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Descent of Man [ 1871]

Charles Darwin [ 1809 - 1882 ]

 

Part One: Descent or Origin of Man

Chapter I - The Evidence of the Descent of Man from some Lower Form


  HE WHO wishes to decide whether man is the modified descendant of
some pre-existing form, would probably first enquire whether man
varies, however slightly, in bodily structure and in mental faculties;
and if so, whether the variations are transmitted to his offspring
in accordance with the laws which prevail with the lower animals.
Again, are the variations the result, as far as our ignorance
permits us to judge, of the same general causes, and are they governed
by the same general laws, as in the case of other organisms; for
instance, by correlation, the inherited effects of use and disuse,
&c.? Is man subject to similar malconformations, the result of
arrested development, of reduplication of parts, &c., and does he
display in any of his anomalies reversion to some former and ancient
type of structure? It might also naturally be enquired whether man,
like so many other animals, has given rise to varieties and sub-races,
differing but slightly from each other, or to races differing so
much that they must be classed as doubtful species? How are such races
distributed over the world; and how, when crossed, do they react on
each other in the first and succeeding generations? And so with many
other points.
  The enquirer would next come to the important point, whether man
tends to increase at so rapid a rate, as to lead to occasional
severe struggles for existence; and consequently to beneficial
variations, whether in body or mind, being preserved, and injurious
ones eliminated. Do the races or species of men, whichever term may be
applied, encroach on and replace one another, so that some finally
become extinct? We shall see that all these questions, as indeed is
obvious in respect to most of them, must be answered in the
affirmative, in the same manner as with the lower animals. But the
several considerations just referred to may be conveniently deferred
for a time: and we will first see how far the bodily structure of
man shows traces, more or less plain, of his descent from some lower
form. In succeeding chapters the mental powers of man, in comparison
with those of the lower animals, will be considered.
  The Bodily Structure of Man. It is notorious that man is constructed
on the same general type or model as other mammals. All the bones in
his skeleton can be compared with corresponding bones in a monkey,
bat, or seal. So it is with his muscles, nerves, blood-vessels and
internal viscera. The brain, the most important of all the organs,
follows the same law, as shewn by Huxley and other anatomists.
Bischoff,* who is a hostile witness, admits that every chief fissure
and fold in the brain of man has its analogy in that of the orang; but
he adds that at no period of development do their brains perfectly
agree; nor could perfect agreement be expected, for otherwise their
mental powers would have been the same. Vulpian*(2) remarks: "Les
differences reelles qui existent entre l'encephale de l'homme et celui
des singes superieurs, sont bien minimes. It ne faut pas se faire
d'illusions a cet egard. L'homme est bien plus pres des singes
anthropomorphes par les caracteres anatomiques de son cerveau que
ceux-ci ne le sont non seulement des autres mammiferes, mais meme de
certains quadrumanes, des guenons et des macaques." But it would be
superfluous here to give further details on the correspondence between
man and the higher mammals in the structure of the brain and all other
parts of the body.

  * Grosshirnwindungen des Menschen, 1868, s. 96. The conclusions of
this author, as well as those of Gratiolet and Aeby, concerning the
brain, will be discussed by Prof. Huxley in the appendix.
  *(2) Lec. sur la Phys., 1866, p. 890, as quoted by M. Dally, L'Ordre
des Primates et le Transformisme, 1868, p. 29.

  It may, however, be worth while to specify a few points, not
directly or obviously connected with structure, by which this
correspondence or relationship is well shewn.
  Man is liable to receive from the lower animals, and to
communicate to them, certain diseases, as hydrophobia, variola, the
glanders, syphilis, cholera, herpes, &c.;* and this fact proves the
close similarity*(2) of their tissues and blood, both in minute
structure and composition, far more plainly than does their comparison
under the best microscope, or by the aid of the best chemical
analysis. Monkeys are liable to many of the same non-contagious
diseases as we are; thus Rengger,*(3) who carefully observed for a
long time the Cebus azarae in its native land, found it liable to
catarrh, with the usual symptoms, and which, when often recurrent, led
to consumption. These monkeys suffered also from apoplexy,
inflammation of the bowels, and cataract in the eye.The younger ones
when shedding their milk-teeth often died from fever. Medicines
produced the same effect on them as on us. Many kinds of monkeys
have a strong taste for tea, coffee, and spirituous liquors: they will
also, as I have myself seen, smoke tobacco with pleasure.*(4) Brehm
asserts that the natives of north-eastern Africa catch the wild
baboons by exposing vessels with strong beer, by which they are made
drunk. He has seen some of these animals, which he kept in
confinement, in this state; and he gives a laughable account of
their behaviour and strange grimaces. On the following morning they
were very cross and dismal; they held their aching heads with both
hands, and wore a most pitiable expression: when beer or wine was
offered them, they turned away with disgust, but relished the juice of
lemons.*(5) An American monkey, an Ateles, after getting drunk on
brandy, would never touch it again, and thus was wiser than many
men. These trifling facts prove how similar the nerves of taste must
be in monkeys and man, and how similarly their whole nervous system is
affected.

  * Dr. W. Lauder Lindsay has treated this subject at some length in
the Journal of Mental Science, July, 1871: and in the Edinburgh
Veterinary Review, July, 1858.
  *(2) A reviewer has criticised (British Quarterly Review, Oct. 1,
1871, p. 472) what I have here said with much severity and contempt:
but as I do not use the term identity, I cannot see that I am
greatly in error. There appears to me a strong analogy between the
same infection or contagion producing the same result, or one
closely similar, in two distinct animals, and the testing of two
distinct fluids by the same chemical reagent.
  *(3) Naturgeschichte der Saugethiere von Paraguay, 1830, s. 50.
  *(4) The same tests are common to some animals much lower in the
scale. Mr. A. Nicols informs me that he kept in Queensland, in
Australia, three individuals of the Phaseolarctus cinereus, and
that, without having been taught in any way, they acquired a strong
taste for rum, and for smoking tobacco.
  *(5) Brehm, Illustriertes Thierleben, B. i., 1864, 75, 86. On the
Ateles, s. 105. For other analogous statements, see ss. 25, 107.

  Man is infested with internal parasites, sometimes causing fatal
effects; and is plagued by external parasites, all of which belong
to the same genera or families as those infesting other mammals, and
in the case of scabies to the same species.* Man is subject, like
other mammals, birds, and even insects,*(2) to that mysterious law,
which causes certain normal processes, such as gestation, as well as
the maturation and duration of various diseases, to follow lunar
periods. His wounds are repaired by the same process of healing; and
the stumps left after the amputation of his limbs, especially during
an early embryonic period, occasionally possess some power of
regeneration, as in the lowest animals.*(3)

  * Dr. W. Lauder Lindsay, Edinburgh Veterinary Review, July, 1858, p.
13.
  *(2) With respect to insects see Dr. Laycock, "On a General Law of
Vital Periodicity," British Association, 1842. Dr. Macculloch,
Silliman's North American Journal of Science, vol. xvii., p. 305,
has seen a dog suffering from tertian ague. Hereafter I shall return
to this subject.
  *(3) I have given the evidence on this head in my Variation of
Animals and Plants under Domestication, vol. ii., p. 15, and more
could be added.

  The whole process of that most important function, the
reproduction of the species, is strikingly the same in all mammals,
from the first act of courtship by the male,* to the birth and
nurturing of the young. Monkeys are born in almost as helpless a
condition as our own infants; and in certain genera the young differ
fully as much in appearance from the adults, as do our children from
their full-grown parents.*(2) It has been urged by some writers, as an
important distinction, that with man the young arrive at maturity at a
much later age than with any other animal: but if we look to the races
of mankind which inhabit tropical countries the difference is not
great, for the orang is believed not to be adult till the age of
from ten to fifteen years.*(3) Man differs from woman in size,
bodily strength, hairiness, &c., as well as in mind, in the same
manner as do the two sexes of many mammals. So that the correspondence
in general structure, in the minute structure of the tissues, in
chemical composition and in constitution, between man and the higher
animals, especially the anthropomorphous apes, is extremely close.

  * Mares e diversis generibus Quadrumanorum sine dubio dignoscunt
feminas humanas a maribus. Primum, credo, odoratu, postea aspectu. Mr.
Youatt, qui diu in Hortis Zoologicis (Bestiariis) medicus animalium
erat, vir in rebus observandis cautus et sagax, hoc mihi certissime
probavit, et curatores ejusdem loci et alii e ministirs
confirmaverunt. Sir Andrew Smith et Brehm notabant idem in
Cynocephalo. Illustrissimus Cuvier etiam narrat multa de hac re, qua
ut opinor, nihil turpius potest indicari inter omnia hominibus et
Quadrumanis communia. Narrat enim Cynocephalum quendam in furorem
incidere aspectu feminarum aliquarem, sed nequaquam accendi tanto
furore ab omnibus. Semper eligebat juniores, et dignoscebat in
turba, et advocabat voce gestuque.
  *(2) This remark is made with respect to Cynocephalus and the
anthropomorphous apes by Geoffroy Saint-Hilaire and F. Cuvier,
Histoire Nat. des Mammiferes, tom. i., 1824.
  *(3) Huxley, Man's Place in Nature, 1863, p. 34.

  Embryonic Development. Man is developed from an ovule, about the
125th of an inch in diameter, which differs in no respect from the
ovules of other animals. The embryo itself at a very early period
can hardly be distinguished from that of other members of the
vertebrate kingdom. At this period the arteries run in arch-like
branches, as if to carry the blood to branchiae which are not
present in the higher Vertebrata, though the slits on the sides of the
neck still remain (see f, g, fig. 1), marking their former position.
At a somewhat later period, when the extremities are developed, "the
feet of lizards and mammals," as the illustrious von Baer remarks,
"the wings and feet of birds, no less than the hands and feet of
man, all arise from the same fundamental form." It is, says Prof.
Huxley,* "quite in the later stages of development that the young
human being presents marked differences from the young ape, while
the latter departs as much from the dog in its developments, as the
man does. Startling as this last assertion may appear to be, it is
demonstrably true."

  * Man's Place in Nature, 1863, p. 67.

  As some of my readers may never have seen a drawing of an embryo,
I have given one of man and another of a dog, at about the same
early stage of development, carefully copied from two works of
undoubted accuracy.*

  * The human embryo (see upper fig.) is from Ecker, Icones Phys.,
1851-1859, tab. xxx., fig. 2. The drawing of this embryo is much
magnified. The embryo of the dog is from Bischoff,
Entwicklungsgeschichte des Hunde-Eies, 1845, tab. xi., fig. 42 B. This
drawing is magnified, the embryo being twenty-five days old. The
internal viscera have been omitted, and the uterine appendages in both
drawings removed. I was directed to these figures by Prof. Huxley,
from whose work, Man's Place in Nature, the idea of giving them was
taken. Haeckel has also given analogous drawings in his
Schopfungsgeschichte.

  After the foregoing statements made by such high authorities, it
would be superfluous on my part to give a number of borrowed
details, shewing that the embryo of man closely resembles that of
other mammals. It may, however, be added, that the human embryo
likewise resembles certain low forms when adult in various points of
structure. For instance, the heart at first exists as a simple
pulsating vessel; the excreta are voided through a cloacal passage;
and the os coccyx projects like a true extending considerably beyond
the rudimentary legs."* In the embryos of all air-breathing
vertebrates, certain glands, called the corpora Wolffiana,
correspond with, and act like the kidneys of mature fishes.*(2) Even
at a later embryonic period, some striking resemblances between man
and the lower animals may be observed. Bischoff says "that the
convolutions of the brain in a human foetus at the end of the
seventh month reach about the same stage of development as in a baboon
when adult."*(3) The great toe, as Professor Owen remarks,*(4)
"which forms the fulcrum when standing or walking, is perhaps the most
characteristic peculiarity in the human structure"; but in an
embryo, about an inch in length, Prof. Wyman*(5) found "that the great
toe was shorter than the others; and, instead of being parallel to
them, projected at an angle from the side of the foot, thus
corresponding with the permanent condition of this part in the
Quadrumana." I will conclude with a quotation from Huxley,*(6) who,
after asking does man originate in a different way from a dog, bird,
frog or fish, says, "The reply is not doubtful for a moment; without
question, the mode of origin, and the early stages of the
development of man, are identical with those of the animals
immediately below him in the scale: without a doubt in these respects,
he is far nearer to apes than the apes are to the dog."

  * Prof. Wyman in Proceedings of the American Academy of Sciences,
vol. iv., 1860, p. 17.
  *(2) Owen, Anatomy of Vertebrates, vol. i., p. 533.
  *(3) Die Grosshirnwindungen des Menschen 1868, s. 95.
  *(4) Anatomy of Vertebrates, vol. ii., p. 553.
  *(5) Proc. Soc. Nat. Hist., Boston, 1863, vol. ix., p. 185.
  *(6) Man's Place in Nature, p. 65.

  Rudiments. This subject, though not intrinsically more important
than the two last, will for several reasons be treated here more
fully.* Not one of the higher animals can be named which does not bear
some part in a rudimentary condition; and man forms no exception to
the rule. Rudimentary organs must be distinguished from those that are
nascent; though in some cases the distinction is not easy. The
former are either absolutely useless, such as the mammee of male
quadrupeds, or the incisor teeth of ruminants which never cut
through the gums; or they are of such slight service to their
present possessors, that we can hardly suppose that they were
developed under the conditions which now exist. Organs in this
latter state are not strictly rudimentary, but they are tending in
this direction. Nascent organs, on the other hand, though not fully
developed, are of high service to their possessors, and are capable of
further development. Rudimentary organs are eminently variable; and
this is partly intelligible, as they are useless, or nearly useless,
and consequently are no longer subjected to natural selection. They
often become wholly suppressed. When this occurs, they are
nevertheless liable to occasional reappearance through reversion- a
circumstance well worthy of attention.

  * I had written a rough copy of this chapter before reading a
valuable paper, "Caratteri rudimentali in ordine all' origine dell'
uomo" (Annuario della Soc. d. Naturalisti, Modena, 1867, p. 81), by G.
Canestrini, to which paper I am considerably indebted. Haeckel has
given admirable discussions on this whole subject, under the title
of "Dysteleology," in his Generelle Morphologie and
Shopfungsgeschichte.

  The chief agents in causing organs to become rudimentary seem to
have been disuse at that period of life when the organ is chiefly used
(and this is generally during maturity), and also inheritance at a
corresponding period of life. The term "disuse" does not relate merely
to the lessened action of muscles, but includes a diminished flow of
blood to a part or organ, from being subjected to fewer alternations
of pressure, or from becoming in any way less habitually active.
Rudiments, however, may occur in one sex of those parts which are
normally present in the other sex; and such rudiments, as we shall
hereafter see, have often originated in a way distinct from those here
referred to. In some cases, organs have been reduced by means of
natural selection, from having become injurious to the species under
changed habits of life. The process of reduction is probably often
aided through the two principles of compensation and economy of
growth; but the later stages of reduction, after disuse has done all
that can fairly be attributed to it, and when the saving to be
effected by the economy of growth would be very small,* are
difficult to understand. The final and complete suppression of a part,
already useless and much reduced in size, in which case neither
compensation or economy can come into play, is perhaps intelligible by
the aid of the hypothesis of pangenesis. But as the whole subject of
rudimentary organs has been discussed and illustrated in my former
works,*(2) I need here say no more on this head.

  * Some good criticisms on this subject have been given by Messrs.
Murie and Mivart, in Transactions, Zoological Society, 1869, vol.
vii., p. 92.
  *(2) Variation of Animals and Plants under Domestication, vol. ii
pp. 317 and 397. See also Origin of Species.(OOS)

  Rudiments of various muscles have been observed in many parts of the
human body;* and not a few muscles, which are regularly present in
some of the lower animals can occasionally be detected in man in a
greatly reduced condition. Every one must have noticed the power which
many animals, especially horses, possess of moving or twitching
their skin; and this is effected by the panniculus carnosus.
Remnants of this muscle in an efficient state are found in various
parts of our bodies; for instance, the muscle on the forehead, by
which the eyebrows are raised. The platysma myoides, which is well
developed on the neck, belongs to this system. Prof. Turner, of
Edinburgh, has occasionally detected, as he informs me, muscular
fasciculi in five different situations, namely in the axillae, near
the scapulae, &c., all of which must be referred to the system of
the panniculus. He has also shewn*(2) that the musculus sternalis or
sternalis brutorum, which is not an extension of the rectus
abdominalis, but is closely allied to the panniculus, occurred in
the proportion of about three per cent. in upward of 600 bodies: he
adds, that this muscle affords "an excellent illustration of the
statement that occasional and rudimentary structures are especially
liable to variation in arrangement."

  * For instance, M. Richard (Annales des Sciences Nat., 3d series,
Zoolog., 1852, tom. xviii., p. 13) describes and figures rudiments
of what he calls the "muscle pedieux de la main," which he says is
sometimes "infiniment petit." Another muscle, called "le tibial
posterieur," is generally quite absent in the hand, but appears from
time to time in a more or less rudimentary condition.
  *(2) Prof. W. Turner, Proceedings of the Royal Society of Edinburgh,
1866-67, p. 65.

  Some few persons have the power of contracting the superficial
muscles on their scalps; and these muscles are in a variable and
partially rudimentary condition. M.A. de Candolle has communicated
to me a curious instance of the long-continued persistence or
inheritance of this power, as well as of its unusual development. He
knows a family, in which one member, the present head of the family,
could, when a youth, pitch several heavy books from his head by the
movement of the scalp alone; and he won wagers by performing this
feat. His father, uncle, grandfather, and his three children possess
the same power to the same unusual degree. This family became
divided eight generations ago into two branches; so that the head of
the above-mentioned branch is cousin in the seventh degree to the head
of the other branch. This distant cousin resides in another part of
France; and on being asked whether he possessed the same faculty,
immediately exhibited his power. This case offers a good
illustration how persistent may be the transmission of an absolutely
useless faculty, probably derived from our remote semi-human
progenitors; since many monkeys have, and frequently use the power, of
largely moving their scalps up and down.*

  * See my Expression of the Emotions in Man and Animals, 1872, p.
144.

  The extrinsic muscles which serve to move the external ear, and
the intrinsic muscles which move the different parts, are in a
rudimentary condition in man, and they all belong to the system of the
panniculus; they are also variable in development, or at least in
function. I have seen one man who could draw the whole ear forwards;
other men can draw it upwards; another who could draw it backwards;*
and from what one of these persons told me, it is probable that most
of us, by often touching our ears, and thus directing our attention
towards them, could recover some power of movement by repeated trials.
The power of erecting and directing the shell of the ears to the
various points of the compass, is no doubt of the highest service to
many animals, as they thus perceive the direction of danger; but I
have never heard, on sufficient evidence, of a man who possessed
this power, the one which might be of use to him. The whole external
shell may be considered a rudiment, together with the various folds
and prominences (helix and anti-helix, tragus and anti-tragus, &c.)
which in the lower animals strengthen and support the ear when
erect, without adding much to its weight. Some authors, however,
suppose that the cartilage of the shell serves to transmit
vibrations to the acoustic nerve; but Mr. Toynbee,*(2) after
collecting all the known evidence on this head, concludes that the
external shell is of no distinct use. The ears of the chimpanzee and
orang are curiously like those of man, and the proper muscles are
likewise but very slightly developed.*(3) I am also assured by the
keepers in the Zoological Gardens that these animals never move or
erect their ears; so that they are in an equally rudimentary condition
with those of man, as far as function is concerned. Why these animals,
as well as the progenitors of man, should have lost the power of
erecting their ears, we can not say. It may be, though I am not
satified with this view, that owing to their arboreal habits and great
strength they were but little exposed to danger, and so during a
lengthened period moved their ears but little, and thus gradually lost
the power of moving them. This would be a parallel case with that of
those large and heavy birds, which, from inhabiting oceanic islands,
have not been exposed to the attacks of beasts of prey, and have
consequently lost the power of using their wings for flight. The
inability to move the ears in man and several apes is, however, partly
compensated by the freedom with which they can move the head in a
horizontal plane, so as to catch sounds from all directions. It has
been asserted that the ear of man alone possesses a lobule; but "a
rudiment of it is found in the gorilla";*(4) and, as I hear from Prof.
Preyer, it is not rarely absent in the negro.

  * Canestrini quotes Hyrtl. (Annuario della Soc. dei Naturalisti,
Modena, 1897, p. 97) to the same effect.
  *(2) The Diseases of the Ear, by J. Toynbee, F. R. S., 1860, p.
12. A distinguished physiologist, Prof. Preyer, informs me that he had
lately been experimenting on the function of the shell of the ear, and
has come to nearly the same conclusion as that given here.
  *(3) Prof. A. Macalister, Annals and Magazine of Natural History,
vol. vii., 1871, p. 342.
  *(4) Mr. St. George Mivart, Elementary Anatomy, 1873, p. 396.

  The celebrated sculptor, Mr. Woolner, informs me of one little
peculiarity in the external ear, which he has often observed both in
men and women, and of which he perceived the full significance. His
attention was first called to the subject whilst at work on his figure
of Puck, to which he had given pointed ears. He was thus led to
examine the ears of various monkeys, and subsequently more carefully
those of man. The peculiarity consists in a little blunt point,
projecting from the inwardly folded margin, or helix. When present, it
is developed at birth, and according to Prof. Ludwig Meyer, more
frequently in man than in woman. Mr. Woolner made an exact model of
one such case, and sent me the accompanying drawing (see fig. 2).
These points not only project inwards towards the centre of the ear,
but often a little outwards from its plane, so as to be visible when
the head is viewed from directly in front or behind. They are variable
in size, and somewhat in position, standing either a little higher
or lower; and they sometimes occur on one ear and not on the other.
They are not confined to mankind, for I observed a case in one of
the spider-monkeys (Ateles beelzebuth) in our Zoological Gardens;
and Mr. E. Ray Lankester informs me of another case in a chimpanzee in
the gardens at Hamburg. The helix obviously consists of the extreme
margin of the ear folded inwards; and this folding appears to be in
some manner connected with the whole external ear being permanently
pressed backwards. In many monkeys, which do not stand high in the
order, as baboons and some species of Macacus,* the upper portion of
the ear is slightly pointed, and the margin is not at all folded
inwards; but if the margin were to be thus folded, a slight point
would necessarily project inwards towards the centre, and probably a
little outwards from the plane of the ear; and this I believe to be
their origin in many cases. On the other hand, Prof. L. Meyer, in an
able paper recently published,*(2) maintains that the whole case is
one of mere variability; and that the projections are not real ones,
but are due to the internal cartilage on each side of the points not
having been fully developed. I am quite ready to admit that this is
the correct explanation in many instances, as in those figured by
Prof. Meyer, in which there are several minute points, or the whole
margin is sinuous. I have myself seen, through the kindness of Dr.
L. Down, the ear of a microcephalus idiot, on which there is a
projection on the outside of the helix, and not on the inward folded
edge, so that this point can have no relation to a former apex of
the ear. Nevertheless in some cases, my original view, that the points
are vestiges of the tips of formerly erect and pointed ears, still
seems to me probable. I think so from the frequency of their
occurrence, and from the general correspondence in position with
that of the tip of a pointed ear. In one case, of which a photograph
has been sent me, the projection is so large, that supposing, in
accordance with Prof. Meyer's view, the ear to be made perfect by
the equal development of the cartilage throughout the whole extent
of the margin, it would have covered fully one-third of the whole ear.
Two cases have been communicated to me, one in North America, and
the other in England, in which the upper margin is not at all folded
inwards, but is pointed, so that it closely resembles the pointed
ear of an ordinary quadruped in outline. In one of these cases,
which was that of a young child, the father compared the ear with
the drawing which I have given*(3) of the ear of a monkey, the
Cynopithecus niger, and says that their outlines are closely
similar. If, in these two cases, the margin had been folded inwards in
the normal manner, an inward projection must have been formed. I may
add that in two other cases the outline still remains somewhat
pointed, although the margin of the upper part of the ear is
normally folded inwards- in one of them, however, very narrowly. The
following woodcut (see fig. 3) is an accurate copy of a photograph
of the foetus of an orang (kindly sent me by Dr. Nitsche), in which it
may be seen how different the pointed outline of the ear is at this
period from its adult condition, when it bears a close general
resemblance to that of man. It is evident that the folding over of the
tip of such an ear, unless it chang greatly during its further
development, would give rise to a point projecting inwards. On the
whole, it still seems to me probable that the points in question are
in some cases, both in man and apes, vestiges of a former condition.

  * See also some remarks, and the drawings of the ears of the
Lemuroidea, in Messrs. Murie and Mivart's excellent paper in
Transactions of the Zoological Society, vol. vii., 1869, pp. 6 and 90.
  *(2) Uber das Darwin'sche Spitzohr," Archiv fur Path. Anst. und
Phys., 1871, p. 485.
  *(3) The Expression of the Emotions, p. 136.

  The nictitating membrane, or third eyelid, with its accessory
muscles and other structures, is especially well developed in birds,
and is of much functional importance to them, as it can be rapidly
drawn across the whole eyeball. It is found in some reptiles and
amphibians, and in certain fishes, as in sharks. It is fairly well
developed in the two lower divisions of the mammalian series,
namely, in the Monotremata and marsupials, and in some few of the
higher mammals, as in the walrus. But in man, the Quadrumana, and most
other mammals, it exists, as is admitted by all anatomists, as a
mere rudiment, called the semilunar fold.*

  * Muller's Elements of Physiology, Eng. translat., 1842, vol. ii.,
p. 1117. Owen, Anatomy of Vertebrates, vol. iii., p. 260; ibid., on
the walrus, Proceedings of the Zoological Society, November 8, 1854.
See also R. Knox, Great Artists and Anatomists, p. 106. This
rudiment apparently is somewhat larger in Negroes and Australians than
in Europeans, see Carl Vogt, Lectures on Man, Eng. translat., p. 129.

  The sense of smell is of the highest importance to the greater
number of mammals- to some, as the ruminants, in warning them of
danger; to others, as the Carnivora, in finding their prey; to others,
again, as the wild boar, for both purposes combined. But the sense
of smell is of extremely slight service, if any, even to the dark
coloured races of men, in whom it is much more highly developed than
in the white and civilised races.* Nevertheless it does not warn
them of danger, nor guide them to their food; nor does it prevent
the Esquimaux from sleeping in the most fetid atmosphere, nor many
savages from eating half-putrid meat. In Europeans the power differs
greatly in different individuals, as I am assured by an eminent
naturalist who possesses this sense highly developed, and who has
attended to the subject. Those who believe in the principle of gradual
evolution, will not readily admit that the sense of smell in its
present state was originally acquired by man, as he now exists. He
inherits the power in an enfeebled and so far rudimentary condition,
from some early progenitor, to whom it was highly serviceable, and
by whom it was continually used. In those animals which have this
sense highly developed, such as dogs and horses, the recollection of
persons and of places is strongly associated with their odour; and
we can thus perhaps understand how it is, as Dr. Maudsley has truly
remarked,*(2) that the sense of smell in man "is singularly
effective in recalling vividly the ideas and images of forgotten
scenes and places."

  * The account given by Humboldt of the power of smell possessed by
the natives of South America is well known, and has been confirmed
by others. M. Houzeau (Etudes sur les Facultes Mentales, &c., tom. i.,
1872, p. 91) asserts that he repeatedly made experiments, and proved
that Negroes and Indians could recognise persons in the dark by
their odour. Dr. W. Ogle has made some curious observations on the
connection between the power of smell and the colouring matter of
the mucous membrane of the olfactory region as well as of the skin
of the body. I have, therefore, spoken in the text of the
dark-coloured races having a finer sense of smell than the white
races. See his paper, Medico-Chirurgical Transactions, London, vol.
liii., 1870, p. 276.
  *(2) The Physiology and Pathology of Mind, 2nd ed., 1868, p. 134.

  Man differs conspicuously from all the other primates in being
almost naked. But a few short straggling hairs are found over the
greater part of the body in the man, and fine down on that of a woman.
The different races differ much in hairiness; and in the individuals
of the same race the hairs are highly variable, not only in abundance,
but likewise in position: thus in some Europeans the shoulders are
quite naked, whilst in others they bear thick tufts of hair.* There
can be little doubt that the hairs thus scattered over the body are
the rudiments of the uniform hairy coat of the lower animals. This
view is rendered all the more probable, as it is known that fine,
short, and pale-coloured hairs on the limbs and other parts of the
body, occasionally become developed into "thickset, long, and rather
coarse dark hairs," when abnormally nourished near old-standing
inflamed surfaces.*(2)

  * Eschricht, "Uber die Richtung der Haare am menschlichen Korper,"
Muller's Archiv fur Anat. und Phys., 1837, s. 47. I shall often have
to refer to this very curious paper.
  *(2) Paget, Lectures on Surgical Pathology, 1853, vol. i., p. 71.

  I am informed by Sir James Paget that often several members of a
family have a few hairs in their eyebrows much longer than the others;
so that even this slight peculiarity seems to be inherited. These
hairs, too, seem to have their representatives; for in the chimpanzee,
and in certain species of Maeacus, there are scattered hairs of
considerable length rising from the naked skin above the eyes, and
corresponding to our eyebrows; similar long hairs project from the
hairy covering of the superciliary ridges in some baboons.
  The fine wool-like hair, or so-called lanugo, with which the human
foetus during the sixth month is thickly covered, offers a more
curious case. It is first developed, during the fifth month, on the
eyebrows and face, and especially round the mouth, where it is much
longer than that on the head. A moustache of this kind was observed by
Eschricht* on a female foetus; but this is not so surprising a
circumstance as it may at first appear, for the two sexes generally
resemble each other in all external characters during an early
period of growth. The direction and arrangement of the hairs on all
parts of the foetal body are the same as in the adult, but are subject
to much variability. The whole surface, including even the forehead
and ears, is thus thickly clothed; but it is a significant fact that
the palms of the hands and the soles of the feet are quite naked, like
the inferior surfaces of all four extremities in most of the lower
animals. As this can hardly be an accidental coincidence, the woolly
covering of the foetus probably represents the first permanent coat of
hair in those mammals which are born hairy. Three or four cases have
been recorded of persons born with their whole bodies and faces
thickly covered with fine long hairs; and this strange condition is
strongly inherited, and is correlated with an abnormal condition of
the teeth.*(2) Prof. Alex. Brandt informs me that he has compared
the hair from the face of a man thus characterised, aged
thirty-five, with the lanugo of a foetus, and finds it quite similar
in texture; therefore, as he remarks, the case may be attributed to an
arrest of development in the hair, together with its continued growth.
Many delicate children, as I have been assured by a surgeon to a
hospital for children, have their backs covered by rather long silky
hairs; and such cases probably come under the same head.

  * Eschricht, ibid., ss. 40, 47.
  *(2) See my Variation of Animals and Plants under Domestication,
vol. ii., p. 327. Prof. Alex. Brandt has recently sent me an
additional case of a father and son, born in Russia, with these
peculiarities. I have received drawings of both from Paris.

  It appears as if the posterior molar or wisdom-teeth were tending to
become rudimentary in the more civilised races of man. These teeth are
rather smaller than the other molars, as is likewise the case with the
corresponding teeth in the chimpanzee and orang; and they have only
two separate fangs. They do not cut through the gums till about the
seventeenth year, and I have been assured that they are much more
liable to decay, and are earlier lost than the other teeth; but this
is denied by some eminent dentists. They are also much more liable
to vary, both in structure and in the period of their development,
than the other teeth.* In the Melanian races, on the other hand, the
wisdom-teeth are usually furnished with three separate fangs, and
are generally sound; they also differ from the other molars in size,
less than in the Caucasian races.*(2) Prof. Schaaffhausen accounts for
this difference between the races by "the posterior dental portion
of the jaw being always shortened" in those that are civilised,*(3)
and this shortening may, I presume, be attributed to civilised men
habitually feeding on soft, cooked food, and thus using their jaws
less. I am informed by Mr. Brace that it is becoming quite a common
practice in the United States to remove some of the molar teeth of
children, as the jaw does not grow large enough for the perfect
development of the normal number.*(4)

  * Dr. Webb, "Teeth in Man and the Anthropoid Apes," as quoted by Dr.
C. Carter Blake in Anthropological Review, July, 1867, p. 299.
  *(2) Owen, Anatomy of Vertebrates, vol. iii., pp. 320, 321, and 325.
  *(3) "On the Primitive Form of the Skull," Eng. translat., in
Anthropological Review, Oct., 1868, p. 426.
  *(4) Prof. Montegazza writes to me from Florence, that he has lately
been studying the last molar teeth in the different races of man,
and has come to the same conclusion as that given in my text, viz.,
that in the higher or civilised races they are on the road towards
atrophy or elimination.

  With respect to the alimentary canal, I have met with an account
of only a single rudiment, namely the vermiform appendage of the
caecum. The caecum is a branch or diverticulum of the intestine,
ending in a cul-de-sac, and is extremely long in many of the lower
vegetable-feeding mammals. In the marsupial koala it is actually
more than thrice as long as the whole body.* It is sometimes
produced into a long gradually-tapering point, and is sometimes
constricted in parts. It appears as if, in consequence of changed diet
or habits, the caecum had become much shortened in various animals,
the vermiform appendage being left as a rudiment of the shortened
part. That this appendage is a rudiment, we may infer from its small
size, and from the evidence which Prof. Canestrini*(2) has collected
of its variability in man. It is occasionally quite absent, or again
is largely developed. The passage is sometimes completely closed for
half or two-thirds of its length, with the terminal part consisting of
a flattened solid expansion. In the orang this appendage is long and
convoluted: in man it arises from the end of the short caecum, and
is commonly from four to five inches in length, being only about the
third of an inch in diameter. Not only is it useless, but it is
sometimes the cause of death, of which fact I have lately heard two
instances: this is due to small hard bodies, such as seeds, entering
the passage, and causing inflammation.*(3)

  * Owen, Anatomy of Vertebrates, vol. iii., pp 416, 434, 441.
  *(2) Annuario della Soc. d. Nat. Modena, 1867, p. 94.
  *(3) M. C. Martins ("De l'Unite Organique," in Revue des Deux
Mondes, June 15, 1862, p. 16) and Haeckel (Generelle Morphologie, B.
ii., s. 278), have both remarked on the singular fact of this rudiment
sometimes causing death.

  In some of the lower Quadrumana, in the Lemuridae and Carnivora,
as well as in many marsupials, there is a passage near the lower end
of the humerus, called the supra-condyloid foramen, through which
the great nerve of the fore limb and often the great artery pass.
Now in the humerus of man, there is generally a trace of this passage,
which is sometimes fairly well developed, being formed by a
depending hook-like process of bone, completed by a band of
ligament. Dr. Struthers,* who has closely attended to the subject, has
now shewn that this peculiarity is sometimes inherited, as it has
occurred in a father, and in no less than four out of his seven
children. When present, the great nerve invariably passes through
it; and this clearly indicates that it is the homologue and rudiment
of the supra-condyloid foramen of the lower animals. Prof. Turner
estimates, as he informs me, that it occurs in about one per cent of
recent skeletons. But if the occasional development of this
structure in man is, as seems probable, due to reversion, it is a
return to a very ancient state of things, because in the higher
Quadrumana it is absent.

  * With respect to inheritance, see Dr. Struthers in the Lancet, Feb.
15, 1873, and another important paper, ibid., Jan. 24, 1863, p. 83.
Dr. Knox, as I am informed, was the first anatomist who drew attention
to this peculiar structure in man; see his Great Artists and
Anatomists, p. 63. See also an important memoir on this process by Dr.
Gruber, in the Bulletin de l'Acad. Imp. de St. Petersbourg, tom. xii.,
1867, p. 448.

  There is another foramen or perforation in the humerus, occasionally
present in man, which may be called the inter-condyloid. This
occurs, but not constantly, in various anthropoid and other apes,* and
likewise in many of the lower animals. It is remarkable that this
perforation seems to have been present in man much more frequently
during ancient times than recently. Mr. Busk*(2) has collected the
following evidence on this head: Prof. Broca "noticed the
perforation in four and a half per cent of the arm-bones collected
in the 'Cimetiere, du Sud,' at Paris; and in the Grotto of Orrony, the
contents of which are referred to the Bronze period, as many as
eight humeri out of thirty-two were perforated; but this extraordinary
proportion, he thinks, might be due to the cavern having been a sort
of 'family vault.' Again, M. Dupont found thirty per cent of
perforated bones in the caves of the Valley of the Lesse, belonging to
the Reindeer period; whilst M. Leguay, in a sort of dolmen at
Argenteuil, observed twenty-five per cent to be perforated; and M.
Pruner-Bey found twenty-six per cent in the same condition in bones
from Vaureal. Nor should it be left unnoticed that M. Pruner-Bey
states that this condition is common in Guanche skeletons." It is an
interesting fact that ancient races, in this and several other
cases, more frequently present structures which resemble those of
the lower animals than do the modern. One chief cause seems to be that
the ancient races stand somewhat nearer in the long line of descent to
their remote animal-like progenitors.

  * Mr. St. George Mivart, Transactions Phil. Soc., 1867, p. 310.
  *(2) "On the Caves of Gibraltar," Transactions of the
International Congress of Prehistoric Archaeology, Third Session,
1869, p. 159. Prof. Wyman has lately shewn (Fourth Annual Report,
Peabody Museum, 1871, p. 20), that this perforation is present in
thirty-one per cent of some human remains from ancient mounds in the
Western United States, and in Florida. It frequently occurs in the
negro.

  In man, the os coccyx, together with certain other vertebrae
hereafter to be described, though functionless as a tail, plainly
represent this part in other vertebrate animals. At an early embryonic
period it is free, and projects beyond the lower extremities; as may
be seen in the drawing (see fig. 1) of a human embryo. Even after
birth it has been known, in certain rare and anomalous cases,* to form
a small external rudiment of a tail. The os coccyx is short, usually
including only four vertebrae, all anchylosed together: and these
are in a rudimentary condition, for they consist, with the exception
of the basal one, of the centrum alone.*(2) They are furnished with
some small muscles; one of which, as I am informed by Prof. Turner,
has been expressly described by Theile as a rudimentary repetition
of the extensor of the tail, a muscle which is so largely developed in
many mammals.

  * Quatrefages has lately collected the evidence on this subject.
Revue des Cours Scientifiques, 1867-1868, p. 625. In 1840
Fleischmann exhibited a human foetus bearing a free tail, which, as is
not always the case, included vertebral bodies; and this tail was
critically examined by the many anatomists present at the meeting of
naturalists at Erlangen (see Marshall in Niederland. Archiv fur
Zoologie, December, 1871).
  *(2) Owen, On the Nature of Limbs, 1849, p. 114.

  The spinal cord in man extends only as far downwards as the last
dorsal or first lumbar vertebra; but a thread-like structure (the
filum terminale) runs down the axis of the sacral part of the spinal
canal, and even along the back of the coccygeal bones. The upper
part of this filament, as Prof. Turner informs me, is undoubtedly
homologous with the spinal cord; but the lower part apparently
consists merely of the pia mater, or vascular investing membrane. Even
in this case the os coccyx may be said to possess a vestige of so
important a structure as the spinal cord, though no longer enclosed
within a bony canal. The following fact, for which I am also
indebted to Prof. Turner, shews how closely the os coccyx
corresponds with the true tail in the lower animals: Luschka has
recently discovered at the extremity of the coccygeal bones a very
peculiar convoluted body, which is continuous with the middle sacral
artery; and this discovery led Krause and Meyer to examine the tail of
a monkey (Maeacus), and of a cat, in both of which they found a
similarly convoluted body, though not at the extremity.
  The reproductive system offers various rudimentary structures; but
these differ in one important respect from the foregoing cases. Here
we are not concerned with the vestige of a part which does not
belong to the species in an efficient state, but with a part efficient
in the one sex, and represented in the other by a mere rudiment.
Nevertheless, the occurrence of such rudiments is as difficult to
explain, on the belief of the separate creation of each species, as in
the foregoing cases. Hereafter I shall have to recur to these
rudiments, and shall shew that their presence generally depends merely
on inheritance, that is, on parts acquired by one sex having been
partially transmitted to the other. I will in this place only give
some instances of such rudiments. It is well known that in the males
of all mammals, including man, rudimentary mammae exist. These in
several instances have become well developed, and have yielded a
copious supply of milk. Their essential identity in the two sexes is
likewise shewn by their occasional sympathetic enlargement in both
during an attack of the measles. The vesicula prostatica, which has
been observed in many male mammals, is now universally acknowledged to
be the homologue of the female uterus, together with the connected
passage. It is impossible to read Leuckart's able description of
this organ, and his reasoning, without admitting the justness of his
conclusion. This is especially clear in the case of those mammals in
which the true female uterus bifurcates, for in the males of these the
vesicula likewise bifurcates.* Some other rudimentary structures
belonging to the reproductive system might have been here adduced.*(2)

  * Leuckart, in Todd's Cyclopaedia of Anatomy, 1849-52, vol. iv.,
p. 1415. In man this organ is only from three to six lines in
length, but, like so many other rudimentary parts, it is variable in
development as well as in other characters.
  *(2) See, on this subject, Owen, Anatomy of Vertebrates, vol.
iii., pp. 675, 676, 706.

  The bearing of the three great classes of facts now given is
unmistakeable. But it would be superfluous fully to recapitulate the
line of argument given in detail in my Origin of Species. The
homological construction of the whole frame in the members of the same
class is intelligible, if we admit their descent from a common
progenitor, together with their subsequent adaptation to diversified
conditions. On any other view, the similarity of pattern between the
hand of a man or monkey, the foot of a horse, the flipper of a seal,
the wing of a bat, &c., is utterly inexplicable.* It is no
scientific explanation to assert that they have all been formed on the
same ideal plan. With respect to development, we can clearly
understand, on the principle of variation supervening at a rather late
embryonic period, and being inherited at a corresponding period, how
it is that the embryos of wonderfully different forms should still
retain, more or less perfectly, the structure of their common
progenitor. No other explanation has ever been given of the marvellous
fact that the embryos of a man, dog, seal, bat, reptile, &c., can at
first hardly be distinguished from each other. In order to
understand the existence of rudimentary organs, we have only to
suppose that a former progenitor possessed the parts in question in
a perfect state, and that under changed habits of life they became
greatly reduced, either from simple disuse, or through the natural
selection of those individuals which were least encumbered with a
superfluous part, aided by the other means previously indicated.

  * Prof. Bianconi, in a recently published work, illustrated by
admirable engravings (La Theorie Darwinienne et la creation dite
independante, 1874), endeavours to show that homological structures,
in the above and other cases, can be fully explained on mechanical
principles, in accordance with their uses. No one has shewn so well,
how admirably such structures are adapted for their final purpose; and
this adaptation can, as I believe, be explained through natural
selection. In considering the wing of a bat, he brings forward (p.
218) what appears to me (to use Auguste Comte's words) a mere
metaphysical principle, namely, the preservation "in its integrity
of the mammalian nature of the animal." In only a few cases does he
discuss rudiments, and then only those parts which are partially
rudimentary, such as the little hoofs of the pig and ox, which do
not touch the ground; these he shows clearly to be of service to the
animal. It is unfortunate that he did not consider such cases as the
minute teeth, which never cut through the jaw in the ox, or the mammae
of male quadrupeds, or the wings of certain beetles, existing under
the soldered wing-covers, or the vestiges of the pistil and stamens in
various flowers, and many other such cases. Although I greatly
admire Prof. Bianconi's work, yet the belief now held by most
naturalists seems to me left unshaken, that homological structures are
inexplicable on the principle of mere adaptation.

  Thus we can understand how it has come to pass that man and all
other vertebrate animals have been constructed on the same general
model, why they pass through the same early stages of development, and
why they retain certain rudiments in common. Consequently we ought
frankly to admit their community of descent: to take any other view,
is to admit that our own structure, and that of all the animals around
us, is a mere snare laid to entrap our judgment. This conclusion is
greatly strengthened, if we look to the members of the whole animal
series, and consider the evidence derived from their affinities or
classification, their geographical distribution and geological
succession. It is only our natural prejudice, and that arrogance which
made our forefathers declare that they were descended from demigods,
which leads us to demur to this conclusion. But the time will before
long come, when it will be thought wonderful that naturalists, who
were well acquainted with the comparative structure and development of
man, and other mammals, should have believed that each was the work of
a separate act of creation.

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