. Perhaps the face of the chimpanzee is the more lively, even more so than that of the human child. Plate XX, Figs 27 and 28, and Plate XXI, Fig. 29 illustrate examples of the receptive individual. The face of the chimpanzee, Napoleon, indicates

disapproval in Fig. 27. In Fig. 28 he seems puzzled and in Fig. 29 his whole attitude indicates uncertainty. To avoid further subjective interpretation the author will allow Fig. 30 of Plate XXI to speak for itself. Plate XXII, Fig. 31 shows a tense gorilla.

CONCLUSION AND DISCUSSION

The foregoing study of facial expression seems to indicate that there are some basic rules governing this mode of expression. While in lower primates the face is almost blank, it has in higher primates become an important organ of communication. In happiness and joy there is a general lifting of the face, mainly due to the zygomatic muscle. Other muscles may come into action as well, dependent on the emotional tension of the individual. Smile and laughter exist already in monkeys, but are better developed in higher forms, culminating in man. There can be no doubt about the preparation for a bite in play being the origin of the smile and laughter.




In fear and sadness there is a general lowering of the face, due to the m.

triangularis. At lower degrees of fear the eyebrows are lifted. At higher motivations lifting of the brows by the frontal muscle is counteracted by other muscles which pull down. In horror most if not all facial muscles come into action and the whole face becomes distorted. Generally speaking, the

theory of an antithesis as put forward by DARWIN (1872) holds good for the

expression of happiness and unhappiness in higher primates. Anger which expresses itself as a preparation for a bite becomes recog-

nisable from the general tension of the face and particularly from the contraction of the muscles around the mouth.

Love and affection are mainly indicated by the mouth. Licking, kissing and love-biting are all modifications of the sucking for comfort in babyhood.

Many of the facial expressions as now observed in higher primates have lost their original function and have become ritualised actions which sym- bolise the emotional condition of the individual.

It is natural that the mouth which originally was the organ of action in the animal, the organ with which it could inflict injury, should be the first and most important organ of expression. The eyes are usually less important in

expressing emotions and the movements of their surroundings are largely dependent on the muscles which act on the mouth. They do, however, have movements of their own which are very expressive. These are either movements connected with aiming at a target for attack or retreat, or a result of a

general tension of muscles, which, strictly speaking, have no connection with the actions required in the current situation.

It is interesting to notice that dogs and monkeys have similar facial ex-

pressions. The muscles they have in common are used in a similar manner when expressing emotion. An exception is possibly the m. buccinator which, in dogs, seems to take the place of the m. triangularis in primates.

The explanation for the similarity may be found in the way in which the animals feed. In dog and primate the mouth is an important instrument which is brought into many different uses. It is the organ which to the observer may spell danger and the movements of which must be watched.

Primates and to some extent dogs are jumping or forward darting animals; they leap on to branches or on to their prey. Neither can afford to fail. Their eyes have moved forwards and they have developed a bifocal vision which gives them a better judgement of distance, but this has happened at the expense of their visual field. This field, and particularly the area over which they can see clearly, has diminished. It is therefore an advantage to the animal to have the area of visual expression concentrated to the smallest possible extent. These two facts, the use of the mouth and the



190 N. BOLWIG

limited field of vision, have probably both contributed to the development of facial expression.

Observing primates and humans, one notices variations which must be due to outside influence. Such variations might be termed "cultural variations" in the mode of expression.

A hand reared monkey, particularly a baboon or a mangaby (Cercocebus) often exhibits exaggerated facial movements or mannerisms which are never observed in wild animals. There may be two explanations for this. Either it attempts to copy its human master or, which is probably more frequent, the human is so unobservant and slow in his interpretation of his animal, that the animal, to make itself understood, is forced to enlarge on its mime. A similar enlargement of the mime may also be observed in some adult humans when talking to children or fellow humans who are hard of hearing.

The criticism may be made that in this study most observations have been made on children. The reason is that the child only knows of simple and

elementary expressions. A number of children aged about four to seven, when presented with diagrams illustrating various facial expressions com- mented in terms such as: "He laughs", "He looks cross", "He is sad", "He cries". Never did they say: "He looks malicious", "He looks worried", "He looks surprised", "He looks doubtful or puzzled" or "He looks disgusted". This may partly be due to a limitation of their vocabulary, but if there is such a limitation then there is a corresponding limitation in their perception. The more subtle expressions such as are known in adults have not developed in the young child. A friend of the author's who had observed his own child one day remarked "It has been interesting to see how he (the child) has passed through a "monkey phase" in his expressions. He is now in a "post monkey phase".

As the human grows older the subtlety increases. Thereafter the expres- siveness decreases and changes due to suppression and cultural habits. In the young child the observer notices mannerisms which are copied from the adult. They are, however, easily recognised and tend to disappear altogether when the child believes itself to be unobserved. Similarly the non-human primate may learn certain mannerisms from humans, which, however, they rarely exhibit in company with other monkeys. Cultural habits have seldom been noticed to develop in a troop of monkeys and never in their mode of facial expression. Here great uniformity is the rule as long as the animals are with their own species. There can thus be no doubt about the reliability of the material used for this study because the observations made on the animal in human company have been checked on animals in association only with their own species.




SUMMARY

In this report of an unfinished study of the evolution of facial expressions the author draws a brief comparison between the most important facial muscles of various primates and of two carnivores, the suricate and the dog.

Before discussing the expressions, definitions of the various elementary emotions are given and the criteria from which the author judges the emotional condition of the animals.

The main conclusions reached from the observations are: I. Certain basic rules govern the facial expressions of the animals studied. 2. Joy and happiness are expressed by a general lifting of the face and a tightening of

the upper lip. The expression originates from preparation for a play-bite. The posture has become completely ritualised in man.

3. Unhappiness expresses itself by a lowering of the face. In horror there is a general tension of the facial muscles and the mouth tends to open while the animal screams. In sadness the animal tends to become less active.

4. Anger is recognisable from a tightening of the facial muscles, particularly those around the mouth in preparation for a hard bite.

5. Threat varies in expression but it contains components of anger and fear. 6. Love and affection find expression through such actions as lipsmacking, love-biting,

sucking and kissing. The oral caressing has its origin in the juvenile sucking for comfort.

7. Concentration is not an emotion but it usually shows itself by a tension of the facial muscles.

8. There is a similarity between the two carnivores under discussion and some of the primates. A common pattern of the facial muscles of the suricate and the lemur indicate a common ancestry and brings the two animals to the same level in their ability to express their emotions.

The dog, although very different from the monkey in its facial musculature never- theless resembles it in its mode of expression. This feature seems related to similarities in their biology which have been facilitated by the development of a bifocal vision.

REFERENCES

BOLWIG, N. (I959a). A study of the behaviour of the chacma baboon, Papio ursinus. - Behaviour 14, p. I36-I63.

- (I959b). Observations and thoughts on the evolution of facial mimic. - Koedoe 2, p. 60-69.

BOVING, E. G. and TITCHENER, E. B. (I923). A model for the demonstration of facial expression. - Amer. Journ. Psych. 34, p. 471-485.

DARWIN, C. (1872). Expression of the emotions - London. HUBER, E. (I93I). Evolution of facial musculature and facial expression. - Oxford

University Press. -(I933). The facial musculature and its innervation. - In C. G. HARTMAN and W. D. STRAUS: The anatomy of the rhesus monkey. Chapter VIII.

KELLOG, W. N. and KELOG, L. A. (I933). The ape and the child - New Rork. KOHTS, N. (I935). Infant ape and human child. - Scientific Memoirs, Museum Darwin-

ianum, Moscow. KRUKENBERG, H. (1920). Der Gesichtsausdruck des Menschen. - Fred. Enke. Stuttgart. LANDIS, C. (1925). Studies of emotional reactions. II. General behaviour and facial

expression. - Journ Compar. Psych. 4, p. 447-50I. SCHENKEL, R. (1948). Ausdrucksstudien an Wolfen. - Behaviour I, p. 8I-I30. Behaviour XXII 15



I92 BOLWIG, FACIAL EXPRESSION IN PRIMATES, ETC.

SISSON, S. and GROSSMAN, J. D. (1940). The anatomy of the domestic animals. - 3rd Edit. W. B. Saunders.

WORNER, R. (1940). Theoretische und experimentelle Beitrage zum Ausdruckproblem. - Z. angew. Psychol. u. Characterkunde 59, p. 257-318.

YERKES, R. M. and YERKES, A. W. (1945). The great apes; a study of anthropoid life. -Yale Univ. Press.

ZUCKERMAN, S. (1932). The social life of monkeys and apes. - London. - S. (I933). Functional affinities of man, monkeys and apes. - London.

ZUSAMMENFASSUNG

Dieser unvollstandige Bericht fiber die Entwicklung von mimischen Ausdrucksbewe- gungen vergleicht die wichtigsten Gesichtsmuskeln verschiedener Herrentiere und zweier Fleischfresser, der Surikate und des Hundes. Vor der Beschreibung der Mimik werden die verschiedenen elementaren Gemiitsbewegungen und die Merkmale definiert, auf Grund welcher Verf. die Stimmungen der Tiere beurteilt. Er kam zu folgenden Schliissen:

I) Es gelten gewisse Grundregeln fur die Mimik aller untersuchten Tierarten. 2) Freudige Affekte driicken sich durch Straffung der ganzen Gesichtsmuskulatur

und Schiirzen der Oberlippe aus. Dieser Gesichtsausdruck entspricht der Vorbereitung auf ein spielerisches Zubeissen. Beim Menschen ist dieser Ausdruck vollkommen ritua- lisiert.

3) Niedergeschlagenheit driickt sich durch Erschlaffung der Gesichtsmuskulatur aus. Beim Entsetzen sind alle Gesichtsmuskeln angespannt; der Mund 6ffnet sich gew6hnlich, wenn das Tier schreit. Das traurige Tier wird gewohnlich unaktiv.

4) Im Zorn ziehen sich vor allem die Gesichtsmuskeln um den Mund herum zusammen, wie zur Vorbereitung eines schweren Bisses.

5) Verschiedene Ausdrucksbewegungen wirken drohend; meist spiegeln sich Zorn und Furcht zugleich.

6) Liebe und Zuneigung werden durch Lippenschmatzen, Liebesbiss, Saugen und Kiissen ausgedriickt. Die orale Liebkosung geht auf das lustvolle Saugen des Jungtieres zuriick.

7) Konzentration ist kein Gemiitszustand, zeigt sich jedoch gewohnlich durch Anspan- nung der Gesichtsmuskeln.

8) Zwischen den beiden beobachteten Fleischfresserarten und einigen Herrentieren fanden sich CTbereinstimmungen, auch solche der Gesichtsmuskulatur von Surikaten und Lemuren, die auf gemeinsame Vorfahren hinweisen und zu gemeinsamen mimischen Ausdrucksbewegungen fiihren.

Obgleich die Gesichtsmuskulatur des Hundes von der des Affen recht verschieden ist, gibt es doch Aehnlichkeiten im Verhalten, besonders in den Gesichtsausdriicken, die auf die gemeinsame Entwicklung zum beidaugigen Sehen zuriickzufiihren sind.



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