have been the determining cause. When the two sexes have inherited all
characters in common they necessarily resemble each other; but as the
successive variations may be differently transmitted, every possible
gradation may be found, even within the same genus, from the closest
similarity to the widest dissimilarity between the sexes. With many
closely-allied species, following nearly the same habits of life, the males
have come to differ from each other chiefly through the action of sexual
selection; whilst the females have come to differ chiefly from partaking
more or less of the characters thus acquired by the males. The effects,
moreover, of the definite action of the conditions of life, will not have
been masked in the females, as in the males, by the accumulation through
sexual selection of strongly-pronounced colours and other ornaments. The
individuals of both sexes, however affected, will have been kept at each
successive period nearly uniform by the free intercrossing of many
individuals.

With species, in which the sexes differ in colour, it is possible or
probable that some of the successive variations often tended to be
transmitted equally to both sexes; but that when this occurred the females
were prevented from acquiring the bright colours of the males, by the
destruction which they suffered during incubation. There is no evidence
that it is possible by natural selection to convert one form of
transmission into another. But there would not be the least difficulty in
rendering a female dull-coloured, the male being still kept bright-
coloured, by the selection of successive variations, which were from the
first limited in their transmission to the same sex. Whether the females
of many species have actually been thus modified, must at present remain
doubtful. When, through the law of the equal transmission of characters to
both sexes, the females were rendered as conspicuously coloured as the
males, their instincts appear often to have been modified so that they were
led to build domed or concealed nests.

In one small and curious class of cases the characters and habits of the
two sexes have been completely transposed, for the females are larger,
stronger, more vociferous and brighter coloured than the males. They have,
also, become so quarrelsome that they often fight together for the
possession of the males, like the males of other pugnacious species for the
possession of the females. If, as seems probable, such females habitually
drive away their rivals, and by the display of their bright colours or
other charms endeavour to attract the males, we can understand how it is
that they have gradually been rendered, by sexual selection and sexually-
limited transmission, more beautiful than the males - the latter being left
unmodified or only slightly modified.

Whenever the law of inheritance at corresponding ages prevails but not that
of sexually-limited transmission, then if the parents vary late in life -
and we know that this constantly occurs with our poultry, and occasionally
with other birds - the young will be left unaffected, whilst the adults of
both sexes will be modified. If both these laws of inheritance prevail and
either sex varies late in life, that sex alone will be modified, the other
sex and the young being unaffected. When variations in brightness or in
other conspicuous characters occur early in life, as no doubt often
happens, they will not be acted on through sexual selection until the
period of reproduction arrives; consequently if dangerous to the young,
they will be eliminated through natural selection. Thus we can understand
how it is that variations arising late in life have so often been preserved
for the ornamentation of the males; the females and the young being left
almost unaffected, and therefore like each other. With species having a
distinct summer and winter plumage, the males of which either resemble or
differ from the females during both seasons or during the summer alone, the
degrees and kinds of resemblance between the young and the old are
exceedingly complex; and this complexity apparently depends on characters,
first acquired by the males, being transmitted in various ways and degrees,
as limited by age, sex, and season.

As the young of so many species have been but little modified in colour and
in other ornaments, we are enabled to form some judgment with respect to
the plumage of their early progenitors; and we may infer that the beauty of
our existing species, if we look to the whole class, has been largely
increased since that period, of which the immature plumage gives us an
indirect record. Many birds, especially those which live much on the
ground, have undoubtedly been obscurely coloured for the sake of
protection. In some instances the upper exposed surface of the plumage has
been thus coloured in both sexes, whilst the lower surface in the males
alone has been variously ornamented through sexual selection. Finally,
from the facts given in these four chapters, we may conclude that weapons
for battle, organs for producing sound, ornaments of many kinds, bright and
conspicuous colours, have generally been acquired by the males through
variation and sexual selection, and have been transmitted in various ways
according to the several laws of inheritance - the females and the young
being left comparatively but little modified. (57. I am greatly indebted
to the kindness of Mr. Sclater for having looked over these four chapters
on birds, and the two following ones on mammals. In this way I have been
saved from making mistakes about the names of the species, and from stating
anything as a fact which is known to this distinguished naturalist to be
erroneous. But, of course, he is not at all answerable for the accuracy of
the statements quoted by me from various authorities.)


CHAPTER XVII.

SECONDARY SEXUAL CHARACTERS OF MAMMALS.

The law of battle - Special weapons, confined to the males - Cause of absence
of weapons in the female - Weapons common to both sexes, yet primarily
acquired by the male - Other uses of such weapons - Their high importance -
Greater size of the male - Means of defence - On the preference shown by
either sex in the pairing of quadrupeds.

With mammals the male appears to win the female much more through the law
of battle than through the display of his charms. The most timid animals,
not provided with any special weapons for fighting, engage in desperate
conflicts during the season of love. Two male hares have been seen to
fight together until one was killed; male moles often fight, and sometimes
with fatal results; male squirrels engage in frequent contests, "and often
wound each other severely"; as do male beavers, so that "hardly a skin is
without scars." (1. See Waterton's account of two hares fighting,
'Zoologist,' vol. i. 1843, p. 211. On moles, Bell, 'Hist. of British
Quadrupeds,' 1st ed., p. 100. On squirrels, Audubon and Bachman,
Viviparous Quadrupeds of N. America, 1846, p. 269. On beavers, Mr. A.H.
Green, in 'Journal of Linnean Society, Zoology,' vol. x. 1869, p. 362.) I
observed the same fact with the hides of the guanacoes in Patagonia; and on
one occasion several were so absorbed in fighting that they fearlessly
rushed close by me. Livingstone speaks of the males of the many animals in
Southern Africa as almost invariably shewing the scars received in former
contests.

The law of battle prevails with aquatic as with terrestrial mammals. It is
notorious how desperately male seals fight, both with their teeth and
claws, during the breeding-season; and their hides are likewise often
covered with scars. Male sperm-whales are very jealous at this season; and
in their battles "they often lock their jaws together, and turn on their
sides and twist about"; so that their lower jaws often become distorted.
(2. On the battles of seals, see Capt. C. Abbott in 'Proc. Zool. Soc.'
1868, p. 191; Mr. R. Brown, ibid. 1868, p. 436; also L. Lloyd, 'Game Birds
of Sweden,' 1867, p. 412; also Pennant. On the sperm-whale see Mr. J.H.
Thompson, in 'Proc. Zool. Soc.' 1867, p. 246.)

All male animals which are furnished with special weapons for fighting, are
well known to engage in fierce battles. The courage and the desperate
conflicts of stags have often been described; their skeletons have been
found in various parts of the world, with the horns inextricably locked
together, shewing how miserably the victor and vanquished had perished.
(3. See Scrope ('Art of Deer-stalking,' p. 17) on the locking of the horns
with the Cervus elaphus. Richardson, in 'Fauna Bor. Americana,' 1829, p.
252, says that the wapiti, moose, and reindeer have been found thus locked
together. Sir. A. Smith found at the Cape of Good Hope the skeletons of
two gnus in the same condition.) No animal in the world is so dangerous as
an elephant in must. Lord Tankerville has given me a graphic description
of the battles between the wild bulls in Chillingham Park, the descendants,
degenerated in size but not in courage, of the gigantic Bos primigenius.
In 1861 several contended for mastery; and it was observed that two of the
younger bulls attacked in concert the old leader of the herd, overthrew and
disabled him, so that he was believed by the keepers to be lying mortally
wounded in a neighbouring wood. But a few days afterwards one of the young
bulls approached the wood alone; and then the "monarch of the chase," who
had been lashing himself up for vengeance, came out and, in a short time,
killed his antagonist. He then quietly joined the herd, and long held
undisputed sway. Admiral Sir B.J. Sulivan informs me that, when he lived
in the Falkland Islands, he imported a young English stallion, which
frequented the hills near Port William with eight mares. On these hills
there were two wild stallions, each with a small troop of mares; "and it is
certain that these stallions would never have approached each other without
fighting. Both had tried singly to fight the English horse and drive away
his mares, but had failed. One day they came in TOGETHER and attacked him.
This was seen by the capitan who had charge of the horses, and who, on
riding to the spot, found one of the two stallions engaged with the English
horse, whilst the other was driving away the mares, and had already
separated four from the rest. The capitan settled the matter by driving
the whole party into the corral, for the wild stallions would not leave the
mares."

Male animals which are provided with efficient cutting or tearing teeth for
the ordinary purposes of life, such as the carnivora, insectivora, and
rodents, are seldom furnished with weapons especially adapted for fighting
with their rivals. The case is very different with the males of many other
animals. We see this in the horns of stags and of certain kinds of
antelopes in which the females are hornless. With many animals the canine
teeth in the upper or lower jaw, or in both, are much larger in the males
than in the females, or are absent in the latter, with the exception
sometimes of a hidden rudiment. Certain antelopes, the musk-deer, camel,
horse, boar, various apes, seals, and the walrus, offer instances. In the
females of the walrus the tusks are sometimes quite absent. (4. Mr.
Lamont ('Seasons with the Sea-Horses,' 1861, p. 143) says that a good tusk
of the male walrus weighs 4 pounds, and is longer than that of the female,
which weighs about 3 pounds. The males are described as fighting
ferociously. On the occasional absence of the tusks in the female, see Mr.
R. Brown, 'Proceedings, Zoological Society,' 1868, p. 429.) In the male
elephant of India and in the male dugong (5. Owen, 'Anatomy of
Vertebrates,' vol. iii. p. 283.) the upper incisors form offensive weapons.
In the male narwhal the left canine alone is developed into the well-known,
spirally-twisted, so-called horn, which is sometimes from nine to ten feet
in length. It is believed that the males use these horns for fighting
together; for "an unbroken one can rarely be got, and occasionally one may
be found with the point of another jammed into the broken place." (6. Mr.
R. Brown, in 'Proc. Zool. Soc.' 1869, p. 553. See Prof. Turner, in
'Journal of Anat. and Phys.' 1872, p. 76, on the homological nature of
these tusks. Also Mr. J.W. Clarke on two tusks being developed in the
males, in 'Proceedings of the Zoological Society,' 1871, p. 42.) The tooth
on the opposite side of the head in the male consists of a rudiment about
ten inches in length, which is embedded in the jaw; but sometimes, though
rarely, both are equally developed on the two sides. In the female both
are always rudimentary. The male cachalot has a larger head than that of
the female, and it no doubt aids him in his aquatic battles. Lastly, the
adult male ornithorhynchus is provided with a remarkable apparatus, namely
a spur on the foreleg, closely resembling the poison-fang of a venomous
snake; but according to Harting, the secretion from the gland is not
poisonous; and on the leg of the female there is a hollow, apparently for
the reception of the spur. (7. Owen on the cachalot and Ornithorhynchus,
ibid. vol. iii. pp. 638, 641. Harting is quoted by Dr. Zouteveen in the
Dutch translation of this work, vol. ii. p. 292.)

When the males are provided with weapons which in the females are absent,
there can be hardly a doubt that these serve for fighting with other males;
and that they were acquired through sexual selection, and were transmitted
to the male sex alone. It is not probable, at least in most cases, that
the females have been prevented from acquiring such weapons, on account of
their being useless, superfluous, or in some way injurious. On the
contrary, as they are often used by the males for various purposes, more
especially as a defence against their enemies, it is a surprising fact that
they are so poorly developed, or quite absent, in the females of so many
animals. With female deer the development during each recurrent season of
great branching horns, and with female elephants the development of immense
tusks, would be a great waste of vital power, supposing that they were of
no use to the females. Consequently, they would have tended to be
eliminated in the female through natural selection; that is, if the
successive variations were limited in their transmission to the female sex,
for otherwise the weapons of the males would have been injuriously
affected, and this would have been a greater evil. On the whole, and from
the consideration of the following facts, it seems probable that when the
various weapons differ in the two sexes, this has generally depended on the
kind of transmission which has prevailed.

As the reindeer is the one species in the whole family of Deer, in which
the female is furnished with horns, though they are somewhat smaller,
thinner, and less branched than in the male, it might naturally be thought
that, at least in this case, they must be of some special service to her.
The female retains her horns from the time when they are fully developed,
namely, in September, throughout the winter until April or May, when she
brings forth her young. Mr. Crotch made particular enquiries for me in
Norway, and it appears that the females at this season conceal themselves
for about a fortnight in order to bring forth their young, and then
reappear, generally hornless. In Nova Scotia, however, as I hear from Mr.
H. Reeks, the female sometimes retains her horns longer. The male on the
other hand casts his horns much earlier, towards the end of November. As
both sexes have the same requirements and follow the same habits of life,
and as the male is destitute of horns during the winter, it is improbable
that they can be of any special service to the female during this season,
which includes the larger part of the time during which she is horned. Nor
is it probable that she can have inherited horns from some ancient
progenitor of the family of deer, for, from the fact of the females of so
many species in all quarters of the globe not having horns, we may conclude
that this was the primordial character of the group. (8. On the structure
and shedding of the horns of the reindeer, Hoffberg, 'Amoenitates Acad.'
vol. iv. 1788, p. 149. See Richardson, 'Fauna Bor. Americana,' p. 241, in
regard to the American variety or species: also Major W. Ross King, 'The
Sportsman in Canada,' 1866, p. 80.

The horns of the reindeer are developed at a most unusually early age; but
what the cause of this may be is not known. The effect has apparently been
the transference of the horns to both sexes. We should bear in mind that
horns are always transmitted through the female, and that she has a latent
capacity for their development, as we see in old or diseased females. (9.
Isidore Geoffroy St.-Hilaire, 'Essais de Zoolog. Generale,' 1841, p. 513.
Other masculine characters, besides the horns, are sometimes similarly
transferred to the female; thus Mr. Boner, in speaking of an old female
chamois ('Chamois Hunting in the Mountains of Bavaria,' 1860, 2nd ed., p.
363), says, "not only was the head very male-looking, but along the back
there was a ridge of long hair, usually to be found only in bucks.")
Moreover the females of some other species of deer exhibit, either normally
or occasionally, rudiments of horns; thus the female of Cervulus moschatus
has "bristly tufts, ending in a knob, instead of a horn"; and "in most
specimens of the female wapiti (Cervus canadensis) there is a sharp bony
protuberance in the place of the horn." (10. On the Cervulus, Dr. Gray,
'Catalogue of Mammalia in the British Museum,' part iii. p. 220. On the
Cervus canadensis or wapiti, see Hon. J.D. Caton, 'Ottawa Academy of Nat.
Sciences,' May 1868, p. 9.) From these several considerations we may
conclude that the possession of fairly well-developed horns by the female
reindeer, is due to the males having first acquired them as weapons for
fighting with other males; and secondarily to their development from some
unknown cause at an unusually early age in the males, and their consequent
transference to both sexes.

Turning to the sheath-horned ruminants: with antelopes a graduated series
can be formed, beginning with species, the females of which are completely
destitute of horns - passing on to those which have horns so small as to be
almost rudimentary (as with the Antilocapra americana, in which species
they are present in only one out of four or five females (11. I am
indebted to Dr. Canfield for this information; see also his paper in the
'Proceedings of the Zoological Society,' 1866, p. 105.)) - to those which
have fairly developed horns, but manifestly smaller and thinner than in the
male and sometimes of a different shape (12. For instance the horns of the
female Ant. euchore resemble those of a distinct species, viz. the Ant.
dorcas var. Corine, see Desmarest, 'Mammalogie,' p. 455.), - and ending with
those in which both sexes have horns of equal size. As with the reindeer,
so with antelopes, there exists, as previously shewn, a relation between
the period of the development of the horns and their transmission to one or
both sexes; it is therefore probable that their presence or absence in the
females of some species, and their more or less perfect condition in the
females of other species, depends, not on their being of any special use,
but simply on inheritance. It accords with this view that even in the same
restricted genus both sexes of some species, and the males alone of others,
are thus provided. It is also a remarkable fact that, although the females
of Antilope bezoartica are normally destitute of horns, Mr. Blyth has seen
no less than three females thus furnished; and there was no reason to
suppose that they were old or diseased.

In all the wild species of goats and sheep the horns are larger in the male
than in the female, and are sometimes quite absent in the latter. (13.
Gray, 'Catalogue of Mammalia, the British Museum,' part iii. 1852, p. 160.)
In several domestic breeds of these two animals, the males alone are
furnished with horns; and in some breeds, for instance, in the sheep of
North Wales, though both sexes are properly horned, the ewes are very
liable to be hornless. I have been informed by a trustworthy witness, who
purposely inspected a flock of these same sheep during the lambing season,
that the horns at birth are generally more fully developed in the male than
in the female. Mr. J. Peel crossed his Lonk sheep, both sexes of which
always bear horns, with hornless Leicesters and hornless Shropshire Downs;
and the result was that the male offspring had their horns considerably
reduced, whilst the females were wholly destitute of them. These several
facts indicate that, with sheep, the horns are a much less firmly fixed
character in the females than in the males; and this leads us to look at
the horns as properly of masculine origin.

With the adult musk-ox (Ovibos moschatus) the horns of the male are larger
than those of the female, and in the latter the bases do not touch. (14.
Richardson, 'Fauna Bor. Americana,' p. 278.) In regard to ordinary cattle
Mr. Blyth remarks: "In most of the wild bovine animals the horns are both
longer and thicker in the bull than in the cow, and in the cow-banteng (Bos
sondaicus) the horns are remarkably small, and inclined much backwards. In
the domestic races of cattle, both of the humped and humpless types, the
horns are short and thick in the bull, longer and more slender in the cow
and ox; and in the Indian buffalo, they are shorter and thicker in the
bull, longer and more slender in the cow. In the wild gaour (B. gaurus)
the horns are mostly both longer and thicker in the bull than in the cow."
(15. 'Land and Water,' 1867, p. 346.) Dr. Forsyth Major also informs me
that a fossil skull, believed to be that of the female Bos etruscus, has
been found in Val d'Arno, which is wholly without horns. In the Rhinoceros
simus, as I may add, the horns of the female are generally longer but less
powerful than in the male; and in some other species of rhinoceros they are
said to be shorter in the female. (16. Sir Andrew Smith, 'Zoology of S.
Africa,' pl. xix. Owen, 'Anatomy of Vertebrates,' vol. iii. p. 624.) From
these various facts we may infer as probable that horns of all kinds, even
when they are equally developed in the two sexes, were primarily acquired
by the male in order to conquer other males, and have been transferred more
or less completely to the female.

The effects of castration deserve notice, as throwing light on this same
point. Stags after the operation never renew their horns. The male
reindeer, however, must be excepted, as after castration he does renew
them. This fact, as well as the possession of horns by both sexes, seems
at first to prove that the horns in this species do not constitute a sexual
character (17. This is the conclusion of Seidlitz, 'Die Darwinsche
Theorie,' 1871, p. 47.); but as they are developed at a very early age,
before the sexes differ in constitution, it is not surprising that they
should be unaffected by castration, even if they were aboriginally acquired
by the male. With sheep both sexes properly bear horns; and I am informed
that with Welch sheep the horns of the males are considerably reduced by
castration; but the degree depends much on the age at which the operation
is performed, as is likewise the case with other animals. Merino rams have
large horns, whilst the ewes "generally speaking are without horns"; and in
this breed castration seems to produce a somewhat greater effect, so that
if performed at an early age the horns "remain almost undeveloped." (18.
I am much obliged to Prof. Victor Carus, for having made enquiries for me
in Saxony on this subject. H. von Nathusius ('Viehzucht,' 1872, p. 64)
says that the horns of sheep castrated at an early period, either
altogether disappear or remain as mere rudiments; but I do not know whether
he refers to merinos or to ordinary breeds.) On the Guinea coast there is
a breed in which the females never bear horns, and, as Mr. Winwood Reade
informs me, the rams after castration are quite destitute of them. With
cattle, the horns of the males are much altered by castration; for instead
of being short and thick, they become longer than those of the cow, but
otherwise resemble them. The Antilope bezoartica offers a somewhat
analogous case: the males have long straight spiral horns, nearly parallel
to each other, and directed backwards; the females occasionally bear horns,