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THE DESCENT OF MAN,
AND
SELECTION IN RELATION TO SEX.
BY CHARLES DARWIN, M.A., F.R.S., &c.
IN TWO VOLUMES.--VOL. I.
WITH ILLUSTRATIONS.
LONDON:
JOHN MURRAY, ALBEMARLE STREET.
1871.
[_The right of Translation is reserved._]
BY THE SAME AUTHOR.
ON THE ORIGIN OF SPECIES BY MEANS OF NATURAL SELECTION; or, THE
PRESERVATION OF FAVOURED RACES IN THE STRUGGLE FOR LIFE; Fifth
Edition (_Tenth Thousand_), with Additions and Corrections.
1869. MURRAY.
THE VARIATION OF ANIMALS AND PLANTS UNDER DOMESTICATION. In two vols.
With Illustrations. 1868. MURRAY.
ON THE VARIOUS CONTRIVANCES BY WHICH BRITISH AND FOREIGN ORCHIDS ARE
FERTILISED BY INSECTS; and on the GOOD EFFECTS OF CROSSING. With
numerous Woodcuts. MURRAY.
A NATURALIST'S VOYAGE ROUND THE WORLD; or, A JOURNAL OF RESEARCHES INTO
THE NATURAL HISTORY AND GEOLOGY OF THE COUNTRIES visited during the
voyage of H.M.S. 'Beagle,' under the command of Captain FITZROY, R.N.
_Eleventh Thousand_. MURRAY.
ON THE STRUCTURE AND DISTRIBUTION OF CORAL REEFS. SMITH, ELDER, & CO.
GEOLOGICAL OBSERVATIONS ON VOLCANIC ISLANDS. SMITH, ELDER, & CO.
GEOLOGICAL OBSERVATIONS ON SOUTH AMERICA. SMITH, ELDER & CO.
A MONOGRAPH OF THE CIRRIPEDIA. With numerous Illustrations. 2 vols.
8vo. HARDWICKE.
ON THE MOVEMENTS AND HABITS OF CLIMBING PLANTS. With Woodcuts. WILLIAMS
& NORGATE.
LONDON: PRINTED BY WILLIAM CLOWES AND SONS, STAMFORD STREET, AND CHARING
CROSS.
CONTENTS.
INTRODUCTION Page 1-5
PART I.
ON THE DESCENT OF MAN.
CHAPTER I.
THE EVIDENCE OF THE DESCENT OF MAN FROM SOME LOWER FORM.
Nature of the evidence bearing on the origin of man--Homologous
structures in man and the lower animals--Miscellaneous points
of correspondence--Development--Rudimentary structures,
muscles, sense-organs, hair, bones, reproductive organs,
&c.--The bearing of these three great classes of facts on the
origin of man 9-33
CHAPTER II.
COMPARISON OF THE MENTAL POWERS OF MAN AND THE LOWER ANIMALS.
The difference in mental power between the highest ape and the
lowest savage, immense--Certain instincts in common--The
emotions--Curiosity--Imitation--Attention--Memory--Imagination--
Reason--Progressive improvement--Tools and weapons used by
animals--Language--Self-consciousness--Sense of beauty--Belief
in God, spiritual agencies, superstitions 34-69
CHAPTER III.
COMPARISON OF THE MENTAL POWERS OF MAN AND THE LOWER
ANIMALS--_continued_.
The moral sense--Fundamental proposition--The qualities of
social animals--Origin of sociability--Struggle between opposed
instincts--Man and social animal--The more enduring social
instincts conquer other less persistent instincts--The social
virtues alone regarded by savages--The self-regarding virtues
acquired at a later stage of development--The importance of the
judgment of the members of the same community on
conduct--Transmission of moral tendencies--Summary 70-106
CHAPTER IV.
ON THE MANNER OF DEVELOPMENT OF MAN FROM SOME LOWER FORM.
Variability of body and mind in man--Inheritance--Causes of
variability--Laws of variation the same in man as in the lower
animals--Direct action of the conditions of life--Effects of
the increased use and disuse of parts--Arrested
development--Reversion--Correlated variation--Rate of
increase--Checks to increase--Natural selection--Man the most
dominant animal in the world--Importance of his corporeal
structure--The causes which have led to his becoming
erect--Consequent changes of structure--Decrease in size of the
canine teeth--Increased size and altered shape of the
skull--Nakedness--Absence of a tail--Defenceless condition of
man 107-157
CHAPTER V.
ON THE DEVELOPMENT OF THE INTELLECTUAL AND MORAL FACULTIES
DURING PRIMEVAL AND CIVILISED TIMES.
The advancement of the intellectual powers through natural
selection--Importance of imitation--Social and moral
faculties--Their development within the limits of the same
tribe--Natural selection as affecting civilised
nations--Evidence that civilised nations were once barbarous 158-184
CHAPTER VI.
ON THE AFFINITIES AND GENEALOGY OF MAN.
Position of man in the animal series--The natural system
genealogical--Adaptive characters of slight value--Various
small points of resemblance between man and the
Quadrumana--Rank of man in the natural system--Birthplace and
antiquity of man--Absence of fossil connecting-links--Lower
stages in the genealogy of man, as inferred, firstly from his
affinities and secondly from his structure--Early androgynous
condition of the Vertebrata--Conclusion 185-213
CHAPTER VII.
ON THE RACES OF MAN.
The nature and value of specific characters--Application to the
races of man--Arguments in favour of, and opposed to, ranking
the so-called races of man as distinct species--Sub-species--
Monogenists and polygenists--Convergence of character--Numerous
points of resemblance in body and mind between the most
distinct races of man--The state of man when he first spread
over the earth--Each race not descended from a single
pair--The extinction of races--The formation of races--
The effects of crossing--Slight influence of the direct
action of the conditions of life--Slight or no influence of
natural selection--Sexual selection. 214-250
PART II. SEXUAL SELECTION.
CHAPTER VIII.
PRINCIPLES OF SEXUAL SELECTION.
Secondary sexual characters--Sexual selection--Manner of
action--Excess of males--Polygamy--The male alone generally
modified through sexual selection--Eagerness of the
male--Variability of the male--Choice exerted by the
female--Sexual compared with natural selection--Inheritance at
corresponding periods of life, at corresponding seasons of the
year, and as limited by sex--Relations between the several
forms of inheritance--Causes why one sex and the young are not
modified through sexual selection--Supplement on the
proportional numbers of the two sexes throughout the animal
kingdom--On the limitation of the numbers of the two sexes
through natural selection 253-320
CHAPTER IX.
SECONDARY SEXUAL CHARACTERS IN THE LOWER CLASSES OF THE ANIMAL
KINGDOM.
These characters absent in the lowest classes--Brilliant
colours--Mollusca--Annelids--Crustacea, secondary sexual
characters strongly developed; dimorphism; colour; characters
not acquired before maturity--Spiders, sexual colours of;
stridulation by the males--Myriapoda 321-340
CHAPTER X.
SECONDARY SEXUAL CHARACTERS OF INSECTS.
Diversified structures possessed by the males for seizing the
females--Differences between the sexes, of which the meaning is
not understood--Difference in size between the
sexes--Thysanura--Diptera--Hemiptera--Homoptera, musical powers
possessed by the males alone--Orthoptera, musical instruments
of the males, much diversified in structure; pugnacity;
colours--Neuroptera, sexual differences in colour--Hymenoptera,
pugnacity and colours--Coleoptera, colours; furnished with
great horns, apparently as an ornament; battles; stridulating
organs generally common to both sexes 341-385
CHAPTER XI.
INSECTS, _continued_.--ORDER LEPIDOPTERA.
Courtship of butterflies--Battles--Ticking noise--Colours
common to both sexes, or more brilliant in the
males--Examples--Not due to the direct action of the conditions
of life--Colours adapted for protection--Colours of
moths--Display--Perceptive powers of the
Lepidoptera--Variability--Causes of the difference in colour
between the males and females--Mimickry, female butterflies
more brilliantly coloured than the males--Bright colours of
caterpillars--Summary and concluding remarks on the secondary
sexual characters of insects--Birds and insects compared 386-423
THE DESCENT OF MAN;
AND ON
SELECTION IN RELATION TO SEX.
INTRODUCTION.
The nature of the following work will be best understood by a brief
account of how it came to be written. During many years I collected
notes on the origin or descent of man, without any intention of
publishing on the subject, but rather with the determination not to
publish, as I thought that I should thus only add to the prejudices
against my views. It seemed to me sufficient to indicate, in the first
edition of my 'Origin of Species,' that by this work "light would be
thrown on the origin of man and his history;" and this implies that man
must be included with other organic beings in any general conclusion
respecting his manner of appearance on this earth. Now the case wears a
wholly different aspect. When a naturalist like Carl Vogt ventures to
say in his address as President of the National Institution of Geneva
(1869), "personne, en Europe au moins, n'ose plus soutenir la creation
independante et de toutes pieces, des especes," it is manifest that at
least a large number of naturalists must admit that species are the
modified descendants of other species; and this especially holds good
with the younger and rising naturalists. The greater number accept the
agency of natural selection; though some urge, whether with justice the
future must decide, that I have greatly overrated its importance. Of the
older and honoured chiefs in natural science, many unfortunately are
still opposed to evolution in every form.
In consequence of the views now adopted by most naturalists, and which
will ultimately, as in every other case, be followed by other men, I
have been led to put together my notes, so as to see how far the general
conclusions arrived at in my former works were applicable to man. This
seemed all the more desirable as I had never deliberately applied these
views to a species taken singly. When we confine our attention to any
one form, we are deprived of the weighty arguments derived from the
nature of the affinities which connect together whole groups of
organisms--their geographical distribution in past and present times,
and their geological succession. The homological structure,
embryological development, and rudimentary organs of a species, whether
it be man or any other animal, to which our attention may be directed,
remain to be considered; but these great classes of facts afford, as it
appears to me, ample and conclusive evidence in favour of the principle
of gradual evolution. The strong support derived from the other
arguments should, however, always be kept before the mind.
The sole object of this work is to consider, firstly, whether man, like
every other species, is descended from some pre-existing form; secondly,
the manner of his development; and thirdly, the value of the
differences between the so-called races of man. As I shall confine
myself to these points, it will not be necessary to describe in detail
the differences between the several races--an enormous subject which has
been fully discussed in many valuable works. The high antiquity of man
has recently been demonstrated by the labours of a host of eminent men,
beginning with M. Boucher de Perthes; and this is the indispensable
basis for understanding his origin. I shall, therefore, take this
conclusion for granted, and may refer my readers to the admirable
treatises of Sir Charles Lyell, Sir John Lubbock, and others. Nor shall
I have occasion to do more than to allude to the amount of difference
between man and the anthropomorphous apes; for Prof. Huxley, in the
opinion of most competent judges, has conclusively shewn that in every
single visible character man differs less from the higher apes than
these do from the lower members of the same order of Primates.
This work contains hardly any original facts in regard to man; but as
the conclusions at which I arrived, after drawing up a rough draft,
appeared to me interesting, I thought that they might interest others.
It has often and confidently been asserted, that man's origin can never
be known: but ignorance more frequently begets confidence than does
knowledge: it is those who know little, and not those who know much, who
so positively assert that this or that problem will never be solved by
science. The conclusion that man is the co-descendant with other species
of some ancient, lower, and extinct form, is not in any degree new.
Lamarck long ago came to this conclusion, which has lately been
maintained by several eminent naturalists and philosophers; for instance
by Wallace, Huxley, Lyell, Vogt, Lubbock, Buechner, Rolle, &c.,[1] and
especially by Haeckel. This last naturalist, besides his great work,
'Generelle Morphologie' (1866), has recently (1868, with a second edit.
in 1870), published his 'Natuerliche Schoepfungsgeschichte,' in which he
fully discusses the genealogy of man. If this work had appeared before
my essay had been written, I should probably never have completed it.
Almost all the conclusions at which I have arrived I find confirmed by
this naturalist, whose knowledge on many points is much fuller than
mine. Wherever I have added any fact or view from Prof. Haeckel's
writings, I give his authority in the text, other statements I leave as
they originally stood in my manuscript, occasionally giving in the
foot-notes references to his works, as a confirmation of the more
doubtful or interesting points.
During many years it has seemed to me highly probable that sexual
selection has played an important part in differentiating the races of
man; but in my 'Origin of Species' (first edition, p. 199) I contented
myself by merely alluding to this belief. When I came to apply this view
to man, I found it indispensable to treat the whole subject in full
detail.[2] Consequently the second part of the present work, treating of
sexual selection, has extended to an inordinate length, compared with
the first part; but this could not be avoided.
I had intended adding to the present volumes an essay on the expression
of the various emotions by man and the lower animals. My attention was
called to this subject many years ago by Sir Charles Bell's admirable
work. This illustrious anatomist maintains that man is endowed with
certain muscles solely for the sake of expressing his emotions. As this
view is obviously opposed to the belief that man is descended from some
other and lower form, it was necessary for me to consider it. I likewise
wished to ascertain how far the emotions are expressed in the same
manner by the different races of man. But owing to the length of the
present work, I have thought it better to reserve my essay, which is
partially completed, for separate publication.
PART I.
THE DESCENT OR ORIGIN OF MAN.
PART I.--THE DESCENT OF MAN.
CHAPTER I.
THE EVIDENCE OF THE DESCENT OF MAN FROM SOME LOWER FORM.
Nature of the evidence bearing on the origin of man--Homologous
structures in man and the lower animals--Miscellaneous points
of correspondence--Development--Rudimentary structures,
muscles, sense-organs, hair, bones, reproductive organs,
&c.--The bearing of these three great classes of facts on the
origin of man.
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; such as
that of the transmission of characters to the same age or sex. 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, both 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 each other, 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 the two 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 with 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,[3] 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 this be
expected, for otherwise their mental powers would have been the same.
Vulpian[4] remarks: "Les differences reelles qui existent entre
l'encephale de l'homme et celui des singes superieurs, sont bien
minimes. Il 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 memes 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.
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, &c.; and
this fact proves the close similarity 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,[5] 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. 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.[6] 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.
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 with those infesting other mammals. Man is
subject like other mammals, birds, and even insects, 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.[7] His wounds are repaired by the same process of healing; and
the stumps left after the amputation of his limbs occasionally possess,
especially during an early embryonic period, some power of regeneration,
as in the lowest animals.[8]
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[9] 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.[10] 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.[11] Man differs
from woman in size, bodily strength, hairyness, &c., as well as in mind,
in the same manner as do the two sexes of many mammals. It is, in short,
scarcely possible to exaggerate the close 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.
_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 (_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,[12] "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."
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.[13]
[Illustration: Fig. 1. Upper figure human embryo, from Ecker. Lower
figure that of a dog, from Bischoff.
_a._ Fore-brain, cerebral hemispheres, &c.
_b._ Mid-brain, corpora quadrigemina.
_c._ Hind-brain, cerebellum, medulla oblongata.
_d._ Eye.
_e._ Ear.
_f._ First visceral arch.
_g._ Second visceral arch.
H. Vertebral columns and muscles in process of development.
_i._ Anterior {~BOX DRAWINGS LIGHT DOWN AND LEFT~}
{~BOX DRAWINGS LIGHT VERTICAL~} extremities.
K. Posterior {~BOX DRAWINGS LIGHT UP AND LEFT~}
L. Tail or os coccyx.]
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 in various
points of structure certain low forms when adult. 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
tail, "extending considerably beyond the rudimentary legs."[14] In the
embryos of all air-breathing vertebrates, certain glands called the
corpora Wolffiana, correspond with and act like the kidneys of mature
fishes.[15] 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.[16] The great toe, as Prof. Owen remarks,[17] "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[18] 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,[19] 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."
_Rudiments._--This subject, though not intrinsically more important than
the two last, will for several reasons be here treated with more
fullness.[20] 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 mammae 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 cannot
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; and
this is a circumstance well worthy of attention.
Disuse at that period of life, when an organ is chiefly used, and this
is generally during maturity, together with inheritance at a
corresponding period of life, seem to have been the chief agents in
causing organs to become rudimentary. 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 parts normally present in
the other sex; and such rudiments, as we shall hereafter see, have often
originated in a distinct manner. 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,[21] are difficult
to understand. The final and complete suppression of a part, already
useless and much reduced in size, in which case neither compensation nor
economy can come into play, is perhaps intelligible by the aid of the
hypothesis of pangenesis, and apparently in no other way. But as the
whole subject of rudimentary organs has been fully discussed and
illustrated in my former works,[22] I need here say no more on this
head.
Rudiments of various muscles have been observed in many parts of the
human body;[23] 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, on the forehead, by which the eyebrows are raised. The
_platysma myoides_, which is well developed on the neck, belongs to this
system, but cannot be voluntarily brought into action. 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[24] 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 3 per cent. in upwards 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."
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 a 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 all 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 persistently an absolutely
useless faculty may be transmitted.
The extrinsic muscles which serve to move the whole external ear, and
the intrinsic muscles which move the different parts, all of which
belong to the system of the panniculus, are in a rudimentary condition
in man; they are also variable in development, or at least in function.
I have seen one man who could draw his ears forwards, and another who
could draw them backwards;[25] 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 by repeated trials recover
some power of movement. The faculty of erecting the ears and of
directing them to different points of the compass, is no doubt of the
highest service to many animals, as they thus perceive the point of
danger; but I have never heard of a man who possessed the least power of
erecting his ears,--the one movement which might be of use to him. The
whole external shell of the ear 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,[26] 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 I am assured by the keepers in the
Zoological Gardens that these animals never move or erect them; so that
they are in an equally rudimentary condition, as far as function is
concerned, as in man. Why these animals, as well as the progenitors of
man, should have lost the power of erecting their ears we cannot say. It
may be, though I am not quite satisfied 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.
[Illustration: Fig. 2. Human Ear, modelled and drawn by Mr. Woolner.
_a._ The projecting point.]
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 signification. 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. Mr. Woolner made an exact model of
one such case, and has sent me the accompanying drawing. (Fig. 2.) These
points not only project inwards, but often a little outwards, so that
they are 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. Now the meaning of these projections is not, I think,
doubtful; but it may be thought that they offer too trifling a character
to be worth notice. This thought, however, is as false as it is natural.
Every character, however slight, must be the result of some definite
cause; and if it occurs in many individuals deserves consideration. 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,[27] 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
and probably a little outwards. This could actually be observed in a
specimen of the _Ateles beelzebuth_ in the Zoological Gardens; and we
may safely conclude that it is a similar structure--a vestige of
formerly pointed ears--which occasionally reappears in man.
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 eye-ball. 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.[28]
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, as the wild
boar, for both purposes combined. But the sense of smell is of extremely
slight service, if any, even to savages, in whom it is generally more
highly developed than in the civilised races. 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. Those who believe in the principle of gradual
evolution, will not readily admit that this sense in its present state
was originally acquired by man, as he now exists. No doubt 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. We can thus perhaps understand how it is, as Dr.
Maudsley has truly remarked,[29] that the sense of smell in man "is
singularly effective in recalling vividly the ideas and images of
forgotten scenes and places;" for we see in those animals, which have
this sense highly developed, such as dogs and horses, that old
recollections of persons and places are strongly associated with their
odour.
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 male sex, and fine down on that of the female sex, In
individuals belonging to the same race these hairs are highly variable,
not only in abundance, but likewise in position: thus the shoulders in
some Europeans are quite naked, whilst in others they bear thick tufts
of hair.[30] 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.[31]
I am informed by Mr. Paget that persons belonging to the same family
often have a few hairs in their eyebrows much longer than the others; so
that this slight peculiarity seems to be inherited. These hairs
apparently represent the vibrissae, which are used as organs of touch by
many of the lower animals. In a young chimpanzee I observed that a few
upright, rather long, hairs, projected above the eyes, where the true
eyebrows, if present, would have stood.
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[32] 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, we must consider the woolly
covering of the foetus to be the rudimental representative of the
first permanent coat of hair in those mammals which are born hairy. This
representation is much more complete, in accordance with the usual law
of embryological development, than that afforded by the straggling hairs
on the body of the adult.
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 am assured by dentists that they are much more
liable to decay, and are earlier lost, than the other teeth. It is also
remarkable that they are much more liable to vary both in structure and
in the period of their development than the other teeth.[33] 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.[34] 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,[35] and this shortening may, I
presume, be safely 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.
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 it 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.[36] 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[37] 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.[38]
In the Quadrumana and some other orders of mammals, especially in the
Carnivora, 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 passes, and often the great artery. Now in the humerus of man, as
Dr. Struthers[39] and others have shewn, there is generally a trace of
this passage, and it is sometimes fairly well developed, being formed by
a depending hook-like process of bone, completed by a band of ligament.
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 during ancient times it appears to have been much more
common. Mr. Busk[40] 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 30 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." The 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 races, is interesting. One chief cause seems to be that ancient
races stand somewhat nearer than modern races in the long line of
descent to their remote animal-like progenitors.
The os coccyx in man, though functionless as a tail, plainly represents
this part in other vertebrate animals. At an early embryonic period it
is free, and, as we have seen, projects beyond the lower extremities. In
certain rare and anomalous cases it has been known, according to Isidore
Geoffroy St.-Hilaire and others,[41] to form a small external rudiment
of a tail. The os coccyx is short, usually including only four vertebrae:
and these are in a rudimental condition, for they consist, with the
exception of the basal one, of the centrum alone.[42] 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, which is so largely developed in many mammals.
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 (Macacus) and of a cat, in both of which
they found, though not at the extremity, a similarly convoluted body.
The reproductive system offers various rudimentary structures; but these
differ in one important respect from the foregoing cases. We are not
here concerned with a vestige of a part which does not belong to the
species in an efficient state; but with a part which is always present
and efficient in the one sex, being 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; namely, on parts acquired by one sex having been partially
transmitted to the other. Here I will 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.[43] Some additional rudimentary structures belonging to the
reproductive system might here have been adduced.[44]
The bearing of the three great classes of facts now given is
unmistakeable. But it would be superfluous here 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
variations 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 embryo 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.
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 demi-gods, 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.