Popular Science Monthly/Volume 65/July 1904/Why Is the Human Ear Immobile?
|WHY IS THE HUMAN EAR IMMOBILE?|
By Dr. WALTER SMITH,
LAKE FOREST COLLEGE.
THE ear has had a varied history. The evolutionist has a remarkable story to tell when he recounts the steps in the making of this organ. He traces the opening of the ear to the gill-slits of the fish forms of whose lineage we are. He shows (though this subject concerns us less at present, and is still discussed with some uncertainty as to details) how various structures in the region of this opening, which had originally a different purpose, were modified to become the series of little bones that propagate the vibrations of the air from the tympanic membrane to the fluid of the inner ear. He shows further, with greater or less completeness, how the cartilage shell grew on the outer side of the head, and was supplied with muscles, so that it could be moved about and even have its shape changed.
To get a good illustration of the mobile ear we only need to watch such an animal as the horse; the ear is as mobile as the eye, or more so. The poet speaks of the horse's ear and eye as twinned; but it is interesting to notice that each of the horse's ears can work independently. And it is evident that nature at one time meant, so to speak, that man's progenitors should possess ears of similar mobility. She gave them the projecting frame of cartilage and she attached to it the muscles for its movement. Then in the course of the generations she changed her mind and withdrew what she had bestowed. The cartilage shell, curiously wrought, is still there, and we regard it as adding to the beauty of the head; yet it is probably only a rudiment. The tip of the ear, when present, is a small outgrowth on the outer fold of the cartilage and is turned towards the center of the ear. The muscles of the ear, seven in number, are also rudimentary. Occasionally an individual is found who can move his ears; but even these movements are generally of an abortive kind, and are so unusual that the sight of them may distress those who are sensitive.
Why has man lost this power? Is it simply a case of retrogression? Or is it a loss for the sake of a greater gain, possible only through it? I think the reasons for this change in the organism can be indicated; one can, at least, point with assurance to a great mental gain in which it has resulted.
It will prove helpful to an appreciation of this gain to inquire first what man has lost in the passing of this mobility. The significance of this loss can be better understood if we consider for a little such a sense as sight.
The eye is movable and is continually shifting its position. From this mobility two results follow which in the present connection it is important to notice. First, the eye can be readily turned so as to get the clearest vision of any object that is to be examined. We do not see equally well with all parts of the eye; we see most distinctly with the central part directly opposite the pupil, and when there is anything seen out of the corner of the eye which we wish to observe more closely, the eye is, in normal circumstances, turned upon it so as to catch the image in this central part. Spontaneously and accurately these changes in the eye's direction are made. It can readily be understood that great help to our perception is gained from them.
There is another result of this free movement which is of equal importance. To it is due the orderly spatial arrangement presented by the world of our vision. It may seem that our knowledge of the position of things in relation to each other is natural or instinctive, and we may be pointed to the behavior of many animals which are able to guide their movements correctly as soon as they enter the world. But such reflex activities do not seem to be strictly parallel to those of the human child. That the child has in its nervous system inherited a predisposition to its future adjustments, may be true. But it is also true that it does not respond to its surroundings as the chick, for instance, does; it gains its conscious appreciation of external relations by experience. What the child's first experience of sight is, it is difficult for the adult to guess; yet some of our perceptions approach to it. The German psychologist Volkmann von Volkmar calls attention to the fact that when we gaze into the blue depths of the sky our color perception has a character similar to that of a musical note. Probably our visual sensations are all, in their original intrinsic nature, of this sort; color feelings with no idea of position as yet developed. It is further to be noted that we might have a succession of color pictures, such as can be afforded by familiar mechanical devices, without any suggestion as to the spatial relations of these various pictures. And were the eye incapable of movement of any kind, its experiences would be a mere succession of vaguely voluminous color-feelings. But, on the other hand, let the eye be considered as capable of movement, and as free to play among these colors; it passes, say, from the image of the door to that of the wall, and then to that of the window. It is not less important to notice that it can by its power of movement reverse the series and pass from window to door. Such series may, to an indefinite extent, be increased, repeated, reversed. Thus the mind gets the idea of a series of images relatively permanent, always open to observation, and arranged in a perfectly definite order. It is thus by virtue of the eye's movements that there is secured the perception of the orderly spatial arrangement of the world revealed to our vision.
Further evidence of the important functions which the eye's movements fulfill in perception might be adduced, but it is not desirable for the purpose in hand to take up what is more complicated and debatable. What has been said may suffice to call attention to the great significance of the mobility of the sense organ.
Evidence not less striking might be brought forward in regard to the sense of touch; it might be shown that it is by the movement of the sense organ, say, the finger tips, that explorations of the body under investigation can be, in ordinary cases, best accomplished, and that it is by the producing and reversing of series of touch sensations that the spatial relations of tangible objects are clearly recognized.
The ear is immobile. Accordingly it is incapable of reflex movements for catching sounds, like those by which the eye is turned so quickly to meet the light coming from an object.
We find likewise that the perception of space by means of sound is in an extremely undeveloped form. Many have gone so far as to deny that sound has any spatial character. Yet surely this view can not be maintained. We locate sounds to the right or left, behind or in front; moreover, we distinguish sounds as differing in volume.
Yet it can readily be seen that the spatial characters of sound do not compare in precision and definiteness with those of the sensations of color and touch. What is the size of the thunder? The question at first seems absurd. Yet it can not be entirely absurd, for we speak of the peal as heaven-filling. The appearance of absurdity is due to the hopeless vagueness of the sound image in respect to extent.
If we analyze this vagueness we find that owing to the immobility of the ear we can not locate sounds with precision. All are familiar with the difficulty of telling, especially in strange surroundings, whence a sound comes, unless the eye gives its help. The ringing of the bell of an unseen bicycle may cause us the most painful perplexity till we can learn its source by sight. Psychological experiments show in detail how untrustworthy are our attempts to localize sounds. Not that they are entirely untrustworthy. It may be that sounds have a special quality according to the direction from which they come and the way in which they strike upon the external ear; and recognition of this quality may give help towards their localization. But at the best, we are not freed from manifold confusions and errors. Thus it is found by experiment that while the change of position of the sounding body may be soon noticed, the direction of the change may be thought to be the opposite of what it is in reality. Again, relatively loud sounds are located preferably in front of the head, even when their source is behind. It can thus be seen that in accuracy of localization the ear can not be compared with the eye. The loss of the reflex apparatus by which the ear turned so as to catch most readily the vibrations in the air, has brought it about that the positions of sound are now so imperfectly apprehended by us.
The loss of this power of localization means two disadvantages. The first may be indicated in the words of Darwin: "The power of erecting and directing the shell of the ears to the various points of the compass is no doubt of the highest service to many animals, as they thus perceive the direction of danger."
Closely connected with this practical disadvantage is another. The space of the ear has not the geometrical character of the spaces of sight and touch. Yet there is surely no good reason for doubting that it might have had much more of this character. Were the ear as mobile as the eye or the fingers, it would resemble them in the orderliness and well-defined character of the spatial forms it would yield. That its spatial form would equal in these respects that of the eye, it would be too much to affirm dogmatically. There may be more conditions to supply than merely that of mobility. Yet the touches from the less mobile parts of the body are singularly vague in their spatial outline as compared with those from the fingers and the tongue. And were the ear to gain mobility, we might expect to find it at least approximating, in its appreciation of form, to the senses which are regarded as so preeminently geometrical.
It is now apparent how serious are the disadvantages involved in the ear's immobility. Darwin thinks that the loss of the ear's movements is partly compensated by the increased ability to move the head about. It is true, these movements of the head are of importance both in seeing and in hearing. Yet in speaking of them as making up for the mobility of the sense-organs, we should be careful not to exaggerate their value. A man whose legs have been smitten with paralysis must find only small compensation for his affliction in the fact that a strong though somewhat slow porter is, when not otherwise occupied, ready to carry him about. It is also to be noticed that the eye has at its disposal the head movements, yet has retained its mobility.
We have now to ask what the mental gain is which has resulted from this loss. It is to be found in the ability to attend to a succession of sounds.
Let us notice how distinct is our perception of succession. A sound comes suddenly and sharply, and then it is gone, and another sound of distinct quality takes its place; thus by its very nature sound lends itself easily to this kind of perception. And when we listen to a sounding object, our interest is in catching the sounds which come in sequence. This is illustrated most distinctly, as we shall see, in attention to discourse. We hear simultaneous sounds, but the predominant characteristic of our perception of sounds is that their variety is given in a succession. Hearing is a time-sense. If the ear had remained mobile, it would have been the organ of a space-sense, for it would have given a number of sounds as practically coexisting and as coexisting in definite relations to each other; the mobility being lost, hearing has become a time-sense.
Contrast with the ear's perceptions those of the eye. We look at an object, and so long as we look, its form may remain the same. It may seem to be the same if we look at it after a day, or a month, or a decade. The great framework of our environment seems to the eye unchangeable.
It is not to be overlooked that we do perceive changes with the eye. We may watch a cloud melt in the summer sky, or we may call up the image of one who no longer lives. The eye can not ignore the fact of change, as the ear can not entirely ignore coexistence. And it is possible for us to school ourselves to note the changes from hour to hour in what we see. Yet the lesson is not naturally learned by the eye; its world is primarily a spatial world; its interest is in forms and the relations of these forms; for it succession is subordinate, as for the ear coexistence is subordinate. And as far as possible our idea of the stability of forms determines our interpretation of the changes we see. We watch a man walking along the street, or the trees waving in the wind. In such cases we see a change, but our mental reading of it is that a part of the spatial picture has been transferred from one point to another without any alteration in the intrinsic nature of the whole or the parts. It is possible that it is under the influence of the visual imagination that science keeps so persistently to the view that atoms shift their places, but do not suffer change. However this may be, the visual images of objects are spatial and in a measure stable; and they owe this peculiarity largely to the fact that the eye flashes from point to point and considers the external relations of figures to each other, to the comparative neglect of other aspects of reality.
On the other hand, the immobility of the ear contributes to the perception of succession inasmuch as the mind, being unable to get in simultaneity, or what is practically such, all the sounds of the environment, finds it easier to attend to the series of sounds. If nature had intended to cultivate the power of attending to a successive series of sensations, would not her first steps have been to make the organ of these sensations stationary? Suppose the eye were to be trained to give special attention to the changes in objects before it, it would be essential that it should be prevented from making its usual excursions round the field open to it, and should be kept looking fixedly at one object. Not that this fixedness involves of necessity the inability to perceive a multiplicity of coexisting objects; it is found by experiment that when the eye is perfectly steady any one of the many points exposed to it can be attended to; and moreover, the attention can be directed from point to point. In hearing, too, we know that we can while remaining motionless, listen first to the sound from one quarter, then to that from another. But this only shows that when the natural instruments for performing certain acts are withdrawn from us, we may make shift to supply their places. We can see an object with the periphery of the eye, but we can not see it so well as when we freely turn the fovea upon it. And though we can direct our listening power from one point of the compass to another it remains true that the ear, smitten with immobility, can best fulfil its perceptive function when there is attention to the successive stimulations forming from one object.
It may seem that we have forgotten that such a sense as smell has an immobile organ, yet does not yield any special perception of succession. It is to be noted, however, that this sense is little developed in its perceptive aspect. We can not get the large number of discrete sensations from this sense that we can from hearing. We may by the ear distinguish five hundred sounds in the second. There is nothing in smell comparable to this. We need not wait to consider whether in its own undeveloped way smell does not after all remotely resemble hearing in the kind of perception it yields.
But we have not yet indicated the special forms assumed by the succession of sounds which it is so important to perceive. They are two—language and music. Language consists of a succession of sounds. When we consider how largely the intellectual life depends on language, we can see the enormous advantage of the development of the faculty of perceiving successive rather than simultaneous sounds. As every one is familiar with the importance of language, the greatness of the gain needs no further emphasis. Of less importance, though its significance for primeval man may yet prove to have been very great, is the appreciation of music. The music that is referred to is that given in melody. There is, apart from the melody, an appeal of each note and complex of notes which does not mean succession at all. Much of the thrill of music is an immediate effect of the individual note. But the appreciation of melody depends on the perception of succession. The eye is appealed to by a spatial combination of colors, the ear by a series of sounds. Headers of Lessing's Laocoon know how finely he has elaborated the contrast between the esthetic characters of the two senses.
What, it will be asked, of the lower animals that have no external ear, or have one that can not be moved? In regard to such, we must carefully distinguish those species which have never possessed the movable ear from those which have lost the power of movement. It is the loss of a faculty once possessed that we are at present more immediately concerned with. Yet, in the case of such animals as the birds, which, though endowed with a highly developed sense of hearing, have no external ear, it is interesting to observe that there is remarkable appreciation of music. And this is not merely a response to individual sounds, as the musical appreciation of some animals may be; there seems to be an enjoyment of melody. Browning happily described the thrush as 'wise' because the bird 'sings each song twice over,' and thus shows his ability to 'recapture'
It is also to be noticed that many birds can imitate other sounds, even those of the human voice. The repetition may be 'parrot-like,' but it gives evidence of the power of attending to a series of sounds.
It should be mentioned that the external ear of certain aquatic mammals is atrophied or lost. But as these animals have taken to a different kind of environment, and have been to so remarkable an extent made over, it seems unnecessary in the present investigation to give special consideration to this particular change in their structure.
The case of the monkeys seems at first to be different. Some of them, the anthropoid apes at least, have like man lost the power to move the ears, yet they have not, it may be said, the faculty of speech. Have we not, then, the loss without any compensation of the special kind that is here being claimed for man? In considering this question we must keep in view the psychologist's ignorance of the mental life of the monkey. Notwithstanding all that has been written of the relationship of man to the monkeys, the psychology of these animals is still for the most part a blank. Yet there are some significant data that may in the present case be appealed to. The howling monkeys, though of low intelligence, find delight in the noise, from which they receive their name. They are gregarious and they howl in company. This noise is not made to drive away enemies; the monkeys gather deliberately for the purpose of making the noise and the leader starts the concert.
The chattering of monkeys should also be regarded as affording evidence of the appreciation which they have of sound. The chattering differs, moreover, from the mere monotonous repetition of a sound and if it has any function, it is probably a function which can be fulfilled only by the apprehension of a series of diverse sounds. It is also of interest to note the statement of Professor Haeckel that he has heard from apes of very different species 'remarkable clicking sounds'; and it has been thought that these sounds are still present in the language of Bushmen.
Mr. E. L. Garner made some years ago a study of the 'speech of monkeys,' and he reached the following conclusions: "The sounds which monkeys make are voluntary, deliberate and articulate. They are always addressed to some certain individual with the evident purpose of having them understood. . . . They wait for and expect an answer, and if they do not receive one they frequently repeat the pounds. They usually look at the person addressed and do not utter these sounds when alone or as a mere pastime. . . . They understand the sounds made by monkeys of their own kind. . . . when imitated by a human being, by a whistle, a phonograph, or other mechanical devices. . . . The fundamental sounds appear to be pure vowels, but faint traces of consonants are found in many words." "As a rule each act of a monkey is attended by some sound." In a later work. Mr. Garner, after study of the apes in their native haunts, says that the chimpanzee has a vocabulary of twenty-five to thirty words; he claims that he learned ten of these words so that he could hold communication with the animals using them.
Mr. Romanes' account of the song, if such it may be called, of the chimpanzee 'Sally' may here be quoted: "It is sung without any regard to notation in a series of rapidly succeeding howls and screams—very loud, and accompanied by a drumming of the legs upon the ground." Mr. Garner has observed similar exhibitions given by chimpanzees. He also heard a performance of the kind in the African forest; the natives and others attributed it to the gorilla, but Mr. Garner thinks it not unlikely that it was given by the chimpanzee.
Darwin calls attention to the fact that two species of the gibbon, the Hylobates agilis and the Hylobates leuciscus have musical powers. In regard to the song of the former he quotes Mr. Waterhouse, who says: "It appeared to me that in ascending and descending the scale, the intervals were always exactly half tones; and I am sure that the highest note was the exact octave to the lowest. The quality of the notes is very musical."
In considering the linguistic development of monkeys it is important to remember that monkeys have to a striking degree developed social qualities. Detailed proof of this sociality need not be given; its existence is known from the accounts of travelers, and of those who have domesticated these animals, and, indeed, from observations in zoological gardens. The knowledge of it is very incomplete; yet enough is known to show that it is often very intimate and not without complexity. Where there is such a social life, it is to be expected that there will be found a development in the use of sounds. Not that the presence of this development is hereby proved, but a presumption is created in favor of the view that it exists. Darwin thought that primeval man probably first used his voice in the production of true musical cadences, especially during courtship; and that the imitation of musical cries by articulate sounds might have given rise to words expressive of various complex emotional states. Should we not rather find the greater development of vocal signs in the apes earlier than primeval man which had variety of vocal utterance combined with the varied emotions of a complex social life, emotions not only of courtship, as Darwin supposes, but of parentage and of the various relations of friendliness and hostility?
It is not meant that all the monkeys referred to have the immobile ear. This is characteristic of the anthropoid apes. It is important, however, to observe in very diverse species of monkeys the peculiar interest in sounds; and in the anthropoid apes, which have lost the mobility of the ear, there is, as we see from the accounts of the gibbon and the chimpanzee, the special development of the use of, and appreciation of, vocal and other sounds.
It seems at first sight that the gain in the use of vocal sound made by the apes is too slight to account for the change in the organ of hearing. Yet we must hesitate to pronounce such a verdict when we consider the immense importance of any improvement in the faculty of language. Let an analogous case be considered. Mr. Fiske has shown that the slow growth of the brain is a condition of the attainment of the preeminent mental faculties possessed by man. This prolongation of infancy is in itself a disadvantage, but the gain resulting from it more than counterbalances the loss. But we find a similar slow growth in the case of the apes. Can we find in them any notable gain in intelligence? While they are intelligent animals, we can not appeal to a distinct and unchallengeable superiority. Nevertheless, we believe on evolutionary principles that there is a gain in mental faculty to warrant the slow maturing of their powers. Even so in the case of language, we must say that any new form in the organism which conduced to the evolution of this faculty would be of such moment that, unless it entailed seriously deleterious effects, its permanence would be ensured.
To sum up, the loss of the ear's mobility has resulted in the fuller appreciation of the succession of sounds, and thus has been in an important sense a condition of the social, intellectual and esthetic development which has come with the use of language and music; and it is in. a high degree probable, though the data are insufficient for conclusive demonstration, that it is to the advantage given in the struggle for existence by the first stages of this development that we are to attribute the permanent alteration in the structure of the ear.
We thus see that the sense organ having originally the form best adapted to the conditions in which the organism lived changed its form to meet the conditions of a higher stage of evolution. It may be that in this form it is most in accord with the special stimulations which appeal to it; it is certainly in this form that it can minister to the highest spiritual activities.
- On the localization of sound, see 'Studies in Space Perception,' by A. H. Pierce.
- 'Descent of Man,' p. 14.
- "The more recent ape ancestors, common to men and to the anthropoid apes (gorilla, chimpanzee, etc.) discontinued the habit of moving their ears and hence the motor muscles gradually became rudimentary and useless." Haeckel, 'Evolution of Man' (English Translation), Vol. II., pp. 270-271.
- 'The Speech of Monkeys,' pp. 169-170.
- 'Apes and Monkeys,' p. 108.
- 'Mental Evolution in Man,' p. 377.
- 'Descent of Man,' p. 567.
- Mr. Garner claims that 'the more pronounced the gregarious habits of any species' of monkey are, the higher 'the type of speech it has.'
- 'Descent of Man,' p. 87.