Descent of Man [ 1871 ]

Charles Darwin [ 1809 – 1882 ]

Chapter II – On the Manner of Development of Man from some Lower Form

IT is manifest that man is now subject to much variability. No two
individuals of the same race are quite alike. We may compare
millions of faces, and each will be distinct. There is an equally
great amount of diversity in the proportions and dimensions of the
various parts of the body; the length of the legs being one of the
most variable points.* Although in some quarters of the world an
elongated skull, and in other quarters a short skull prevails, yet
there is great diversity of shape even within the limits of the same
race, as with the aborigines of America and South Australia- the
latter a race "probably as pure and homogeneous in blood, customs, and
language as any in existence"- and even with the inhabitants of so
confined an area as the Sandwich Islands.*(2) An eminent dentist
assures me that there is nearly as much diversity in the teeth as in
the features. The chief arteries so frequently run in abnormal
courses, that is has been found useful for surgical purposes to
calculate from 1040 corpses how often each course prevails.*(3) The
muscles are eminently variable: thus those of the foot were found by
Prof. Turner*(4) not to be strictly alike in any two out of fifty
bodies; and in some the deviations were considerable. He adds, that
the power of performing the appropriate movements must have been
modified in accordance with the several deviations. Mr. J. Wood has
recorded*(5) the occurrence of 295 muscular variations in thirty-six
subjects, and in another set of the same number no less than 558
variations, those occurring on both sides of the body being only
reckoned as one. In the last set, not one body out of the thirty-six
was "found totally wanting in departures from the standard
descriptions of the muscular system given in anatomical text books." A
single body presented the extraordinary number of twenty-five distinct
abnormalities. The same muscle sometimes varies in many ways: thus
Prof. Macalister describes*(6) no less than twenty distinct variations
in the palmaris accessorius.

* Investigations in the Military and Anthropological Statistics of
American Soldiers, by B. A. Gould, 1869, p. 256.
*(2) With respect to the " Cranial forms of the American
aborigines," see Dr. Aitken Meigs in Proc. Acad. Nat. Sci.
Philadelphia, May, 1868. On the Australians, see Huxley, in Lyell's
Antiquity of Man, 1863, p. 87. On the Sandwich Islanders, Prof. J.
Wyman, Observations on Crania, Boston, 1868, p. 18.
*(3) Anatomy of the Arteries, by R. Quain. Preface, vol. i., 1844.
*(4) Transactions of the Royal Society of Edinburgh, vol. xxiv., pp.
175, 189.
*(5) Proceedings Royal Society, 1867, p. 544; also 1868, pp. 483,
524. There is a previous paper, 1866, p. 229.
*(6) Proc. R. Irish Academy, vol. x., 1868, p. 141.

The famous old anatomist, Wolff,* insists that the internal
viscera are more variable than the external parts: Nulla particula est
quae non aliter et aliter in aliis se habeat hominibus. He has even
written a treatise on the choice of typical examples of the viscera
for representation. A discussion on the beau-ideal of the liver,
lungs, kidneys, &c., as of the human face divine, sounds strange in
our ears.

* Act. Acad. St. Petersburg, 1778, part ii., p. 217.

The variability or diversity of the mental faculties in men of the
same race, not to mention the greater differences between the men of
distinct races, is so notorious that not a word need here be said.
So it is with the lower animals. All who have had charge of menageries
admit this fact, and we see it plainly in our dogs and other
domestic animals. Brehm especially insists that each individual monkey
of those which he kept tame in Africa had its own peculiar disposition
and temper: he mentions one baboon remarkable for its high
intelligence; and the keepers in the Zoological Gardens pointed out to
me a monkey, belonging to the New World division, equally remarkable
for intelligence. Rengger, also, insists on the diversity in the
various mental characters of the monkeys of the same species which
he kept in Paraguay; and this diversity, as he adds, is partly innate,
and partly the result of the manner in which they have been treated or
educated.*

* Brehm, Illustriertes Thierleben, B. i., ss. 58, 87. Rengger,
Saugethiere von Paraguay, s. 57.

I have elsewhere* so fully discussed the subject of Inheritance,
that I need here add hardly anything. A greater number of facts have
been collected with respect to the transmission of the most
trifling, as well as of the most important characters in man, than
in any of the lower animals; though the facts are copious enough
with respect to the latter. So in regard to mental qualities, their
transmission is manifest in our dogs, horses, and other domestic
animals. Besides special tastes and habits, general intelligence,
courage, bad and good temper, &c., are certainly transmitted. With man
we see similar facts in almost every family; and we now know,
through the admirable labours of Mr. Galton,*(2) that genius which
implies a wonderfully complex combination of high faculties, tends
to be inherited; and, on the other hand, it is too certain that
insanity and deteriorated mental powers likewise run in families.

* Variation of Animals and Plants under Domestication, vol. ii.,
chap. xii.
*(2) Hereditary Genius: an Inquiry into its Laws and Consequences,
1869.

With respect to the causes of variability, we are in all cases
very ignorant; but we can see that in man as in the lower animals,
they stand in some relation to the conditions to which each species
has been exposed, during several generations. Domesticated animals
vary more than those in a state of nature; and this is apparently
due to the diversified and changing nature of the conditions to
which they have been subjected. In this respect the different races of
man resemble domesticated animals, and so do the individuals of the
same race, when inhabiting. a very wide area, like that of America. We
see the influence of diversified conditions in the more civilised
nations; for the members belonging to different grades of rank, and
following different occupations, present a greater range of
character than do the members of barbarous nations. But the uniformity
of savages has often been exaggerated, and in some cases can hardly be
said to exist.* It is, nevertheless, an error to speak of man, even if
we look only to the conditions to which he has been exposed, as "far
more domesticated"*(2) than any other animal. Some savage races,
such as the Australians, are not exposed to more diversified
conditions than are many species which have a wide range. In another
and much more important respect, man differs widely from any
strictly domesticated animal; for his breeding has never long been
controlled, either by methodical or unconscious selection. No race
or body of men has been so completely subjugated by other men, as that
certain individuals should be preserved, and thus unconsciously
selected, from somehow excelling in utility to their masters. Nor have
certain male and female individuals been intentionally picked out
and matched, except in the well-known case of the Prussian grenadiers;
and in this case man obeyed, as might have been expected, the law of
methodical selection; for it is asserted that many tall men were
reared in the villages inhabited by the grenadiers and their tall
wives. In Sparta, also, a form of selection was followed, for it was
enacted that all children should be examined shortly after birth;
the well-formed and vigorous being preserved, the others left to
perish.*(3)

* Mr. Bates remarks (The Naturalist on the Amazons, 1863, vol. ii p.
159), with respect to the Indians of the same South American tribe,
"no two of them were at all similar in the shape of the head; one
man had an oval visage with fine features, and another was quite
Mongolian in breadth and prominence of cheek, spread of nostrils,
and obliquity of eyes."
*(2) Blumenbach, Treatises on Anthropology., Eng. translat., 1865,
p. 205.
*(3) Mitford's History of Greece, vol. i., p. 282. It appears from a
passage in Xenophon's Memorabilia, B. ii. 4 (to which my attention has
been called by the Rev. J. N. Hoare), that it was a well recognised
principle with the Greeks, that men ought to select their wives with a
view to the health and vigour of their children. The Grecian poet,
Theognis, who lived 550 B. C., clearly saw how important selection, if
carefully applied, would be for the improvement of mankind. He saw,
likewise, that wealth often checks the proper action of sexual
selection. He thus writes:

With kine and horses, Kurnus! we proceed
By reasonable rules, and choose a breed
For profit and increase at any price:
Of a sound stock, without defect or vice.
But, in the daily matches that we make,
The price is everything: for money's sake,
Men marry: women are in marriage given
The churl or ruffian, that in wealth has thriven,
May match his offspring with the proudest race:
Thus everything is mix'd, noble and base!
If then in outward manner, form, and mind,
You find us a degraded, motley kind,
Wonder no more, my friend! the cause is plain,
And to lament the consequence is vain.

(The Works of J. Hookham Frere, vol. ii., 1872, p. 334.)

If we consider all the races of man as forming a single species, his
range is enormous; but some separate races, as the Americans and
Polynesians, have very wide ranges. It is a well-known law that
widely-ranging species are much more variable than species with
restricted ranges; and the variability of man may with more truth be
compared with that of widely-ranging species, than with that of
domesticated animals.
Not only does variability appear to be induced in man and the
lower animals by the same general causes, but in both the same parts
of the body are effected in a closely analogous manner. This has
been proved in such full detail by Godron and Quatrefages, that I need
here only refer to their works.* Monstrosities, which graduate into
slight variations, are likewise so similar in man and the lower
animals, that the same classification and the same terms can be used
for both, as has been shewn by Isidore Geoffroy St-Hilaire.*(2) In
my work on the variation of domestic animals, I have attempted to
arrange in a rude fashion the laws of variation under the following
heads:- The direct and definite action of changed conditions, as
exhibited by all or nearly all the individuals of the same species,
varying in the same manner under the same circumstances. The effects
of the long-continued use or disuse of parts. The cohesion of
homologous parts. The variability of multiple parts. Compensation of
growth; but of this law I have found no good instance in the case of
man. The effects of the mechanical pressure of one part on another; as
of the pelvis on the cranium of the infant in the womb. Arrests of
development, leading to the diminution or suppression of parts. The
reappearance of long-lost characters through reversion. And lastly,
correlated variation. All these so-called laws apply equally to man
and the lower animals; and most of them even to plants. It would be
superfluous here to discuss all of them;*(3) but several are so
important, that they must be treated at considerable length.

* Godron, De l'Espece, 1859, tom. ii., livre 3. Quatrefages, Unite
de l'Espece Humaine, 1861. Also Lectures on Anthropology, given in the
Revue des Cours Scientifiques, 1866-1868.
*(2) Hist. Gen. et Part. des Anomalies de l'Organisation, tom. i.,
1832.
*(3) I have fully discussed these laws in my Variation of Animals
and Plants under Domestication, vol. ii., chaps. xxii. and xxiii. M.
J. P. Durand has lately (1868) published a valuable essay, De
l'Influence des Milieux, &c. He lays much stress, in the case of
plants, on the nature of the soil.

The Direct and Definite Action of Changed Conditions.- This is a
most perplexing subject. It cannot be denied that changed conditions
produce some, and occasionally a considerable effect, on organisms
of all kinds; and it seems at first probable that if sufficient time
were allowed this would be the invariable result. But I have failed to
obtain clear evidence in favour of this conclusion; and valid
reasons may be urged on the other side, at least as far as the
innumerable structures are concerned, which are adapted for special
ends. There can, however, be no doubt that changed conditions induce
an almost indefinite amount of fluctuating variability, by which the
whole organisation is rendered in some degree plastic.
In the United States, above 1,000,000 soldiers, who served in the
late war, were measured, and the States in which they were born and
reared were recorded.* From this astonishing number of observations it
is proved that local influences of some kind act directly on
stature; and we further learn that "the State where the physical
growth has in great measure taken place, and the State of birth, which
indicates the ancestry, seem to exert a marked influence on the
stature." For instance, it is established, "that residence in the
Western States, during the years of growth, tends to produce
increase of stature." On the other hand, it is certain that with
sailors, their life delays growth, as shewn "by the great difference
between the statures of soldiers and sailors at the ages of
seventeen and eighteen years." Mr. B. A. Gould endeavoured to
ascertain the nature of the influences which thus act on stature;
but he arrived only at negative results, namely that they did not
relate to climate, the elevation of the land, soil, nor even "in any
controlling degree" to the abundance or the need of the comforts of
life. This latter conclusion is directly opposed to that arrived at
by, Villerme, from the statisties of the height of the conscripts in
different parts of France. When we compare the differences in
stature between the Polynesian chiefs and the lower orders within
the same islands, or between the inhabitants of the fertile volcanic
and low barren coral islands of the same ocean,*(2) or again between
the Fuegians on the eastern and western shores of their country, where
the means of subsistence are very different, it is scarcely possible
to avoid the conclusion that better food and greater comfort do
influence stature. But the preceding statements shew how difficult
it is to arrive at any precise result. Dr. Beddoe has lately proved
that, with the inhabitants of Britain, residence in towns and
certain occupations have a deteriorating influence on height; and he
infers that the result is to a certain extent inherited, as is
likewise the case in the United States. Dr. Beddoe further believes
that wherever a "race attains its maximum of physical development,
it rises highest in energy and moral vigour."*(3)

* Investigations in Military and Anthrop. Statistics, &c., 1869,
by B. A. Gould, pp. 93, 107, 126, 131, 134.
*(2) For the Polynesians, see Prichard's Physical History of
Mankind, vol. v., 1847, pp. 145, 283. Also Godron, De l'Espece, tom.
ii., p. 289. There is also a remarkable difference in appearance
between the closely-allied Hindoos inhabiting the Upper Ganges and
Bengal; see Elphinstone's History of India, vol. i., p. 324.
*(3) Memoirs, Anthropological Society, vol. iii., 1867-69, pp.
561, 565, 567.

Whether external conditions produce any other direct effect on man is
not known. It might have been expected that differences of climate
would have had a marked influence, inasmuch as the lungs and kidneys
are brought into activity under a low temperature, and the liver and
skin under a high one.* It was formerly thought that the colour of the
skin and the character of the hair were determined by light or heat;
and although it can hardly be denied that some effect is thus
produced, almost all observers now agree that the effect has been very
small, even after exposure during many ages. But this subject will
be more properly discussed when we treat of the different races of
mankind. With our domestic animals there are grounds for believing
that cold and damp directly affect the growth of the hair; but I
have not met with any evidence on this head in the case of man.

* Dr. Brakenridge, "Theory of Diathesis," Medical Times, June 19 and
July 17, 1869.

Effects of the increased Use and Disuse of Parts.- It is well
known that use strengthens the muscles in the individual, and complete
disuse, or the destruction of the proper nerve, weakens them. When the
eye is destroyed, the optic nerve often becomes atrophied. When an
artery is tied, the lateral channels increase not only in diameter,
but in the thickness and strength of their coats. When one kidney
ceases to act from disease, the other increases in size, and does
double work. Bones increase not only in thickness, but in length, from
carrying a greater weight.* Different occupations, habitually
followed, lead to changed proportions in various parts of the body.
Thus it was ascertained by the United States Commission*(2) that the
legs of the sailors employed in the late war were longer by 0.217 of
an inch than those of the soldiers, though the sailors were on an
average shorter men; whilst their arms were shorter by 1.09 of an
inch, and therefore, out of proportion, shorter in relation to their
lesser height. This shortness of the arms is apparently due to their
greater use, and is an unexpected result: but sailors chiefly use
their arms in pulling, and not in supporting weights. With sailors,
the girth of the neck and the depth of the instep are greater,
whilst the circumference of the chest, waist, and hips is less, than
in soldiers.

* I have given authorities for these several statements in my
Variation of Animals and Plants under Domestication, vol. ii., pp.
297-300. Dr. Jaeger, "Uber das Langenwachsthum der Knochen," Jenaische
Zeitschrift, B. v., Heft. i.
*(2) Investigations, &c., by B. A. Gould, 1869, p. 288.

Whether the several foregoing modifications would become hereditary,
if the same habits of life were followed during many generations, is
not known, but it is probable. Rengger* attributes the thin legs and
thick arms of the Payaguas Indians to successive generations having
passed nearly their whole lives in canoes, with their lower
extremities motionless. Other writers have come to a similar
conclusion in analogous cases. According to Cranz,*(2) who lived for a
long time with the Esquimaux, "The natives believe that ingenuity
and dexterity in seal-catching (their highest art and virtue) is
hereditary; there is is really something in it, for the son of a
celebrated seal-catcher will distinguish himself, though he lost his
father in childhood." But in this case it is mental aptitude, quite as
much as bodily structure, which appears to be inherited. It is
asserted that the hands of English labourers are at birth larger
than those of the gentry.*(3) From the correlation which exists, at
least in some cases,*(4) between the development of the extremities
and of the jaws, it is possible that in those classes which do not
labour much with their hands and feet, the jaws would be reduced in
size from this cause. That they are generally smaller in refined and
civilized men than in hard-working men or savages, is certain. But
with savages, as Mr. Herbert Spencer*(5) has remarked, the greater use
of the jaws in chewing coarse, uncooked food, would act in a direct
manner on the masticatory muscles, and on the bones to which they
are attached. In infants, long before birth, the skin on the soles
of the feet is thicker than on any other part of the body;*(6) and
it can hardly be doubted that this is due to the inherited effects
of pressure during a long series of generations.

* Saugethiere von Paraguay, 1830, s. 4.
*(2) History of Greenland, Eng. translat., 1767, vol. i., p. 230
*(3) Intermarriage, by Alex. Walker, 1838, p. 377.
*(4) The Variation of Animals and Plants under Domestication, vol.
i., p. 173.
*(5) Principles of Biology, vol. i., p. 455.
*(6) Paget, Lectures on Surgical Pathology, vol. ii, 1853, p. 209.

It is familiar to every one that watchmakers and engravers are
liable to be short-sighted, whilst men living much out of doors, and
especially savages, are generally long-sighted.* Short-sight and
long-sight certainly tend to be inherited.*(2) The inferiority of
Europeans, in comparison with savages, in eyesight and in the other
senses, is no doubt the accumulated and transmitted effect of lessened
use during many generations; for Rengger*(3) states that he has
repeatedly observed Europeans, who had been brought up and spent their
whole lives with the wild Indians, who nevertheless did not equal them
in the sharpness of their senses. The same naturalist observes that
the cavities in the skull for the reception of the several
sense-organs are larger in the American aborigines than in
Europeans; and this probably indicates a corresponding difference in
the dimensions of the organs themselves. Blumenbach has also
remarked on the large size of the nasal cavities in the skulls of
the American aborigines, and connects this fact with their
remarkably acute power of smell. The Mongolians of the plains of
northern Asia, according to Pallas, have wonderfully perfect senses;
and Prichard believes that the great breadth of their skulls across
the zygomas follows from their highly-developed sense organs.*(4)

* It is a singular and unexpected fact that sailors are inferior
to landsmen in their mean distance of distinct vision. Dr. B. A. Gould
(Sanitary Memoirs of the War of the Rebellion, 1869 p. 530), has
proved this to be the case; and he accounts for it by the ordinary
range of vision in sailors being "restricted to the length of the
vessel and the height of the masts."
*(2) The Variation of Animal and Plants under Domestication, vol.
i., p. 8.
*(3) Saugethiere von Paraguay, s. 8, 10. I have had good
opportunities for observing the extraordinary power of eyesight in the
Fuegians. See also Lawrence (Lectures on Physiology, &c., 1822, p.
404) on this same subject. M. Giraud-Teulon has recently collected
(Revue des Cours Scientifiques, 1870, p. 625) a large and valuable
body of evidence proving that the cause of short-sight, "C'est le
travail assidu, de pres."
*(4) Prichard, Physical History of Mankind, on the authority of
Blumenbach, vol. i., 1841, p. 311; for the statement by Pallas, vol.
iv., 1844, p. 407.

The Quechua Indians inhabit the lofty plateaux of Peru; and Alcide
d'Orbigny states* that, from continually breathing a highly rarefied
atmosphere, they have acquired chests and lungs of extraordinary
dimensions. The cells, also, of the lungs are larger and more numerous
than in Europeans. These observations have been doubted, but Mr. D.
Forbes carefully measured many Aymaras, an allied race, living at
the height of between 10,000 and 15,000 feet; and he informs me*(2)
that they differ conspicuously from the men of all other races seen by
him in the circumference and length of their bodies. In his table of
measurements, the stature of each man is taken at 1000, and the
other measurements are reduced to this standard. It is here seen
that the extended arms of the Aymaras are shorter than those of
Europeans, and much shorter than those of Negroes. The legs are
likewise shorter; and they present this remarkable peculiarity, that
in every Aymara measured, the femur is actually shorter than the
tibia. On an average, the length of the femur to that of the tibia
is as 211 to 252; whilst in two Europeans, measured at the same
time, the femora to the tibiae were as 244 to 230; and in three
Negroes as 258 to 241. The humerus is likewise shorter relatively to
the forearm. This shortening of that part of the limb which is nearest
to the body, appears to be, as suggested to me by Mr. Forbes, a case
of compensation in relation with the greatly increased length of the
trunk. The Aymaras present some other singular points of structure,
for instance, the very small projection of the heel.

* Quoted by Prichard, Researches into the Physical History of
Mankind, vol. v., p. 463.
*(2) Mr. Forbes' valuable paper is now published in the Journal of
the Ethnological Society of London, new series, vol. ii., 1870, p.
193.

These men are so thoroughly acclimatised to their cold and lofty
abode, that when formerly carried down by Spaniards to the low eastern
plains, and when now tempted down by high wages to the
gold-washings, they suffer a frightful rate of mortality. Nevertheless
Mr. Forbes found a few pure families which had survived during two
generations: and he observed that they still inherited their
characteristic peculiarities. But it was manifest, even without
measurement, that these peculiarities had all decreased; and on
measurement, their bodies were found not to be so much elongated as
those of the men on the high plateau; whilst their femora had become
somewhat lengthened, as had their tibiae, although in a less degree.
The actual measurements may be seen by consulting Mr. Forbes's memoir.
From these observations, there can, I think, be no doubt that
residence during many generations at a great elevation tends, both
directly and indirectly, to induce inherited modifications in the
proportions of the body.*

* Dr. Wilckens (Landwirthschaft. Wochenblatt, No. 10, 1869) has
lately published an interesting essay shewing how domestic animals,
which live in mountainous regions, have their frames modified.

Although man may not have been much modified during the latter
stages of his existence through the increased or decreased use of
parts, the facts now given shew that his liability in this respect has
not been lost; and we positively know that the same law holds good
with the lower animals. Consequently we may infer that when at a
remote epoch the progenitors of man were in a transitional state,
and were changing from quadrupeds into bipeds, natural selection would
probably have been greatly aided by the inherited effects of the
increased or diminished use of the different parts of the body.

Arrests of Development.- There is a difference between arrested
development and arrested growth, for parts in the former state
continue to grow whilst still retaining their early condition. Various
monstrosities come under this head; and some, as a cleft palate, are
known to be occasionally inherited. It will suffice for our purpose to
refer to the arrested brain-development of microcephalous idiots, as
described in Vogt's memoir.* Their skulls are smaller, and the
convolutions of the brain are less complex than in normal men. The
frontal sinus, or the projection over the eyebrows, is largely
developed, and the jaws are prognathous to an "effrayant" degree; so
that these idiots somewhat resemble the lower types of mankind.
Their intelligence, and most of their mental faculties, are
extremely feeble. They cannot acquire the power of speech, and are
wholly incapable of prolonged attention, but are much given to
imitation. They are strong and remarkably active, continually
gambolling and jumping about, and making grimaces. They often ascend
stairs on all-fours; and are curiously fond of climbing up furniture
or trees. We are thus reminded of the delight shewn by almost all boys
in climbing trees; and this again reminds us how lambs and kids,
originally alpine animals, delight to frisk on any hillock, however
small. Idiots also resemble the lower animals in some other
respects; thus several cases are recorded of their carefully
smelling every mouthful of food before eating it. One idiot is
described as often using his mouth in aid of his hands, whilst hunting
for lice. They are often filthy in their habits, and have no sense
of decency; and several cases have been published of their bodies
being remarkably hairy.*(2)

* Memoires sur les Microcephales, 1867, pp. 50, 125, 169, 171,
184-198.
*(2) Prof. Laycock sums up the character of brute-like idiots by
calling them theroid; Journal of Mental Science,, July, 1863. Dr.
Scott (The Deaf and Dumb, 2nd ed., 1870, p. 10) has often observed the
imbeciles smelling their food. See, on this same subject, and on the
hairiness of idiots, Dr. Maudsley, Body and Mind, 1870, pp. 46-51.
Pinel has also given a striking case of hairiness in an idiot.

Reversion.- Many of the cases to be here given, might have been
introduced under the last heading. When a structure is arrested in its
development, but still continues growing, until it closely resembles a
corresponding structure in some lower and adult member of the same
group, it may in one sense be considered as a case of reversion. The
lower members in a group give us some idea how the common progenitor
was probably constructed; and it is hardly credible that a complex
part, arrested at an early phase of embryonic development, should go
on growing so as ultimately to perform its proper function, unless
it had acquired such power during some earlier state of existence,
when the present exceptional or arrested structure was normal. The
simple brain of a microcephalous idiot, in as far as it resembles that
of an ape' may in this sense be said to offer a case of reversion.*
There are other cases which come more strictly under our present
head of reversion. Certain structures, regularly occurring in the
lower members of the group to which man belongs, occasionally make
their appearance in him, though not found in the normal human
embryo; or, if normally present in the human embryo, they become
abnormally developed, although in a manner which is normal in the
lower members of the group. These remarks will be rendered clearer
by the following illustrations.

* In my Variation of Animals under Domestication (vol. ii., p.
57), I attributed the not very rare cases of supernumerary mammae in
women to reversion. I was led to this as a probable conclusion, by the
additional mammae being generally placed symmetrically on the
breast; and more especially from one case, in which a single efficient
mamma occurred in the inguinal region of a woman, the daughter of
another woman with supernumerary mammae. But I now find (see, for
instance, Prof. Preyer, Der Kampf um das Dasein, 1869, s. 45) that
mammae erraticae, occur in other situations, as on the back, in the
armpit, and on the thigh; the mammae in this latter instance having
given so much milk that the child was thus nourished. The
probability that the additional mammae are due to reversion is thus
much weakened; nevertheless, it still seems to me probable, because
two pairs are often found symmetrically on the breast; and of this I
myself have received information in several cases. It is well known
that some lemurs normally have two pairs of mammae on the breast. Five
cases have been recorded of the presence of more than a pair of mammee
(of course rudimentary) in the male sex of mankind; see Journal of
Anat. and Physiology, 1872, p. 56, for a case given by Dr. Handyside
in which two brothers exhibited this peculiarity; see also a paper
by Dr. Bartels, in Reichert's and du Bois-Reymond's Archiv., 1872,
p. 304. In one of the cases alluded to by Dr. Bartels, a man bore five
mammae, one being medial and placed above the navel; Meckel von
Hemsbach thinks that this latter case is illustrated by a medial mamma
occurring in certain Cheiroptera. On the whole, we may well doubt if
additional mammae would ever have been developed in both sexes of
mankind, had not his early progenitors been provided with more than
a single pair.
In the above work (vol. ii., p. 12), I also attributed, though
with much hesitation, the frequent cases of polydactylism in men and
various animals to reversion. I was partly led to this through Prof.
Owen's statement, that some of the Ichthyopterygia possesses more than
five digits, and therefore, as I supposed, had retained a primordial
condition; but Prof. Gegenbaur (Jenaische Zeitschrift, B. v., Heft
3, s. 341), disputes Owen's conclusion. On the other hand, according
to the opinion lately advanced by Dr. Gunther, on the paddle of
Ceratodus, which is provided with articulated bony rays on both
sides of a central chain of bones, there seems no great difficulty
in admitting that six or more digits on one side, or on both sides,
might reappear through reversion. I am informed by Dr. Zouteveen
that there is a case on record of a man having twenty-four fingers and
twenty-four toes! I was chiefly led to the conclusion that the
presence of supernumerary digits might be due to reversion from the
fact that such digits, not only are strongly inherited, but, as I then
believed, had the power of regrowth after amputation, like the
normal digits of the lower Vertebrata. But I have explained in the
second edition of my Variation under Domestication why I now place
little reliance on the recorded cases of such regrowth. Nevertheless
it deserves notice, inasmuch as arrested development and reversion are
intimately related processes; that various structures in an
embryonic or arrested condition, such as a cleft palate, bifid uterus,
&c., are frequently accompanied by polydactylism. This has been
strongly insisted on by Meckel and Isidore Geoffroy St-Hilaire. But at
present it is the safest course to give up altogether the idea that
there is any relation between the development of supernumerary
digits and reversion to some lowly organized progenitor of man.

In various mammals the uterus graduates from a double organ with two
distinct orifices and two passages, as in the marsupials, into a
single organ, which is in no way double except from having a slight
internal fold, as in the higher apes and man. The rodents exhibit a
perfect series of gradations between these two extreme states. In
all mammals the uterus is developed from two simple primitive tubes,
the inferior portions of which form the cornua; and it is in the words
of Dr. Farre, "by the coalescence of the two cornua at their lower
extremities that the body of the uterus is formed in man; while in
those animals in which no middle portion or body exists, the cornua
remain ununited. As the development of the uterus proceeds, the two
cornua become gradually shorter, until at length they are lost, or, as
it were, absorbed into the body of the uterus." The angles of the
uterus are still produced into cornua, even in animals as high up in
the scale as the lower apes and lemurs.
Now in women, anomalous cases are not very infrequent, in which
the mature uterus is furnished with cornua, or is partially divided
into two organs; and such cases, according to Owen, repeat "the
grade of concentrative development," attained by certain rodents. Here
perhaps we have an instance of a simple arrest of embryonic
development, with subsequent growth and perfect functional
development; for either side of the partially double uterus is capable
of performing the proper office of gestation. In other and rarer
cases, two distinct uterine cavities are formed, each having its
proper orifice and passage.* No such stage is passed through during
the ordinary development of the embryo; and it is difficult to
believe, though perhaps not impossible, that the two simple, minute,
primitive tubes should know how (if such an expression may be used) to
grow into two distinct uteri, each with a well-constructed orifice,and
passage, and each furnished with numerous muscles, nerves, glands
and vessels, if they had not formerly passed through a similar
course of development, as in the case of existing marsupials. No one
will pretend that so perfect a structure as the abnormal double uterus
in woman could be the result of mere chance. But the principle of
reversion, by which a long-lost structure is called back into
existence, might serve as the guide for its full development, even
after the lapse of an enormous interval of time.

* See Dr. A. Farre's well-known article in the Cyclopaedia of
Anatomy and Physiology, vol. v., 1859, p. 642. Owen, Anatomy of
Vertebrates, vol. iii., 1868, p. 687. Professor Turner, in Edinburgh
Medical Journal, February, 1865.

Professor Canestrini, after discussing the foregoing and various
analogous cases, arrives at the same conclusion as that just given. He
adduces another instance, in the case of the malar bone,* which, in
some of the Quadrumana and other mammals, normally consists of two
portions. This is its condition in the human foetus when two months
old; and through arrested development, it sometimes remains thus in
man when adult, more especially in the lower prognathous races.
Hence Canestrini concludes that some ancient progenitor of man must
have had this bone normally divided into two portions, which
afterwards became fused together. In man the frontal bone consists
of a single piece, but in the embryo, and in children, and in almost
all the lower mammals, it consists of two pieces separated by a
distinct suture. This suture occasionally persists more or less
distinctly in man after maturity; and more frequently in ancient
than in recent crania, especially, as Canestrini has observed, in
those exhumed from the Drift, and belonging to the brachycephalic
type. Here again he comes to the same conclusion as in the analogous
case of the malar bones. In this, and other instances presently to
be given, the cause of ancient races approaching the lower animals
in certain characters more frequently than do the modern races,
appears to be, that the latter stand at a somewhat greater distance in
the long line of descent from their early semi-human progenitors.

* Annuario della Soc. dei Naturalisti, Modena, 1867, p. 83. Prof.
Canestrini gives extracts on this subject from various authorities.
Laurillard remarks, that as he has found a complete similarity in
the form, proportions, and connection of the two malar bones in
several human subjects and in certain apes, he cannot consider this
disposition of the parts as simply accidental. Another paper on this
same anomaly has been published by Dr. Saviotti in the Gazzetta
delle Cliniche, Turin, 1871, where he says that traces of the division
may be detected in about two per cent of adult skulls; he also remarks
that it more frequently occurs in prognathous skulls, not of the Aryan
race, than in others. See also G. Delorenzi on the same subject;
"Tre nuovi casi d'anomalia dell' osso malare," Torino, 1872. Also,
E. Morselli, "Sopra una rara anomalia dell' osso malare," Modena,
1872. Still more recently Gruber has written a pamphlet on the
division of this bone. I give these references because a reviewer,
without any grounds or scruples, has thrown doubts on my statements.

Various other anomalies in man, more or less analogous to the
foregoing, have been advanced by different authors, as cases of
reversion; but these seem not a little doubtful, for we have to
descend extremely low in the mammalian series, before we find such
structures normally present.*

* A whole series of cases is given by Isidore Geoffroy St-Hilaire,
Hist. des Anomalies, tom, iii, p. 437. A reviewer (Journal of
Anatomy and Physiology, 1871, p. 366) blames me much for not having
discussed the numerous cases, which have been recorded, of various
parts arrested in their development. He says that, according to my
theory, "every transient condition of an organ, during its
development, is not only a means to an end, but once was an end in
itself." This does not seem to me necessarily to hold good. Why should
not variations occur during an early period of development, having
no relation to reversion; yet such variations might be preserved and
accumulated, if in any way serviceable, for instance, in shortening
and simplifying the course of development? And again, why should not
injurious abnormalities, such as atrophied or hypertrophied parts,
which have no relation to a former state of existence, occur at an
early period, as well as during maturity?

In man, the canine teeth are perfectly efficient instruments for
mastication. But their true canine character, as Owen* remarks, "is
indicated by the conical form of the crown, which terminates in an
obtuse point, is convex outward and flat or sub-concave within, at the
base of which surface there is a feeble prominence. The conical form
is best expressed in the Melanian races, especially the Australian.
The canine is more deeply implanted, and by a stronger fang than the
incisors." Nevertheless, this tooth no longer serves man as a
special weapon for tearing his enemies or prey; it may, therefore,
as far as its proper function is concerned, be considered as
rudimentary. In every large collection of human skulls some may be
found, as Haeckel*(2) observes, with the canine teeth projecting
considerably beyond the others in the same manner as in the
anthropomorphous apes, but in a less degree. In these cases, open
spaces between the teeth in the one jaw are left for the reception
of the canines of the opposite jaw. An inter-space of this kind in a
Kaffir skull, figured by Wagner, is surprisingly wide.*(3) Considering
how few are the ancient skulls which have been examined, compared to
recent skulls, it is an interesting fact that in at least three
cases the canines project largely; and in the Naulette jaw they are
spoken of as enourmous.*(4)

* Anatomy of Vertebrates, vol. iii., 1868, p. 323.
*(2) Generelle Morphologie, 1866, B. ii., s. clv.
*(3) Carl Vogt's Lectures on Man, Eng. translat., 1864, p. 151.
*(4) C. Carter Blake, on a jaw from La Naulette, Anthropological
Review, 1867, p. 295. Schaaffhausen, ibid., 1868, p. 426.

Of the anthropomorphous apes the males alone have their canines
fully developed; but in the female gorilla, and in a less degree in
the female orang, these teeth project considerably beyond the
others; therefore the fact, of which I have been assured, that women
sometimes have considerably projecting canines, is no serious
objection to the belief that their occasional great development in man
is a case of reversion to an ape-like progenitor. He who rejects
with scorn the belief that the shape of his own canines, and their
occasional great development in other men, are due to our early
forefathers having been provided with these formidable weapons, will
probably reveal, by sneering, the line of his descent. For though he
no longer intends, nor has the power, to use these teeth as weapons,
he will unconsciously retract his "snarling muscles" (thus named by
Sir C. Bell),* so as to expose them ready for action, like a dog
prepared to fight.

* The Anatomy of Expression, 1844, pp. 110, 131.

Many muscles are occasionally developed in man, which are proper
to the Quadrumana or other mammals. Professor Vlacovich* examined
forty male subjects, and found a muscle, called by him the
ischio-pubic, in nineteen of them; in three others there was a
ligament which represented this muscle; and in the remaining
eighteen no trace of it. In only two out of thirty female subjects was
this muscle developed on both sides, but in three others the
rudimentary ligament was present. This muscle, therefore, appears to
be much more common in the male than in the female sex; and on the
belief in the descent of man from some lower form, the fact is
intelligible; for it has been detected in several of the lower
animals, and in all of these it serves exclusively to aid the male
in the act of reproduction.

* Quoted by Prof. Canestrini in the Annuario, della Soc. dei
Naturalisti, 1867, p. 90.

Mr. J. Wood, in his valuable series of papers,* has minutely
described a vast number of muscular variations in man, which
resemble normal structures in the lower animals. The muscles which
closely resemble those regularly present in our nearest allies, the
Quadrumans, are too numerous to be here even specified. In a single
male subject, having a strong bodily frame, and well-formed skull,
no less than seven muscular variations were observed, all of which
plainly represented muscles proper to various kinds of apes. This man,
for instance, had on both sides of his neck a true and powerful
"levator claviculae," such as is found in all kinds of apes, and which
is said to occur in about one out of sixty human subjects.*(2)
Again, this man had "a special abductor of the metatarsal bone of
the fifth digit, such as Professor Huxley and Mr. Flower have shewn to
exist uniformly in the higher and lower apes." I will give only two
additional cases; the acromio-basilar muscle is found in all mammals
below man, and seems to be correlated with a quadrupedal gait,*(3) and
it occurs in about one out of sixty human subjects. In the lower
extremities Mr. Bradley*(4) found an abductor ossis metatarsi quinti
in both feet of man; this muscle had not up to that time been recorded
in mankind, but is always present in the anthropomorphous apes. The
muscles of the hands and arms- parts which are so eminently
characteristic of man- are extremely liable to vary, so as to resemble
the corresponding muscles in the lower animals.*(5) Such
resemblances are either perfect or imperfect; yet in the latter case
they are manifestly of a transitional nature. Certain variations are
more common in man, and others in woman, without our being able to
assign any reason. Mr. Wood, after describing numerous variations,
makes the following pregnant remark. "Notable departures from the
ordinary type of muscular structures run in grooves or directions,
which must be taken to indicate some unknown factor, of much
importance to a comprehensive knowledge of general and scientific
anatomy."*(6)

* These papers deserve careful study by any one who desires to learn
how frequently our muscles vary, and in varying come to resemble those
of the Quadrumana. The following references relate to the few points
touched on in my text: Proc. Royal Soc., vol. xiv., 1865, pp. 379-384;
vol. xv., 1866, pp. 241, 242; vol. xv., 1867, p. 544; vol. xvi., 1868,
p. 524. I may here add that Dr. Murie and Mr. St. George Mivart have
shewn in their Memoir on the Lemuroidea (Transactions, Zoological
Society, vol. vii., 1869, p. 96), how extraordinarily variable some of
the muscles are in these animals, the lowest members of the
primates. Gradations, also, in the muscles leading to structures found
in animals still lower in the scale, are numerous in the Lemuroidea.
*(2) See also Prof. Macalister in Proceedings, Royal Irish
Academy, vol. x., 1868, p. 124.
*(3) Mr. Champneys in Journal of Anatomy and Physiology, Nov., 1871,
p. 178.
*(4) Ibid., May, 1872, p. 421.
*(5) Prof. Macalister (ibid., p. 121) has tabulated his
observations, and finds that muscular abnormalities are most
frequent in the fore-arms, secondly, in the face, thirdly, in the
foot, &c.
*(6) The Rev. Dr. Haughton, after giving (Proc. R. Irish Academy,
June 27, 1864, p. 715) a remarkable case of variation in the human
flexor pollicis longus, adds, "This remarkable example shows that
man may sometimes possess the arrangement of tendons of thumb and
fingers characteristic of the macaque; but whether such a case
should be regarded as a macaque passing upwards into a man, or a man
passing downwards into a macaque, or as a congenital freak of
nature, I cannot undertake to say." It is satisfactory to hear so
capable an anatomist, and so embittered an opponent of evolutionism,
admitting even the possibility of either of his first propositions.
Prof. Macalister has also described (Proceedings Royal Irish
Academy, vol. x., 1864, p. 138) variations in the flexor pollicis
longus, remarkable from their relations to the same muscle in the
Quadrumana.

That this unknown factor is reversion to a former state of existence
may be admitted as in the highest degree probable.* It is quite
incredible that a man should through mere accident abnormally resemble
certain apes in no less than seven of his muscles, if there had been
no genetic connection between them. On the other hand, if man is
descended from some ape-like creature, no valid reason can be assigned
why certain muscles should not suddenly reappear after an interval
of many thousand generations, in the same manner as with horses,
asses, and mules, dark-coloured stripes suddenly reappear on the legs,
and shoulders, after an interval of hundreds, or more probably of
thousands of generations.

* Since the first edition of this book appeared, Mr. Wood has
published another memoir in the Philosophical Transactions, 1870, p.
83, on the varieties of the muscles of the human neck, shoulder, and
chest. He here shows how extremely variable these muscles are, and how
often and how closely the variations resemble the normal muscles of
the lower animals. He sums up by remarking, "It will be enough for
my purpose if I have succeeded in shewing the more important forms
which, when occurring as varieties in the human subject, tend to
exhibit in a sufficiently marked manner what may be considered as
proofs and examples of the Darwinian principle of reversion, or law of
inheritance, in this department of anatomical science."

These various cases of reversion are so closely related to those
of rudimentary organs given in the first chapter, that many of them
might have been indifferently introduced either there or here. Thus
a human uterus furnished with cornua may be said to represent, in a
rudimentary condition, the same organ in its normal state in certain
mammals. Some parts which are rudimentary in man, as the os coccyx
in both sexes, and the mammae in the male sex, are always present;
whilst others, such as the supracondyloid foramen, only occasionally
appear, and therefore might have been introduced under the head of
reversion. These several reversionary structures, as well as the
strictly rudimentary ones, reveal the descent of man from some lower
form in an unmistakable manner.

Correlated Variation.- In man, as in the lower animals, many
structures are so intimately related, that when one part varies so
does another, without our being able, in most cases, to assign any
reason. We cannot say whether the one part governs the other, or
whether both are governed by some earlier developed part. Various
monstrosities, as I. Geoffroy repeatedly insists, are thus
intimately connected. Homologous structures are particularly liable to
change together, as we see on the opposite sides of the body, and in
the upper and lower extremities. Meckel long ago remarked, that when
the muscles of the arm depart from their proper type, they almost
always imitate those of the leg; and so, conversely, with the
muscles of the legs. The organs of sight and hearing, the teeth and
hair, the colour of the skin and of the hair, colour and constitution,
are more or less correlated.* Professor Schaaffhausen first drew
attention to the relation apparently existing between a muscular frame
and the strongly-pronounced supra-orbital ridges, which are so
characteristic of the lower races of man.

* The authorities for these several statements are given in my
Variation of Animals and Plants under Domestication, vol. ii., pp.
320-335.

Besides the variations which can be grouped with more or less
probability under the foregoing heads, there is a large class of
variations which may be provisionally called spontaneous, for to our
ignorance they appear to arise without any exciting cause. It can,
however, be shewn that such variations, whether consisting of slight
individual differences, or of strongly-marked and abrupt deviations of
structure, depend much more on the constitution of the organism than
on the nature of the conditions to which it has been subjected.*

* This whole subject has been discussed in chap. xxiii., vol. ii. of
my Variation of Animals and Plants under Domestication.

Rate of Increase.- Civilised populations have been known under
favourable conditions, as in the United States, to double their
numbers in twenty-five years; and, according to a calculation, by
Euler, this might occur in a little over twelve years.* At the
former rate, the present population of the United States (thirty
millions), would in 657 years cover the whole terraqueous globe so
thickly, that four men would have to stand on each square yard of
surface. The primary or fundamental check to the continued increase of
man is the difficulty of gaining subsistence, and of living in
comfort. We may infer that this is the case from what we see, for
instance, in the United States, where subsistence is easy, and there
is plenty of room. If such means were suddenly doubled in Great
Britain, our number would be quickly doubled. With civilised nations
this primary check acts chiefly by restraining marriages. The
greater death-rate of infants in the poorest classes is also very
important; as well as the greater mortality, from various diseases, of
the inhabitants of crowded and miserable houses, at all ages. The
effects of severe epidemics and wars are soon counterbalanced, and
more than counterbalanced, in nations placed under favourable
conditions. Emigration also comes in aid as a temporary check, but,
with the extremely poor classes, not to any great extent.

* See the ever memorable Essay on the Principle of Population, by
the Rev. T. Malthus, vol. i. 1826. pp. 6, 517.

There is great reason to suspect, as Malthus has remarked, that
the reproductive power is actually less in barbarous, than in
civilised races. We know nothing positively on this head, for with
savages no census has been taken; but from the concurrent testimony of
missionaries, and of others who have long resided with such people, it
appears that their families are usually small, and large ones rare.
This may be partly accounted for, as it is believed, by the women
suckling their infants during a long time; but it is highly probable
that savages, who often suffer much hardships, and who do not obtain
so much nutritious food as civilised men, would be actually less
prolific. I have shewn in a former work,* that all our domesticated
quadrupeds and birds, and all our cultivated plants, are more
fertile than the corresponding species in a state of nature. It is
no valid objection to this conclusion that animals suddenly supplied
with an excess of food, or when grown very fat; and that most plants
on sudden removal from very poor to very rich soil, are rendered
more or less sterile. We might, therefore, expect that civilised
men, who in one sense are highly domesticated, would be more
prolific than wild men. It is also probable that the increased
fertility of civilised nations would become, as with our domestic
animals, an inherited character: it is at least known that with
mankind a tendency to produce twins runs in families.*(2)

* Variation of Animals and Plants under Domestication, vol ii.,
pp. 111-113, 163.
*(2) Mr. Sedgwick, British and Foreign Medico-Chirurgical Review,
July, 1863, p. 170.

Notwithstanding that savages appear to be less prolific than
civilised people, they would no doubt rapidly increase if their
numbers were not by some means rigidly kept down. The Santali, or
hill-tribes of India, have recently afforded a good illustration of
this fact; for, as shewn by Mr. Hunter,* they have increased at an
extraordinary rate since vaccination has been introduced, other
pestilences mitigated, and war sternly repressed. This increase,
however, would not have been possible had not these rude people spread
into the adjoining districts, and worked for hire. Savages almost
always marry; yet there is some prudential restraint, for they do
not commonly marry at the earliest possible age. The young men are
often required to shew that they can support a wife; and they
generally have first to earn the price with which to purchase her from
her parents. With savages the difficulty of obtaining subsistence
occasionally limits their number in a much more direct manner than
with civilised people, for all tribes periodically suffer from
severe famines. At such times savages are forced to devour much bad
food, and their health can hardly fail to be injured. Many accounts
have been published of their protruding stomachs and emaciated limbs
after and during famines. They are then, also, compelled to wander
much, and, as I was assured in Australia, their infants perish in
large numbers. As famines are periodical, depending chiefly on extreme
seasons, all tribes must fluctuate in number. They cannot steadily and
regularly increase, as there is no artificial increase in the supply
of food. Savages, when hard pressed, encroach on each other's
territories, and war is the result; but they are indeed almost
always at war with their neighbours. They are liable to many accidents
on land and water in their search for food; and in some countries they
suffer much from the larger beasts of prey. Even in India, districts
have been depopulated by the ravages of tigers.

* The Animals of Rural Bengal, by W. W. Hunter, 1868, p. 259.

Malthus has discussed these several checks, but he does not lay
stress enough on what is probably the most important of all, namely
infanticide, especially of female infants and the habit of procuring
abortion. These practices now prevail in many quarters of the world;
and infanticide seems formerly to have prevailed, as Mr. M'Lennan* has
shewn on a still more extensive scale. These practices appear to
have originated in savages recognising the difficulty, or rather the
impossibility of supporting all the infants that are born.
Licentiousness may also be added to the foregoing checks; but this
does not follow from failing means of subsistence; though there is
reason to believe that in some cases (as in Japan) it has been
intentionally encouraged as a means of keeping down the population.

* Primitive Marriage, 1865.

If we look back to an extremely remote epoch, before man had arrived
at the dignity of manhood, he would have been guided more by
instinct and less by reason than are the lowest savages at the present
time. Our early semi-human progenitors would not have practised
infanticide or polyandry; for the instincts of the lower animals are
never so perverted* as to lead them regularly to destroy their own
offspring, or to be quite devoid of jealousy. There would have been no
prudential restraint from marriage, and the sexes would have freely
united at an early age. Hence the progenitors of man would have tended
to increase rapidly; but checks of some kind, either periodical or
constant, must have kept down their numbers, even more severely than
with existing savages. What the precise nature of these checks were,
we cannot say, any more than with most other animals. We know that
horses and cattle, which are not extremely prolific animals, when
first turned loose in South America, increased at an enormous rate.
The elephant, the slowest breeder of all known animals, would in a few
thousand years stock the whole world. The increase of every species of
monkey must be checked by some means; but not, as Brehm remarks, by
the attacks of beasts of prey. No one will assume that the actual
power of reproduction in the wild horses and cattle of America, was at
first in any sensible degree increased; or that, as each district
became fully stocked, this same power was diminished. No doubt, in
this case, and in all others, many checks concur, and different checks
under different circumstances; periodical dearths, depending on
unfavourable seasons, being probably the most important of all. So
it will have been with the early progenitors of man.

* A writer in the Spectator (March 12, 1871, p. 320) comments as
follows on this passage:- "Mr. Darwin finds himself compelled to
reintroduce a new doctrine of the fall of man. He shews that the
instincts of the higher animals are far nobler than the habits of
savage races of men, and he finds himself, therefore, compelled to
re-introduce,- in a form of the substantial orthodoxy of which he
appears to be quite unconscious,- and to introduce as a scientific
hypothesis the doctrine that man's gain of knowledge was the cause
of a temporary but long-enduring moral deterioration as indicated by
the many foul customs, especially as to marriage, of savage tribes.
What does the Jewish tradition of the moral degeneration of man
through his snatching at a knowledge forbidden him by his highest
instinct assert beyond this?"

Natural Selection.- We have now seen that man is variable in body
and mind; and that the variations are induced, either directly or
indirectly, by the same general causes, and obey the same general
laws, as with the lower animals. Man has spread widely over the face
of the earth, and must have been exposed, during his incessant
migration,* to the most diversified conditions. The inhabitants of
Tierra del Fuego, the Cape of Good Hope, and Tasmania in the one
hemisphere, and of the arctic regions in the other, must have passed
through many climates, and changed their habits many times, before
they reached their present homes.*(2) The early progenitors of man
must also have tended, like all other animals, to have increased
beyond their means of subsistence; they must, therefore,
occasionally have been exposed to a struggle for existence, and
consequently to the rigid law of natural selection. Beneficial
variations of all kinds will thus, either occasionally or
habitually, have been preserved and injurious ones eliminated. I do
not refer to strongly-marked deviations of structure, which occur only
at long intervals of time, but to mere individual differences. We
know, for instance, that the muscles of our hands and feet, which
determine our powers of movement, are liable, like those of the
lower animals,*(3) to incessant variability. If then the progenitors
of man inhabiting any district, especially one undergoing some
change in its conditions, were divided into two equal bodies, the
one half which included all the individuals best adapted by their
powers of movement for gaining subsistence, or for defending
themselves, would on an average survive in greater numbers, and
procreate more offspring than the other and less well endowed half.

* See some good remarks to this effect by W. Stanley Jevons, "A
Deduction from Darwin's Theory," Nature 1869, p. 231.
*(2) Latham, Man and his Migrations, 1851, p. 135.
*(3) Messrs. Murie and Mivart in their "Anatomy of the Lemuroidea"
(Transact. Zoolog. Soc., vol. vii., 1869, pp. 96-98) say, " some
muscles are so irregular in their distribution that they cannot be
well classed in any of the above groups." These muscles differ even on
the opposite sides of the same individual.

Man in the rudest state in which he now exists is the most
dominant animal that has ever appeared on this earth. He has spread
more widely than any other highly organised form: and all others
have yielded before him. He manifestly owes this immense superiority
to his intellectual faculties, to his social habits, which lead him to
aid and defend his fellows, and to his corporeal structure. The
supreme importance of these characters has been proved by the final
arbitrament of the battle for life. Through his powers of intellect,
articulate language has been evolved; and on this his wonderful
advancement has mainly depended. As Mr. Chauncey Wright remarks: "A
psychological analysis of the faculty of language shews, that even the
smallest proficiency in it might require more brain power than the
greatest proficiency in any other direction."* He has invented and
is able to use various weapons, tools, traps, &c., with which he
defends himself, kills or catches prey, and otherwise obtains food. He
has made rafts or canoes for fishing or crossing over to
neighbouring fertile islands. He has discovered the art of making
fire, by which hard and stringy roots can be rendered digestible,
and poisonous roots or herbs innocuous. This discovery of fire,
probably the greatest ever made by man, excepting language, dates from
before the dawn of history. These several inventions, by which man
in the rudest state has become so pre-eminent, are the direct
results of the development of his powers of observation, memory,
curiosity, imagination, and reason. I cannot, therefore, understand
how it is that Mr. Wallace*(2) maintains, that "natural selection
could only have endowed the savage with a brain a little superior to
that of an ape."

* "Limits of Natural Selection," North American Review, Oct.,
1870, p. 295.
*(2) Quarterly Review, April, 1869, p. 392. This subject is more
fully discussed in Mr. Wallace's Contributions to the Theory of
Natural Selection, 1870, in which all the essays referred to in this
work are re-published. The "Essay on Man," has been ably criticised by
Prof. Claparede, one of the most distinguished zoologists in Europe,
in an article published in the Bibliotheque Universelle, June, 1870.
The remark quoted in my text will surprise every one who has read
Mr. Wallace's celebrated paper on "The Origin of Human Races Deduced
from the Theory of Natural Selection," originally published in the
Anthropological Review, May, 1864, p. clviii. I cannot here resist
quoting a most just remark by Sir J. Lubbock (Prehistoric Times, 1865,
p. 479) in reference to this paper, namely, that Mr. Wallace, "with
characteristic unselfishness, ascribes it (i. e. the idea of natural
selection) unreservedly to Mr. Darwin, although, as is well known,
he struck out the idea independently, and published it, though not
with the same elaboration, at the same time."

Although the intellectual powers and social habits of man are of
paramount importance to him, we must not underrate the importance of
his bodily structure, to which subject the remainder of this chapter
will be devoted; the development of the intellectual and social or
moral faculties being discussed in a later chapter.
Even to hammer with precision is no easy matter, as every one who
has tried to learn carpentry will admit. To throw a stone with as true
an aim as a Fuegian in defending himself, or in killing birds,
requires the most consummate perfection in the correlated action of
the muscles of the hand, arm, and shoulder, and, further, a fine sense
of touch. In throwing a stone or spear, and in many other actions, a
man must stand firmly on his feet; and this again demands the
perfect co-adaptation of numerous muscles. To chip a flint into the
rudest tool, or to form a barbed spear or hook from a bone, demands
the use of a perfect hand; for, as a most capable judge, Mr.
Schoolcraft,* remarks, the shaping fragments of stone into knives,
lances, or arrow-heads, shews "extraordinary ability and long
practice." This is to a great extent proved by the fact that
primeval men practised a division of labour; each man did not
manufacture his own flint tools or rude pottery, but certain
individuals appear to have devoted themselves to such work, no doubt
receiving in exchange the produce of the chase. Archaeologists are
convinced that an enormous interval of time elapsed before our
ancestors thought of grinding chipped flints into smooth tools. One
can hardly doubt, that a man-like animal who possessed a hand and
arm sufficiently perfect to throw a stone with precision, or to form a
flint into a rude tool, could, with sufficient practice, as far as
mechanical skill alone is concerned, make almost anything which a
civilised man can make. The structure of the hand in this respect
may be compared with that of the vocal organs, which in the apes are
used for uttering various signal-cries, or, as in one genus, musical
cadences; but in man the closely similar vocal organs have become
adapted through the inherited effects of use for the utterance of
articulate language.

* Quoted by Mr. Lawson Tait in his "Law of Natural Selection,"
Dublin Quarterly Journal of Medical Science, Feb., 1869. Dr. Keller is
likewise quoted to the same effect.

Turning now to the nearest allies of men, and therefore to the
best representatives of our early progenitors, we find that the
hands of the Quadrumana are constructed on the same general pattern as
our own, but are far less perfectly adapted for diversified uses.
Their hands do not serve for locomotion so well as the feet of a
dog; as may be seen in such monkeys as the chimpanzee and orang, which
walk on the outer margins of the palms, or on the knuckles.* Their
hands, however, are admirably adapted for climbing trees. Monkeys
seize thin branches or ropes, with the thumb on one side and the
fingers and palm on the other, in the same manner as we do. They can
thus also lift rather large objects, such as the neck of a bottle,
to their mouths. Baboons turn over stones, and scratch up roots with
their hands. They seize nuts, insects, or other small objects with the
thumb in opposition to the fingers, and no doubt they thus extract
eggs and young from the nests of birds. American monkeys beat the wild
oranges on the branches until the rind is cracked, and then tear it
off with the fingers of the two hands. In a wild state they break open
hard fruits with stones. Other monkeys open mussel-shells with the two
thumbs. With their fingers they pull out thorns and burs, and hunt for
each other's parasites. They roll down stones, or throw them at
their enemies: nevertheless, they are clumsy in these various actions,
and, as I have myself seen, are quite unable to throw a stone with
precision.

* Owen, Anatomy of Vertebrates, vol. iii., p. 71.

It seems to me far from true that because "objects are grasped
clumsily" by monkeys, "a much less specialised organ of prehension"
would have served them* equally well with their present hands. On
the contrary, I see no reason to doubt that more perfectly constructed
hands would have been an advantage to them, provided that they were
not thus rendered less fitted for climbing trees. We may suspect
that a hand as perfect as that of man would have been
disadvantageous for climbing; for the most arboreal monkeys in the
world, namely, Ateles in America, Colobus in Africa, and Hylobates
in Asia, are either thumbless, or their toes partially cohere, so that
their limbs are converted into mere grasping hooks.*(2)

* Quarterly Review, April, 1869, p. 392.
*(2) In Hylobates syndactylus, as the name expresses, two of the
toes regularly cohere; and this, as Mr. Blyth informs me, is
occasionally the case with the toes of H. agilis, lar, and
leuciscus. Colobus is strictly arboreal and extraordinarily active
(Brehm, Illustriertes Thierleben, B. i., s. 50), but whether a
better climber than the species of the allied genera, I do not know.
It deserves notice that the feet of the sloths, the most arboreal
animals in the world, are wonderfully hooklike.

As soon as some ancient member in the great series of the primates
came to be less arboreal, owing to a change in its manner of procuring
subsistence, or to some change in the surrounding conditions, its
habitual manner of progression would have been modified: and thus it
would have been rendered more strictly quadrupedal or bipedal. Baboons
frequent hilly and rocky districts, and only from necessity climb high
trees;* and they have acquired almost the gait of a dog. Man alone has
become a biped; and we can, I think, partly see how he has come to
assume his erect attitude, which forms one of his most conspicuous
characters. Man could not have attained his present dominant
position in the world without the use of his hands, which are so
admirably adapted to act in obedience to his will. Sir C. Bell*(2)
insists that "the hand supplies all instruments, and by its
correspondence with the intellect gives him universal dominion." But
the hands and arms could hardly have become perfect enough to have
manufactured weapons, or to have hurled stones and spears with a
true aim, as long as they were habitually used for locomotion and
for supporting the whole weight of the body, or, as before remarked,
so long as they were especially fitted for climbing trees. Such
rough treatment would also have blunted the sense of touch, on which
their delicate use largely depends. From these causes alone it would
have been an advantage to man to become a biped; but for many
actions it is indispensable that the arms and whole upper part of
the body should be free; and he must for this end stand firmly on
his feet. To gain this great advantage, the feet have been rendered
flat; and the great toe has been peculiarly modified, though this
has entailed the almost complete loss of its power of prehension. It
accords with the principle of the division of physiological labour,
prevailing throughout the animal kingdom, that as the hands became
perfected for prehension, the feet should have become perfected for
support and locomotion. With some savages, however, the foot has not
altogether lost its prehensile power, as shewn by their manner of
climbing trees, and of using them in other ways.*(3)

* Brehm, Illustriertes Thierleben, B. i., s. 80.
*(2) "The Hand," &c., Bridgewater Treatise, 1833, p. 38.
*(3)  Haeckel has an excellent discussion on the steps by which
man became a biped: Naturliche Schopfungsgeschicte, 1868, s. 507.
Dr. Buchner (Conferences sur la Theorie Darwinienne, 1869, p. 135) has
given good cases of the use of the foot as a prehensile organ by
man; and has also written on the manner of progression of the higher
apes, to which I allude in the following paragraph: see also Owen
(Anatomy of Vertebrates, vol. iii., p. 71) on this latter subject.

If it be an advantage to man to stand firmly on his feet and to have
his hands and arms free, of which, from his pre-eminent success in the
battle of life, there can be no doubt, then I can see no reason why it
should not have been advantageous to the progenitors of man to have
become more and more erect or bipedal. They would thus have been
better able to defend themselves with stones or clubs, to attack their
prey, or otherwise to obtain food. The best built individuals would in
the long run have succeeded best, and have survived in larger numbers.
If the gorilla and a few allied forms had become extinct, it might
have been argued, with great force and apparent truth, that an
animal could not have been gradually converted from a quadruped into a
biped, as all the individuals in an intermediate condition would
have been miserably ill-fitted for progression. But we know (and
this is well worthy of reflection) that the anthropomorphous apes
are now actually in an intermediate condition; and no one doubts
that they are on the whole well adapted for their conditions of
life. Thus the gorilla runs with a sidelong shambling gait, but more
commonly progresses by resting on its bent hands. The long-armed
apes occasionally use their arms like crutches, swinging their
bodies forward between them, and some kinds of Hylobates, without
having been taught, can walk or run upright with tolerable
quickness; yet they move awkwardly, and much less securely than man.
We see, in short, in existing monkeys a manner of progression
intermediate between that of a quadruped and a biped; but, as an
unprejudiced judge* insists, the anthropomorphous apes approach in
structure more nearly to the bipedal than to the quadrupedal type.

* Prof. Broca, "La Constitution des vertebres caudales"; La Revue
d'Anthropologie, 1872, p. 26, (separate copy).

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*
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, &c., 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.

* "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.

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,* 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.

* Die Grenzen der Thierwelt, eine Betrachtung zu Darwin's Lehre,
1868, s. 51.

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.* 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.

* 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.

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,* 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*(2)
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 braincases" 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.*(3)
With respect to the lower animals, M. E. Lartet,*(4) 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*(5) 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.

* Philosophical Transactions, 1869, p. 513.
*(2) "Les Selections," M. P. Broca, Revue d'Anthropologie,, 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.
*(3) 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.
*(4) Comptes-rendus des Sciences, &c., June 1, 1868.
*(5) The Variation of Animals and Plants under Domestication, vol.
i., pp. 124-129.

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 effected. 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.* 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.*(2) 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";*(3) and tall men may
be compared with the larger and longer-bodied rabbits, all of which
have elongated skulls or are dolichocephalic.

* 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.
*(2) 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.
*(3) Quoted by Schaaffhausen, in Anthropological Review, Oct., 1868,
p. 419.

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* 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,*(2) is opposed to the supposition that man became naked
through the action of the sun. Mr. Belt believes*(3) that within the
tropies 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.

* Owen, Anatomy of Vertebrates, vol. iii., p. 619.
*(2) 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.
*(3) 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."

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,* 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*(2) 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.

* 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.
*(2) Revue d'Anthropologie, 1872; "La Constitution des vertebres
caudales."

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* 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,*(2) 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,*(3) 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.

* Proceedings Zoological Society, 1872, p. 210.
*(2) Proceedings Zoological Society, 1872, p. 786.
*(3) 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
motmots 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.

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;* 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.

* The Variation of Animals and Plants under Domestication, vol. ii.,
pp. 280, 282.

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.

Conclusion.- In this chapter we have seen that as man at the present
day is liable, like every other animal, to multiform individual
differences or slight variations, so no doubt were the early
progenitors of man; the variations being formerly induced by the
same general causes, and governed by the same general and complex laws
as at present. As all animals tend to multiply beyond their means of
subsistence, so it must have been with the progenitors of man; and
this would inevitably lead to a struggle for existence and to
natural selection. The latter process would be greatly aided by the
inherited effects of the increased use of parts, and these two
processes would incessantly react on each other. It appears, also,
as we shall hereafter see, that various unimportant characters have
been acquired by man through sexual selection. An unexplained residuum
of change must be left to the assumed uniform action of those
unknown agencies, which occasionally induce strongly marked and abrupt
deviations of structure in our domestic productions.
Judging from the habits of savages and of the greater number of
the Quadrumana, primeval men, and even their ape-like progenitors,
probably lived in society. With strictly social animals, natural
selection sometimes acts on the individual, through the preservation
of variations which are beneficial to the community. A community which
includes a large number of well-endowed individuals increases in
number, and is victorious over other less favoured ones; even although
each separate member gains no advantage over the others of the same
community. Associated insects have thus acquired many remarkable
structures, which are of little or no service to the individual,
such as the pollen-collecting apparatus, or the sting of the
worker-bee, or the great jaws of soldier-ants. With the higher
social animals, I am not aware that any structure has been modified
solely for the good of the community, though some are of secondary
service to it. For instance, the horns of ruminants and the great
canine teeth of baboons appear to have been acquired by the males as
weapons for sexual strife, but they are used in defence of the herd or
troop. In regard to certain mental powers the case, as we shall see in
the fifth chapter, is wholly different; for these faculties have
been chiefly, or even exclusively, gained for the benefit of the
community, and the individuals thereof have at the same time gained an
advantage indirectly.

It has often been objected to such views as the foregoing, that
man is one of the most helpless and defenceless creatures in the
world; and that during his early and less well-developed condition, he
would have been still more helpless. The Duke of Argyll, for instance,
insists* that "the human frame has diverged from the structure of
brutes, in the direction of greater physical helplessness and
weakness. That is to say, it is a divergence which of all others it is
most impossible to ascribe to mere natural selection." He adduces
the naked and unprotected state of the body, the absence of great
teeth or claws for defence, the small strength and speed of man, and
his slight power of discovering food or of avoiding danger by smell.
To these deficiencies there might be added one still more serious,
namely, that he cannot climb quickly, and so escape from enemies.
The loss of hair would not have been a great injury to the inhabitants
of a warm country. For we know that the unclothed Fuegians can exist
under a wretched climate. When we compare the defenceless state of man
with that of apes, we must remember that the great canine teeth with
which the latter are provided, are possessed in their full development
by the males alone, and are chiefly used by them for fighting with
their rivals; yet the females, which are not thus provided, manage
to survive.

* Primeval Man, 1869, p. 66.

In regard to bodily size or strength, we do not know whether man
is descended from some small species, like the chimpanzee, or from one
as powerful as the gorilla; and, therefore, we cannot say whether
man has become larger and stronger, or smaller and weaker, than his
ancestors. We should, however, bear in mind that an animal
possessing great size, strength, and ferocity, and which, like the
gorilla, could defend itself from all enemies, would not perhaps
have become social: and this would most effectually have checked the
acquirement of the higher mental qualities, such as sympathy and the
love of his fellows. Hence it might have been an immense advantage
to man to have sprung from some comparatively weak creature.
The small strength and speed of man, his want of natural weapons,
&c., are more than counterbalanced, firstly, by his intellectual
powers, through which he has formed for himself weapons, tools, &c.,
though still remaining in a barbarous state, and, secondly, by his
social qualities which lead him to give and receive aid from his
fellow-men. No country in the world abounds in a greater degree with
dangerous beasts than southern Africa; no country presents more
fearful physical hardships than the arctic regions; yet one of the
puniest of races, that of the bushmen, maintains itself in southern
Africa, as do the dwarfed Esquimaux in the arctic regions. The
ancestors of man were, no doubt, inferior in intellect, and probably
in social disposition, to the lowest existing savages; but it is quite
conceivable that they might have existed, or even flourished, if
they had advanced in intellect, whilst gradually losing their
brute-like powers such as that of climbing trees, &c. But these
ancestors would not have been exposed to any special danger, even if
far more helpless and defenceless than any existing savages, had
they inhabited some warm continent or large island, such as Australia,
New Guinea, or Borneo, which is now the home of the orang. And natural
selection arising from the competition of tribe with tribe, in some
such large area as one of these, together with the inherited effects
of habit, would, under favourable conditions, have sufficed to raise
man to his present high position in the organic scale.