HABITS AND HAIR OF PRIMATES.
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 _quâ 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.
[55] _Direction of Hair in Animals and Man._
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.
[Illustration: Fig. 41.--Arrangement of hair on the back of
lemur--chimpanzee--man.]
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.
[Illustration: Fig. 42.--Arrangement of hair on the chest of
lemur--chimpanzee--man.]
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
book[56] 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.
[56] _Direction of Hair_, pp. 88–93.
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.