MUSCLES.
A work of great value to the biologist has been written by one whose
work has led him in the widening path of human physiology and its very
title is instinct with meaning. The Integrative action of the Nervous
System may not aid the systematist or the student of genetics, but for
insight into formative powers, where the former can but record facts
and find no interpretation, such a work is of supreme importance.
When the plant sealed its fate and enclosed itself in a cell-wall
and abandoned a life of movement, it was foreordained that its rival
would be that cell and its descendants which could adopt a free
life, and that the future of the world would lie at the proud foot
of that conqueror who could command and mobilize the resources of a
nervous system. And, as we know, it has fallen to man to receive the
rewards of this promise and potency of a higher life. If one seeks to
understand the steps by which man has arrived at his primacy it can
only be by the highway of nervous progress, however much the tracing of
certain connecting or collateral paths may throw light on contributing
causes. So that man’s place in Nature is nearly synonymous with the
structural evolution of his brain, as Huxley has shown in his clear and
simple manner. Even if man is to remain still an animal Melchisedec
for generations to come, or to put it lower, a foundling, no future
discoveries that can be imagined will disprove Huxley’s declaration,
“Evolution is no longer an hypothesis, but an historical fact.” And
yet if man has become adapted to his world, and, in it, crowned with
glory and honour by the unfolding of some original complexity, or as
the result of some fortunate mutations in the distant past, the human
brain, with its cranial capacity of nearly three times the number of
cubic centimetres to that of the gorilla, has been making false claims
to a paramountcy over all factors in the wonderful initiative of fresh
capacities and their mobilisation for conquest. Nothing less than such
a “claim” was understood by the ancients, and, though metaphysics
had to supply the lack of anatomy and physiology, it has always been
held that mind was lord of matter, and now scientific research has
told us why. But no one, even the most hard-shelled scholastic, can
refuse to the brain organ its predominant share in the making of man.
This is seen even in the frigid sphere of science by the difference
of interest there is shown between any great discovery bearing on the
evolution of man, or on some new lower animal form. When Sir. H. H.
Johnston astonished zoologists in 1901 by his discovery and proof
of the existence of an archaic large mammal which had been interned
for an incalculable time in the Semliki Forest, the thrill felt at
that historic meeting passed off very soon when the leading British
biologist had monographed the Okapi, settled its name and surname
and introduced it into text-books. This is never the fate of such
as Pithecanthropus or Eoanthropus dawsoni, or of the more recent
genealogical theory and researches as to arboreal man. The call of
these studies of man’s evolution is felt by all, and the difference in
the two branches of biology may account for what must have struck many
others, that is the neglect of adding the blue ribbon of science to the
honours of the discoverer of the Okapi.
These few trite remarks as to the importance of the nervous system in
the making of man have been introduced here, though they bear more
closely on the next two chapters, because this importance comes in at
every stage of the present treatment of the origin of modifications in
muscle.
Anatomists’ Views of Muscles.
There is a very strict and austere custom among anatomists, which
doubtless is in a measure necessary, of insisting upon following
rigorously the homologies of muscles, especially in human anatomy,
and in this branch of a greater subject the canons are followed to an
extent that surprises the seeker after origins. A remarkable example
of this is in a paper by an eminent anatomist, now Professor at King’s
College, Dr. E. Barclay Smith. It is a paper on the “Morphology of
the short extensor of the human fingers.”[72] He says “the precise
significance of this occasional _extensor brevis digitorum manus_
is a matter of considerable interest.” He gives four possible
interpretations of this unusual muscle. The last, viz., that it is
derived from a new muscle-germ alone interests us here because of the
remarkable caution and austerity of his remarks on this interpretation.
“If an _ext. brevis dig. manus_ cannot be regarded as an atavistic
anomaly, or as a derivative from any existing musculature, the only
way in which its presence can be accounted for is to suppose that
it is of entirely new origin--the product of a new muscle-germ.
Such an explanation is, of course, the last resort, and all other
possible derivations must be disproved before it can be accepted.”
The physiologist would probably think such an interpretation was
the obviously first resort. The same writer discusses at length the
homology of an exceedingly rare anomaly among muscles, the _extensor
ossis metacarpi hallucis_, and his desire on the one hand to find a
missing parent for Japhet, and his honesty and accuracy on the other
hand lead him to say “even when it is present, it cannot be regarded
as directly atavistic, since it does not represent a normal mammalian
tendency.” And he adds a gentle but remote suggestion--“Brooks
certainly describes such a muscle in _menobranchus_ and _hatteria_--two
rare and remote reptiles!” But, lawful and necessary though this be,
there must be stages on the path of human evolution where such a method
must fail and the anatomists can do no more than hold aloof from theory
or speculation, with a certain grim enjoyment of the disputes and
difficulties of the genealogists.
[72] Anatomical Society of Great Britain and Ireland, Trans., p. 54.
Initiative in Muscles.
Initiative in the evolution of muscles clearly occurs somewhere in
the stem, and behind the formed expression of an altered habit is the
integrating action of the nervous system. This will be by some looked
at askance as a _deus ex machinâ_ and reckoned as part of the argument
from ignorance in a way which recalls Weismann’s scorn of Lamarckian
factors in germinal selection. I submit that what he and Osborn call
“the unknown factor” of use and habit, arising in response to new
stimuli meets as no other proposed suggestion does the formation of
new muscles. Given a certain fundamental architecture of skeleton and
musculature, such as of primitive vertebrates, one can, without doing
violence to any known facts, place the formation of new organs of
movement in the following order:--
1. Neural changes and habits.
2. Muscular modifications.
3. Consequent modifications of bone. It carries the question no further
to say that these are correlated, however loose may be the meaning
of that word that is understood. If the prerogatives of Selection
within the germ, of segregation of unit-characters and dominance,
and of mutations are not unlimited in the construction of organisms,
there still remains a sphere of action for the initiating power of
the nervous system. Bones grow and change their form in response to
increased or altered muscular action on them, and it is necessary to
look back a stage further in the story to the neural changes however
produced. There have been abundant opportunities in the long history
of mammalian evolution for primitive forms to take a new course of
life, and they have done so on an extensive scale. The impulses that
have led them may have been started by some “needs” such as Lamarck
taught, some change in their surroundings involving new stimuli, or
“insults,” as Haeckel called them, but the first of the structural
stages must have been in the cerebral cortex.
Cross-Roads in Evolution.
The most instructive levels of animal evolution are those where two or
more great stocks have diverged from a primitive one. There may have
been several factors leading to the division of the early Ungulates
into the odd-toed and even-toed groups, of the Carnivora into cats,
dogs and bears, the Felidæ into the highly-specialised genera of that
intense family, the early parting of gibbons from the common anthropoid
stem, and then the division of this line into the three great genera
with which we are familiar. Whatever may have been the unknown factors
in the environment such as changes of climate and level, geographical
isolation, increase of foes, profusion or lack of food, to which these
diverging stocks became adapted in their organs and form, in fact
whatever we do _not_ know, we know this--that in their measure they
acquired more convoluted and often larger brains, and the stimuli
passing through their receptors into their consciousness increased
with an everflowing tide, in volume, intensity and complexity. Many an
archaic habit of their race they must unlearn, and it is doubtful if
germinal selection would avail in this valuable process of economy as
it is held to do in the case of the human little toe.
It may be taken as granted that increasing complexity of brain in their
own lines of life did accompany these adventurers of small or large
groups. It follows that muscular changes from the original stock would
follow neural changes, for movement and activity is inseparable from
the animal, and the integrating action of the nervous system would
constantly initiate, maintain and establish fresh habits and these
be expressed in new muscular structure. Whatever higher uses, as we
believe them to be, man makes of his brain, as reflection, reasoning,
imagination and association, such were not the new properties acquired
by these adventurers. They were very much concerned with hunger and
love, and for them “philosophy” did not sustain the structure of
their world. But more varied movements of head, trunk and limbs, and
greater agility and strength brought them such prizes as were within
their reach. This may be only another way of expressing Sir E. Ray
Lankester’s conception of educability, which he maintains to be the
only acquired character the organism inherits, and it may be therefore
assumed to be under the iron law of selection. This must be accepted
with the respect due to the high authority from which it proceeds. But
such a conception, while it removes a false light in certain regions,
sheds no light on the pathway of animal evolution, unless modifications
be transmitted, and we can now take it that man does not inherit the
power to speak which for incalculable ages he has been learning,
nor to write, even though in the days of the early Pyramid-builders
and the Sumerians in the plains of Chaldea they possessed the power
of writing, nor can a musician’s child learn to play an instrument
without teaching, or indeed man perform any of his arts and crafts by
second nature: so, negatively, this knowledge is valuable, and the
neo-Lamarckian must proceed on his quest without anything more than
educability to aid him--but it will serve. The fact is that we do not
inherit habits or associations as such at all, but the neurones of
the grey matter in spine and brain which subserve, direct and control
them. Though a fresh neurone or two in the brain of an early ungulate
deliberating, so to speak, as to the life he shall take up, whether
that of oxen or horses, may be trifling in itself as to immediate value
to the animal, it may be to him as much a matter of fate to acquire
those microscopic cells as it was to the undifferentiated organism
that paused before it sealed its fate as plant. Under the free and
enlightened government of the integrating nervous system liberty to
express itself to an almost unlimited extent, in accordance with
progress, is thus open to the hypothetical adventurers.
When considering such an aspect of the organism as the “choice”
between the career of an odd-toed or even-toed ungulate, a cat or
dog, a lion or tiger, a gibbon or other of the four anthropoid genera
which assuredly was presented to certain groups of primitive ungulates
carnivores, felidæ or apes, as historical beings, the vision of the
process is sore let and hindered by the limiting force of certain
expressions which have been sanctioned with the _imprimatur_ of fifty
years’ high thinking in the realms of high biology. I refer of course
to the terms Selection and Evolution which, though they cannot be
replaced by better terms, have the power and sometimes have had the
effect of impressing on the story of organic existence an aspect of
_determinism_ which does not allow, for any purposive action of the
individual, the working out of its own salvation, on the part of higher
forms at any rate. As among nations self-expression has become of late
a powerful force in their development, and indeed of individuals, so
it may be argued by analogy that the total experience of an organism,
may result in its co-operation in the process of its progress towards
higher things. Bergson hints at such a process in organisms, but
appears to allow nothing for the individual in his _élan vital_, where
the mass alone counts. So if the two binding terms of Selection and
Evolution must be granted their enormous power over our thoughts, there
must be also a loosing as well as a binding, and we, as well as certain
young ecclesiastics in a hurry, may put in a plea for Life and Liberty.
Thus is Lamarckism immortal, and the integrative action of the nervous
system supplies the reason.
This well-worn subject is not out of place here, where I am trying to
show evidence of self-expression in terms of muscular modification
arising from fresh activities of the brain.
New Muscles.
If it can be said without fear of question that “the differentiation
of muscle and nerve is the morphological result of division of labour,
whereby the unit of protoplasm, in which irritability and contractility
are combined, has, on the one hand, become modified into muscle, which
retains the property of contractility, and on the other into nerve,
which retains that of irritability,”[73] and if Wolff’s _Law of Bone
Transformation_ teaches that if a normal bone is used in a new way its
structure and form will change to meet its new function, which Sir
Charles Bell had more vaguely taught in 1834, it cannot well be denied
that at certain turning-points in the history of animal organisms the
sequence of changes which arise is neural change, muscular modification
and finally change of bone, whether ungulates, carnivores, felidæ,
gibbons or big anthropoids or man, be the _dramatis personæ_. The only
question is whether selection or use and habit initiates the subtle and
slow process.
[73] Macalister, _op. cit._, p. 62.
Unstriped Muscles.
The simplest of the muscular acquirements of mammals is of course
that great mass of little structures which constitutes the unstriped
musculature. I must admit that here again I am engaged with what the
professed biologist may call trifles, but these, like some others of
a corresponding rank, have a provoking quality of persistence, and
display, if one may personify them, an insistent desire to know whence
they come and why they are here. Some of these, like the one before
us, may be comprehended in the great chapter of the Evolution of the
Indifferent of which they form a page. This world, at any rate in the
moral sphere, would be an intolerable house of bondage if there were
not many _things that matter not_ as well as _things that matter_, and
there is reason to believe that in the process of the making of man and
a vast number of forms below him there is a large field of structures,
parts and organs, where things that matter not are to be found. One
strange province of this realm is the colouration of animals in certain
regions where no eye ever can see the colour or can take any heed of
the markings, treated very fully many years ago by Mr. Beddard in
_Animal Colouration_.
Unstriped muscle arises, as the striped variety does, from the
mesoblastic muscle-plate and appears in nearly all organs,
blood-vessels and skin, and as trade is said to follow the flag, so
a development of new unstriped muscles must speedily be found in
every new structure of the regions where unstriped muscle is found.
The skin is the simplest, and less complicated by the presence of
other structures than vessels and organs, where it also exists, but
where it trespasses too much on the territory of selection for my
immediate purpose. A small band of this muscle called an _arrector_,
or _erector_, _pili_ is attached to most, if not all, of the third of
a million hairs which cover the skin of man, and is inserted into that
side of each hair which forms an obtuse angle with the plane of the
skin. This tiny structure is endowed with the quality of contracting
in response to certain stimuli falling on the skin, so that it causes
the hair to which it is attached to stand erect instead of sloping, and
incidentally squeezes some of the secretion out of the sebaceous gland
which lies in each angle. The human skin thus possesses about a third
of a million minute muscular bands and shows no sign of parting with
this old gift from a lower hairy stock, and whatever value, if any,
their function be to their possessor they show a remarkable readiness
to perform it efficiently. It makes their existence and persistence no
clearer to call them vestigial, for one only thus throws the question
of their origin much farther back. Undoubtedly they come from afar
and were in full development in the earliest hair-clad mammals, so an
ancestry reaching back to Monotremes or Marsupials is not to be lightly
set aside. The raw material was undoubtedly formed in response to
stimuli conveyed to the brain, and the earliest appearance of muscles
which erected the hairs must have been wholly insignificant either upon
the survival or comfort of the possessors.
A Remarkable Example.
The _arrectores pili_ exhibit very little evidence of control or
interference from the action of the brain, but there is one region of
one animal, like the Rosetta stone that set Champollion at work, where
a very simple hieroglyph is recorded. I have been able to find no other
in all the hairy mammals I have examined than that startling pattern
which the back of the lion, shown in Fig. 37, sometimes displays. That
well-formed patch of reversed hair of roughly triangular shape which
is frequently found on the back of a lion has been described and, as
I interpret this strange structure, it would seem clear that neural
change in some examples of this species has led to so persistent
contraction of the _arrectores pilorum_ over a certain area of skin,
and that these have permanently reversed the normal and primitive slope
of the hair. I have never found it present in a lioness, and not in
all cases of male lions. It marks its possessor with the brand of a
fierce and especially savage character, and he is not able to screen
it from the eye of the Zoologist as well as Milady did her brand of
shame, until that fatal day when D’Artagnan disclosed it. This pattern
on a lion’s back is strangely reminiscent of the ridge of bristling
hair we see on the corresponding region of a fierce dog’s back when he
is infuriated. In the latter it may be said to have selective value,
as perhaps also is the bristling hair on the head of a gorilla when
enraged, much in the same way as the Chinese warriors sought to alarm
their enemies by terrifying grimaces, or those terrifying tones and
expressions of face which the Tyrant man, really a coward, is said by
such as Miss Wisk to exercise over the women of his circle. We may
present all these to the Pan-Selectionist, but inasmuch as the short,
bristling hairs on the back of a lion are on the one hand hidden by
the mane from an animal in front, and on the other are so small as
to be seen quite close if at all, the survival-value of the reversed
pattern of hair in question is quite outside the province of selection.
It is so manifestly under the control of cerebral action, that it may
be compared, as an undesigned experiment, with that of man in placing
harness upon a horse, as to the power of cerebral action in producing
structure. Though, as far as I can learn, it stands alone, it is
difficult to believe that such a thing as a unique example occurs in
nature, but it is interesting and suggestive from the Lamarckian point
of view, and even the opposing counsel must admit that it is among
indifferent structures.
Facial Muscles of Expression.
This record in terms of hair of personal and ancestral emotions has,
however, a link with certain more numerous and important striated
muscles, such as the facial muscles of man and apes, modifications of
the great platysma-sheet, and which are disposed in two layers, a deep
and a superficial. This covers like a hood at the third month the head
and neck of the embryo, and later assumes on the face its specialised
form of certain bands which operate round the eyes and mouth. As they
are of the striated kind these muscles can be moved at will, but their
main action is much more under the government of the mental processes
of their possessor. As they are fundamentally the same in apes and man
very little new muscular structure arises in man, and little more than
shaping or refining takes place.
The facial muscles which operate round the orbit have less mental
action represented in them than those of the mouth, though the action
of the special elevator of the upper eyelid is conspicuous among the
expressions of a vigorous person. Both apes and man have muscles on
each side which raise or lower the angles of the mouth, draw the
angles upwards and outwards, and raise the upper and depress the
lower lip; and, though the muscle of the mouth which corresponds
to the _orbicularis_ of the eye is not a continuous structure, but
formed of interrupted bundles of fibres, it is powerful in closing the
lips and active in the expressions. There are also in man scattered
oblique fibres in the substance of the lower lip, well-developed and
closely-set in a sucking child, and these in the adult are scattered
and less conspicuous.
There is thus a remarkable set of structures in the face of a higher
primate which convey mental emotion. As they also belong to animals
with a high degree of convolution of brain, though certain are found
in lower mammals, their specialisation is only to be accounted for by
the long-continued involuntary expression of mental states existing
in the particular form of primate. Professor Keith says in the work
before referred to: “Muscles supplied by the facial nerve are the
physical basis into which many mental states are reflected, and in
which they are realised. Through them mental conditions are manifested.
It is found that the differentiation of this sheet into well-marked
and separate muscles proceeds _pari passu_ with the development of the
brain. The more highly convoluted the brain of any primate the more
highly specialised are its facial muscles,”[74] and he points out in
a smaller work[75] that in the gibbon, and monkeys of the Old and New
Worlds the facial system becomes simpler and at the same time more
robust, and he pictures the facial muscles as the “servants of the
brain.”
[74] _Embryology._
[75] _The Human Body._
If an ape can express a good many of the coarser emotions of an animal
by the action of its facial muscles, and through kindness and training
exhibit some of the finer ones, there is a wide distance between this
level of attainment and the multiplied moods and unnumbered varieties
of expression which give to the human face its unique charm. If we can
express pleasure, pain, anger, contempt, hatred, surprise, affection,
sympathy, fear, hope, reflection, perplexity, gaiety, melancholy,
cunning (and many another can be supplied) what a remarkable field of
physiology in terms of anatomy we have in the facial muscles! There is
a very obvious reason why none of these emotions have been fixed in an
objective form in ape or man, as the patch of reversed hair is on the
back of a lion, for moods and states of feeling in every individual man
are subject to such endless variations that it would be impossible for
them to stamp any individual face with a record of even one emotion
which could be transmitted to descendants, to say nothing of the
inconceivably great probability that heredity would at once swamp any
initial modification.
Three Stages.
The stages then are but three--mental states, specialisation of small
muscular bundles from an existing simple sheet of muscle, and disuse
of the remaining portions, and in this small but highly significant
field we see structures created independently of will as servants of
the brain, and without any survival-value in their earliest stages.
It is more than likely no monkey, ape, or early man whose face was
covered with thick hair from his eyes downwards, ever saved his life
or gained a better mate by reason of the subtle modification of a tiny
muscle which was proceeding _pari passu_ with the growing complexity
of his convolutions and their manifested emotions. This is not to
claim that a more modern man or woman would not find sexual selection
of value by reason of his or her more pleasing or commanding facial
expression. That the initiative of these alluring modifications was
simple and Lamarckian cannot be gainsaid, whatever the fruit of the
finished process may be to-day. We know in our own experience that many
a handsome person with good features and little expression is often
unsuccessful in the matrimonial market, when another with defective
features and a fine, delicate, attractive expression takes the prize.
So the early story of the formation of muscles of expression is seen to
be a page in the evolution of the indifferent.
The Fly-shaker Muscle.
The panniculus carnosus, of which the facial muscles are part, is a
great system of musculature found in various animal forms, and it
furnishes a field for study of the evolution of the indifferent and the
initial stages of the formation of a muscle. This is a servant of the
brain in a more indirect manner than the facial muscles, but it, too,
arises in obedience to the integrative action of the brain. The early
specialisation of it need not be considered here. It may be considered
unwarrantable to claim the great Fly-shaker muscle of Ungulates as an
indifferent structure, but the arguments by which the Pan-Selectionist
would annex it to his sceptre, as a triumph of the minute care of the
organism by selection, rest only on the assumption that he knows how
it has become an adaptation to the life of its possessors. This is
now more than it used to be a matter of opinion since the publication
of Professor Bateson’s revolutionary _Materials_, and others beside
he have reserved to themselves the liberty of doubting the accepted
explanations by the tangled path of adaptation. The statement of
Weismann, “Everything is adapted in animated nature” was necessary
to his theory of germinal selection, but it admits of extensive and
numerous exceptions in view of the fact that so much of adaptation is
partial and imperfect. If he had said that _every organism_ as a being
is adapted he would have been nearer the truth, but that every tissue
and part of an organism is adapted is demonstrably untrue. A large
number of organisms, themselves apparently well adapted, flourish well
enough and reproduce their kind in spite of faulty and rudimentary
tissues and parts. If it were not so we should have seen little of
progress except what come under the laws of genetics,--a distributional
matter. Even the super-Geddes could not distribute what was not there,
for he could not deal with raw materials and change them by a fairy
wand into manufactured articles. In the great field of domesticated
plants and animals man has to find not only some mutation or some
dominant strain and breed it to his will, but to cultivate the domestic
qualities of animals and employ cultural conditions for plants. There
is doubt expressed as to the length of time or numbers of generations
during which these cultural conditions can extend, but Professor
Thiselton Dyer many years ago made the remarkable statement as to
plants:--“While specific stability under constant conditions appears
to be the rule in nature, it is widely different in cultivation. When
a plant is brought under cultural conditions it maintains its type for
some time unaltered, then gives way and becomes practically plastic.
From my experience at Kew, where I saw the process continually going
on, I hazarded the generalisation that any species, annually reproduced
from seed, could be broken down in five years. During that period
specific stability, though menaced, tends to maintain itself. Darwin
was well aware of this.”[76]
[76] _Nature_, November 28th, 1907, p. 78.
Most biologists from time to time betray the fact that their minds can
only be relieved from an intolerable burden, in accounting for the
numberless adaptations in organisms, by the view that many of them
originate through factors of use and stimuli from environment, and
at first are entirely indifferent as regards the survival or better
mating of their possessors. To which the stern opponent replies, “What
is there to show that in the existing scheme of things there is any
provision made which will minister relief to the burden of your little
mind?” To which, “answer came there none,” except a subdued reflection
that everything we see of living, striving nature around us has a
most provoking way of speaking to us of daily, hourly and incessant
action and reaction, stimulus and response, and that those who view the
process thus do seem to bring some order into what would otherwise be
chaos--and yet all the while someone is being grossly deceived! This
“may be magnificent but it is not proof,” some will say, and will ask
if the older observers of the heavenly bodies were not wrong in their
complete conviction that the sun went round the earth. This digression
introduces the role of the fly-shaker. If I am told that this muscular
sheet in a cow or horse to-day is a relic of raw material inherited
from a remote ungulate stock little evolved, and that it contributes in
hot weather in the time of flies to the comfort and better mental state
of the cow or horse, that it shall be able to keep those enemies at
bay, and that the muscle is kept well in order by two or three months’
practice in each year I can understand in a measure its presence
to-day. It has an efficient ally in the sweeping tail of a cow and
that of a wild horse, and both of these weapons are further aided by
the mobile ears of cow and horse, and the stretching movements of its
head and neck. Thus the body of a cow, for example, is like a map with
four territories delimited, that of the fly-shaker, the tail, the ears
and the head and neck. Between these offensive weapons a cow is better
defended against flies than a European in India by his punkah, or China
was by its great wall, or Britain by the wall of _Vallum_ of Hadrian
or the wall of Severus, which with forts and garrisons was designed
to protect it. Speaking in allegory the evolving brain of an early
ungulate occupies the position of an ancient Chinese Emperor or a Roman
Proconsul in Britain in its provision against “barbarians,” either
Asiatic or Celtic. The resemblance goes further, for no experienced
Roman General, whatever the Celestial minds in China may have thought,
would fear that the loss of a sector of his wall would imperil the army
of occupation in Britain or the fabric of the Roman Empire. But as, in
the long run it contributes to one’s welfare to be comfortable, and
even the domestic ungulate is somewhat of a hedonist, a well-developed
fly-shaker is maintained, the occasional use of which in winter and
frequent use in summer and the active purposeful switching of tail,
twitching of ears and jerking of head have their limited value. Here
there is ample room for diverse opinion and the opponent will ask
with some degree of force how we know that there is no more benefit
to the cow from its fly-shaker than a mild degree of comfort, and may
assert that the possession and use of it may have survival-value by its
defence against deadly parasites. We do not know, nor does he, but it
would seem that except for the tsetse fly in Africa the plague of flies
does little to an ungulate beyond irritating its brain, and if he had
no fly-shaker, he would still be able to reach a considerable distance
with his tail, ears and head over the irritated regions. The question
of survival indeed resolves itself into the vigour and energy of his
integrating brain.
To this view of the function and origin of the panniculus carnosus the
busy systematist and student of genetics may refuse to listen, and pass
to the order of the day, but I submit that in stating a position it is
useful to put forward a crude example in which the issue is plain, and
which subsumes an immense number of smaller and more subtle cases, and
in a region where the most hardy rebel will not dispute altogether the
sway of _personal_ selection. It is a question here of the manner in
which, speaking in metaphor, the early ungulate first set about making
his eolithic or palæolithic weapons and fashioned them into what we see
to-day. “Forged by the incident of use” and habit meets the story of
the fly-shaker far better than some mutation arising in far back ages
or some dominant variation, or “useful variation within the germ.” At
any rate Lamarck finds the raw material to hand, and there are supplied
adequate noci-cipient stimuli with response, in regions where these are
most active under the dominating action of the brain.
Other Muscles.
In the skeletal muscles of the primates many muscles offer themselves
for consideration as examples of inherited structures arising under
the stimuli of altered function, and only a few of these will be dealt
with. It might appear sufficient to those who yield, perhaps too
willingly, to authority, if I were here to try and prove my point by
quoting the statements of one of the greatest anatomists of our time
and country, and so pass on--but it is to be feared authority cannot
carry one far in a dispute so important. Macalister says, however, “The
anatomical arrangement of the muscular system is the physical exponent
of habitual actions and those actions are the chief factors in moulding
the bones and in regulating the position of the somato-pleural vessels
and nerves”--and “the locomotory function and consequent utility of the
trunk-muscles were lost when the early vertebrates became terrestrial.
In higher vertebrates, and notably in man, the mobility of several
regions of the vertebral column differs both in degree and kind: the
outgrowing vertebrate processes show consequent variations, and _the
muscular system is varied accordingly_.”[77] Also “as both origins
and insertions (of muscles) are the creatures of habit, they are both
equally variable with variation of function; but, as in higher animals
the kind of work to be done is more constant than its degree, so,
as a rule, insertions alter less than origins.”[78] Macalister, at
any rate, held a very clear dynamical rather than static view of the
making of the muscular system. But as the days of authority are in a
certain sense gone for ever, and we live under the reign of experiment,
research and questioning, every biologist, within certain limits, does
what is right in his own eyes; there is no King in these days.
[77] _Op. cit._, p. 71. (Italics not in original.)
[78] _Op. cit._, p. 73.
Skeletal muscles are structures in which, if ever, the factors of use
and habit and disuse would be shown, because muscle is a tissue, with
highly active metabolism, so that it has been called “an expensive
tissue” for the animal to maintain.
Muscles of Primates.
This physiological fact agrees with the anatomical results of an
extended study in the musculature of primates, especially of man, and
Hartmann’s book on Anthropoid Apes supplies abundant evidence of the
variations of the muscles of these animals, which are not at all more
striking than their differing modes of life would suggest. It would be
wearisome to quote all these, but a single muscle may be given as an
example of a special ape’s muscle with variable distribution. It is
called _latissimo-condyloideus_ and starts from the insertion of the
_latissimus dorsi_ and passes along the inner aspect of the humerus
for a variable distance. In the _baboon_ and others it goes to be
inserted into the inner inter-muscular septum and the internal condyle
of the humerus, in the _orang_ to the condyle, and in the _gibbon_ to
the centre of the shaft. As to origin it proceeds from the insertion of
the _latissimus dorsi_, but in the _gorilla_ from the coracoid process
of the scapula and from two portions of the _pectoralis minor_, and is
finally attached to the inter-muscular septum between the _brachialis
anticus_ and the _triceps_; in the _chimpanzee_ it divides into an
anterior and posterior portion, the former being attached to the inner
condyle, the latter to the middle and inner head of the _triceps_;
in the _orang_ it divides similarly, but in one particular example
it had an anterior thin portion attached by a slender tendon to the
coracoid process of the scapula and a posterior portion arose from the
_latissimus dorsi_; in the _white-handed gibbon_ it arose from the
function of tendons from the _latissimus dorsi_ and _teres major_ and
was inserted into the fascia between the tendon of the _biceps_ and the
_brachialis anticus_.
Such a divergence as this within the strict limits of an anthropoid
muscle, concerned in the various forms of climbing action of these
apes, can only suggest an origin from a divergent set of functions and
small details in their respective modes of climbing.
Hand and Foot of Man.
Both the hand and foot of man supply a small muscle for consideration
in the present connection of habit with formation of new structure.
If man be regarded as of simian origin there are not as many entirely
new muscles in his equipment as would be expected from his departure
from the habits of simian ancestors, though many muscles are found to
be altered in size and shifted from the ancestral positions. But the
human hand presents one suggestive example of a little muscle not found
in any other animal, the special small extensor of the thumb, arising
from the interosseous membrane between the radius and ulna, and from
the radius, being segmented off from the _extensor of the metacarpal of
the thumb_, and it accompanies this muscle and tendon to be inserted
into the first phalanx of the thumb, and is peculiar to man. It can be
easily seen at the radial border of the well-known “snuff-box” which is
produced by it when it is fully extended. This is of course a muscle of
small importance to the functions of the hand, and its appearance in
man can only be supposed to be a subordinate detail easily derived from
the _greater extensor_ by reason of the more delicate adjustment to
complicated movements of the hand under the directing power of higher
cerebral development.
Peroneus Tertius.
The foot of man possesses the small _peroneus tertius_ which was
referred to as one of the evertors of the foot concerned in the
construction of his plantar arch. Macalister and Professor Keith both
speak of it as peculiar to man, and the latter refers to it at some
length,[79] the whole passage being worth quoting here. “Although
the evolution of the human method of progression was attended by a
profound alteration in the form and action of every muscle and bone
with lower limbs, yet this great transformation was produced without
the appearance of any really new element. One new muscle--the _peroneus
tertius_--did appear, and the history of its evolution throws an
interesting sidelight on the origin of new structures. It arises by
the outer fibres of the common extensor muscles of the toes being
separated. In all the anthropoids the feet are so articulated at the
ankle-joints that the soles are directed towards each other, and only
the outer edge of the foot comes to rest on the ground when the animal
tries to stand. The feet have a tendency to assume a similar position
in children at birth. The advantage of a muscle, such as the _peroneus
tertius_, is apparent in the human foot, for it tends to raise the
outer border of the foot, so that the sole is properly applied to the
ground. If we examine the muscles which, rising from the front of
the leg, cross the ankle-joint to end on the back of the foot on the
toes of fifty men, we shall find every stage in the evolution of this
muscle. In one man at least it will be undeveloped; in two or perhaps
three it will be represented by a part of the tendon of the extensor
muscle of the little toe, which in place of ending entirely on the
toe sends a part to end on the metatarsal bone of the little toe. In
only forty of the fifty men will the _peroneus tertius_ be found quite
isolated from the parent muscle--_the extensor communis digitorum_, and
to have a distinct origin from the fibula in the leg, and a separate
insertion to the base of the fifth metatarsal bone in the foot. In a
series of fifty specimens every stage in the isolation of this new
muscle will be seen. It has never been found in any anthropoid, and is
more often absent or undeveloped in African than European races.”
[79] _The Human Body_, p. 92.
To this excellent account I have only to add one comment. It can
hardly be an accident or without significance that this special human
evertor of the foot concerned in the construction of the plantar arch
is “often absent or undeveloped” in African races, which are well-known
in some groups to have adapted themselves to a form of foot which shows
no plantar arch, being normally flat-footed. In this small field of
observation, a mere plot of lentils like that which Shammah defended of
old, there is set forth a mimic battlefield, and it is not difficult
to see that the forces at work can owe allegiance to one and one only
of various commanders. The problem as to the origin of the _peroneus
tertius_ would no more attract the Mendelian than did the trousseau
and approaching marriage of Caddie Jellyby attract the far-away gaze
of her mother, fixed upon the world of Borria-boula-gha, and, for that
matter, de Vries would hardly pay it more attention--to him it would
be indifferent; whereas Weismann would have as much to say about it
as about the little toe of man, which furnished for him and Herbert
Spencer such fruitful material for debate many years ago. This muscle
resembles the results of some of Michael Angelo’s first attempts at
sculpture, thrown aside perhaps in his place of work and from time to
time taken up, rough-hewn again and again and finally shaped into a
form far from perfect, but with the value and teaching of a failure
for him who was some day to outshine all modern rivals. If the history
of this muscle be not one of initiative in evolution through the
factor of use and habit the Pan-Selectionist must do the best he can
with an incalculable number of “trials and errors,” and must suppose
that, rather than allow this small territory to the neo-Lamarckian, a
long series of man’s ancestors have been making experiments for the
benefit of man’s walking power under the guidance of selection with
an insignificant muscle whose only function is that of aiding in the
eversion of the foot, and that in the rudimentary condition described
by Professor Keith it had selective value. No one who was not committed
to a dominating theory could hesitate for a moment which of the two
alternative views of the origin of the _peroneus tertius_ he would
choose. Dr. Barclay Smith speaks in the paper referred to above of the
_extensor brevis pollicis_, or _minor_, as a muscle of extremely late
appearance, and as “peculiarly human,” and says all the evidence points
to its being a segmentation product of the _extensor ossis metacarpi
pollicis_, its appearance being foreshadowed in the anthropoid by an
extension of that muscle on to the proximal phalanx of the thumb.
It is not without interest to the thesis before us to read the rather
bewildering story of the early life of a very insignificant muscle such
as the small extensor of the thumb of man.
As illustrations of the moulding and pruning of perfected muscles it
may be remembered that, as Macalister says, “portions of muscles may
also become detached and degenerated so as to act as ligaments,” and
“the adult muscular system of man bears everywhere traces of earlier
cleavings and subsequent fusions, partial disappearances and local
outgrowths.”[80] This passage recalls one in which Huxley says in
watching certain phases of development you can almost see the hidden
artist at work, and here the sculptor may be pictured in his chipping,
trimming, rejecting and finally shaping, some creation of his brain;
and from a biological point of view a vision of the processes of use
and disuse may be obtained. Professor Keith also speaks often of the
migrations of muscular attachments in a way which agrees with the
passage quoted from Macalister.
[80] _Op. cit._, p. 73