A	>>	B	>>	C	>>	D	>>	E
F	>>	G	>>	H	>>	I	>>	J
K	>>	L	>>	M	>>	N	>>	O
P	>>	R	>>	S	>>	T	>>	U
V	>>	W	>>			X	>>	Z

William Congreve - "The Double Dealer"

Andrew Lang - "Old Friends Essays in Epistolary Parody"

Honore de Balzac - "Letters of Two Brides"

Richard Harding Davis - "The Man Who Could Not Lose"

The Descent of Man and Selection in Relation to Sex

C >> Charles Darwin >> The Descent of Man and Selection in Relation to Sex




As the progenitors of man became more and more erect, with their hands and
arms more and more modified for prehension and other purposes, with their
feet and legs at the same time transformed for firm support and
progression, endless other changes of structure would have become
necessary. The pelvis would have to be broadened, the spine peculiarly
curved, and the head fixed in an altered position, all which changes have
been attained by man. Prof. Schaaffhausen (76. 'On the Primitive Form of
the Skull,' translated in 'Anthropological Review,' Oct. 1868, p. 428.
Owen ('Anatomy of Vertebrates,' vol. ii. 1866, p. 551) on the mastoid
processes in the higher apes.) maintains that "the powerful mastoid
processes of the human skull are the result of his erect position;" and
these processes are absent in the orang, chimpanzee, etc., and are smaller
in the gorilla than in man. Various other structures, which appear
connected with man's erect position, might here have been added. It is
very difficult to decide how far these correlated modifications are the
result of natural selection, and how far of the inherited effects of the
increased use of certain parts, or of the action of one part on another.
No doubt these means of change often co-operate: thus when certain
muscles, and the crests of bone to which they are attached, become enlarged
by habitual use, this shews that certain actions are habitually performed
and must be serviceable. Hence the individuals which performed them best,
would tend to survive in greater numbers.

The free use of the arms and hands, partly the cause and partly the result
of man's erect position, appears to have led in an indirect manner to other
modifications of structure. The early male forefathers of man were, as
previously stated, probably furnished with great canine teeth; but as they
gradually acquired the habit of using stones, clubs, or other weapons, for
fighting with their enemies or rivals, they would use their jaws and teeth
less and less. In this case, the jaws, together with the teeth, would
become reduced in size, as we may feel almost sure from innumerable
analogous cases. In a future chapter we shall meet with a closely parallel
case, in the reduction or complete disappearance of the canine teeth in
male ruminants, apparently in relation with the development of their horns;
and in horses, in relation to their habit of fighting with their incisor
teeth and hoofs.

In the adult male anthropomorphous apes, as Rutimeyer (77. 'Die Grenzen
der Thierwelt, eine Betrachtung zu Darwin's Lehre,' 1868, s. 51.), and
others, have insisted, it is the effect on the skull of the great
development of the jaw-muscles that causes it to differ so greatly in many
respects from that of man, and has given to these animals "a truly
frightful physiognomy." Therefore, as the jaws and teeth in man's
progenitors gradually become reduced in size, the adult skull would have
come to resemble more and more that of existing man. As we shall hereafter
see, a great reduction of the canine teeth in the males would almost
certainly affect the teeth of the females through inheritance.

As the various mental faculties gradually developed themselves the brain
would almost certainly become larger. No one, I presume, doubts that the
large proportion which the size of man's brain bears to his body, compared
to the same proportion in the gorilla or orang, is closely connected with
his higher mental powers. We meet with closely analogous facts with
insects, for in ants the cerebral ganglia are of extraordinary dimensions,
and in all the Hymenoptera these ganglia are many times larger than in the
less intelligent orders, such as beetles. (78. Dujardin, 'Annales des
Sciences Nat.' 3rd series, Zoolog., tom. xiv. 1850, p. 203. See also Mr.
Lowne, 'Anatomy and Phys. of the Musca vomitoria,' 1870, p. 14. My son,
Mr. F. Darwin, dissected for me the cerebral ganglia of the Formica rufa.)
On the other hand, no one supposes that the intellect of any two animals or
of any two men can be accurately gauged by the cubic contents of their
skulls. It is certain that there may be extraordinary mental activity with
an extremely small absolute mass of nervous matter: thus the wonderfully
diversified instincts, mental powers, and affections of ants are notorious,
yet their cerebral ganglia are not so large as the quarter of a small pin's
head. Under this point of view, the brain of an ant is one of the most
marvellous atoms of matter in the world, perhaps more so than the brain of
a man.

The belief that there exists in man some close relation between the size of
the brain and the development of the intellectual faculties is supported by
the comparison of the skulls of savage and civilised races, of ancient and
modern people, and by the analogy of the whole vertebrate series. Dr. J.
Barnard Davis has proved (79. 'Philosophical Transactions,' 1869, p.
513.), by many careful measurements, that the mean internal capacity of the
skull in Europeans is 92.3 cubic inches; in Americans 87.5; in Asiatics
87.1; and in Australians only 81.9 cubic inches. Professor Broca (80.
'Les Selections,' M. P. Broca, 'Revue d'Anthropologies,' 1873; see also, as
quoted in C. Vogt's 'Lectures on Man,' Engl. translat., 1864, pp. 88, 90.
Prichard, 'Physical History of Mankind,' vol. i. 1838, p. 305.) found that
the nineteenth century skulls from graves in Paris were larger than those
from vaults of the twelfth century, in the proportion of 1484 to 1426; and
that the increased size, as ascertained by measurements, was exclusively in
the frontal part of the skull--the seat of the intellectual faculties.
Prichard is persuaded that the present inhabitants of Britain have "much
more capacious brain-cases" than the ancient inhabitants. Nevertheless, it
must be admitted that some skulls of very high antiquity, such as the
famous one of Neanderthal, are well developed and capacious. (81. In the
interesting article just referred to, Prof. Broca has well remarked, that
in civilised nations, the average capacity of the skull must be lowered by
the preservation of a considerable number of individuals, weak in mind and
body, who would have been promptly eliminated in the savage state. On the
other hand, with savages, the average includes only the more capable
individuals, who have been able to survive under extremely hard conditions
of life. Broca thus explains the otherwise inexplicable fact, that the
mean capacity of the skull of the ancient Troglodytes of Lozere is greater
than that of modern Frenchmen.) With respect to the lower animals, M.E.
Lartet (82. 'Comptes-rendus des Sciences,' etc., June 1, 1868.), by
comparing the crania of tertiary and recent mammals belonging to the same
groups, has come to the remarkable conclusion that the brain is generally
larger and the convolutions are more complex in the more recent forms. On
the other hand, I have shewn (83. The 'Variation of Animals and Plants
under Domestication,' vol. i. pp. 124-129.) that the brains of domestic
rabbits are considerably reduced in bulk, in comparison with those of the
wild rabbit or hare; and this may be attributed to their having been
closely confined during many generations, so that they have exerted their
intellect, instincts, senses and voluntary movements but little.

The gradually increasing weight of the brain and skull in man must have
influenced the development of the supporting spinal column, more especially
whilst he was becoming erect. As this change of position was being brought
about, the internal pressure of the brain will also have influenced the
form of the skull; for many facts shew how easily the skull is thus
affected. Ethnologists believe that it is modified by the kind of cradle
in which infants sleep. Habitual spasms of the muscles, and a cicatrix
from a severe burn, have permanently modified the facial bones. In young
persons whose heads have become fixed either sideways or backwards, owing
to disease, one of the two eyes has changed its position, and the shape of
the skull has been altered apparently by the pressure of the brain in a new
direction. (84. Schaaffhausen gives from Blumenbach and Busch, the cases
of the spasms and cicatrix, in 'Anthropological Review,' Oct. 1868, p. 420.
Dr. Jarrold ('Anthropologia,' 1808, pp. 115, 116) adduces from Camper and
from his own observations, cases of the modification of the skull from the
head being fixed in an unnatural position. He believes that in certain
trades, such as that of a shoemaker, where the head is habitually held
forward, the forehead becomes more rounded and prominent.) I have shewn
that with long-eared rabbits even so trifling a cause as the lopping
forward of one ear drags forward almost every bone of the skull on that
side; so that the bones on the opposite side no longer strictly correspond.
Lastly, if any animal were to increase or diminish much in general size,
without any change in its mental powers, or if the mental powers were to be
much increased or diminished, without any great change in the size of the
body, the shape of the skull would almost certainly be altered. I infer
this from my observations on domestic rabbits, some kinds of which have
become very much larger than the wild animal, whilst others have retained
nearly the same size, but in both cases the brain has been much reduced
relatively to the size of the body. Now I was at first much surprised on
finding that in all these rabbits the skull had become elongated or
dolichocephalic; for instance, of two skulls of nearly equal breadth, the
one from a wild rabbit and the other from a large domestic kind, the former
was 3.15 and the latter 4.3 inches in length. (85. 'Variation of Animals
and Plants under Domestication,' vol. i. p. 117, on the elongation of the
skull; p. 119, on the effect of the lopping of one ear.) One of the most
marked distinctions in different races of men is that the skull in some is
elongated, and in others rounded; and here the explanation suggested by the
case of the rabbits may hold good; for Welcker finds that short "men
incline more to brachycephaly, and tall men to dolichocephaly" (86. Quoted
by Schaaffhausen, in 'Anthropological Review,' Oct. 1868, p. 419.); and
tall men may be compared with the larger and longer-bodied rabbits, all of
which have elongated skulls or are dolichocephalic.

From these several facts we can understand, to a certain extent, the means
by which the great size and more or less rounded form of the skull have
been acquired by man; and these are characters eminently distinctive of him
in comparison with the lower animals.

Another most conspicuous difference between man and the lower animals is
the nakedness of his skin. Whales and porpoises (Cetacea), dugongs
(Sirenia) and the hippopotamus are naked; and this may be advantageous to
them for gliding through the water; nor would it be injurious to them from
the loss of warmth, as the species, which inhabit the colder regions, are
protected by a thick layer of blubber, serving the same purpose as the fur
of seals and otters. Elephants and rhinoceroses are almost hairless; and
as certain extinct species, which formerly lived under an Arctic climate,
were covered with long wool or hair, it would almost appear as if the
existing species of both genera had lost their hairy covering from exposure
to heat. This appears the more probable, as the elephants in India which
live on elevated and cool districts are more hairy (87. Owen, 'Anatomy of
Vertebrates,' vol. iii. p. 619.) than those on the lowlands. May we then
infer that man became divested of hair from having aboriginally inhabited
some tropical land? That the hair is chiefly retained in the male sex on
the chest and face, and in both sexes at the junction of all four limbs
with the trunk, favours this inference--on the assumption that the hair was
lost before man became erect; for the parts which now retain most hair
would then have been most protected from the heat of the sun. The crown of
the head, however, offers a curious exception, for at all times it must
have been one of the most exposed parts, yet it is thickly clothed with
hair. The fact, however, that the other members of the order of Primates,
to which man belongs, although inhabiting various hot regions, are well
clothed with hair, generally thickest on the upper surface (88. Isidore
Geoffroy St.-Hilaire remarks ('Histoire Nat. Generale,' tom. ii. 1859, pp.
215-217) on the head of man being covered with long hair; also on the upper
surfaces of monkeys and of other mammals being more thickly clothed than
the lower surfaces. This has likewise been observed by various authors.
Prof. P. Gervais ('Histoire Nat. des Mammiferes,' tom. i. 1854, p. 28),
however, states that in the Gorilla the hair is thinner on the back, where
it is partly rubbed off, than on the lower surface.), is opposed to the
supposition that man became naked through the action of the sun. Mr. Belt
believes (89. The 'Naturalist in Nicaragua,' 1874, p. 209. As some
confirmation of Mr. Belt's view, I may quote the following passage from Sir
W. Denison ('Varieties of Vice-Regal Life,' vol. i. 1870, p. 440): "It is
said to be a practice with the Australians, when the vermin get
troublesome, to singe themselves.") that within the tropics it is an
advantage to man to be destitute of hair, as he is thus enabled to free
himself of the multitude of ticks (acari) and other parasites, with which
he is often infested, and which sometimes cause ulceration. But whether
this evil is of sufficient magnitude to have led to the denudation of his
body through natural selection, may be doubted, since none of the many
quadrupeds inhabiting the tropics have, as far as I know, acquired any
specialised means of relief. The view which seems to me the most probable
is that man, or rather primarily woman, became divested of hair for
ornamental purposes, as we shall see under Sexual Selection; and, according
to this belief, it is not surprising that man should differ so greatly in
hairiness from all other Primates, for characters, gained through sexual
selection, often differ to an extraordinary degree in closely related
forms.

According to a popular impression, the absence of a tail is eminently
distinctive of man; but as those apes which come nearest to him are
destitute of this organ, its disappearance does not relate exclusively to
man. The tail often differs remarkably in length within the same genus:
thus in some species of Macacus it is longer than the whole body, and is
formed of twenty-four vertebrae; in others it consists of a scarcely
visible stump, containing only three or four vertebrae. In some kinds of
baboons there are twenty-five, whilst in the mandrill there are ten very
small stunted caudal vertebrae, or, according to Cuvier (90. Mr. St.
George Mivart, 'Proc. Zoolog. Soc.' 1865, pp. 562, 583. Dr. J.E. Gray,
'Cat. Brit. Mus.: 'Skeletons.' Owen, 'Anatomy of Vertebrates,' vol. ii.
p. 517. Isidore Geoffroy, 'Hist. Nat. Gen.' tom. ii. p. 244.), sometimes
only five. The tail, whether it be long or short, almost always tapers
towards the end; and this, I presume, results from the atrophy of the
terminal muscles, together with their arteries and nerves, through disuse,
leading to the atrophy of the terminal bones. But no explanation can at
present be given of the great diversity which often occurs in its length.
Here, however, we are more specially concerned with the complete external
disappearance of the tail. Professor Broca has recently shewn (91. 'Revue
d'Anthropologie,' 1872; 'La Constitution des vertebres caudales.') that the
tail in all quadrupeds consists of two portions, generally separated
abruptly from each other; the basal portion consists of vertebrae, more or
less perfectly channelled and furnished with apophyses like ordinary
vertebrae; whereas those of the terminal portion are not channelled, are
almost smooth, and scarcely resemble true vertebrae. A tail, though not
externally visible, is really present in man and the anthropomorphous apes,
and is constructed on exactly the same pattern in both. In the terminal
portion the vertabrae, constituting the os coccyx, are quite rudimentary,
being much reduced in size and number. In the basal portion, the vertebrae
are likewise few, are united firmly together, and are arrested in
development; but they have been rendered much broader and flatter than the
corresponding vertebrae in the tails of other animals: they constitute
what Broca calls the accessory sacral vertebrae. These are of functional
importance by supporting certain internal parts and in other ways; and
their modification is directly connected with the erect or semi-erect
attitude of man and the anthropomorphous apes. This conclusion is the more
trustworthy, as Broca formerly held a different view, which he has now
abandoned. The modification, therefore, of the basal caudal vertebrae in
man and the higher apes may have been effected, directly or indirectly,
through natural selection.

But what are we to say about the rudimentary and variable vertebrae of the
terminal portion of the tail, forming the os coccyx? A notion which has
often been, and will no doubt again be ridiculed, namely, that friction has
had something to do with the disappearance of the external portion of the
tail, is not so ridiculous as it at first appears. Dr. Anderson (92.
'Proceedings Zoological Society,' 1872, p. 210.) states that the extremely
short tail of Macacus brunneus is formed of eleven vertebrae, including the
imbedded basal ones. The extremity is tendinous and contains no vertebrae;
this is succeeded by five rudimentary ones, so minute that together they
are only one line and a half in length, and these are permanently bent to
one side in the shape of a hook. The free part of the tail, only a little
above an inch in length, includes only four more small vertebrae. This
short tail is carried erect; but about a quarter of its total length is
doubled on to itself to the left; and this terminal part, which includes
the hook-like portion, serves "to fill up the interspace between the upper
divergent portion of the callosities;" so that the animal sits on it, and
thus renders it rough and callous. Dr. Anderson thus sums up his
observations: "These facts seem to me to have only one explanation; this
tail, from its short size, is in the monkey's way when it sits down, and
frequently becomes placed under the animal while it is in this attitude;
and from the circumstance that it does not extend beyond the extremity of
the ischial tuberosities, it seems as if the tail originally had been bent
round by the will of the animal, into the interspace between the
callosities, to escape being pressed between them and the ground, and that
in time the curvature became permanent, fitting in of itself when the organ
happens to be sat upon." Under these circumstances it is not surprising
that the surface of the tail should have been roughened and rendered
callous, and Dr. Murie (93. 'Proceedings Zoological Society,' 1872, p.
786.), who carefully observed this species in the Zoological Gardens, as
well as three other closely allied forms with slightly longer tails, says
that when the animal sits down, the tail "is necessarily thrust to one side
of the buttocks; and whether long or short its root is consequently liable
to be rubbed or chafed." As we now have evidence that mutilations
occasionally produce an inherited effect (94. I allude to Dr. Brown-
Sequard's observations on the transmitted effect of an operation causing
epilepsy in guinea-pigs, and likewise more recently on the analogous
effects of cutting the sympathetic nerve in the neck. I shall hereafter
have occasion to refer to Mr. Salvin's interesting case of the apparently
inherited effects of mot-mots biting off the barbs of their own tail-
feathers. See also on the general subject 'Variation of Animals and Plants
under Domestication,' vol. ii. pp. 22-24.), it is not very improbable that
in short-tailed monkeys, the projecting part of the tail, being
functionally useless, should after many generations have become rudimentary
and distorted, from being continually rubbed and chafed. We see the
projecting part in this condition in the Macacus brunneus, and absolutely
aborted in the M. ecaudatus and in several of the higher apes. Finally,
then, as far as we can judge, the tail has disappeared in man and the
anthropomorphous apes, owing to the terminal portion having been injured by
friction during a long lapse of time; the basal and embedded portion having
been reduced and modified, so as to become suitable to the erect or semi-
erect position.

I have now endeavoured to shew that some of the most distinctive characters
of man have in all probability been acquired, either directly, or more
commonly indirectly, through natural selection. We should bear in mind
that modifications in structure or constitution which do not serve to adapt
an organism to its habits of life, to the food which it consumes, or
passively to the surrounding conditions, cannot have been thus acquired.
We must not, however, be too confident in deciding what modifications are
of service to each being: we should remember how little we know about the
use of many parts, or what changes in the blood or tissues may serve to fit
an organism for a new climate or new kinds of food. Nor must we forget the
principle of correlation, by which, as Isidore Geoffroy has shewn in the
case of man, many strange deviations of structure are tied together.
Independently of correlation, a change in one part often leads, through the
increased or decreased use of other parts, to other changes of a quite
unexpected nature. It is also well to reflect on such facts, as the
wonderful growth of galls on plants caused by the poison of an insect, and
on the remarkable changes of colour in the plumage of parrots when fed on
certain fishes, or inoculated with the poison of toads (95. The 'Variation
of Animals and Plants under Domestication,' vol. ii. pp. 280, 282.); for we
can thus see that the fluids of the system, if altered for some special
purpose, might induce other changes. We should especially bear in mind
that modifications acquired and continually used during past ages for some
useful purpose, would probably become firmly fixed, and might be long
inherited.

Thus a large yet undefined extension may safely be given to the direct and
indirect results of natural selection; but I now admit, after reading the
essay by Nageli on plants, and the remarks by various authors with respect
to animals, more especially those recently made by Professor Broca, that in
the earlier editions of my 'Origin of Species' I perhaps attributed too
much to the action of natural selection or the survival of the fittest. I
have altered the fifth edition of the 'Origin' so as to confine my remarks
to adaptive changes of structure; but I am convinced, from the light gained
during even the last few years, that very many structures which now appear
to us useless, will hereafter be proved to be useful, and will therefore
come within the range of natural selection. Nevertheless, I did not
formerly consider sufficiently the existence of structures, which, as far
as we can at present judge, are neither beneficial nor injurious; and this
I believe to be one of the greatest oversights as yet detected in my work.
I may be permitted to say, as some excuse, that I had two distinct objects
in view; firstly, to shew that species had not been separately created, and
secondly, that natural selection had been the chief agent of change, though
largely aided by the inherited effects of habit, and slightly by the direct
action of the surrounding conditions. I was not, however, able to annul
the influence of my former belief, then almost universal, that each species
had been purposely created; and this led to my tacit assumption that every
detail of structure, excepting rudiments, was of some special, though
unrecognised, service. Any one with this assumption in his mind would
naturally extend too far the action of natural selection, either during
past or present times. Some of those who admit the principle of evolution,
but reject natural selection, seem to forget, when criticising my book,
that I had the above two objects in view; hence if I have erred in giving
to natural selection great power, which I am very far from admitting, or in
having exaggerated its power, which is in itself probable, I have at least,
as I hope, done good service in aiding to overthrow the dogma of separate
creations.

It is, as I can now see, probable that all organic beings, including man,
possess peculiarities of structure, which neither are now, nor were
formerly of any service to them, and which, therefore, are of no
physiological importance. We know not what produces the numberless slight
differences between the individuals of each species, for reversion only
carries the problem a few steps backwards, but each peculiarity must have
had its efficient cause. If these causes, whatever they may be, were to
act more uniformly and energetically during a lengthened period (and
against this no reason can be assigned), the result would probably be not a
mere slight individual difference, but a well-marked and constant
modification, though one of no physiological importance. Changed
structures, which are in no way beneficial, cannot be kept uniform through
natural selection, though the injurious will be thus eliminated.
Uniformity of character would, however, naturally follow from the assumed
uniformity of the exciting causes, and likewise from the free intercrossing
of many individuals. During successive periods, the same organism might in
this manner acquire successive modifications, which would be transmitted in
a nearly uniform state as long as the exciting causes remained the same and
there was free intercrossing. With respect to the exciting causes we can
only say, as when speaking of so-called spontaneous variations, that they
relate much more closely to the constitution of the varying organism, than
to the nature of the conditions to which it has been subjected.

Copyright (c) 2007. fullstories.net. All rights reserved.