Every one must have heard or have read of the supposed perfect
adaptation of the human frame to bipedal locomotion and to an upright
attitude, as well as the advantages which we gain by this erect
position. We are told, and with perfect truth, that in man the occipital
foramen--the aperture through which the brain is connected with the
spinal cord--is so placed that the head is nearly in equilibrium when he
stands upright. In other mammalia this aperture lies further back, and
takes a more oblique direction, so that the head is thrown forward,
and requires to be upheld partly by muscular effort and partly by the
ligamentum nuchæ, popularly known in cattle as the "pax-wax."
Again, the relative lengths of the bones of the hinder extremities in
man form an obstacle to his walking on all-fours. If we keep the legs
straight we may touch the ground in front of our feet with the tips of
the fingers, but we cannot place the palms of the hands upon the ground
and use them to support any part of our weight in walking. Not a few
other points of a similar tendency have been so often enlarged upon, in
works of a teleological character, that there can be no need even to
specify them at present.
But till lately it has never been asked, "Is man's adaptation to
an upright posture perfect?" and "Is this posture attended with no
drawbacks?" These questions have been raised by Dr. S. V. Clevenger in a
lecture delivered before the Chicago University Club, on April 18, 1882,
and recently published in the _American Naturalist_. This lecture,
we may add, cost the speaker the chair of Comparative Anatomy and
Physiology at the Chicago University!
Dr. Clevenger first discusses the position of the valves in the veins.
The teleologists have long told us that the valves in the veins of
the arms and legs assist in the return of blood to the heart against
gravitation. But what earthly use has a man for valves in the
intercostal veins which carry blood almost horizontally backward to the
azygos veins? When recumbent, these valves are an actual obstacle to
the free flow of the blood. The inferior thyroid veins which drop their
blood into the innominate are obstructed by valves at their junction.
Two pairs of valves are situate in the external jugular, and another
pair in the internal jugular, but they do not prevent regurgitation of
blood upward.
An anomaly exists in the absence of valves from parts where they are
most needed, such as the venæ cavæ, the spinal, iliac, hæmorrhoidal, and
portal veins.
But if we place man upon all-fours these anomalies disappear, and a law
is found regulating the presence or absence of valves, and, according to
Dr. Clevenger, it is applicable to all quadrupeds and to the so-called
Quadrumana. Veins flowing toward the back, i.e., against gravitation in
the all-fours posture--are fitted with valves; those flowing in
other directions are without. For the few exceptions a very feasible
explanation is given.
Valves in the hæmorrhoidal veins would be useless to quadrupeds; but to
man, in his upright position, they would be very valuable. "To their
absence in man many a life has been and will be sacrificed, to say
nothing of the discomfort and distress occasioned by the engorgement
known as piles, which the presence of valves in their veins would
obviate."
A noticeable departure from the rule obtaining in the vascular system of
mammalia also occurs to the exposed situation of the femoral artery in
man. The arteries lie deeper than the veins, or are otherwise protected,
for the purpose--as a teleologist would say--of preventing serious loss
of blood from superficial cuts. Translating this view into evolutionary
language, it appears that only animals with deeply placed arteries can
survive and transmit their structural peculiarities to their offspring.
The ordinary abrasions to which all animals are exposed, not to mention
their onslaughts upon each other, would quickly kill off species with
superficially placed arteries. But when man assumed the upright posture
the femoral artery, which in the quadrupedal position is placed out of
reach on the inner part of the thigh, became exposed. Were not this
defect greatly compensated by man's ability to protect this part in ways
not open to brutes, he, too, might have become extinct. As it is, this
exposure of so large an artery is a fruitful cause of trouble and death.
We may here mention some other disadvantages of the upright position
which Dr. Clevenger has omitted. Foremost comes the liability to fall
due to an erect posture supported upon two feet only. Four-footed
animals in their natural haunts are little liable to fall; if one foot
slips or fails to find hold, the other three are available. If a fall
does occur on level ground, there is very little danger to any mammal
nearly approaching man in bulk and weight. Their vital parts, especially
the heart and the head, are ordinarily so near the ground that to them
the shock is comparatively slight. To human beings the effects of a
fall on smooth, level ground are often serious, or even deadly. We need
merely call to mind the case of the illustrious physicist whom we have
so recently and suddenly lost.
The upright attitude involves a further sourge of danger. In few parts
(if any) of the body is a blow more fatal than over what is popularly
called the "pit of the stomach." In the quadruped this part is little
exposed either to accidental or intentional injuries. In man it is quite
open to both. A blow, a kick, a fall among stones, etc., may thus easily
prove fatal.
Another point is the exposure and prominence of the generative organs,
which in most other animals are well protected. Leaving danger out of
the question, it may be asked whether we have not here the origin of
clothing? The assumption of the upright posture may have made primitive
man aware of his nakedness.
Returning to the illustrations furnished by Dr. Clevenger, we are
reminded that another disadvantage which occurs from the upright
position of man is his greater liability to inguinal hernia. In
quadrupeds the main weight of the abdominal viscera is supported by the
ribs and by strong pectoral and abdominal muscles. The weakest part of
the latter group of muscles is in the region of Poupart's ligament,
above the groin. Inguinal hernia is rare in other vertebrates because
this weak part is relieved by the pressure of the viscera. In man the
pelvis receives almost the entire load of the intestines, and hence Art
is called in to compensate the deficiencies of nature, and an immense
number of trusses have to be manufactured and used. It is calculated
that 20 per cent. of the human family suffer in this way. Strangulated
hernia frequently causes death. The liability to femoral hernia is in
like manner increased by the upright position.
Now, if man has always been erect from his creation--or, if that term be
disliked, from his origin--we have evidently nothing to hope from the
future in the way of an amendment of this and other defects. But if we
have sprung from a quadrupedal animal, and have by degrees adopted
an upright position, to which we are as yet imperfectly adapted, the
muscular tissues of the abdomen will doubtless in the lapse of ages
become strengthened to meet the demand made upon them, so that the
liability to rupture will decrease. In like manner the other defects
above enumerated may gradually be rendered less serious.
A most important point remains; the peritoneal ligaments of the uterus
fully subserve suspensory functions. The anterior, posterior, and
lateral ligaments are mainly concerned in preventing the gravid uterus,
in quadrupeds, from pitching too far forward toward the diaphragm. The
round ligaments are utterly unmeaning in the human female, but in the
lower animals they serve the same purpose as the other ligaments.
Prolapsus uteri, from the erect position and the absence of supports
adapted to the position, is thus rendered common, destroying the health
and happiness of multitudes.
As a simple deduction from mechanical laws, it would readily follow that
any animal or race of men which had for the longest time maintained an
erect position would have straighter abdomens, wider pelvic brims with
contracted pelvic outlets, and that the weight of the spinal column
would force the sacrum lower down. This, generally speaking, we find to
be the case. In quadrupeds the box-shaped pelvis, which admits of easy
parturition, is prevalent. Where the position of the animal is such as
to throw the weight of the viscera into the pelvis, the brim necessarily
widens, these weighty organs sink lower, and the beads of the
thigh-bones acting as fulcra permit the crest of the ilium to be
carried outward, while the lower part of the pelvis is at the same time
contracted.
In the innominate bones of a young child the box-shape exists, while its
prominent abdomen resembles that of the gorilla. The gibbon exhibits
this iliac expansion through the sitting posture which developed his
ischial callosities. Similarly iliac expansion occurs in the chimpanzee.
The megatherium had wide iliacal expansions due to its semi-erect
habits; but as its weight was in great part supported by the huge tail,
and as the fermora rested in acetabula placed far forward, the leverage
necessary to contract the lower portion of the pelvis was absent.
Prof. Weber, of Bonn, quoted in Karl Vogt's "Vorlesungen ueber den
Mensohen," distinguishes four chief forms of the pelvis in mankind--the
oval in Aryans, the round among the Red Indians, the square in the
Mongols, and the wedge-shaped in the Negro. Examining this question
mechanically it would seem that the longer a race had remained in
an upright position the lower is the sacrum, and the greater is the
tendency to approximate to the larger lateral diameter of the European
female. The front to back diameter of the ape's pelvis is usually
greater than the measurement from side to side. A similar condition
affords the cuneiform, from which it may be inferred that the erect
position in the Negro has not been maintained so long as in the Mongol,
whose pelvis has assumed the quadrilateral shape owing to persistence
of spinal axis weight for a greater time. This pressure has finally
culminated in forcing the sacrum of the European nearer the pubes, with
consequent lateral expansion and contraction of the diameter from
front to back. From the marsupials to the lemurs the box-shaped pelvis
remains. With the wedge-shape occasioned in the lowest human types there
occurs a further remarkable phenomenon in the increased size of the
foetal head accompanying the contraction of the pelvic outlet. While the
marsupial head is about one-sixth the size of the narrowest part of the
bony parturient canal, the moment we pass to erect animals the greater
relative increase is there seen in cranial size, with a coexisting
decrease in the area of the outlet. This altered condition of things
has caused the death of millions of otherwise perfectly healthy and
well-formed human mothers and children. The palæontologist might tell us
if some such case of ischial approximation by natural mechanical causes
has not caused the probable extinction of whole genera of vertebrates.
"If we are to believe that for our original sin the pangs and labor
of childbirth were increased, and if we also believe in the
disproportionate contraction of the pelvic space being an efficient
cause of the same difficulties of parturition, the logical inference is
that man's original sin consisted in his getting upon his hind legs."
This subject is not without direct applications. Accoucheurs cause their
patients to assume what is called the knee-chest position, a prone one,
for the purpose of restoring the uterus to something near a natural
position. Brown-Sequard recommends, in myelitis, or spinal congestion,
drawing away the blood from the spine by placing the patient on his
abdomen or side, with hands and feet somewhat hanging down. The
liability to _spina bifida_ is greatest in the human infant, through
the stress thrown on the spine. The easy parturition in the lower human
races is due to the discrepancy between cranial and pelvic sizes not
having been as yet reached by those races. The Sandwich Island mother
has a difficult delivery only when her child is half white, and has
consequently a longer head than the unmixed native strain.
At present the world goes on in its blindness, apparently satisfied
that everything is all right because its exists, ignorant of the evil
consequences of apparently beneficial pecularities, vaunting man's
erectness and its advantages, while ignoring the disadvantages.
The observation that the lower the animal the more prolific (not
universally true!) would warrant the belief that the higher the animal
the more difficulties encompass its propagation and development. The
cranio-pelvic difficulty may perhaps settle the Malthusian question as
far as the higher races of men are concerned by their extinction.
[If the facts brought forward by Dr. Clevenger cannot be controverted,
they seem to prove that man must have originated by gradual development
from a four-footed being. Had he been created an erect, bipedal animal,
as we find him, his structure would have been not in partial, but in
perfect, adaptation to the conditions of that attitude. That some of the
peculiarities of his structure are better in harmony with a horizontal
than a vertical position of the spinal column, is perhaps the strongest
argument against the theory of direct creation and the radical _toto
coelo_ distinction between man and beast that has yet been advanced. We
cannot at the moment lay our hands upon any thorough and trustworthy
account of the valves in the veins of the sloth: as that animal spends
its life hanging, back downward, the structure of the veins would be
interesting in this connection.--ED. J. S.]--_Journal of Science_.
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