The Descent Of Man

Chapter II

ON THE MANNER OF DEVELOPMENT OF MAN FROM SOME LOWER FORM.

Variability of body and mind in man--Inheritance--Causes of variability--
Laws of variation the same in man as in the lower animals--Direct action of
the conditions of life--Effects of the increased use and disuse of parts--
Arrested development--Reversion--Correlated variation--Rate of increase--
Checks to increase--Natural selection--Man the most dominant animal in the
world--Importance of his corporeal structure--The causes which have led to
his becoming erect--Consequent changes of structure--Decrease in size of
the canine teeth--Increased size and altered shape of the skull--Nakedness
--Absence of a tail--Defenceless condition of man.

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. (1.
'Investigations in Military and Anthropological Statistics of American
Soldiers,' by B.A. Gould, 1869, p. 256.) 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. 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.) 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 it has been found
useful for surgical purposes to calculate from 1040 corpses how often each
course prevails. (3. 'Anatomy of the Arteries,' by R. Quain. Preface,
vol. i. 1844.) The muscles are eminently variable: thus those of the foot
were found by Prof. Turner (4. 'Transactions of the Royal Society of
Edinburgh,' vol. xxiv. pp. 175, 189.) 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. 'Proceedings Royal Society,' 1867, p. 544; also 1868, pp.
483, 524. There is a previous paper, 1866, p. 229.) 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. 'Proc. R. Irish Academy,' vol. x. 1868, p. 141.)
no less than twenty distinct variations in the palmaris accessorius.

The famous old anatomist, Wolff (7. 'Act. Acad. St. Petersburg,' 1778,
part ii. p. 217.), 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, etc., as of the human face divine,
sounds strange in our ears.

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. (8. Brehm, 'Thierleben,' B. i. ss. 58, 87. Rengger,
'Saugethiere von Paraguay,' s. 57.)

I have elsewhere (9. 'Variation of Animals and Plants under
Domestication,' vol. ii. chap. xii.) 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,
etc., are certainly transmitted. With man we see similar facts in almost
every family; and we now know, through the admirable labours of Mr. Galton
(10. 'Hereditary Genius: an Inquiry into its Laws and Consequences,'
1869.), 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.

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. (11. 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.") 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" (12. Blumenbach, 'Treatises on Anthropology.' Eng.
translat., 1865, p. 205.) 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. (13. Mitford's
'History of Greece,' vol. i. p. 282. It appears also 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
affected 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. (14. 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.) 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. (15. 'Hist.
Gen. et Part. des Anomalies de l'Organisation,' in three volumes, tom. i.
1832.) 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 (16.
I have fully discussed these laws in my 'Variation of Animals and Plants
under Domestication,' vol. ii. chap. xxii. and xxiii. M. J.P. Durand has
lately (1868) published a valuable essay, 'De l'Influence des Milieux,'
etc. He lays much stress, in the case of plants, on the nature of the
soil.); but several are so important, that they must be treated at
considerable length.

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. (17. 'Investigations in Military and Anthrop. Statistics,'
etc., 1869, by B.A. Gould, pp. 93, 107, 126, 131, 134.) 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 statistics 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 (18. 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.) 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." (19. '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.
(20. Dr. Brakenridge, 'Theory of Diathesis,' 'Medical Times,' June 19 and
July 17, 1869.) 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.

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. (21. 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," 'Jenaischen
Zeitschrift,' B. v. Heft. i.) Different occupations, habitually followed,
lead to changed proportions in various parts of the body. Thus it was
ascertained by the United States Commission (22. 'Investigations,' etc.,
by B.A. Gould, 1869, p. 288.) 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.

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 (23. 'Saugethiere von Paraguay,' 1830, s. 4.)
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 (24. 'History
of Greenland,' Eng. translat., 1767, vol. i. p. 230.), 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
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. (25.
'Intermarriage,' by Alex. Walker, 1838, p. 377.) From the correlation
which exists, at least in some cases (26. 'The Variation of Animals under
Domestication,' vol. i. p. 173.), 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
civilised men than in hard-working men or savages, is certain. But with
savages, as Mr. Herbert Spencer (27. 'Principles of Biology,' vol. i. p.
455.) 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;
(28. Paget, 'Lectures on Surgical Pathology,' vol. ii, 1853, p. 209.) and
it can hardly be doubted that this is due to the inherited effects of
pressure during a long series of generations.

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. (29. 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.") Short-sight and long-sight
certainly tend to be inherited. (30. 'The Variation of Animals under
Domestication,' vol. i. p. 8.) 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 (31. '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,' etc., 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.")
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. (32.
Prichard, 'Physical History of Mankind,' on the authority of Blumenbach,
vol. i. 1851, 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 (33. Quoted by Prichard, 'Researches into the Physical
History of Mankind,' vol. v. p. 463.) 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 (34. Mr.
Forbes' valuable paper is now published in the 'Journal of the Ethnological
Society of London,' new series, vol. ii. 1870, p.193.) 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.

These men are so thoroughly acclimatised to their cold and lofty abode,
that when formerly carried down by the 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. (35. 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. (36. 'Memoires sur
les Microcephales,' 1867, pp. 50, 125, 169, 171, 184-198.) 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 eye-brows, 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. (37. 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 imbecile 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. (38. 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 mammae (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 possess more than five digits, and
therefore, as I supposed, had retained a primordial condition; but Prof.
Gegenbaur ('Jenaischen 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, etc., 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 organised progenitor of man.) 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 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. (39. 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.) 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.

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 (40. '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.), 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.

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. (41. 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 (42. 'Anatomy of
Vertebrates,' vol. iii. 1868, p. 323.) 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 (43. 'Generelle Morphologie,' 1866, B. ii. s. clv.) 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. (44. Carl
Vogt's 'Lectures on Man,' Eng. translat., 1864, p. 151.) 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 enormous.
(45. 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) (46. The Anatomy of Expression, 1844, pp. 110, 131.), so as to
expose them ready for action, like a dog prepared to fight.

Many muscles are occasionally developed in man, which are proper to the
Quadrumana or other mammals. Professor Vlacovich (47. Quoted by Prof.
Canestrini in the 'Annuario della Soc. dei Naturalisti,' 1867, p. 90.)
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.

Mr. J. Wood, in his valuable series of papers (48. 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.), 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 Quadrumana, 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. (49. See also Prof.
Macalister in 'Proceedings, Royal Irish Academy,' vol. x. 1868, p. 124.)
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, (50. Mr. Champneys in
'Journal of Anatomy and Physiology,' Nov. 1871, p. 178.) and it occurs in
about one out of sixty human subjects. In the lower extremities Mr.
Bradley (51. Ibid. May 1872, p. 421.) 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. (52. 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, etc.) 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 the 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."
(53. 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 shews 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. (54. 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 shews 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.") 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.

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.
(55. The authorities for these several statements are given in my
'Variation of Animals under Domestication,' vol. ii. pp. 320-335.)
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.

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. (56. 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. (57. See the ever memorable 'Essay on the Principle of
Population,' by the Rev. T. Malthus, vol. i. 1826. pp. 6, 517.) 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.

There is 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 hardship, and who do
not obtain so much nutritious food as civilised men, would be actually less
prolific. I have shewn in a former work (58. 'Variation of Animals and
Plants under Domestication,' vol ii. pp. 111-113, 163.), 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. (59. 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 (60. 'The Annals of Rural Bengal,' by W.W. Hunter, 1868, p. 259.),
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.

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 (61. 'Primitive Marriage,'
1865.) 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.

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 (62. 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?") 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.

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 migrations (63. See some good remarks to this effect
by W. Stanley Jevons, "A Deduction from Darwin's Theory," 'Nature,' 1869,
p. 231.), to the most diversified conditions. The inhabitants of Tierra
del Fuego, the