In spite of the satires of Swift we may not cavil at the natural pride which has led man, Homo Sapiens, as he also calls himself, to confer boldly on himself, and his lineal ancestors at any rate, the name of Primates. This large and highest group of hair-clad mammals includes broadly and somewhat loosely lemurs, monkeys, apes and man. The last has not lost his hairy endowment, though it is sadly curtailed, and it is well to remember that, except on the palms of the hands, the soles of the feet and the terminal rows of phalanges of fingers and toes, man is a hair-clad mammal. Shakespeare calls him “paragon of animals,” and Huxley “head of the sentient world,” and no reasonable person will attempt to improve upon such pregnant tributes to his greatness. I desire only to adhere that qu animal he is the best of all for my humble purpose of historian of the chequered course of the mammalian hair, better even than the domestic horse. His hair varies from a coat so fine as to need a lens for the discovery of the separate hairs, to a truly Simian profusion of thick and long hair such as that of the Ainu or hairy aborigines of Japan.

Hair and Habits of Man.

The streams of his hair demonstrate two important facts about man: first what he has been; secondly what he has done, that is to say, his ancestry and habits of life, through an immense stretch of time. These stories in hair are the culmina­tion of a large number of characters inherited and acquired, and their study in two selected regions of lemurs, apes and man will be pursued in this chapter on the lines which I laid down in Chapter VI. I have thought it well not to give any connected account of the rest of his hairy covering so as to concentrate attention on the two simplest and most striking regions. The charts of his hair-streams and those of the lemur and ape have been described with sufficient fulness elsewhere,55 and no cartographer has hitherto sought to improve upon them.

The back and the front surfaces of the trunk afford the two best and most instructive fields of study, for the forces which act upon them are of a simple kind, and may be traced upwards from the lemurs to man as in the case of the forearms. The three drawings (Fig.41) represent the backs of a lemur, chimpanzee and man, most of the details of the hair being omitted and their place taken by thick dark arrows which show the line of the different hair-streams. This diagrammatic method will make any misunderstanding of the main facts impossible.

The lemur has on the back of its neck a forward or headward slope of hair and this passes on to the head itself, and on the back of the trunk, as the arrows show, there is no departure from the normal arrangement of the lower mammals. The lemur, therefore, requires neither further descrip­tion nor explana­tion.

The ape shows no material change in this region from the arrangement of its lemur or monkey ancestor, in spite of the greater propor­tion of its life which is spent in the upright posture; indeed, this is what one would expect.

Hair of the Back of Man.

When the hair on the back of man is examined a remarkable change from the patterns of any of his known or supposed ancestors is found. It is by no means easy to trace the course of the hairs on the human back. A young, hairy and dark-haired person gives much the best field, and a lens may be necessary. In older subjects the hair is often so much worn away by friction that the direction can no longer be followed. Suffice it to say that the examina­tion, though somewhat difficult, can well be carried out if the proper conditions are observed; and that it bears out the results which have come from the corresponding examina­tion of infants. The arrangement is congenital.

From the neck the hair passes on each side nearly downwards, and in the middle directly downwards in a narrow stream between the two muscular borders of the vertebral furrows, and continues in this normal direction to the end of the spinal region. It will be seen that below the two upper arrows there are three levels of arrows, the first with one, the second with two, and the third with one, on each side of the surface of the back. At the level of the shoulder-joints the side-streams curve upwards towards the spine and join the central stream; at the second the direction is rather more upwards before it curves inwards and downwards to the vertebral furrow; at the third the streams curve slightly upwards and towards the middle-line and coalesce with the other streams. The contrast between the straight, simple slope of the hair on the lemur’s and ape’s back, and that of man is very great. In the latter the side-streams make an angle of 45° or less with the axis of the spine and this arrangement is unique among mammals. It will be, therefore, necessary to inquire into its history and causation, for it goes far towards reversing the well-established and accredited pattern of apes, monkeys and lemurs. If the reader will carry his mind back to the arrangement of hair on man’s forearm he will see that it exhibits some features analogous to those on the back of man. In the forearm there is that curious little stream on the extensor surface which may be looked upon as a relic from the ape-stock, but in the rest of that limb-segment man has boldly gone back, beyond the ape, to an arrangement found in the lemur; and in the case of the back of man there is the small primitive area down the vertebral furrow and an entirely novel arrangement on each side such as might startle the leaders of animal fashions in hair.

The question at once arises: “How has this change come to pass?” In the case of the strange arrangement on man’s forearms I have shown that the Pan-Selectionist thought he detected there one of his particular kinds of vestige. He cannot find any such here. I can conceive a biologist making play with Heredity, Variation and Selection in the case of an ape, monkey, or lemur whose hairs are long and thick and functionally very active. There he might make use of the well-known “argument from ignorance,” and maintain that we cannot be sure that such and such factors might not have survival-value, but I defy the most hardy among the Pan-Selectionist High Command to put in that plea in connec­tion with the fine short hairs of man which even require a lens for their detection; they have little value as a protec­tion of the skin from friction; their arrangement has none. And if some leader did attempt this task I doubt if the most docile Prussian would not rebel against the statement that the withdrawal in question was “according to plan.” My purpose, however, in this book being to build up and not to pull down, I must perforce show a reasonable and better explana­tion of a remarkable little fact.

Passive Habits.

The habits of man concerned in the modus operandi of this change are passive, and two in number; that of sitting with his back against some supporting object, and of lying in sleep with his head more or less raised on a pillow or its equivalent. In contrast with man, lemurs and apes inhabit trees during their many hours of rest, and I doubt if the number of hours thus spent by these and other wild animals to that spent in active exercise is less than three to one, so that their attitudes of rest would, if calculated to do so, contribute much towards any change occurring in the patterns of hair. But, seeing that the ape-fashion is similar to that of the lemur, and that this normal arrangement is calculated only to be confirmed by the action of gravity and the dripping of rain, and that they do not greatly indulge themselves, if at all, in their equivalent for man’s armchairs, nothing else would be expected in the hairy covering of their backs than what we find.

The increasing tendency to the upright position in Eoanthropus Dawsoni and Pithecanthropus Erectus to say nothing of the men of Cromagnon—led man to use as supports for his back the walls of his rough caves which he had adopted as dwellings instead of the branches of trees and the nests of the ape. He no longer affected entirely those hardy habits of sitting without support for his back that were de rigueur in his ancestors, who probably looked upon him with as much disapproval as certain erect old ladies of the old school display towards the use of easy chairs by the rising genera­tion. Wearied with the struggle for food, and against his savage rivals, he rested his back against the sides of his rude abode. When he slept in this attitude the relaxa­tion of his voluntary muscles allowed mechanical forces to come into action which tended to oppose the downward trend of the hair. We know from our own experience that when sitting asleep with our backs supported there always occurs a certain amount of sinking down of the trunk. In this attitude are present, then, such conditions of the back and its hairy covering as give rise to mechanical forces which would interfere with the direction of the hair. These are, a heavy body, tending to slip downwards slightly while resting against a fixed surface, a growing tissue easily diverted from its normal course, and many hours spent in the attitude in question.

The effects of these conditions increased with the increasing tendency of developing man to attend to his bodily comfort.

But man spends also on the average at least a third of his whole existence lying in sleep with his head on a pillow of some kind, perhaps the skull of a Felis Groeneveldtii in the case of Pithecanthropus Erectus, and other such better objects, as he made more study of the art of being comfortable. Those who know much of children and sick persons and have watched them in sleep know that the habit of lying on one or other side prevails largely over that of lying on the back. The head being more or less raised by a pillow, the human sleeper, even when lying on his back and more so when lying on his side, is in a potentially and actually sliding position, a fact well known to most persons from their own experience. It is easy to see how such conditions are tending for a third of a man’s whole life to reverse in some degree the direction of his hair and how they act as we saw in the case of the sitting posture. But the very common lateral position in sleep contributes its own peculiar share in pushing the hair towards the spine, ceasing to do so only when the prominent muscular border of the vertebral furrow is reached. I think it will escape no careful observer of these simple facts of man’s resting life, who also notes the remarkable course of the arrows on his back, that the facts and their present explana­tion fit one another like a Chubb lock and its key. The only alternative sugges­tion of the facts is that some being with diabolic power has been at work and laying a trap for poor human biologists in the 20th century A.D.

In confirma­tion of this process I would refer to an example which agrees very closely with the above explana­tion. I knew an invalid suffering from pleurisy and lung-disease who was much confined to bed, spending much of his time propped high up on pillows. He had long dark hair on his back and I was often struck, when examining him, with the remarkable way in which the hairs were dragged upon so that they pointed nearly in a vertical upward direction. Here was a little instance of an undesigned experiment in the dynamics of hair.

Hair of the Chest.

In the hair-streams on the chest of our chosen three, lemur, ape and man, there are also some remarkable contrasts in the course they take. Fig.42 shows these in a vivid manner. Precisely as in the case of the hair on the backs of lemurs, apes and man, we find on the chest of those three types a normal direction on the two lower ancestors and an entirely novel arrangement in man; the former, therefore, will need no verbal descrip­tion.

Man, the ever bold explorer and innovator has initiated on his chest, as on his back, a fashion in hair unknown in any of the primates. He is, in respect of his hair on these two regions, sui generis. On the chest there is a critical area extending across the sternum at the level of the second rib from a whorl which is found on each side somewhat above the nipples. This is not less an ancient battle-field than the Border which separated England and Scotland, and it has been the site of its little conflicts, more especially north of the Border, corresponding to those of the wild days of Border warfare of which Scottish history is full.

At this level of the chest two streams of hair are directly opposed to one another. That which covers the chest below the dividing line maintains in true old English style its conservative fashion and passes downwards as in the ape and lemur. The more independent or Scottish stream goes upwards on its way to the neck, the side streams passing somewhat outwards towards the side of the neck, the central upwards and inwards, converging gently on to the front of the neck. The arrows in the figure show this very clearly. On the front of the neck the stream pursues its upward way until it meets the downward flowing stream from the lower jaw, and the junction of these two streams lies over the level of the upper border of the larynx in front, winding gently outwards and upwards to the surface just below the lobes of the ears. The opposi­tion of the two streams in the neck is very familiar, as a piece of practical experience, to those who shave, for it affords a decided little resistance to the razor as it is drawn downwards, and many persons change the position of the razor in consequence of it, without troubling their heads with any scientific reason for the fact.

These are the facts of the distribu­tion of hair on man’s chest, but what is the interpreta­tion? I would remark here that in my former book56 I gave what seemed to be then the best reason for it, but further reflec­tion on the matter has shown me that it was incorrect and inadequate. I refer to this and one or two other corrections of earlier views in a later chapter.

Interpretation of Records.

In discussing such a striking little fact as the one in question, an illustra­tion may serve as an introduc­tion. From the glaciers of Mont St. Gothard two great rivers take their rise. The eastern side of its slopes gives rise to the Rhine, which flows in a northerly direction to the Lake of Constance, the western to the Rhone, whence it pursues a south-westerly course to the Lake of Geneva. No geographer would doubt that certain physical features of the country were to be sought in accounting for the contrary courses of two rivers arising from a comparatively small region, and he finds it by a simple study of the topography concerned. By similar methods we must ascertain why from our little Mont St. Gothard at the level of the second rib, two streams of hair separate and pursue nearly opposite directions.

A little knowledge of the superficial anatomy of the chest and neck throws some light at once on the problem. It so happens that if one made a simple map of these hair streams, and at the side of it a drawing of the platysma myoides muscle, it could not fail to strike one that the correspondence of the surfaces occupied by the two phenomena was very significant. It is going too far to say that the correspondence is complete, but it is so nearly so that one may fairly say that the reversed stream of hair which begins at the second rib and goes up the neck, lies over the platysma muscle. The stream of hair does not extend up to the lower part of the face and lower jaw, it does not cover the outlying portion of the platysma on the side of the neck and it begins on the chest a little above the rather uncertain origin of the platysma fibres from the fascia of the chest. But the correspondence of its surface with the main part, or about five-sixths of the platysma, is most suggestive.

This muscle is one of the subdermal sheets that are found in many mammals, and though it is not a continua­tion or descendant of the fly-shaker or panniculus carnosus, which is often referred to in these pages, it is an analogous feature of man. It is closely attached at its lower part to the skin over it and more loosely at its upper. It has various functions attributed to it, as I will mention later; but there is one effect of its action which is very evident in a thin person, that is to say, it wrinkles the skin over it in a vertical direction. This it does, whatever else it may do.

Struggles of the Platysma.

In interpreting this novel hair stream of man’s chest and neck we are again brought into an atmosphere of struggle of forces. Something has occurred in the course of man’s descent from the ape to interfere very sharply with the course of the hair; and certainly if there be anything in organisms that Heredity, Variation and Selection are unable to do (even when adorned with capital letters, to make them, as Huxley said, “like grenadiers with bearskins,” appear much finer fellows than they are), it is to provide in this reversed stream of hair on man’s chest some cunning “adapta­tion” to his needs. Selection will not serve; but I think use and habit will. There can be little, if any, doubt that the frequent and active contractions of the platysma muscle in the course of man’s life are the efficient cause of the change of arrangement of hair from a downward simian to an upward human slope. To this opinion the anatomist will promptly reply: “Ah! I have thee there, friend Lamarckian; are there not any number of apes and monkeys that also have an active and efficient platysma?” Undoubtedly there are, and I give here, through the kindness of Professor Keith, a short account of that muscle in simiadÆ. It is taken from an unpublished work of his on The Myology of the Catarrhini—a Study in Evolution. The account may be only interesting to the professed anatomist, but the conclusions in the summary bear closely on the present problem. I give the exact words from Chapter II., pp.472, 479. The simian forms examined are semnopithecus, gorilla, chimpanzee, orang, gibbon, macacus, cercopitheci, cynocephali. “Summary: Every gradation is found between the cynocephalic and human forms. The evolution lies in the disappearance of the supra-trapezial origin and the superficial labio-mental insertion. The opposite nuchal and mental angles of a trapezoidal sheet are obliterated and a rhomboidal figure is left. The change may be seen step by step through the macaci, semnopitheci, hylobates, troglodytes and the orang to Man.

“The maxillary insertion in man is more extensive than the others, and the insertion is more distinctly demarcated from the quadratus menti origin. But slips between the two muscles are not uncommon.

“The sub-mental interdigita­tion occurs frequently in man, and although its extent varies in the other Catarrhini it is always present.

“The upper nuchal fibres, being cut loose in the higher members of the orthorachitial group from their primary origin, became aberrant in their behaviour. Auriculo-labial slips, slips of union with the zygomatici, or simulating a risorius, or a relapse to the primitive medial dorsal origin and connec­tion with the occipito-auricular muscles may occur in man as in the others.

“Fasciculation of the muscle may occur in man and the troglodytes.

“That the functions of this muscle are indefinite is shown by the numerous individual and generic variations. But that its presence is essential may be judged by its persistence. It may depress the angle of the mouth or the lower jaw, or help to flex the head upon the chest, or help to empty the laryngeal air-sac if it be present. But as a matter of fact all these functions are otherwise provided for. When tense it protects the deep part of the neck somewhat, and it is usually active in temper. The axillary part of the same sheet in the cynomorphÆ offers a similar puzzle as regards its functions.”

We have it thus on the highest authority that the platysma muscle is active and persistent in a large series of monkeys, apes and man. But the whole work has for its sub-title, “A Study in Evolution,” and in the story of the platysma there is a picture of its progressive development to that of man. There is evidence in the above account of the muscle that a structure is found in monkeys and man which might operate on the overlying streams of hair in any of these animal forms—or might not—in accordance with the concep­tion of struggle between opposing forces which I have kept in view all through this volume.

It is evident that in all animals below man the platysma has not achieved any victory by its action over the streams of hair on the chest and neck, and to my mind it is equally evident that in the case of man it has carried through a very manifest “turning-movement.” It will be objected, quite properly, that this is a matter of opinion, and the pertinent question will be asked, “How do you account for the absence of this reversed hair-pattern in apes and monkeys and its absence in man, both having an efficient platysma muscle?”

The essence of a struggle is that it ends with the victory of one adversary over the other, and as the race is not always to the swift nor the battle to the strong, there is of necessity some uncertainty as to the result of any struggle. The factors of time as well as of overwhelming force are required for most of the victories of man over man, and it is not less so in the victories of habit over ancestry in the direction of hair, as I have repeatedly shown. The required time is clearly at one’s disposal for this victory, and the “overwhelming force” of habit and use is purely a question of the degree of repeti­tion and the efficiency of the contractions of the platysma, and its greater use in man than in apes and monkeys. The uses to which it was put in the lower forms not having been sufficiently overwhelming for victory, no change in them has been shown. The cumulative effects of the actions of a developing platysma in man, under the guiding influence of his more complex habits of life, have turned the scale in favour of the reinforced forces of habit, and the direction of the hair becomes reversed nearly all over the area covering the muscle.

We must consider all the forces engaged in this struggle for mastery on the neck and chest of man, and remember on one hand the power of the normal slope of hair, the greater difficulty of altering the direction of the thick long hairs of monkeys and apes, and their relatively long resting hours; and on the other the shorter and finer hairs of man and the increasing efficiency of his platysma muscle in varied actions. Professor Keith mentions four functions of the platysma: that of depressing the angle of the mouth and lower jaw, helping to flex the head upon the chest, and to empty the laryngeal air-sac, and protecting the deep parts of the neck when it is tense—adding the significant comment that “it is usually active in temper”—I presume this to mean bad temper!

Leaving out of account the emptying of the laryngeal air-sac, is it not evident that the remaining three actions of the platysma are very much more exerted in the case of man with all the numerous occupations and movements of his head and neck, in obedience to his higher brain, than in the apes, monkeys and lemurs, endowed with a fitful activity, with fewer and less variable movements of their head, and long, long hours spent in their particular form of medita­tion?

So, when the muscular sheet, which, as I have said, is closely attached to the skin of the chest and more loosely to that of the neck, contracts and becomes shortened between its origin on the chest to its insertion in the face and jaw, it gives a most obvious pull on the skin over it and wrinkles it vertically in a manner which will strike any thin person who contracts it voluntarily before a looking-glass. The connec­tion shown between the action of the platysma muscle and the change of hair is so close that it can hardly be questioned that one is the cause of the other. If it be not proved to demonstra­tion it is “tremendously probable” and the connec­tion falls into line with the previous demonstrated cases.

I must add here a remark suggested by the views of man’s descent put forward since this was written. The claim that man has changed the direction of his hair on his back and chest by use and habit owing to altered modes of life is not dependent on the simian theory of his descent. The change to his present patterns on those two regions from those of any “active arboreal pioneer” among insectivores is just as striking and is open to the same line of explana­tion.

It would serve no useful purpose here to travel further over the varied streams of hair on the body of man.