Isreal Smith Clare.

Library of Universal history and popular science ... (Volume 20) online

. (page 11 of 60)
Online LibraryIsreal Smith ClareLibrary of Universal history and popular science ... (Volume 20) → online text (page 11 of 60)
Font size
QR-code for this ebook

types. Thus we have obtained the genealogical-trees of the deer, the
camel, the musk, the horse, tapir, and the rhinoceros; of the cats and
dogs, of the lemurs and monkeys, and have important evidence as to the
origin of man."


M. Gaudry, the celebrated discoverer of the fossil treasures of the
Upper Miocene of Pikermi, repeats the same thing. He says "If we
take a skeleton of a fossil mammalian species, and compare it with one
of an analogous living species" as for instance a Mammoth or Mastodon
with a modern elephant " placing the heads, vertebrae, humerus, radius,
femurs, feet, &c. , of the one, side by side with those of the other, the sum
of the likenesses will appear so much greater than that of the differences,
that the idea of family relationship will impose itself on the mind. In
vain would sceptics try to throw doubts on this relationship by pointing
out some slight shades of difference. We see too many points of re-
semblance to admit that they can be all fallacious. " And again he says,
" Where our predecessors saw ten or one hundred distinct beings, we see
only one ; and instead of creations thrown, as it were, into the world at
haphazard, without law and without connection, we follow the trace of a
few types whose essential characters are so similar as to enable us to com-
prehend them in still simpler types, and thus hope to arrive some day at
understanding the plan which God has followed in producing and devel-
oping life in the world."

This is almost identical with Bishop Temple's profession of faith ' ' that
it seems something more majestic, more befitting of Him to whom a
thousand years are as one day, thus to impress His will once for all on
His creation, and provide for all its countless varieties by this one origi-
nal impress, than by special acts of creation to be perpetually modifying
what He had previously made."

A clear popular conception of this question of "missing links" is so
important for all who desire to understand the latest conclusions of mod-
ern science, that it may be well to illustrate it by a homely example.
Fifty years ago, the popular belief respecting the animal creation was
summed up in the simple words of Dr. Watts' hymn:

" Let dogs delight to bark and bite,

For 'tis their nature to;
And bears and lions growl and fight,
For God has made them so."

Science could only shrug its shoulders and say, " So it seems ; I have no
better explanation to give."

How different are the terms in which science would now reply.
' ' Made, if you like, but how made ? As individuals, each from a cell not
distinguishable from any other microscopic cell of the lowest animal and
vegetable organisms, but endowed with such an impress of evolution that
it develops through the stages of fish, reptile, and mammal, into the
special mammalian form of its parents. As species, traceable through a
similar progression backwards from the living form, through intermediate
ancestral forms graduating by slight distinctions into one another, up to
the generalized Eocene type of the Placental mammal, and thence back-


wards by less definite but still traceable variations, to the types of the
marsupial, the reptilian, the fish, the vertebrate, and so up to the primi-
tive cell in which the individual living animal originated."

Thus the dog and bear, now so distinct, can be traced up to Amphi-
cyon and Hysenarctus, which combined the qualities of both ; the former
being rather more dog than bear, the latter rather more bear than dog ;
and these again, either through the Creodonta to the Bunodonta of the
early Eocene, or through the Ictitherium to the Cynodictis, or weasel-like
dog of the same formation, which is clearly a descendant of the insectivo-
rous Marsupials of the Secondary age.

The horse affords the best example of this progressive evolution, the
specialization from the generalized Eocene type of a five-toed and tuber-
cular toothed mammal being clearly traced, step by step, down to the
present one-toed horse. The evolution took the course of adapting the
original form to the requirements of an animal which had to live on wide
prairies or desert plains, where a bulky body had to be transported at
high speed, by leaps and bounds, over great distances, both to find food
and to escape from enemies by flight For this purpose, evidently, one
solid toe, protected by a single enlarged nail or hoof, was preferable to
five or three weak toes terminating each in a separate nail or claw; and in
like manner, teeth adapted for cutting and masticating grass were better
than the more millstone-like tubercular teeth adapted for grinding down
shrubs and branches of trees. Accordingly, we find the evolution of the
horse constantly following this line. In Europe, the Hipparion, who is
the immediate ancestor of the horse whom it closely resembles, has al-
ready the two lateral toes so rudimental as to have become wholly useless;
in the Anchitherium the tips of the outer toes just touch the ground,
while the Palaeotherium is a distinctly three-toed animal, though the mid-
dle toe is larger than the two side toes. We have thus a complete pro-
gression from a slow, heavy animal, adapted for living on marshy ground,
like the tapir, to the courser of the plains, whose latest development,
under artificial selection, is seen in an Ormonde or a Donovan.

In America the links in the pedigree of the fossil horse are still more
numerous, and the transitions closer. The line begins in the Early Eo-
cene with the Eohippus, an animal of the size of a fox, which in addition
to four well-developed toes of the forefoot, had the remnants of the hoofed
fifth toe. In the Upper Eocene, the Eohippus was replaced by the
Orohippus, in which the rudimentary first digit had disappeared, and
the fifth was reduced to a splint. In the Lower Miocene the Mesohippus,
which was about as large as a sheep, had only three toes with a rudi-
mentary splint on the foreleg, and in its teeth and other particulars ap-
proached more closely to the horse. In the Upper Miocene, Mesohippus
is replaced by Miohippus, which approaches closely to the Anchitherium
of Europe ; while in the Lower Pliocene this gives way to the Protohip-
pus, which approached the horse very closely, and was about the size of


an ass. Like the Hipparion of Europe, which in many respects ix re-
sembles, it had three toes, of which only the middle one reached the
ground. In the Middle Pliocene we have the Pliohippus, which has lost
the small hooflets on the rudimentary toes, and is in all respects very like
a horse ; and finally in the Upper Pliocene we have the true horse.
This progression gives rise to two important remarks. First, that size
cannot be accepted as of much importance in tracing lines of descent, as
might indeed have been anticipated from the wide variations in the size
of dogs and other domestic animals introduced by artificial selection.
Secondly, that the extinction of wide-spread and apparently unexhausted
races of animals is a fact which has to be reckoned with. The total dis-
appearance of the horse in America, where it and its ancestors had ex-
isted in such numbers from the Early Eocene down to quite recent times,
is a most perplexing problem. There is no appearance of any great
change of environment since the horse roamed in countless numbers over
the continent of America, and we know from the experience of Europe
that it was a hardy animal, capable of resisting both the torrid heat of
Arabia, and the intense cold of the Glacial period. And so many other
species survived in America, from the Pliocene to the Quaternary and
recent periods, as to show that the extinction of the horse was an isolated
phenomenon. And as of extinction, so of creation. We do not fully
understand the exact process by which types and species have either
appeared or disappeared, and this affords the only ground left to those
who, from theological or other prepossessions, are hostile to Darwinism.
They say his theory of natural selection from spontaneous variations does
not account for everything, and does not explain fully all the laws of
these variations. This may be partly true, but it in no way affects the
truth of evolution, which is a fact and not a theory, and is quite inde-
pendent of the subsidiary question, whether natural selection can account
for all, or only for a principal part of the facts which, in some way or
other, have to be accounted for. Thus, whether the long neck of the
giraffe was developed by natural selection taking advantage of accidental
variations in this direction, or partly by this and partly by heredity fixing
variations induced by use and disuse of organs in stretching to reach the
branches of palms, in no way affects the question whether the animal is a
product of evolution or a miraculous creation.

To return to the pedigree of the horse, which may be taken as the
typical instance of descent traced by progressive specialization. What is
a horse ? It is essentially an animal specialized for a particular object,
that of the rapid progression of a bulky body over open plains or deserts.
When mammalian life first appears abundantly in the lower Tertiaries, it
is in the primitive generalized type, in which nature seems always to make
its first essays, as if it were trying its 'prentice hand on a simple sketch,
to be gradually developed into a series of finished pictures. The primitive
sketch in this instance took the form of what Professor Cope calls a


" pentadactyle, plantigrade, bunodont," by which formidable collocation
of words we are to understand an animal which had five toes at the ex-
tremities of each of its limbs ; which walked on the flat of its feet, and
whose molar teeth presented a flat surface, with four, or in the very earli-
est form, three little cones or tubercles, to assist in grinding its food. It
may give some idea of the precision and certainty to which such re-
searches have attained, to say that this primitive form was predicted by
Professor Cope in 1874, from the progress towards it traced in following
backwards various lines of later descent; and that seven years later, in
1 88 1, the prophecy was fulfilled by the discovery that such a type of mam-
mals, now known as the Condylarthra, actually existed in large numbers in
North America, in the early Eocene period.

Consider now what the specialization from this original type to the
horse implied. The first step was to walking on the toes instead of on
the flat of the foot, a change which, whether owing or not to the lady
Condylartha having adopted the modern fashion of wearing high-heeled
boots, became general in most lines of their descendants. For galloping
on hard ground it is evident that one strong and long toe, protected by a
solid hoof, was more serviceable than four short and weak toes, protected
by separate nails. Accordingly, coalescence of the toes is the funda-
mental fact in the progress of structural changes through successive
species, by which the primitive Bunodont was converted into the modern
horse. Corresponding with this are other progressive changes in the
articulation of the joints, especially those of the bones corresponding to
the ankle and wrist joints, which are modified from a contact of plane
surfaces into a system of tongues and grooves, which give freedom of
action in direct progression, but secure them against the dislocations from
shocks and strains, to which they would be exposed in galloping or
jumping. So in other types the specialization takes different forms, but
always towards the sharper distinction of species formerly more united and
generalized. Thus the half-bear, half-dog, and half-cat original type of
the Eocene, becomes differentiated into the three distinct types of the
wholly bear, dog, and cat of later formations.

Nor is this tracing back of existing mammalian species to ancestral
forms in the Early Tertiary all that recent science has accomplished. The
course of geological discovery for the last twenty, and specially for the
last ten years, may almost be summed up as that of the discovery of
' ' missing links, " until gap after gap, which seemed to separate not only
species, but genera and orders, by insurmountable barriers, has been
bridged over by intermediate forms. Thus to take one of the most strik-
ing instances What can, at first sight, appear more unlike than reptile
and bird, and who would have ventured to predict that any relationship
could be traced between a tortoise and a swallow ? And yet nothing is
more certain than that the Reptilia pass over into the Aves, by successive
gradations, which make it difficult to pronounce where one ends and the


other begins. The pterodactyle, or flying dragon of the lias, approaches
in structure and habits towards the bird type; the ostrich retains some re-
semblance to the pterodactyle, but the complete transitional type, or " miss-
ing link," has been found in those feathered reptiles, or birds with reptilian
heads and teeth, whose remains have fortunately been preserved in a fossil
state. The Archaeopteryx, from the CEningen slate of the Upper Oolite,
in the museum of South Kensington, is a beautiful specimen of such a
missing link, and would certainly be taken for a bird by any casual ob-
server, though comparative anatomists find many of its essential features
to be reptilian.

The Archaeopteryx and other transitional types which have been dis-
covered in Europe and America between birds and reptiles, afford perhaps
the most obvious and universally intelligible instances of what recent
geology has done in the way of the discovery of " missing links," between
genera and orders now widely separated; but similar discoveries have gone
a long way towards establishing the continuity of life from the earliest
periods in which it appears, down to the present day, and showing the
kind and progress of the changes in structure, which, in the course of
evolution, have linked the various orders and species of living forms
together. Thus the higher form of Placental mammals which became
predominant in the Early Tertiary, differs from the Marsupials, which
extend into the trias of the Secondary period, by the greater extension of
the allantoid or membrane which surrounds the foetus. In the Placentals
this completely surrounds it, so that the foetus remains part of the mother
until birth; while in the Marsupial the young are born incomplete, and
take refuge for a time in a pouch which is attached to the mother's
stomach. But there are fossil animals in the Eocene which combine the
two characters, showing a Marsupial brain and dentition, with a Placental
development. They are, in effect, Marsupials in which the allantoid,
instead of being arrested at an early stage, has continued to grow.

Again, the Marsupials are linked on to still lower forms of animal life
through the Monotremata, of which a few specimens survive in Australia,
typified by the Ornithorynchus, or water-mole, which has the bill of a
duck, and lays eggs. This order has only one opening, called the cloaca,
for the purposes which, in higher orders, are performed by separate or-
gans, and it is remarkable that this stage is passed through by man and
the higher mammals in the course of their embryonic development

Going still further back, the lines of demarcation between orders are,
as in the case of birds and reptiles, more and more broken down every
day by the discovery of intermediate forms, and we can almost trace the
evolution from the Ascidian or lowest vertebrate type into the fish, the
amphibia, the reptile, and so upwards. And it is remarkable that this
course of evolution invariably corresponds with the general progressive
evolution of types through geological ages, and with the embryonic evo-
lution of individual life from the primitive cell. It is not too much,


therefore, to assume evolution to be the demonstrated law of the world of
life as well as of that of matter, and to confine ourselves to the question
whether man is or is not a solitary exception to this law.

We are now in a position to examine more closely the bearings of this
question of missing "links" on that of human origins. Geologically
speaking, man is one of the order of Primates, which includes also the
catarrhine apes and monkeys of the Old World, the platyrhine apes and
monkeys of America, and the lemurs or half-monkeys which are found
principally in Madagascar and a few districts of continental and insular
Asia and Africa. Of these, the anthropoid apes the chimpanzee, gorilla,
and orang approach most closely to man in their structure.

In fact, considered as mere machines, the resemblance between them
and man is something wonderful. It is much closer than is suggested by
a mere comparison of outward forms. One must have read the results
arrived at by the most distinguished comparative anatomists, to under-
stand how close is the identity. Not merely does every bone, every
muscle, and every nerve in the one, find its analogue more or less de-
veloped in the other, but even in such minute particulars as the direction
of the hairs on the forearm converging towards the elbow, there is an ab-
solute correspondence.

It is in the brain, however, which is the most important organ, as
being that on which the specially human faculty of intelligence depends,
that the close physical resemblance between man and the other quadru-
mana is most striking. The brain of all quadrumanous animals is dis-
tinguished from that of quadrupeds by certain well-defined characters.
Those of lemurs, monkeys, baboons, and apes, show a progression of
these characters from the lemurs, whose brain differs little from that of
rodents, up to the anthropoid apes, the chimpanzee, the gorilla, and the
orang, who have a brain which in its most essential particulars closely
resembles that of man. In fact, the brain of these apes bridges over
much more than half the interval between the simplest quadrumanous
form of the lemur and the most advanced that of man ; while in like
manner the brains of some of the inferior races of mankind, and of idiots,
where the development of the brain has been arrested, bridge over the
interval between man and ape, and in some extreme cases approach
more nearly to the latter than to the former type both in size and struc-

Attempt after attempt has been made to find some fundamental char-
acters in the human brain on which to base a generic distinction between
man and the brute creation, but such attempts have invariably broken
down under a close investigation. Thus, in the celebrated controversy
between Owen and Huxley, the former distinguished anatomist thought
that he had found such a distinction in the hinder part of the human
brain, but it turned out that he had been misled by relying on the plates
in the work of the Dutch anatomists Camper and Vrolik ; and Huxley.,


confirmed by them, proved by actual dissection that all the characters on
which Owen relied were to be found equally in the brain of the chimpan-
zee and other higher quadrumana.

The distinction also on which the very term quadrumana is founded
is proved to be fallacious, for Huxley has shown that the termination of
the hinder limbs of the anthropoids is really a foot with a prehensile great
toe, and not a hand, and there are many instances, both of human indi-
viduals and races, in which this toe has considerable flexibility, and is
used in climbing trees or picking up small objects. And so in innumera-
ble other cases in which anatomical observations, supposed to be speci-
fically human, have either been found wanting in some individual men,
and present in some individual quadrumana, or have been traced in both
in some undeveloped or faetal condition.

And yet with this close identity of anatomical conditions there is, as
Huxley emphatically asserts, a wide gap between man and the highest
ape, which has never been bridged over, and which precludes the idea of
direct lineal descent from one to the other, though it implies close rela-
tionship. The differences are partly physical and partly intellectual
Of the former, it may be said that they may be all summed up in the fact
that man is specialized for erect posture.

Speaking broadly, it may be said that man is a member of the order
of Primates, specialized for erect posture ; while monkeys are specialized
for climbing trees, and anthropoid apes are a sort of intermediate link,
specialized mainly for forest life, but with a certain amount of capability
for walking erect and on the ground.

Thus, to begin at the foundation of the human structure, the foot,
with its solid heel bone, arch of the instep, and short toes, is obviously
better adapted for walking and worse for climbing than that of monkeys.
The upright basis of the foot corresponds with longer, stronger, and
straighter bones of the leg, and a greater development of muscles to move
them. The erect posture determines the shape of the pelvis and haunch
bones, which have to support the weight of the vertebral column and in-
testines in a vertical direction. The vertebral column, again, is arranged
with a slight double curvature, so as to enable the body to maintain an
upright posture, and to afford a vertical support for the head. And final-
ly, the larger brain is rendered possible by its weight being nicely bal-
anced on a vertical column, instead of hanging down and being supported
by powerful muscles requiring strong processes for lateral attachment in
the vertebrae of the neck.

Again, the fore-limbs being entirely relieved from the necessity of be-
ing used as supports, acquire the marvellous flexibility and adaptability
of the human arm and hand; a specialization which has doubtless a good
deal to do with man's superior intelligence, for as we see in the case of
the elephant, the intelligence of an animal depends not merely on the
mass of the brain, but very much on the nature of the organs by which it


is placed in relation with the surrounding environment In this respect

there is no animal organ comparable to the human hand, and we may
probably trace its influence in other divergencies of the human from the
bestial type. Thus, the greater development of the jaws and bones of the
face in animals, giving rise to a projecting muzzle, is no longer requisite
when the arm and hand afford so much better an instrument than the
mouth for seizing objects, and for attack or defence; while from the same
cause the canine teeth tend to diminish. In fact, the specialization of
improved types from the early generalized type, takes very often the form
of a reduction of the number of teeth to that required for the relations of
the new types to their environment Thus, in the pure carnivora, like
the cats, the molars disappear and the canines and sectorial premolars
assume a great development. In the Herbivora, on the other hand, the
molars are developed at the expense of the flesh-cutting teeth; and in civ-
ilized man there is a progressive diminution in the size of the jaws, which
hardly leaves room for the normal number of teeth, some of which are
probably destined to disappear, as the so-called wisdom-teeth have already
almost done.

Thus, from the single point of view of specialization for erect posture
we arrive at all the physical characteristics which distinguish man from the
monkeys and anthropoid apes. At the same time, it is a difference only
of adaptation and not of essense. The machine man differs from the
machine ape, much as the modern railway locomotive differs from the
old-fashoned pumping steam-engine. The essential parts, boiler, pistons,
cylinders, valves, are the same, but differently modified; those of the
locomotive being vastly better adapted for condensed energy and rapid
motion in a smaller compass. Still, no one can doubt their affinity and
common origin, or suppose that while the Newcomen engine owed its
existence to human invention, the Wild Irishman or Flying Scotchman
could only be accounted for by invoking supernatural agency.

This is precisely the case as regards man in his physical aspect It is
difficult to imagine that the combination of bones, muscles, and nerves,
which make a man, originated in any different manner than did the com-
bination of the same identical bones, muscles, and nerves, which make a
chimpanzee or gorilla. If one originated by evolution, the other must

Online LibraryIsreal Smith ClareLibrary of Universal history and popular science ... (Volume 20) → online text (page 11 of 60)