John Mason Tyler.

The Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895 online

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body. 2. The appendages start as fins, and end as the legs and arms
of man. 3. The circulatory and respiratory systems developed so as
to carry with the utmost rapidity and certainty fuel and oxygen to
the muscular and nervous high-pressure engines. Or, to change the
figure, they are the roads along which supplies and munitions can be
carried to the army suddenly mobilized at any point on the frontier.
4. Above all, the brain, especially the cerebrum, the crown and goal
of vertebrate structure. The improvement is now practically
altogether in the animal organs of locomotion and thought. Still,
among these animal organs, the lower systems will lead in point of
time. The brain must to a certain extent wait for the skeleton.

1. The skeleton. The axial skeleton consists, in the lowest fish, of
the notochord, a cylindrical unsegmented rod of cartilage running
nearly the length of the body. This is surrounded by a sheath of
connective tissue, at first merely membranous, later becoming
cartilaginous or gristly. Pieces of cartilage extend upward over the
spinal marrow, and downward around the great aortic artery, forming
the neural and hæmal arches. These unite with the masses of
cartilage surrounding the notochord to form cartilaginous vertebræ,
which may be stiffened by an infiltration of carbonate of lime. The
vertebral column of sharks has reached this stage. Then the
cartilaginous vertebræ ossify and form a true backbone. I have
described the process as if it were very simple. But only the
student of comparative osteology can have any conception of the
number of experiments which were tried in different groups before
the definite mode of forming a bony vertebra was attained. At the
same time the skull was developing in a somewhat similar manner. But
the skull is far more complex in origin and undergoes far more
numerous and important changes than the simpler vertebral column.
Into its history we have no time to enter.

And what shall we say of bone itself as a mere material or tissue,
with its admirable lightness, compactness, and flawlessness. And
every bone in our body is a triumph of engineering architecture. No
engineer could better recognize the direction of strain and stress,
and arrange his rods and columns, arches and buttresses, to suitably
meet them, than these problems are solved in the long bone of our
thigh. And they must be lengthened while the child is leaping upon
them. An engineer is justly proud if he can rebuild or lengthen a
bridge without delaying the passage of a single train. But what
would he say if you asked him to rebuild a locomotive, while it was
running even twenty miles an hour? And yet a similar problem had to
be solved in our bodies.

But the vertebral column is not perfected by fish. The vertebræ with
few exceptions are hollow in front and behind, biconcave; and
between each two vertebræ there is a large cavity still occupied by
the notochord. Thus these vertebræ join one another by their edges,
like two shallow wine-glasses placed rim to rim. Only gradually is
the notochord crowded out so that the vertebræ join by their whole
adjacent surfaces. Even in highest forms, for the sake of mobility,
they are united by washer-like disks of cartilage. Biconcave
vertebræ persisted through the oldest amphibia, reptiles, and
birds. But finally a firm backbone and skull were attained.

2. The appendages. Of these we can say but little. The fish has
oar-like fins, attached to the body by a joint, but themselves
unjointed. By the amphibia legs, with the same regions as our own
and with five toes, have already appeared. The development of the
leg out of the fin is one of the most difficult and least understood
problems of vertebrate comparative anatomy. The legs are at first
weak and scarcely capable of supporting the body. Only gradually do
they strengthen into the fore- and hind-legs of mammals, or into the
legs and wings of birds and old flying reptiles.

3. Changes in the circulatory and respiratory systems. The fish
lives altogether in the water and breathes by gills, but the dipnoi
among fishes breathes by lungs as well as gills. As long as
respiration takes place by gills alone, the circulation is simple;
the blood flows from the heart to the gills, and thence directly all
over the body; the oxygenated blood from the gills does not return
directly to the heart. But the blood from the lungs does return to
the heart; and there at first mixes in the ventricle with the impure
blood which has returned from the rest of the body. Gradually a
partition arises in the ventricle, dividing it into a right and left
half. Thus the two circulations of the venous blood to the lungs,
and of the oxygenated blood over the body, are more and more
separated until, in higher reptiles, they become entirely distinct.

As the animal came on land and breathed the air, more completely
oxygenated blood was carried to the organs, and their activity was
greatly heightened. As more and more heat was produced by the
combustion in muscular and nervous tissues, and less was lost by
conduction, the temperature of the body rose, and in birds and
mammals becomes constant several degrees above the highest summer
temperature of the surrounding air.

The changes in the brain affect mainly the large and small brain.
The cerebellum increases with the greater locomotive powers of the
animal. But its development is evidently limited. The large brain,
or cerebrum, is in fish hardly as heavy as the mid-brain; in
amphibia the reverse is true. In higher recent reptiles the cerebrum
would somewhat outweigh all the other portions of the brain put
together. In mammals it extends upward and backward, has already in
lower forms overspread the mid-brain, and is beginning to cover the
small brain. But this was not so in the earliest mammals. Here the
cerebrum was small, more like that of reptiles. But during the
tertiary period the large brain began to increase with marvellous
rapidity. It was very late in arriving at the period of rapid
development, but it kept on after all the other organs of the body
had settled down into comparative rest, perhaps retrogression.

We have given thus a rapid sketch in outline of the changes in the
most characteristic systems between fish and mammals. Some of the
changes which took place in mammals were along the same lines, but
one at least is so new and unexpected that this highest class
demands more careful and detailed examination.

The mammal is a vertebrate. Hence all its organs are at their best.
But mammals stand, all things considered, at the head of
vertebrates. The skeleton is firm and compact. The muscles are
beautifully moulded and fitted to the skeleton so as to produce the
greatest effect with the least mass and weight of tissue. The
sense-organs are keen, and the eye and ear especially delicate, and
fitted for perception at long range. Yet in all these respects they
are surpassed by birds. As a mere anatomical machine the bird always
seems to me superior to the mammal. It is not easy to see why it
failed, as it has, to reach the goal of possibility of indefinite
development and dominance in the animal world. Why he stopped short
of the higher brain development I cannot tell. The fact remains that
the mammal is pre-eminent in brain power, and that this gave him the
supremacy.

But mammals came very late to the throne, and the probability of
their ever gaining it must for ages have appeared very doubtful.
They seem to have been a fairly old group with a very slow early
development. Reptiles especially, and even birds, were far more
precocious than these slower and weaker forms which crept along the
earth. But reptiles and birds, like many other precocious children,
soon reached the limit of their development. They had muscle, the
mammal brain and nerve; the mammal had the staying power and the
future. Bitter and discouraging must have been the struggle of these
feeble early mammals with their larger, swifter, and more powerful,
reptilian relatives. And yet, perhaps, by this very struggle the
mammal was trained to shrewdness and endurance.

The primitive mammals laid eggs like reptiles or birds. Only two
genera, echidna and platypus, survive to bear witness of these old
oviparous groups, and these only in New Zealand. These retain
several old reptilian characteristics. Their lower position is shown
also by the fact that the temperature of their bodies is, at least,
ten degrees Fahrenheit below that of higher mammals. One of these
carries the egg in a pouch on the ventral surface; the other, living
largely in water, deposits its eggs in a nest in a burrow in the
side of the bank of the stream.

After these came the marsupials. In these the eggs develop in a sort
of uterus; but there is no placenta, in the sense of an organic
connection between the embryo and the uterus of the mother. The
young are at birth exceedingly small and feeble. The adult giant
Kangaroo weighs over one hundred pounds; the young are at birth not
as large as your thumb. They are placed by the mother in a marsupial
pouch on her ventral surface, and here nourished till able to care
for themselves.

Pardon a moment's digression. The marsupials, except the opossum,
are confined to Australia, and the oviparous mammals, or monotremes,
to New Zealand. Formerly the marsupials, at least, ranged all over
Europe and Asia, for we have indisputable evidence in their fossil
remains. But they have survived only in this isolated area, and here
apparently only because their isolation preserved them from the
competition with higher forms. If the Australian continent had not
been thus early cut off from all the rest of the world, the only
trace of both these lower groups would have been the opossum in
America and certain peculiarities in the development of the egg in
higher mammals. This shows us how much weight should be assigned to
the formerly popular argument of the "missing links." The wonder is
not that so many links are missing, but that any of these primitive
forms have come down to us. For we see here another proof of the
fearful extermination of lower forms during the progress of life on
the globe. It seems as if the intermediate forms were less common
among these most recent animals than among the older types. This may
not be true, for it is not easy to compare the gap between two
mammals with that between two worms or insects, and mistakes are
very easily made. But it seems as if extermination had done its work
more ruthlessly among these highest forms than among their humbler
and lower ancestors. I would not lay much weight on such an opinion;
but, if true, it has a meaning and is worthy of study.

In higher, true, placental mammals the period of pregnancy is much
longer, and the young are born in a far higher stage of development,
or rather, growth. The stage of growth at which the young are born
differs markedly in different groups. A new-born kitten is a much
feebler, less developed being than a new-born calf. An embryonic
appendage, the allantois, used in reptiles and birds for
respiration, has here been turned to another purpose. It lays itself
against the walls of the uterus, uterine projections interlock with
those which it puts forth, and the blood of the mother circulates
through a host of capillaries separated from those of the blood
system of the embryo only by the thinnest membrane. This is the
placenta, developed, in part from the allantois of the embryo, in
part from the uterus of the mother. It is not a new organ, but an
old one turned to better and fuller use. In these closely
associated systems of blood-vessels, nutriment and oxygen diffuse
from the blood of the mother into that of the embryo, and thus rapid
growth is assured. The importance and far-reaching effect of this
new modification in the old reproductive system cannot be
over-estimated. The internal intra-uterine development of the young,
and the mammalian habit of suckling them, far more than any other
factors, have made man what he is. Some explanation must be sought
for such a fact.

We have already seen that any animal devotes to reproduction the
balance between income and expenditure of nutriment. Now, the
digestive system is here well developed, and the income is large.
But we have already noticed that, as animals grow larger, the ratio
between the digestive surface and the mass to be supported grows
continually smaller. On account of size alone the mammal has but a
small balance. But the amount of expenditure is proportional to the
mass and activity of the muscular and nervous systems. And the
mammal is, and from the beginning had to be, an exceedingly active,
energetic, and nervous animal. The income has increased, but the
expenses have far outrun the increase. The mammal can devote but
little to reproduction.

Moreover, it requires a large amount of material to form a mammalian
egg, such as that of the monotreme. It requires indefinitely more
nutriment to build a mammal than a worm, for the former is not only
larger and more perfect at birth; it is also vastly more
complicated. The embryonic journey has, so to speak, lengthened out
immensely. One monotreme egg represents more economy and saving than
a thousand eggs of a worm. Moreover, where the individuals are
longer lived and the generations follow one another at longer
intervals, the number of favorable variations and the possibility of
conformity to environment through these is greatly lessened. In such
a group it is of the utmost importance that every egg should
develop; the destruction of a single one is a real and important
loss to the species. It is not enough to produce such an egg; it
must be most scrupulously guarded. Even the egg of the platypus is
deposited in a nest in a hole in the bank, and the female Echidna
carries the egg in a marsupial pouch until it develops.

Notice further that among certain species of fish, amphibia, and
reptiles, the females carry the eggs in the body until the embryos
or young are fairly developed. Viviparous forms are unknown by
birds, probably because this mode of development is incompatible
with flight, their dominant characteristic. Putting these facts
together, what more probable than that certain primitive egg-laying
mammals should have carried the eggs as long as possible in the
uterus. The embryo under these conditions would be better nourished
by a secretion of the uterine glands than by a very large amount of
yolk. The yolk would diminish and the egg decrease in size, and thus
the marsupial mode of development would have resulted. And, given
the marsupial mode of development and an embryo possessing an
allantois, it is almost a physiological necessity that in some forms
at least a placenta should develop. That the placenta has resulted
from some such process of evolution is proven by its different
stages of development in different orders of mammals. And even the
feeblest attachment of the allantois of the embryo to the wall of
the uterus would be of the greatest advantage to the species.

This is not the whole explanation; other factors still undiscovered
were undoubtedly concerned. But even this shows us that the internal
development of the young and the habit of suckling them was a
logical result of mammalian structure and position. The grand
results of this change we shall trace farther on.

The changes from the lower true mammals to the apes are of great
interest, but we can notice only one or two of the more important.
The prosimii, or "half apes," including the lemurs, are nearly all
arboreal forms. Perhaps they were driven to this life by their more
powerful competitors. The arboreal life developed the fingers and
toes, and most of these end, not with a claw, but with a nail. The
little group has much diversity of structure, and at present finds
its home mainly in Madagascar; though in earlier times apparently
occurring all over the globe. The brain is more highly developed
than in the average mammal, but far inferior to that of the apes.
They have a fairly opposable thumb.

The highest mammals are the primates. Their characteristics are the
following: Fingers and toes all armed with nails, the eyes
comparatively near together and fully enclosed in a bony case. The
cerebrum with well-developed furrows covers the other portions of
the brain. There is but one pair of milk-glands, and these on the
breast. The differences between hand and foot become most strongly
marked by the "anthropoid" apes. These have become accustomed to an
upright gait in their climbing; hence the feet are used for
supporting the body and the hands for grasping. Both thumb and
great toe are opposable; but the foot is a true foot, and the hand a
true hand, in anatomical structure. The face, hands, and feet have
mainly lost the covering of hair. They have no tail, or rather its
rudiments are concealed beneath the skin. These include the gibbon,
the orang, the gorilla, and the chimpanzee.

We can sum up the few attainments of mammals in a line. The lower
forms attained the placental mode of embryonic development; the
higher attained upright gait, hands and feet, and a great increase
of brain. Anatomically considered these were but trifles, but the
addition of these trifles revolutionized life on the globe. The
principal anatomical differences between man and the anthropoid ape
are the following: Man is a strictly erect animal. The foot of the
ape is less fitted for walking on the ground, where he usually "goes
on all fours." The skull is almost balanced on the condyles by which
it articulates with the neck, and has but slight tendency to tip
forward. The facial portion, nose and jaws, is less developed and
retracted beneath the larger cranium or brain-case. This has greatly
changed the appearance of the head. Protruding jaws and chin, even
when combined with large cranium and brain, always give man the
appearance of brutality and low intelligence.

The pelvis is broad and comparatively shallow. The legs, especially
the thighs, are long. The foot is long and strong, and rests its
lower surface, not merely the outer margin as in apes, on the
ground. The elastic arch of the instep must be excepted in the above
description, and adds lightness and swiftness to his otherwise slow
gait. The great toe is short and generally not opposable. The
muscles of the leg are heavy and the knee-joint has a very broad
articulating surface. But the great result of man's erect posture is
that the hand is set free from the work of locomotion, and has
become a delicate tactile and tool-using organ. The importance of
this change we cannot over-estimate. The hand was the servant of the
brain for trying all experiments. Had not our arboreal ancestors
developed the hand for us we could never have invented tools nor
used them if invented. And its reflex influence in developing the
brain has been enormous. The arm is shorter and the hand smaller.
The brain is absolutely and relatively large, and its surface
greatly convoluted. This gives place for a large amount of "gray
matter," whose functions are perception, thought, and will. For this
gray matter forms a layer on the outside of the brain.

Thus, even anatomically, man differs from the anthropoid apes. His
whole structure is moulded to and by the higher mental powers, so
that he is the "Anthropos" of the old Greek philosophers, the being
who "turns his face upward." Yet in all these anatomical respects
some of the apes differ less from him than from the lower apes or
"half apes." And every one of these can easily be explained as the
result of progressive development and modification. Whoever will
deny the possibility or probability of man's development from some
lower form must argue on psychological, not on anatomical, grounds;
and it grows clearer every day that even the former but poorly
justify such a denial.

But it is interesting to note that no one ape most closely
approaches man in all anatomical respects. Thus among the
anthropoids the orang is perhaps most similar to man in cerebral
structure, the chimpanzee in form of skull, the gorilla in feet and
hands. No evolutionist would claim that any existing ape represents
the ancestor of man. The anthropoids represent very probably the
culmination of at least three distinct lines of development. But we
must remember that in early tertiary times apes occurred all over
Europe, and probably Asia, many degrees farther north than now. In
those days, as later, the fauna and flora of northern climates were
superior in vigor and height of development to that of Africa or
Australia. It is thus, to say the least, not at all improbable that
there existed in those times apes considerably, if not far, superior
to any surviving forms. Whether the palæontologist will find for us
remains of such anthropoids is still to be seen.

But you will naturally ask, "Is there not, after all, a vast
difference between the brain of man and that of the ape?" Let us
examine this question as fully as our very brief time will allow.
Considerable emphasis used to be laid on the facial angle between a
line drawn parallel to the base of the skull and one obliquely
vertical touching the teeth and most prominent portion of the
forehead. Now this angle is in man very large - from seventy-five to
eighty-five degrees, or even more, and rarely falling below
sixty-five degrees. But this angle depends largely on the protrusion
of the jaws, and varies greatly in species of animals showing much
the same grade of intelligence. In some not especially intelligent
South American monkeys the facial angle amounts to about sixty-five
degrees. In this respect the skull of a chimpanzee reminds us of a
human skull of small cranial capacity and large jaws, in which the
cranium has been pressed back and the jaws crowded forward and
slightly upward.

The weight of the brain in proportion to that of the body has been
considered as of great importance, and within certain limits this is
undoubtedly correct. Thus, according to Leuret, the weight of the
brain is to that of the whole body: In fish, 1:5,668; in reptiles,
1:1,320; in birds, 1:212; in mammals, 1:186. These figures give the
averages of large numbers of observations and have a certain
amount of value. But within the same class the ratio varies
extraordinarily. Thus the weight of the brain is to that of the
whole body: In the elephant, 1:500; in the largest dogs, 1:305; in
the cat, 1:156; in the rat, 1:76; in the chimpanzee, 1:50; in man,
1:36; in the field-mouse, 1:31; in the goldfinch, 1:24.

From this series it is evident that the relative weight of the brain
is no index of the intelligence of the animal. Indeed if the brain
were purely an organ of mind, there is no reason that it should be
any larger in an elephant than in a mouse, provided they had the
same mental capacity. As animals grow larger the weight of the
brain, relatively to that of the body, decreases, and considering
the size of man it is remarkable that it should form so large a
fraction of his weight. Still the fraction in the chimpanzee is not
so much smaller. It is still possible that this fraction is above
the normal for the chimpanzee, for some of the observations may have
been taken on animals which had died of consumption or some other
wasting disease. I have not been able to find whether this
possibility of error has been scrupulously avoided.

A fair idea of the size of the brain may be obtained by measuring
the cranial capacity. This varies in man from almost one-hundred
cubic inches to less than seventy. In the gorilla its average is
perhaps thirty, in the orang and chimpanzee rather less, about
twenty-eight. This is certainly a vast difference, especially when
we remember that the gorilla far exceeds man in weight.

Le Bon tells us that of a series of skulls forty-five per cent, of
the Australian had a cranial capacity of 1,200 to 1,300 c.c., while
46.7 per cent. of modern Parisian skulls showed a capacity of
between 1,500 and 1,600 c.c. The skull of the gorilla contains about
five hundred and seventy cubic centimetres. Broca found that the
cranial capacity of 115 Parisian skulls, of probably the higher
classes from the twelfth century, averaged about 1,426 cubic
centimetres, while ninety of those of the poorer classes of the
nineteenth century averaged about 1,484. His observations seemed to
prove that there has been a steady increase in Parisian cranial
capacity from the twelfth to the nineteenth century.

Turning to the actual weight of the brain, that of Cuvier weighed
64.5 ounces, and a few cases of weights exceeding 65 ounces have


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Online LibraryJohn Mason TylerThe Whence and the Whither of Man A Brief History of His Origin and Development through Conformity to Environment; Being the Morse Lectures of 1895 → online text (page 7 of 23)