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The Variation of Animals and Plants under Domestication by Charles Darwin

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This etext was prepared by Sue Asscher asschers@dingoblue.net.au
from the etext prepared by Robert J. Robbins, PhD of the ESP Project
http://www.esp.org/rjr

THE VARIATION OF

ANIMALS AND PLANTS

UNDER DOMESTICATION

BY

CHARLES DARWIN, M.A., F.R.S., ETC.

IN TWO VOLUMES

VOLUME II.

CONTENTS.

CHAPTER 2.XIII.--INHERITANCE continued--REVERSION OR ATAVISM.

DIFFERENT FORMS OF REVERSION--IN PURE OR UNCROSSED BREEDS, AS IN PIGEONS,
FOWLS, HORNLESS CATTLE AND SHEEP, IN CULTIVATED PLANTS--REVERSION IN FERAL
ANIMALS AND PLANTS--REVERSION IN CROSSED VARIETIES AND SPECIES--REVERSION
THROUGH BUD-PROPAGATION, AND BY SEGMENTS IN THE SAME FLOWER OR FRUIT--IN
DIFFERENT PARTS OF THE BODY IN THE SAME ANIMAL--THE ACT OF CROSSING A DIRECT
CAUSE OF REVERSION, VARIOUS CASES OF, WITH INSTINCTS--OTHER PROXIMATE CAUSES
OF REVERSION--LATENT CHARACTERS--SECONDARY SEXUAL CHARACTERS--UNEQUAL
DEVELOPMENT OF THE TWO SIDES OF THE BODY--APPEARANCE WITH ADVANCING AGE OF
CHARACTERS DERIVED FROM A CROSS--THE GERM, WITH ALL ITS LATENT CHARACTERS, A
WONDERFUL OBJECT--MONSTROSITIES--PELORIC FLOWERS DUE IN SOME CASES TO
REVERSION.

CHAPTER 2.XIV.--INHERITANCE continued.--FIXEDNESS OF CHARACTER--PREPOTENCY--
SEXUAL LIMITATION--CORRESPONDENCE OF AGE.

FIXEDNESS OF CHARACTER APPARENTLY NOT DUE TO ANTIQUITY OF INHERITANCE--
PREPOTENCY OF TRANSMISSION IN INDIVIDUALS OF THE SAME FAMILY, IN CROSSED
BREEDS AND SPECIES; OFTEN STRONGER IN ONE SEX THAN THE OTHER; SOMETIMES DUE TO
THE SAME CHARACTER BEING PRESENT AND VISIBLE IN ONE BREED AND LATENT IN THE
OTHER--INHERITANCE AS LIMITED BY SEX--NEWLY-ACQUIRED CHARACTERS IN OUR
DOMESTICATED ANIMALS OFTEN TRANSMITTED BY ONE SEX ALONE, SOMETIMES LOST BY ONE
SEX ALONE--INHERITANCE AT CORRESPONDING PERIODS OF LIFE--THE IMPORTANCE OF THE
PRINCIPLE WITH RESPECT TO EMBRYOLOGY; AS EXHIBITED IN DOMESTICATED ANIMALS: AS
EXHIBITED IN THE APPEARANCE AND DISAPPEARANCE OF INHERITED DISEASES; SOMETIMES
SUPERVENING EARLIER IN THE CHILD THAN IN THE PARENT--SUMMARY OF THE THREE
PRECEDING CHAPTERS.

CHAPTER 2.XV.--ON CROSSING.

FREE INTERCROSSING OBLITERATES THE DIFFERENCES BETWEEN ALLIED BREEDS--WHEN THE
NUMBERS OF TWO COMMINGLING BREEDS ARE UNEQUAL, ONE ABSORBS THE OTHER--THE RATE
OF ABSORPTION DETERMINED BY PREPOTENCY OF TRANSMISSION, BY THE CONDITIONS OF
LIFE, AND BY NATURAL SELECTION--ALL ORGANIC BEINGS OCCASIONALLY INTERCROSS;
APPARENT EXCEPTIONS--ON CERTAIN CHARACTERS INCAPABLE OF FUSION; CHIEFLY OR
EXCLUSIVELY THOSE WHICH HAVE SUDDENLY APPEARED IN THE INDIVIDUAL--ON THE
MODIFICATION OF OLD RACES, AND THE FORMATION OF NEW RACES BY CROSSING--SOME
CROSSED RACES HAVE BRED TRUE FROM THEIR FIRST PRODUCTION--ON THE CROSSING OF
DISTINCT SPECIES IN RELATION TO THE FORMATION OF DOMESTIC RACES.

CHAPTER 2.XVI.--CAUSES WHICH INTERFERE WITH THE FREE CROSSING OF VARIETIES--
INFLUENCE OF DOMESTICATION ON FERTILITY.

DIFFICULTIES IN JUDGING OF THE FERTILITY OF VARIETIES WHEN CROSSED--VARIOUS
CAUSES WHICH KEEP VARIETIES DISTINCT, AS THE PERIOD OF BREEDING AND SEXUAL
PREFERENCE--VARIETIES OF WHEAT SAID TO BE STERILE WHEN CROSSED--VARIETIES OF
MAIZE, VERBASCUM, HOLLYHOCK, GOURDS, MELONS, AND TOBACCO, RENDERED IN SOME
DEGREE MUTUALLY STERILE--DOMESTICATION ELIMINATES THE TENDENCY TO STERILITY
NATURAL TO SPECIES WHEN CROSSED--ON THE INCREASED FERTILITY OF UNCROSSED
ANIMALS AND PLANTS FROM DOMESTICATION AND CULTIVATION.

CHAPTER 2.XVII.--ON THE GOOD EFFECTS OF CROSSING, AND ON THE EVIL EFFECTS OF
CLOSE INTERBREEDING.

DEFINITION OF CLOSE INTERBREEDING--AUGMENTATION OF MORBID TENDENCIES--GENERAL
EVIDENCE OF THE GOOD EFFECTS DERIVED FROM CROSSING, AND ON THE EVIL EFFECTS OF
CLOSE INTERBREEDING--CATTLE, CLOSELY INTERBRED; HALF-WILD CATTLE LONG KEPT IN
THE SAME PARKS--SHEEP--FALLOW-DEER--DOGS, RABBITS, PIGS--MAN, ORIGIN OF HIS
ABHORRENCE OF INCESTUOUS MARRIAGES--FOWLS--PIGEONS--HIVE-BEES--PLANTS, GENERAL
CONSIDERATIONS ON THE BENEFITS DERIVED FROM CROSSING--MELONS, FRUIT-TREES,
PEAS, CABBAGES, WHEAT, AND FOREST-TREES--ON THE INCREASED SIZE OF HYBRID
PLANTS, NOT EXCLUSIVELY DUE TO THEIR STERILITY--ON CERTAIN PLANTS WHICH EITHER
NORMALLY OR ABNORMALLY ARE SELF-IMPOTENT, BUT ARE FERTILE, BOTH ON THE MALE
AND FEMALE SIDE, WHEN CROSSED WITH DISTINCT INDIVIDUALS EITHER OF THE SAME OR
ANOTHER SPECIES--CONCLUSION.

CHAPTER 2.XVIII.--ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED CONDITIONS OF
LIFE: STERILITY FROM VARIOUS CAUSES.

ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OF LIFE--STERILITY
FROM CHANGED CONDITIONS, IN ANIMALS, IN THEIR NATIVE COUNTRY AND IN
MENAGERIES--MAMMALS, BIRDS, AND INSECTs--LOSS OF SECONDARY SEXUAL CHARACTERS
AND OF INSTINCTS--CAUSES OF STERILITY--STERILITY OF DOMESTICATED ANIMALS FROM
CHANGED CONDITIONS--SEXUAL INCOMPATIBILITY OF INDIVIDUAL ANIMALS--STERILITY OF
PLANTS FROM CHANGED CONDITIONS OF LIFE--CONTABESCENCE OF THE ANTHERS--
MONSTROSITIES AS A CAUSE OF STERILITY--DOUBLE FLOWERS--SEEDLESS FRUIT--
STERILITY FROM THE EXCESSIVE DEVELOPMENT OF THE ORGANS OF VEGETATION--FROM
LONG-CONTINUED PROPAGATION BY BUDS--INCIPIENT STERILITY THE PRIMARY CAUSE OF
DOUBLE FLOWERS AND SEEDLESS FRUIT.

CHAPTER 2.XIX.--SUMMARY OF THE FOUR LAST CHAPTERS, WITH REMARKS ON HYBRIDISM.

ON THE EFFECTS OF CROSSING--THE INFLUENCE OF DOMESTICATION ON FERTILITY--CLOSE
INTERBREEDING--GOOD AND EVIL RESULTS FROM CHANGED CONDITIONS OF LIFE--
VARIETIES WHEN CROSSED NOT INVARIABLY FERTILE--ON THE DIFFERENCE IN FERTILITY
BETWEEN CROSSED SPECIES AND VARIETIES--CONCLUSIONS WITH RESPECT TO HYBRIDISM--
LIGHT THROWN ON HYBRIDISM BY THE ILLEGITIMATE PROGENY OF HETEROSTYLED PLANTS--
STERILITY OF CROSSED SPECIES DUE TO DIFFERENCES CONFINED TO THE REPRODUCTIVE
SYSTEM--NOT ACCUMULATED THROUGH NATURAL SELECTION--REASONS WHY DOMESTIC
VARIETIES ARE NOT MUTUALLY STERILE--TOO MUCH STRESS HAS BEEN LAID ON THE
DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND CROSSED VARIETIES--
CONCLUSION.

CHAPTER 2.XX.--SELECTION BY MAN.

SELECTION A DIFFICULT ART--METHODICAL, UNCONSCIOUS, AND NATURAL SELECTION--
RESULTS OF METHODICAL SELECTION--CARE TAKEN IN SELECTION--SELECTION WITH
PLANTS--SELECTION CARRIED ON BY THE ANCIENTS AND BY SEMI-CIVILISED PEOPLE--
UNIMPORTANT CHARACTERS OFTEN ATTENDED TO--UNCONSCIOUS SELECTION--AS
CIRCUMSTANCES SLOWLY CHANGE, SO HAVE OUR DOMESTICATED ANIMALS CHANGED
THROUGH THE ACTION OF UNCONSCIOUS SELECTION--INFLUENCE OF DIFFERENT BREEDERS
ON THE SAME SUB-VARIETY--PLANTS AS AFFECTED BY UNCONSCIOUS SELECTION--EFFECTS
OF SELECTION AS SHOWN BY THE GREAT AMOUNT OF DIFFERENCE IN THE PARTS MOST
VALUED BY MAN.

CHAPTER 2.XXI.--SELECTION, continued.

NATURAL SELECTION AS AFFECTING DOMESTIC PRODUCTIONS--CHARACTERS WHICH APPEAR
OF TRIFLING VALUE OFTEN OF REAL IMPORTANCE--CIRCUMSTANCES FAVOURABLE TO
SELECTION BY MAN--FACILITY IN PREVENTING CROSSES, AND THE NATURE OF THE
CONDITIONS--CLOSE ATTENTION AND PERSEVERANCE INDISPENSABLE--THE PRODUCTION OF
A LARGE NUMBER OF INDIVIDUALS ESPECIALLY FAVOURABLE--WHEN NO SELECTION IS
APPLIED, DISTINCT RACES ARE NOT FORMED--HIGHLY-BRED ANIMALS LIABLE TO
DEGENERATION--TENDENCY IN MAN TO CARRY THE SELECTION OF EACH CHARACTER TO AN
EXTREME POINT, LEADING TO DIVERGENCE OF CHARACTER, RARELY TO CONVERGENCE--
CHARACTERS CONTINUING TO VARY IN THE SAME DIRECTION IN WHICH THEY HAVE
ALREADY VARIED--DIVERGENCE OF CHARACTER, WITH THE EXTINCTION OF INTERMEDIATE
VARIETIES, LEADS TO DISTINCTNESS IN OUR DOMESTIC RACES--LIMIT TO THE POWER OF
SELECTION--LAPSE OF TIME IMPORTANT--MANNER IN WHICH DOMESTIC RACES HAVE
ORIGINATED--SUMMARY.

CHAPTER 2.XXII.--CAUSES OF VARIABILITY.

VARIABILITY DOES NOT NECESSARILY ACCOMPANY REPRODUCTION--CAUSES ASSIGNED BY
VARIOUS AUTHORS--INDIVIDUAL DIFFERENCES--VARIABILITY OF EVERY KIND DUE TO
CHANGED CONDITIONS OF LIFE--ON THE NATURE OF SUCH CHANGES--CLIMATE, FOOD,
EXCESS OF NUTRIMENT--SLIGHT CHANGES SUFFICIENT--EFFECTS OF GRAFTING ON THE
VARIABILITY OF SEEDLING-TREES--DOMESTIC PRODUCTIONS BECOME HABITUATED TO
CHANGED CONDITIONS--ON THE ACCUMULATIVE ACTION OF CHANGED CONDITIONS--CLOSE
INTERBREEDING AND THE IMAGINATION OF THE MOTHER SUPPOSED TO CAUSE VARIABILITY
--CROSSING AS A CAUSE OF THE APPEARANCE OF NEW CHARACTERS--VARIABILITY FROM
THE COMMINGLING OF CHARACTERS AND FROM REVERSION--ON THE MANNER AND PERIOD OF
ACTION OF THE CAUSES WHICH EITHER DIRECTLY, OR INDIRECTLY THROUGH THE
REPRODUCTIVE SYSTEM, INDUCE VARIABILITY.

CHAPTER 2.XXIII.--DIRECT AND DEFINITE ACTION OF THE EXTERNAL CONDITIONS OF
LIFE.

SLIGHT MODIFICATIONS IN PLANTS FROM THE DEFINITE ACTION OF CHANGED CONDITIONS,
IN SIZE, COLOUR, CHEMICAL PROPERTIES, AND IN THE STATE OF THE TISSUES--LOCAL
DISEASES--CONSPICUOUS MODIFICATIONS FROM CHANGED CLIMATE OR FOOD, ETC.--
PLUMAGE OF BIRDS AFFECTED BY PECULIAR NUTRIMENT, AND BY THE INOCULATION OF
POISON--LAND-SHELLS--MODIFICATIONS OF ORGANIC BEINGS IN A STATE OF NATURE
THROUGH THE DEFINITE ACTION OF EXTERNAL CONDITIONS--COMPARISON OF AMERICAN AND
EUROPEAN TREES--GALLS--EFFECTS OF PARASITIC FUNGI--CONSIDERATIONS OPPOSED TO
THE BELIEF IN THE POTENT INFLUENCE OF CHANGED EXTERNAL CONDITIONS--PARALLEL
SERIES OF VARIETIES--AMOUNT OF VARIATION DOES NOT CORRESPOND WITH THE DEGREE
OF CHANGE IN THE CONDITIONS--BUD-VARIATION--MONSTROSITIES PRODUCED BY
UNNATURAL TREATMENT--SUMMARY.

CHAPTER 2.XXIV.--LAWS OF VARIATION--USE AND DISUSE, ETC.

NISUS FORMATIVUS, OR THE CO-ORDINATING POWER OF THE ORGANISATION--ON THE
EFFECTS OF THE INCREASED USE AND DISUSE OF ORGANS--CHANGED HABITS OF LIFE--
ACCLIMATISATION WITH ANIMALS AND PLANTS--VARIOUS METHODS BY WHICH THIS CAN BE
EFFECTED--ARRESTS OF DEVELOPMENT--RUDIMENTARY ORGANS.

CHAPTER 2.XXV.--LAWS OF VARIATION, continued.--CORRELATED VARIABILITY.

EXPLANATION OF TERM CORRELATION--CONNECTED WITH DEVELOPMENT--MODIFICATIONS
CORRELATED WITH THE INCREASED OR DECREASED SIZE OF PARTS--CORRELATED VARIATION
OF HOMOLOGOUS PARTS--FEATHERED FEET IN BIRDS ASSUMING THE STRUCTURE OF THE
WINGS--CORRELATION BETWEEN THE HEAD AND THE EXTREMITIES--BETWEEN THE SKIN AND
DERMAL APPENDAGES--BETWEEN THE ORGANS OF SIGHT AND HEARING--CORRELATED
MODIFICATIONS IN THE ORGANS OF PLANTS--CORRELATED MONSTROSITIES--CORRELATION
BETWEEN THE SKULL AND EARS--SKULL AND CREST OF FEATHERS--SKULL AND HORNS--
CORRELATION OF GROWTH COMPLICATED BY THE ACCUMULATED EFFECTS OF NATURAL
SELECTION--COLOUR AS CORRELATED WITH CONSTITUTIONAL PECULIARITIES.

CHAPTER 2.XXVI.--LAWS OF VARIATION, continued.--SUMMARY.

THE FUSION OF HOMOLOGOUS PARTS--THE VARIABILITY OF MULTIPLE AND HOMOLOGOUS
PARTS--COMPENSATION OF GROWTH--MECHANICAL PRESSURE--RELATIVE POSITION OF
FLOWERS WITH RESPECT TO THE AXIS, AND OF SEEDS IN THE OVARY, AS INDUCING
VARIATION--ANALOGOUS OR PARALLEL VARIETIES--SUMMARY OF THE THREE LAST
CHAPTERS.

CHAPTER 2.XXVII.--PROVISIONAL HYPOTHESIS OF PANGENESIS.

PRELIMINARY REMARKS.
FIRST PART:--THE FACTS TO BE CONNECTED UNDER A SINGLE POINT OF VIEW, NAMELY,
THE VARIOUS KINDS OF REPRODUCTION--REGROWTH OF AMPUTATED PARTS--GRAFT-HYBRIDS
--THE DIRECT ACTION OF THE MALE ELEMENT ON THE FEMALE--DEVELOPMENT--THE
FUNCTIONAL INDEPENDENCE OF THE UNITS OF THE BODY--VARIABILITY--INHERITANCE--
REVERSION.
SECOND PART:--STATEMENT OF THE HYPOTHESIS--HOW FAR THE NECESSARY ASSUMPTIONS
ARE IMPROBABLE--EXPLANATION BY AID OF THE HYPOTHESIS OF THE SEVERAL CLASSES OF
FACTS SPECIFIED IN THE FIRST PART--CONCLUSION.

CHAPTER 2.XXVIII.--CONCLUDING REMARKS.

DOMESTICATION--NATURE AND CAUSES OF VARIABILITY--SELECTION--DIVERGENCE AND
DISTINCTNESS OF CHARACTER--EXTINCTION OF RACES--CIRCUMSTANCES FAVOURABLE TO
SELECTION BY MAN--ANTIQUITY OF CERTAIN RACES--THE QUESTION WHETHER EACH
PARTICULAR VARIATION HAS BEEN SPECIALLY PREORDAINED.

INDEX.

THE VARIATION OF ANIMALS AND PLANTS UNDER DOMESTICATION.

VOLUME II.

CHAPTER 2.XIII.

INHERITANCE continued--REVERSION OR ATAVISM.

DIFFERENT FORMS OF REVERSION.
IN PURE OR UNCROSSED BREEDS, AS IN PIGEONS, FOWLS, HORNLESS CATTLE AND SHEEP,
IN CULTIVATED PLANTS.
REVERSION IN FERAL ANIMALS AND PLANTS.
REVERSION IN CROSSED VARIETIES AND SPECIES.
REVERSION THROUGH BUD-PROPAGATION, AND BY SEGMENTS IN THE SAME FLOWER OR
FRUIT.
IN DIFFERENT PARTS OF THE BODY IN THE SAME ANIMAL.
THE ACT OF CROSSING A DIRECT CAUSE OF REVERSION, VARIOUS CASES OF, WITH
INSTINCTS.
OTHER PROXIMATE CAUSES OF REVERSION.
LATENT CHARACTERS.
SECONDARY SEXUAL CHARACTERS.
UNEQUAL DEVELOPMENT OF THE TWO SIDES OF THE BODY.
APPEARANCE WITH ADVANCING AGE OF CHARACTERS DERIVED FROM A CROSS.
THE GERM, WITH ALL ITS LATENT CHARACTERS, A WONDERFUL OBJECT.
MONSTROSITIES.
PELORIC FLOWERS DUE IN SOME CASES TO REVERSION.

The great principle of inheritance to be discussed in this chapter has been
recognised by agriculturists and authors of various nations, as shown by the
scientific term ATAVISM, derived from atavus, an ancestor; by the English
terms of REVERSION, or THROWING-BACK; by the French PAS-EN-ARRIERE; and by the
German RUCKSCHLAG, or RUCKSCHRITT. When the child resembles either grandparent
more closely than its immediate parents, our attention is not much arrested,
though in truth the fact is highly remarkable; but when the child resembles
some remote ancestor or some distant member in a collateral line,--and in the
last case we must attribute this to the descent of all the members from a
common progenitor,--we feel a just degree of astonishment. When one parent
alone displays some newly-acquired and generally inheritable character, and
the offspring do not inherit it, the cause may lie in the other parent having
the power of prepotent transmission. But when both parents are similarly
characterised, and the child does not, whatever the cause may be, inherit the
character in question, but resembles its grandparents, we have one of the
simplest cases of reversion. We continually see another and even more simple
case of atavism, though not generally included under this head, namely, when
the son more closely resembles his maternal than his paternal grand-sire in
some male attribute, as in any peculiarity in the beard of man, the horns of
the bull, the hackles or comb of the cock, or, as in certain diseases
necessarily confined to the male sex; for as the mother cannot possess or
exhibit such male attributes, the child must inherit them, through her blood,
from his maternal grandsire.

The cases of reversion may be divided into two main classes which, however, in
some instances, blend into one another; namely, first, those occurring in a
variety or race which has not been crossed, but has lost by variation some
character that it formerly possessed, and which afterwards reappears. The
second class includes all cases in which an individual with some
distinguishable character, a race, or species, has at some former period been
crossed, and a character derived from this cross, after having disappeared
during one or several generations, suddenly reappears. A third class,
differing only in the manner of reproduction, might be formed to include all
cases of reversion effected by means of buds, and therefore independent of
true or seminal generation. Perhaps even a fourth class might be instituted,
to include reversions by segments in the same individual flower or fruit, and
in different parts of the body in the same individual animal as it grows old.
But the two first main classes will be sufficient for our purpose.

REVERSION TO LOST CHARACTERS BY PURE OR UNCROSSED FORMS.

Striking instances of this first class of cases were given in the sixth
chapter, namely, of the occasional reappearance, in variously-coloured breeds
of the pigeon, of blue birds with all the marks characteristic of the wild
Columba livia. Similar cases were given in the case of the fowl. With the
common ass, as the legs of the wild progenitor are almost always striped, we
may feel assured that the occasional appearance of such stripes in the
domestic animal is a case of simple reversion. But I shall be compelled to
refer again to these cases, and therefore here pass them over.

The aboriginal species from which our domesticated cattle and sheep are
descended, no doubt possessed horns; but several hornless breeds are now well
established. Yet in these--for instance, in Southdown sheep--"it is not
unusual to find among the male lambs some with small horns." The horns, which
thus occasionally reappear in other polled breeds, either "grow to the full
size," or are curiously attached to the skin alone and hang "loosely down, or
drop off." (13/1. 'Youatt on Sheep' pages 20, 234. The same fact of loose
horns occasionally appearing in hornless breeds has been observed in Germany;
Bechstein 'Naturgesch. Deutschlands.' b. 1 s. 362.) The Galloways and Suffolk
cattle have been hornless for the last 100 or 150 years, but a horned calf,
with the horn often loosely attached, is occasionally produced. (13/2. 'Youatt
on Cattle' pages 155, 174.)

There is reason to believe that sheep in their early domesticated condition
were "brown or dingy black;" but even in the time of David certain flocks were
spoken of as white as snow. During the classical period the sheep of Spain are
described by several ancient authors as being black, red, or tawny. (13/3.
'Youatt on Sheep' 1838 pages 17, 145.) At the present day, notwithstanding the
great care which is taken to prevent it, particoloured lambs and some entirely
black are occasionally, or even frequently, dropped by our most highly
improved and valued breeds, such as the Southdowns. Since the time of the
famous Bakewell, during the last century, the Leicester sheep have been bred
with the most scrupulous care; yet occasionally grey-faced, or black-spotted,
or wholly black lambs appear. (13/4. I have been informed of this fact through
the Rev. W.D. Fox on the excellent authority of Mr. Wilmot: see also remarks
on this subject in an article in the 'Quarterly Review' 1849 page 395.) This
occurs still more frequently with the less improved breeds, such as the
Norfolks. (13/5. Youatt pages 19, 234.) As bearing on this tendency in sheep
to revert to dark colours, I may state (though in doing so I trench on the
reversion of crossed breeds, and likewise on the subject of prepotency) that
the Rev. W.D. Fox was informed that seven white Southdown ewes were put to a
so-called Spanish ram, which had two small black spots on his sides, and they
produced thirteen lambs, all perfectly black. Mr. Fox believes that this ram
belonged to a breed which he has himself kept, and which is always spotted
with black and white; and he finds that Leicester sheep crossed by rams of
this breed always produce black lambs: he has gone on recrossing these crossed
sheep with pure white Leicesters during three successive generations, but
always with the same result. Mr. Fox was also told by the friend from whom the
spotted breed was procured, that he likewise had gone on for six or seven
generations crossing with white sheep, but still black lambs were invariably
produced.

Similar facts could be given with respect to tailless breeds of various
animals. For instance, Mr. Hewitt (13/6. 'The Poultry Book' by Mr. Tegetmeier
1866 page 231.) states that chickens bred from some rumpless fowls, which were
reckoned so good that they won a prize at an exhibition, "in a considerable
number of instances were furnished with fully developed tail-feathers." On
inquiry, the original breeder of these fowls stated that, from the time when
he had first kept them, they had often produced fowls furnished with tails;
but that these latter would again reproduce rumpless chickens.

Analogous cases of reversion occur in the vegetable kingdom; thus "from seeds
gathered from the finest cultivated varieties of Heartsease (Viola tricolor),
plants perfectly wild both in their foliage and their flowers are frequently
produced;" (13/7. Loudon's 'Gardener's Mag.' volume 10 1834 page 396: a
nurseryman, with much experience on this subject, has likewise assured me that
this sometimes occurs.) but the reversion in this instance is not to a very
ancient period, for the best existing varieties of the heartsease are of
comparatively modern origin. With most of our cultivated vegetables there is
some tendency to reversion to what is known to be, or may be presumed to be,
their aboriginal state; and this would be more evident if gardeners did not
generally look over their beds of seedlings, and pull up the false plants or
"rogues" as they are called. It has already been remarked, that some few
seedling apples and pears generally resemble, but apparently are not identical
with, the wild trees from which they are descended. In our turnip (13/8.
'Gardener's Chronicle' 1855 page 777.) and carrot-beds a few plants often
"break "--that is, flower too soon; and their roots are generally hard and
stringy, as in the parent-species. By the aid of a little selection, carried
on during a few generations, most of our cultivated plants could probably be
brought back, without any great change in their conditions of life, to a wild
or nearly wild condition: Mr. Buckman has effected this with the parsnip
(13/9. Ibid 1862 page 721.); and Mr. Hewett C. Watson, as he informs me,
selected, during three generations, "the most diverging plants of Scotch kail,
perhaps one of the least modified varieties of the cabbage; and in the third
generation some of the plants came very close to the forms now established in
England about old castle-walls, and called indigenous."

REVERSION IN ANIMALS AND PLANTS WHICH HAVE RUN WILD.

In the cases hitherto considered, the reverting animals and plants have not
been exposed to any great or abrupt change in their conditions of life which
could have induced this tendency; but it is very different with animals and
plants which have become feral or run wild. It has been repeatedly asserted in
the most positive manner by various authors, that feral animals and plants
invariably return to their primitive specific type. It is curious on what
little evidence this belief rests. Many of our domesticated animals could not
subsist in a wild state; thus, the more highly improved breeds of the pigeon
will not "field" or search for their own food. Sheep have never become feral,
and would be destroyed by almost every beast of prey. (13/10. Mr. Boner speaks
('Chamois-hunting' 2nd edition 1860 page 92) of sheep often running wild in
the Bavarian Alps; but, on making further inquiries at my request, he found
that they are not able to establish themselves; they generally perish from the
frozen snow clinging to their wool, and they have lost the skill necessary to
pass over steep icy slopes. On one occasion two ewes survived the winter, but
their lambs perished.) In several cases we do not know the aboriginal parent-
species, and cannot possibly tell whether or not there has been any close
degree of reversion. It is not known in any instance what variety was first
turned out; several varieties have probably in some cases run wild, and their
crossing alone would tend to obliterate their proper character. Our
domesticated animals and plants, when they run wild, must always be exposed to
new conditions of life, for, as Mr. Wallace (13/11. See some excellent remarks
on this subject by Mr. Wallace 'Journal Proc. Linn. Soc.' 1858 volume 3 page
60.) has well remarked, they have to obtain their own food, and are exposed to
competition with the native productions. Under these circumstances, if our
domesticated animals did not undergo change of some kind, the result would be
quite opposed to the conclusions arrived at in this work. Nevertheless, I do
not doubt that the simple fact of animals and plants becoming feral, does
cause some tendency to reversion to the primitive state; though this tendency
has been much exaggerated by some authors.

[I will briefly run through the recorded cases. With neither horses nor cattle
is the primitive stock known; and it has been shown in former chapters that
they have assumed different colours in different countries. Thus the horses
which have run wild in South America are generally brownish-bay, and in the
East dun-coloured; their heads have become larger and coarser, and this may be
due to reversion. No careful description has been given of the feral goat.
Dogs which have run wild in various countries have hardly anywhere assumed a
uniform character; but they are probably descended from several domestic
races, and aboriginally from several distinct species. Feral cats, both in
Europe and La Plata, are regularly striped; in some cases they have grown to
an unusually large size, but do not differ from the domestic animal in any
other character. When variously-coloured tame rabbits are turned out in
Europe, they generally reacquire the colouring of the wild animal; there can
be no doubt that this does really occur, but we should remember that oddly-
coloured and conspicuous animals would suffer much from beasts of prey and
from being easily shot; this at least was the opinion of a gentleman who tried
to stock his woods with a nearly white variety; if thus destroyed, they would
be supplanted by, instead of being transformed into, the common rabbit. We
have seen that the feral rabbits of Jamaica, and especially of Porto Santo,
have assumed new colours and other new characters. The best known case of
reversion, and that on which the widely spread belief in its universality
apparently rests, is that of pigs. These animals have run wild in the West
Indies, South America, and the Falkland Islands, and have everywhere acquired
the dark colour, the thick bristles, and great tusks of the wild boar; and the
young have reacquired longitudinal stripes. But even in the case of the pig,
Roulin describes the half-wild animals in different parts of South America as
differing in several respects. In Louisiana the pig (13/12. Dureau de la Malle
'Comptes Rendus' tome 41 1855 page 807. From the statements above given, the
author concludes that the wild pigs of Louisiana are not descended from the
European Sus scrofa.) has run wild, and is said to differ a little in form,
and much in colour, from the domestic animal, yet does not closely resemble
the wild boar of Europe. With pigeons and fowls (13/13. Capt. W. Allen, in his
'Expedition to the Niger' states that fowls have run wild on the island of
Annobon, and have become modified in form and voice. The account is so meagre
and vague that it did not appear to me worth copying; but I now find that
Dureau de la Malle ('Comptes Rendus' tome 41 1855 page 690) advances this as a
good instance of reversion to the primitive stock, and as confirmatory of a
still more vague statement in classical times by Varro.), it is not known what
variety was first turned out, nor what character the feral birds have assumed.
The guinea-fowl in the West Indies, when feral, seems to vary more than in the
domesticated state.

With respect to plants run wild, Dr. Hooker (13/14. 'Flora of Australia' 1859
Introduction page 9.) has strongly insisted on what slight evidence the common
belief in their reversion to a primitive state rests. Godron (13/15. 'De
l'Espece' tome 2 pages 54, 58, 60.) describes wild turnips, carrots, and
celery; but these plants in their cultivated state hardly differ from their
wild prototypes, except in the succulency and enlargement of certain parts,--
characters which would certainly be lost by plants growing in poor soil and
struggling with other plants. No cultivated plant has run wild on so enormous
a scale as the cardoon (Cynara cardunculus) in La Plata. Every botanist who
has seen it growing there, in vast beds, as high as a horse's back, has been
struck with its peculiar appearance; but whether it differs in any important
point from the cultivated Spanish form, which is said not to be prickly like
its American descendant, or whether it differs from the wild Mediterranean
species, which is said not to be social (though this may be due merely to the
nature of the conditions), I do not know.]

REVERSION TO CHARACTERS DERIVED FROM A CROSS, IN THE CASE OF SUB-VARIETIES,
RACES, AND SPECIES.

When an individual having some recognisable peculiarity unites with another of
the same sub-variety, not having the peculiarity in question, it often
reappears in the descendants after an interval of several generations. Every
one must have noticed, or heard from old people of children closely resembling
in appearance or mental disposition, or in so small and complex a character as
expression, one of their grandparents, or some more distant collateral
relation. Very many anomalies of structure and diseases (13/16. Mr. Sedgwick
gives many instances in the 'British and Foreign Med.-Chirurg. Review' April
and July 1863 pages 448, 188.) of which instances have been given in the last
chapter, have come into a family from one parent, and have reappeared in the
progeny after passing over two or three generations. The following case has
been communicated to me on good authority, and may, I believe, be fully
trusted: a pointer-bitch produced seven puppies; four were marked with blue
and white, which is so unusual a colour with pointers that she was thought to
have played false with one of the greyhounds, and the whole litter was
condemned; but the gamekeeper was permitted to save one as a curiosity. Two
years afterwards a friend of the owner saw the young dog, and declared that he
was the image of his old pointer-bitch Sappho, the only blue and white pointer
of pure descent which he had ever seen. This led to close inquiry, and it was
proved that he was the great-great-grandson of Sappho; so that, according to
the common expression, he had only 1/16th of her blood in his veins. I may
give one other instance, on the authority of Mr. R. Walker, a large cattle-
breeder in Kincardineshire. He bought a black bull, the son of a black cow
with white legs, white belly and part of the tail white; and in 1870 a calf
the gr.-gr.-gr.-gr.-grandchild of this cow was born coloured in the same very
peculiar manner; all the intermediate offspring having been black. In these
cases there can hardly be a doubt that a character derived from a cross with
an individual of the same variety reappeared after passing over three
generations in the one case, and five in the other.

When two distinct races are crossed, it is notorious that the tendency in the
offspring to revert to one or both parent-forms is strong, and endures for
many generations. I have myself seen the clearest evidence of this in crossed
pigeons and with various plants. Mr. Sidney (13/17. In his edition of 'Youatt
on the Pig' 1860 page 27.) states that, in a litter of Essex pigs, two young
ones appeared which were the image of the Berkshire boar that had been used
twenty-eight years before in giving size and constitution to the breed. I
observed in the farmyard at Betley Hall some fowls showing a strong likeness
to the Malay breed, and was told by Mr. Tollet that he had forty years before
crossed his birds with Malays; and that, though he had at first attempted to
get rid of this strain, he had subsequently given up the attempt in despair,
as the Malay character would reappear.

This strong tendency in crossed breeds to revert has given rise to endless
discussions in how many generations after a single cross, either with a
distinct breed or merely with an inferior animal, the breed may be considered
as pure, and free from all danger of reversion. No one supposes that less than
three generations suffices, and most breeders think that six, seven, or eight
are necessary, and some go to still greater lengths. (13/18. Dr. P. Lucas,
'Hered. Nat.' tome 2 pages 314, 892: see a good practical article on the
subject in 'Gardener's Chronicle' 1856 page 620. I could add a vast number of
references, but they would be superfluous.) But neither in the case of a breed
which has been contaminated by a single cross, nor when, in the attempt to
form an intermediate breed, half-bred animals have been matched together
during many generations, can any rule be laid down how soon the tendency to
reversion will be obliterated. It depends on the difference in the strength or
prepotency of transmission in the two parent-forms, on their actual amount of
difference, and on the nature of the conditions of life to which the crossed
offspring are exposed. But we must be careful not to confound these cases of
reversion to characters which were gained by a cross, with those under the
first class, in which characters originally common to BOTH parents, but lost
at some former period, reappear; for such characters may recur after an almost
indefinite number of generations.

The law of reversion is as powerful with hybrids, when they are sufficiently
fertile to breed together, or when they are repeatedly crossed with either
pure parent-form, as in the case of mongrels. It is not necessary to give
instances. With plants almost every one who has worked on this subject, from
the time of Kolreuter to the present day, has insisted on this tendency.
Gartner has recorded some good instances; but no one has given more striking
ones than Naudin. (13/19. Kolreuter gives curious cases in his 'Dritte
Fortsetzung' 1766 ss. 53, 59; and in his well-known 'Memoirs on Lavatera and
Jalapa.' Gartner 'Bastarderzeugung' ss. 437, 441, etc. Naudin in his
"Recherches sur l'Hybridite" 'Nouvelles Archives du Museum' tome 1 page 25.)
The tendency differs in degree or strength in different groups, and partly
depends, as we shall presently see, on whether the parent-plants have been
long cultivated. Although the tendency to reversion is extremely general with
nearly all mongrels and hybrids, it cannot be considered as invariably
characteristic of them; it may also be mastered by long-continued selection;
but these subjects will more properly be discussed in a future chapter on
Crossing. From what we see of the power and scope of reversion, both in pure
races, and when varieties or species are crossed, we may infer that characters
of almost every kind are capable of reappearing after having been lost for a
great length of time. But it does not follow from this that in each particular
case certain characters will reappear; for instance, this will not occur when
a race is crossed with another endowed with prepotency of transmission.
Sometimes the power of reversion wholly fails, without our being able to
assign any cause for the failure: thus it has been stated that in a French
family in which 85 out of above 600 members, during six generations, had been
subject to night-blindness, "there has not been a single example of this
affection in the children of parents who were themselves free from it."
(13/20. Quoted by Mr. Sedgwick in 'Med.-Chirurg. Review' April 1861 page 485.
Dr. H. Dobell in 'Med.-Chirurg. Transactions' volume 46 gives an analogous
case in which, in a large family, fingers with thickened joints were
transmitted to several members during five generations; but when the blemish
once disappeared it never reappeared.)

REVERSION THROUGH BUD-PROPAGATION--PARTIAL REVERSION, BY SEGMENTS IN THE SAME
FLOWER OR FRUIT, OR IN DIFFERENT PARTS OF THE BODY IN THE SAME INDIVIDUAL
ANIMAL.

In the eleventh chapter many cases of reversion by buds, independently of
seminal generation, were given--as when a leaf-bud on a variegated, a curled,
or laciniated variety suddenly reassumes its proper character; or as when a
Provence-rose appears on a moss-rose, or a peach on a nectarine-tree. In some
of these cases only half the flower or fruit, or a smaller segment, or mere
stripes, reassume their former character; and here we have reversion by
segments. Vilmorin (13/21. Verlot 'Des Varietes' 1865 page 63.) has also
recorded several cases with plants derived from seed, of flowers reverting by
stripes or blotches to their primitive colours: he states that in all such
cases a white or pale-coloured variety must first be formed, and, when this is
propagated for a length of time by seed, striped seedlings occasionally make
their appearance; and these can afterwards by care be multiplied by seed.

The stripes and segments just referred to are not due, as far as is known, to
reversion to characters derived from a cross, but to characters lost by
variation. These cases, however, as Naudin (13/22. 'Nouvelles Archives du
Museum' tome 1 page 25. Alex. Braun (in his 'Rejuvenescence' Ray Soc. 1853
page 315) apparently holds a similar opinion.) insists in his discussion on
disjunction of character, are closely analogous with those given in the
eleventh chapter, in which crossed plants have been known to produce half-and-
half or striped flowers and fruit, or distinct kinds of flowers on the same
root resembling the two parent-forms. Many piebald animals probably come under
this same head. Such cases, as we shall see in the chapter on Crossing,
apparently result from certain characters not readily blending together, and,
as a consequence of this incapacity for fusion, the offspring either perfectly
resemble one of their two parents, or resemble one parent in one part, and the
other parent in another part; or whilst young are intermediate in character,
but with advancing age revert wholly or by segments to either parent-form, or
to both. Thus, young trees of the Cytisus adami are intermediate in foliage
and flowers between the two parent-forms; but when older the buds continually
revert either partially or wholly to both forms. The cases given in the
eleventh chapter on the changes which occurred during growth in crossed plants
of Tropaeolum, Cereus, Datura, and Lathyrus are all analogous. As, however,
these plants are hybrids of the first generation, and as their buds after a
time come to resemble their parents and not their grandparents, these cases do
not at first appear to come under the law of reversion in the ordinary sense
of the word; nevertheless, as the change is effected through a succession of
bud-generations on the same plant, they may be thus included.

Analogous facts have been observed in the animal kingdom, and are more
remarkable, as they occur in the same individual in the strictest sense, and
not as with plants through a succession of bud-generations. With animals the
act of reversion, if it can be so designated, does not pass over a true
generation, but merely over the early stages of growth in the same individual.
For instance, I crossed several white hens with a black cock, and many of the
chickens were, during the first year, perfectly white, but acquired during the
second year black feathers; on the other hand, some of the chickens which were
at first black, became during the second year piebald with white. A great
breeder (13/23. Mr. Teebay in 'The Poultry Book' by Mr. Tegetmeier 1866 page
72.) says, that a Pencilled Brahma hen which has any of the blood of the Light
Brahma in her, will "occasionally produce a pullet well pencilled during the
first year, but she will most likely moult brown on the shoulders and become
quite unlike her original colours in the second year." The same thing occurs
with light Brahmas if of impure blood. I have observed exactly similar cases
with the crossed offspring from differently coloured pigeons. But here is a
more remarkable fact: I crossed a turbit, which has a frill formed by the
feathers being reversed on its breast, with a trumpeter; and one of the young
pigeons thus raised at first showed not a trace of the frill, but, after
moulting thrice, a small yet unmistakably distinct frill appeared on its
breast. According to Girou (13/24. Quoted by Hofacker 'Ueber die
Eigenschaften' etc. s. 98.) calves produced from a red cow by a black bull, or
from a black cow by a red bull, are not rarely born red, and subsequently
become black. I possess a dog, the daughter of a white terrier by a fox-
coloured bulldog; as a puppy she was quite white, but when about six months
old a black spot appeared on her nose, and brown spots on her ears. When a
little older she was badly wounded on the back, and the hair which grew on the
cicatrix was of a brown colour, apparently derived from her father. This is
the more remarkable, as with most animals having coloured hair, that which
grows on a wounded surface is white.

In the foregoing cases, the characters which with advancing age reappeared,
were present in the immediately preceding generations; but characters
sometimes reappear in the same manner after a much longer interval of time.
Thus the calves of a hornless race of cattle which originated in Corrientes,
though at first quite hornless, as they become adult sometimes acquire small,
crooked, and loose horns; and these in succeeding years occasionally become
attached to the skull. (13/25. Azara 'Essais Hist. Nat. de Paraguay' tome 2
1801 page 372.) White and black Bantams, both of which generally breed true,
sometimes assume as they grow old a saffron or red plumage. For instance, a
first-rate black bantam has been described, which during three seasons was
perfectly black, but then annually became more and more red; and it deserves
notice that this tendency to change, whenever it occurs in a bantam, "is
almost certain to prove hereditary." (13/26. These facts are given on the high
authority of Mr. Hewitt in 'The Poultry Book' by Mr. Tegetmeier 1866 page
248.) The cuckoo or blue-mottled Dorking cock, when old, is liable to acquire
yellow or orange hackles in place of his proper bluish-grey hackles. (13/27.
'The Poultry Book' by Tegetmeier 1866 page 97.) Now as Gallus bankiva is
coloured red and orange, and as Dorking fowls and bantams are descended from
this species, we can hardly doubt that the change which occasionally occurs in
the plumage of these birds as their age advances, results from a tendency in
the individual to revert to the primitive type.

CROSSING AS A DIRECT CAUSE OF REVERSION.

It has long been notorious that hybrids and mongrels often revert to both or
to one of their parent-forms, after an interval of from two to seven or eight,
or, according to some authorities, even a greater number of generations. But
that the act of crossing in itself gives an impulse towards reversion, as
shown by the reappearance of long-lost characters, has never, I believe, been
hitherto proved. The proof lies in certain peculiarities, which do not
characterise the immediate parents, and therefore cannot have been derived
from them, frequently appearing in the offspring of two breeds when crossed,
which peculiarities never appear, or appear with extreme rarity, in these same
breeds, as long as they are precluded from crossing. As this conclusion seems
to me highly curious and novel, I will give the evidence in detail.

[My attention was first called to this subject, and I was led to make numerous
experiments, by MM. Boitard and Corbie having stated that, when they crossed
certain breeds of pigeons, birds coloured like the wild C. livia, or the
common dovecote--namely, slaty-blue, with double black wing-bars, sometimes
chequered with black, white loins, the tail barred with black, with the outer
feathers edged with white,--were almost invariably produced. The breeds which
I crossed, and the remarkable results attained, have been fully described in
the sixth chapter. I selected pigeons belonging to true and ancient breeds,
which had not a trace of blue or any of the above specified marks; but when
crossed, and their mongrels recrossed, young birds were often produced, more
or less plainly coloured slaty-blue, with some or all of the proper
characteristic marks. I may recall to the reader's memory one case, namely,
that of a pigeon, hardly distinguishable from the wild Shetland species, the
grandchild of a red-spot, white fantail, and two black barbs, from any of
which, when purely-bred, the production of a pigeon coloured like the wild C.
livia would have been almost a prodigy.

I was thus led to make the experiments, recorded in the seventh chapter, on
fowls. I selected long-established pure breeds, in which there was not a trace
of red, yet in several of the mongrels feathers of this colour appeared; and
one magnificent bird, the offspring of a black Spanish cock and white Silk
hen, was coloured almost exactly like the wild Gallus bankiva. All who know
anything of the breeding of poultry will admit that tens of thousands of pure
Spanish and of pure white Silk fowls might have been reared without the
appearance of a red feather. The fact, given on the authority of Mr.
Tegetmeier, of the frequent appearance, in mongrel fowls, of pencilled or
transversely-barred feathers, like those common to many gallinaceous birds, is
likewise apparently a case of reversion to a character formerly possessed by
some ancient progenitor of the family. I owe to the kindness of this excellent
observer the opportunity of inspecting some neck-hackles and tail-feathers
from a hybrid between the common fowl and a very distinct species, the Gallus
varius; and these feathers are transversely striped in a conspicuous manner
with dark metallic blue and grey, a character which could not have been
derived from either immediate parent.

I have been informed by Mr. B.P. Brent, that he crossed a white Aylesbury
drake and a black so-called Labrador duck, both of which are true breeds, and
he obtained a young drake closely like the mallard (A. boschas). Of the musk-
duck (Cairina moschata, Linn.) there are two sub-breeds, namely, white and
slate-coloured; and these I am informed breed true, or nearly true. But the
Rev. W.D. Fox tells me that, by putting a white drake to a slate-coloured
duck, black birds, pied with white, like the wild musk-duck, were always
produced. I hear from Mr. Blyth that hybrids from the canary and gold-finch
almost always have streaked feathers on their backs; and this streaking must
be derived from the original wild canary.

We have seen in the fourth chapter, that the so-called Himalayan rabbit, with
its snow-white body, black ears, nose, tail, and feet, breeds perfectly true.
This race is known to have been formed by the union of two varieties of
silver-grey rabbits. Now, when a Himalayan doe was crossed by a sandy-coloured
buck, a silver-grey rabbit was produced; and this is evidently a case of
reversion to one of the parent varieties. The young of the Himalayan rabbit
are born snow-white, and the dark marks do not appear until some time
subsequently; but occasionally young Himalayan rabbits are born of a light
silver-grey, which colour soon disappears; so that here we have a trace of
reversion, during an early period of life, to the parent varieties,
independently of any recent cross.

In the third chapter it was shown that at an ancient period some breeds of
cattle in the wilder parts of Britain were white with dark ears, and that the
cattle now kept half wild in certain parks, and those which have run quite
wild in two distant parts of the world, are likewise thus coloured. Now, an
experienced breeder, Mr. J. Beasley, of Northamptonshire (13/28. 'Gardener's
Chronicle and Agricultural Gazette' 1866 page 528.), crossed some carefully
selected West Highland cows with purely-bred shorthorn bulls. The bulls were
red, red and white, or dark roan; and the Highland cows were all of a red
colour, inclining to a light or yellow shade. But a considerable number of the
offspring--and Mr. Beasley calls attention to this as a remarkable fact--were
white, or white with red ears. Bearing in mind that none of the parents were
white, and that they were purely-bred animals, it is highly probable that here
the offspring reverted, in consequence of the cross, to the colour of some
ancient and half-wild parent-breed. The following case, perhaps, comes under
the same head: cows in their natural state have their udders but little
developed, and do not yield nearly so much milk as our domesticated animals.
Now there is some reason to believe (13/29. Ibid 1860 page 343. I am glad to
find that so experienced a breeder of cattle as Mr. Willoughby Wood,
'Gardener's Chronicle' 1869 page 1216, admits my principle of a cross giving a
tendency to reversion.) that cross-bred animals between two kinds, both of
which are good milkers, such as Alderneys and Shorthorns, often turn out
worthless in this respect.

In the chapter on the Horse reasons were assigned for believing that the
primitive stock was striped and dun-coloured; and details were given, showing
that in all parts of the world stripes of a dark colour frequently appear
along the spine, across the legs, and on the shoulders, where they are
occasionally double or treble, and even sometimes on the face and body of
horses of all breeds and of all colours. But the stripes appear most
frequently on the various kinds of duns. In foals they are sometimes plainly
seen, and subsequently disappear. The dun-colour and the stripes are strongly
transmitted when a horse thus characterised is crossed with any other; but I
was not able to prove that striped duns are generally produced from the
crossing of two distinct breeds, neither of which are duns, though this does
sometimes occur.

The legs of the ass are often striped, and this may be considered as a
reversion to the wild parent form, the Equus taeniopus of Abyssinia (13/30.
Sclater in 'Proc. Zoolog. Soc.' 1862 page 163.), which is generally thus
striped. In the domestic animal the stripes on the shoulder are occasionally
double, or forked at the extremity, as in certain zebrine species. There is
reason to believe that the foal is more frequently striped on the legs than
the adult animal. As with the horse, I have not acquired any distinct evidence
that the crossing of differently-coloured varieties of the ass brings out the
stripes.

But now let us turn to the result of crossing the horse and ass. Although
mules are not nearly so numerous in England as asses, I have seen a much
greater number with striped legs, and with the stripes far more conspicuous
than in either parent-form. Such mules are generally light-coloured, and might
be called fallow-duns. The shoulder-stripe in one instance was deeply forked
at the extremity, and in another instance was double, though united in the
middle. Mr. Martin gives a figure of a Spanish mule with strong zebra-like
marks on its legs (13/31. 'History of the Horse' page 212.), and remarks that
mules are particularly liable to be thus striped on their legs. In South
America, according to Roulin (13/32. 'Mem. presentes par divers Savans a
l'Acad. Royale' tome 6 1835 page 338.), such stripes are more frequent and
conspicuous in the mule than in the ass. In the United States, Mr. Gosse
(13/33. 'Letters from Alabama' 1859 page 280.), speaking of these animals,
says, "that in a great number, perhaps in nine out of every ten, the legs are
banded with transverse dark stripes."

Many years ago I saw in the Zoological Gardens a curious triple hybrid, from a
bay mare, by a hybrid from a male ass and female zebra. This animal when old
had hardly any stripes; but I was assured by the superintendent, that when
young it had shoulder-stripes, and faint stripes on its flanks and legs. I
mention this case more especially as an instance of the stripes being much
plainer during youth than in old age.

As the zebra has such a conspicuously striped body and legs, it might have
been expected that the hybrids from this animal and the common ass would have
had their legs in some degree striped; but it appears from the figures given
in Dr. Gray's 'Knowsley Gleanings' and still more plainly from that given by
Geoffroy and F. Cuvier (13/34. 'Hist. Nat. des Mammiferes' 1820 tome 1), that
the legs are much more conspicuously striped than the rest of the body; and
this fact is intelligible only on the belief that the ass aids in giving,
through the power of reversion, this character to its hybrid offspring.

The quagga is banded over the whole front part of its body like a zebra, but
has no stripes on its legs, or mere traces of them. But in the famous hybrid
bred by Lord Morton (13/35. 'Philosoph. Transact.' 1821 page 20.) from a
chestnut, nearly purely-bred, Arabian mare, by a male quagga, the stripes were
"more strongly defined and darker than those on the legs of "the quagga." The
mare was subsequently put to a black Arabian horse, and bore two colts, both
of which, as formerly stated, were plainly striped on the legs, and one of
them likewise had stripes on the neck and body.

The Equus indicus (13/36. Sclater in 'Proc. Zoolog. Soc.' 1862 page 163: this
species is the Ghor-Khur of N.W. India, and has often been called the Hemionus
of Pallas. See also Mr. Blyth's excellent paper in 'Journal of Asiatic Soc. of
Bengal' volume 28 1860 page 229.) is characterised by a spinal stripe, without
shoulder or leg stripes; but traces of these latter stripes may occasionally
be seen even in the adult (13/37. Another species of wild ass, the true E.
hemionus or Kiang, which ordinarily has no shoulder-stripes, is said
occasionally to have them; and these, as with the horse and ass, are sometimes
double: see Mr. Blyth in the paper just quoted and in 'Indian Sporting Review'
1856 page 320: and Col. Hamilton Smith in 'Nat. Library, Horses' page 318; and
'Dict. Class. d'Hist. Nat.' tome 3 page 563.) and Colonel S. Poole, who has
had ample opportunities for observation, informs me that in the foal, when
first born, the head and legs are often striped, but the shoulder-stripe is
not so distinct as in the domestic ass; all these stripes, excepting that
along the spine, soon disappear. Now a hybrid, raised at Knowsley (13/38.
Figured in the 'Gleanings from the Knowsley Menageries' by Dr. J.E. Gray.)
from a female of this species by a male domestic ass, had all four legs
transversely and conspicuously striped, had three short stripes on each
shoulder and had even some zebra-like stripes on its face! Dr. Gray informs me
that he has seen a second hybrid of the same parentage, similarly striped.

From these facts we see that the crossing of the several equine species tends
in a marked manner to cause stripes to appear on various parts of the body,
especially on the legs. As we do not know whether the parent-form of the genus
was striped, the appearance of the stripes can only hypothetically be
attributed to reversion. But most persons, after considering the many
undoubted cases of variously coloured marks reappearing by reversion in my
experiments on crossed pigeons and fowls, will come to the same conclusion
with respect to the horse-genus; and if so, we must admit that the progenitor
of the group was striped on the legs, shoulders, face, and probably over the
whole body, like a zebra.

Lastly, Professor Jaeger has given (13/39. 'Darwin'sche Theorie und ihre
Stellung zu Moral und Religion' page 85.) a good case with pigs. He crossed
the Japanese or masked breed with the common German breed, and the offspring
were intermediate in character. He then re-crossed one of these mongrels with
the pure Japanese, and in the litter thus produced one of the young resembled
in all its characters a wild pig; it had a long snout and upright ears, and
was striped on the back. It should be borne in mind that the young of the
Japanese breed are not striped, and that they have a short muzzle and ears
remarkably dependent.]

A similar tendency to the recovery of long lost characters holds good even
with the instincts of crossed animals. There are some breeds of fowls which
are called "everlasting layers," because they have lost the instinct of
incubation; and so rare is it for them to incubate that I have seen notices
published in works on poultry, when hens of such breeds have taken to sit.
(13/40. Cases of both Spanish and Polish hens sitting are given in the
'Poultry Chronicle' 1855 volume 3 page 477.) Yet the aboriginal species was of
course a good incubator; and with birds in a state of nature hardly any
instinct is so strong as this. Now, so many cases have been recorded of the
crossed offspring from two races, neither of which are incubators, becoming
first-rate sitters, that the reappearance of this instinct must be attributed
to reversion from crossing. One author goes so far as to say, "that a cross
between two non-sitting varieties almost invariably produces a mongrel that
becomes broody, and sits with remarkable steadiness." (13/41. 'The Poultry
Book' by Mr. Tegetmeier 1866 pages 119, 163. The author, who remarks on the
two negatives ('Journ. of Hort.' 1862 page 325), states that two broods were
raised from a Spanish cock and Silver-pencilled Hamburgh hen, neither of which
are incubators, and no less than seven out of eight hens in these two broods
"showed a perfect obstinacy in sitting." The Rev. E.S. Dixon ('Ornamental
Poultry' 1848 page 200) says that chickens reared from a cross between Golden
and Black Polish fowls, are "good and steady birds to sit." Mr. B.P. Brent
informs me that he raised some good sitting hens by crossing Pencilled
Hamburgh and Polish breeds. A cross-bred bird from a Spanish non-incubating
cock and Cochin incubating hen is mentioned in the 'Poultry Chronicle' volume
3 page 13, as an "exemplary mother." On the other hand, an exceptional case is
given in the 'Cottage Gardener' 1860 page 388 of a hen raised from a Spanish
cock and black Polish hen which did not incubate.) Another author, after
giving a striking example, remarks that the fact can be explained only on the
principle that "two negatives make a positive." It cannot, however, be
maintained that hens produced from a cross between two non-sitting breeds
invariably recover their lost instinct, any more than that crossed fowls or
pigeons invariably recover the red or blue plumage of their prototypes. Thus I
raised several chickens from a Polish hen by a Spanish cock,--breeds which do
not incubate,--and none of the young hens at first showed any tendency to sit;
but one of them--the only one which was preserved--in the third year sat well
on her eggs and reared a brood of chickens. So that here we have the
reappearance with advancing age of a primitive instinct, in the same manner as
we have seen that the red plumage of the Gallus bankiva is sometimes
reacquired both by crossed and purely-bred fowls of various kinds as they grow
old.

The parents of all our domesticated animals were of course aboriginally wild
in disposition; and when a domesticated species is crossed with a distinct
species, whether this is a domesticated or only a tamed animal, the hybrids
are often wild to such a degree, that the fact is intelligible only on the
principle that the cross has caused a partial return to a primitive
disposition. Thus, the Earl of Powis formerly imported some thoroughly
domesticated humped cattle from India, and crossed them with English breeds,
which belong to a distinct species; and his agent remarked to me, without any
question having been asked, how oddly wild the cross-bred animals were. The
European wild boar and the Chinese domesticated pig are almost certainly
specifically distinct: Sir F. Darwin crossed a sow of the latter breed with a
wild Alpine boar which had become extremely tame, but the young, though having
half-domesticated blood in their veins, were "extremely wild in confinement,
and would not eat swill like common English pigs." Captain Hutton, in India,
crossed a tame goat with a wild one from the Himalaya, and he remarked to me
how surprisingly wild the offspring were. Mr. Hewitt, who has had great
experience in crossing tame cock-pheasants with fowls belonging to five
breeds, gives as the character of all "extraordinary wildness" (13/42. 'The
Poultry Book' by Tegetmeier 1866 pages 165, 167.); but I have myself seen one
exception to this rule. Mr. S. J. Salter (13/43. 'Natural History Review' 1863
April page 277.) who raised a large number of hybrids from a bantam-hen by
Gallus sonneratii, states that "all were exceedingly wild." Mr. Waterton
(13/44. 'Essays on Natural History' page 917.) bred some wild ducks from eggs
hatched under a common duck, and the young were allowed to cross freely both
amongst themselves and with the tame ducks; they were "half wild and half
tame; they came to the windows to be fed, but still they had a wariness about
them quite remarkable."

On the other hand, mules from the horse and ass are certainly not in the least
wild, though notorious for obstinacy and vice. Mr. Brent, who has crossed
canary-birds with many kinds of finches, has not observed, as he informs me,
that the hybrids were in any way remarkably wild: but Mr. Jenner Weir who has
had still greater experience, is of a directly opposite opinion. He remarks
that the siskin is the tamest of finches, but its mules are as wild, when
young, as newly caught birds, and are often lost through their continued
efforts to escape. Hybrids are often raised between the common and musk duck,
and I have been assured by three persons, who have kept these crossed birds,
that they were not wild; but Mr. Garnett (13/45. As stated by Mr. Orton in his
'Physiology of Breeding' page 12.) observed that his hybrids were wild, and
exhibited "migratory propensities" of which there is not a vestige in the
common or musk duck. No case is known of this latter bird having escaped and
become wild in Europe or Asia, except, according to Pallas, on the Caspian
Sea; and the common domestic duck only occasionally becomes wild in districts
where large lakes and fens abound. Nevertheless, a large number of cases have
been recorded (13/46. M. E. de Selys-Longchamps refers ('Bulletin Acad. Roy.
de Bruxelles' tome 12 No. 10) to more than seven of these hybrids shot in
Switzerland and France. M. Deby asserts ('Zoologist' volume 5 1845-46 page
1254) that several have been shot in various parts of Belgium and Northern
France. Audubon ('Ornitholog. Biography' volume 3 page 168), speaking of these
hybrids, says that, in North America, they "now and then wander off and become
quite wild.") of hybrids from these two ducks having been shot in a completely
wild state, although so few are reared in comparison with purely-bred birds of
either species. It is improbable that any of these hybrids could have acquired
their wildness from the musk-duck having paired with a truly wild duck; and
this is known not to be the case in North America; hence we must infer that
they have reacquired, through reversion, their wildness, as well as renewed
powers of flight.

These latter facts remind us of the statements, so frequently made by
travellers in all parts of the world, on the degraded state and savage
disposition of crossed races of man. That many excellent and kind-hearted
mulattos have existed no one will dispute; and a more mild and gentle set of
men could hardly be found than the inhabitants of the island of Chiloe, who
consist of Indians commingled with Spaniards in various proportions. On the
other hand, many years ago, long before I had thought of the present subject,
I was struck with the fact that, in South America, men of complicated descent
between Negroes, Indians, and Spaniards, seldom had, whatever the cause might
be, a good expression. (13/47. 'Journal of Researches' 1845 page 71.)
Livingstone--and a more unimpeachable authority cannot be quoted,--after
speaking of a half-caste man on the Zambesi, described by the Portuguese as a
rare monster of inhumanity, remarks, "It is unaccountable why half-castes,
such as he, are so much more cruel than the Portuguese, but such is
undoubtedly the case." An inhabitant remarked to Livingstone, "God made white
men, and God made black men, but the Devil made halfcastes." (13/48.
'Expedition to the Zambesi' 1865 pages 25, 150.) When two races, both low in
the scale, are crossed the progeny seems to be eminently bad. Thus the noble-
hearted Humboldt, who felt no prejudice against the inferior races, speaks in
strong terms of the bad and savage disposition of Zambos, or half-castes
between Indians and Negroes; and this conclusion has been arrived at by
various observers. (13/49. Dr. P. Broca on 'Hybridity in the Genus Homo'
English translation 1864 page 39.) From these facts we may perhaps infer that
the degraded state of so many half-castes is in part due to reversion to a
primitive and savage condition, induced by the act of crossing, even if mainly
due to the unfavourable moral conditions under which they are generally
reared.

SUMMARY ON THE PROXIMATE CAUSES LEADING TO REVERSION.

When purely-bred animals or plants reassume long-lost characters,--when the
common ass, for instance, is born with striped legs, when a pure race of black
or white pigeons throws a slaty-blue bird, or when a cultivated heartsease
with large and rounded flowers produces a seedling with small and elongated
flowers,--we are quite unable to assign any proximate cause. When animals run
wild, the tendency to reversion, which, though it has been greatly
exaggerated, no doubt exists, is sometimes to a certain extent intelligible.
Thus, with feral pigs, exposure to the weather will probably favour the growth
of the bristles, as is known to be the case with the hair of other
domesticated animals, and through correlation the tusks will tend to be
redeveloped. But the reappearance of coloured longitudinal stripes on young
feral pigs cannot be attributed to the direct action of external conditions.
In this case, and in many others, we can only say that any change in the
habits of life apparently favour a tendency, inherent or latent in the
species, to return to the primitive state.

It will be shown in a future chapter that the position of flowers on the
summit of the axis, and the position of seeds within the capsule, sometimes
determine a tendency towards reversion; and this apparently depends on the
amount of sap or nutriment which the flower-buds and seeds receive. The
position, also, of buds, either on branches or on roots, sometimes determines,
as was formerly shown, the transmission of the character proper to the
variety, or its reversion to a former state.

We have seen in the last section that when two races or species are crossed
there is the strongest tendency to the reappearance in the offspring of long-
lost characters, possessed by neither parent nor immediate progenitor. When
two white, or red, or black pigeons, of well-established breeds, are united,
the offspring are almost sure to inherit the same colours; but when
differently-coloured birds are crossed, the opposed forces of inheritance
apparently counteract each other, and the tendency which is inherent in both
parents to produce slaty-blue offspring becomes predominant. So it is in
several other cases. But when, for instance, the ass is crossed with E.
indicus or with the horse--animals which have not striped legs--and the
hybrids have conspicuous stripes on their legs and even on their faces, all
that can be said is, that an inherent tendency to reversion is evolved through
some disturbance in the organisation caused by the act of crossing.

Another form of reversion is far commoner, indeed is almost universal with the
offspring from a cross, namely, to the characters proper to either pure
parent-form. As a general rule, crossed offspring in the first generation are
nearly intermediate between their parents, but the grandchildren and
succeeding generations continually revert, in a greater or lesser degree, to
one or both of their progenitors. Several authors have maintained that hybrids
and mongrels include all the characters of both parents, not fused together,
but merely mingled in different proportions in different parts of the body;
or, as Naudin (13/50. 'Nouvelles Archives du Museum' tome 1 page 151.) has
expressed it, a hybrid is a living mosaic-work, in which the eye cannot
distinguish the discordant elements, so completely are they intermingled. We
can hardly doubt that, in a certain sense, this is true, as when we behold in
a hybrid the elements of both species segregating themselves into segments in
the same flower or fruit, by a process of self-attraction or self-affinity;
this segregation taking place either by seminal or bud-propagation. Naudin
further believes that the segregation of the two specific elements or essences
is eminently liable to occur in the male and female reproductive matter; and
he thus explains the almost universal tendency to reversion in successive
hybrid generations. For this would be the natural result of the union of
pollen and ovules, in both of which the elements of the same species had been
segregated by self-affinity. If, on the other hand, pollen which included the
elements of one species happened to unite with ovules including the elements
of the other species, the intermediate or hybrid state would still be
retained, and there would be no reversion. But it would, as I suspect, be more
correct to say that the elements of both parent-species exist in every hybrid
in a double state, namely, blended together and completely separate. How this
is possible, and what the term specific essence or element may be supposed to
express, I shall attempt to show in the chapter on the hypothesis of
pangenesis.

But Naudin's view, as propounded by him, is not applicable to the reappearance
of characters lost long ago by variation; and it is hardly applicable to races
or species which, after having been crossed at some former period with a
distinct form, and having since lost all traces of the cross, nevertheless
occasionally yield an individual which reverts (as in the case of the great-
great-grandchild of the pointer Sappho) to the crossing form. The most simple
case of reversion, namely, of a hybrid or mongrel to its grandparents, is
connected by an almost perfect series with the extreme case of a purely-bred
race recovering characters which had been lost during many ages; and we are
thus led to infer that all the cases must be related by some common bond.

Gartner believed that only highly sterile hybrid plants exhibit any tendency
to reversion to their parent-forms. This erroneous belief may perhaps be
accounted for by the nature of the genera crossed by him, for he admits that
the tendency differs in different genera. The statement is also directly
contradicted by Naudin's observations, and by the notorious fact that
perfectly fertile mongrels exhibit the tendency in a high degree,--even in a
higher degree, according to Gartner himself, than hybrids. (13/51.
'Bastarderzeugung' s. 582, 438, etc.)

Gartner further states that reversions rarely occur with hybrid plants raised
from species which have not been cultivated, whilst, with those which have
been long cultivated, they are of frequent occurrence. This conclusion
explains a curious discrepancy: Max Wichura (13/52. 'Die Bastardbefruchtung...
der Weiden' 1865 s. 23. For Gartner's remarks on this head, see
'Bastarderzeugung' s. 474, 582.) who worked exclusively on willows which had
not been subjected to culture, never saw an instance of reversion; and he goes
so far as to suspect that the careful Gartner had not sufficiently protected
his hybrids from the pollen of the parent-species: Naudin, on the other hand,
who chiefly experimented on cucurbitaceous and other cultivated plants,
insists more strenuously than any other author on the tendency to reversion in
all hybrids. The conclusion that the condition of the parent-species, as
affected by culture, is one of the proximate causes leading to reversion,
agrees well with the converse case of domesticated animals and cultivated
plants being liable to reversion when they become feral; for in both cases the
organisation or constitution must be disturbed, though in a very different
way. (13/53. Prof. Weismann in his very curious essay on the different forms
produced by the same species of butterfly at different seasons ('Saison-
Dimorphismus der Schmetterlinge' pages 27, 28), has come to a similar
conclusion, namely, that any cause which disturbs the organisation, such as
the exposure of the cocoons to heat or even to much shaking, gives a tendency
to reversion.)

Finally, we have seen that characters often reappear in purely-bred races
without our being able to assign any proximate cause; but when they become
feral this is either indirectly or directly induced by the change in their
conditions of life. With crossed breeds, the act of crossing in itself
certainly leads to the recovery of long-lost characters, as well as of those
derived from either parent-form. Changed conditions, consequent on
cultivation, and the relative position of buds, flowers, and seeds on the
plant, all apparently aid in giving this same tendency. Reversion may occur
either through seminal or bud generation, generally at birth, but sometimes
only with an advance of age. Segments or portions of the individual may alone
be thus affected. That a being should be born resembling in certain characters
an ancestor removed by two or three, and in some cases by hundreds or even
thousands of generations, is assuredly a wonderful fact. In these cases the
child is commonly said to inherit such characters directly from its
grandparent, or more remote ancestors. But this view is hardly conceivable.
If, however, we suppose that every character is derived exclusively from the
father or mother, but that many characters lie latent or dormant in both
parents during a long succession of generations, the foregoing facts are
intelligible. In what manner characters may be conceived to lie latent, will
be considered in a future chapter to which I have lately alluded.

LATENT CHARACTERS.

But I must explain what is meant by characters lying latent. The most obvious
illustration is afforded by secondary sexual characters. In every female all
the secondary male characters, and in every male all the secondary female
characters, apparently exist in a latent state, ready to be evolved under
certain conditions. It is well known that a large number of female birds, such
as fowls, various pheasants, partridges, peahens, ducks, etc., when old or
diseased, or when operated on, assume many or all of the secondary male
characters of their species. In the case of the hen-pheasant this has been
observed to occur far more frequently during certain years than during others.
(13/54. Yarrell 'Phil. Transact.' 1827 page 268; Dr. Hamilton in 'Proc.
Zoolog. Soc.' 1862 page 23.) A duck ten years old has been known to assume
both the perfect winter and summer plumage of the drake. (13/55. 'Archiv.
Skand. Beitrage zur Naturgesch.' 8 s. 397-413.) Waterton (13/56. In his
'Essays on Nat. Hist.' 1838 Mr. Hewitt gives analogous cases with hen-
pheasants in 'Journal of Horticulture' July 12, 1864 page 37. Isidore Geoffroy
Saint-Hilaire in his 'Essais de Zoolog. Gen.' ('Suites a Buffon' 1842 pages
496-513), has collected such cases in ten different kinds of birds. It appears
that Aristotle was well aware of the change in mental disposition in old hens.
The case of the female deer acquiring horns is given at page 513.) gives a
curious case of a hen which had ceased laying, and had assumed the plumage,
voice, spurs, and warlike disposition of the cock; when opposed to an enemy
she would erect her hackles and show fight. Thus every character, even to the
instinct and manner of fighting, must have lain dormant in this hen as long as
her ovaria continued to act. The females of two kinds of deer, when old, have
been known to acquire horns; and, as Hunter has remarked, we see something of
an analogous nature in the human species.

On the other hand, with male animals, it is notorious that the secondary
sexual characters are more or less completely lost when they are subjected to
castration. Thus, if the operation be performed on a young cock, he never, as
Yarrell states, crows again; the comb, wattles, and spurs do not grow to their
full size, and the hackles assume an intermediate appearance between true
hackles and the feathers of the hen. Cases are recorded of confinement, which
often affects the reproductive system, causing analogous results. But
characters properly confined to the female are likewise acquired by the male;
the capon takes to sitting on eggs, and will bring up chickens; and what is
more curious, the utterly sterile male hybrids from the pheasant and the fowl
act in the same manner, "their delight being to watch when the hens leave
their nests, and to take on themselves the office of a sitter." (13/57.
'Cottage Gardener' 1860 page 379.) That admirable observer Reaumur (13/58.
'Art de faire Eclore' etc. 1749 tome 2 page 8.) asserts that a cock, by being
long confined in solitude and darkness, can be taught to take charge of young
chickens; he then utters a peculiar cry, and retains during his whole life
this newly acquired maternal instinct. The many well-ascertained cases of
various male mammals giving milk shows that their rudimentary mammary glands
retain this capacity in a latent condition.

We thus see that in many, probably in all cases, the secondary characters of
each sex lie dormant or latent in the opposite sex, ready to be evolved under
peculiar circumstances. We can thus understand how, for instance, it is
possible for a good milking cow to transmit her good qualities through her
male offspring to future generations; for we may confidently believe that
these qualities are present, though latent, in the males of each generation.
So it is with the game-cock, who can transmit his superiority in courage and
vigour through his female to his male offspring; and with man it is known
(13/59. Sir H. Holland 'Medical Notes and Reflections' 3rd edition 1855 page
31.) that diseases, such as hydrocele, necessarily confined to the male sex,
can be transmitted through the female to the grandson. Such cases as these
offer, as was remarked at the commencement of this chapter, the simplest
possible examples of reversion; and they are intelligible on the belief that
characters common to the grandparent and grandchild of the same sex are
present, though latent, in the intermediate parent of the opposite sex.

The subject of latent characters is so important, as we shall see in a future
chapter, that I will give another illustration. Many animals have the right
and left sides of their body unequally developed: this is well known to be the
case with flat-fish, in which the one side differs in thickness and colour and
in the shape of the fins, from the other, and during the growth of the young
fish one eye is gradually twisted from the lower to the upper surface. (13/60.
See Steenstrup on the 'Obliquity of Flounders' in Annals and Mag. of Nat.
Hist.' May 1865 page 361. I have given an abstract of Malm's explanation of
this wonderful phenomenon in the 'Origin of Species' 6th Edition page 186.) In
most flat-fishes the left is the blind side, but in some it is the right;
though in both cases reversed or "wrong fishes," are occasionally developed;
and in Platessa flesus the right or left side is indifferently the upper one.
With gasteropods or shell-fish, the right and left sides are extremely unlike;
the far greater number of species are dextral, with rare and occasional
reversals of development; and some few are normally sinistral; but certain
species of Bulimus, and many Achatinellae (13/61. Dr. E. von Martens in
'Annals and Mag. of Nat. Hist.' March 1866 page 209.) are as often sinistral
as dextral. I will give an analogous case in the great articulate kingdom: the
two sides of Verruca (13/62. Darwin 'Balanidae' Ray Soc. 1854 page 499: see
also the appended remarks on the apparently capricious development of the
thoracic limbs on the right and left sides in the higher crustaceans.) are so
wonderfully unlike, that without careful dissection it is extremely difficult
to recognise the corresponding parts on the opposite sides of the body; yet it
is apparently a mere matter of chance whether it be the right or the left side
that undergoes so singular amount of change. One plant is known to me (13/63.
Mormodes ignea: Darwin 'Fertilisation of Orchids' 1862 page 251.) in which the
flower, according as it stands on the one or other side of the spike, is
unequally developed. In all the foregoing cases the two sides are perfectly
symmetrical at an early period of growth. Now, whenever a species is as liable
to be unequally developed on the one as on the other side, we may infer that
the capacity for such development is present, though latent, in the
undeveloped side. And as a reversal of development occasionally occurs in
animals of many kinds, this latent capacity is probably very common.

The best yet simplest cases of characters lying dormant are, perhaps, those
previously given, in which chickens and young pigeons, raised from a cross
between differently coloured birds, are at first of one colour, but in a year
or two acquire feathers of the colour of the other parent; for in this case
the tendency to a change of plumage is clearly latent in the young bird. So it
is with hornless breeds of cattle, some of which acquire small horns as they
grow old. Purely bred black and white bantams, and some other fowls,
occasionally assume, with advancing years, the red feathers of the parent-
species. I will here add a somewhat different case, as it connects in a
striking manner latent characters of two classes. Mr. Hewitt (13/64. 'Journal
of Horticulture' July 1864 page 38. I have had the opportunity of examining
these remarkable feathers through the kindness of Mr. Tegetmeier.) possessed
an excellent Sebright gold-laced bantam hen, which, as she became old, grew
diseased in her ovaria, and assumed male characters. In this breed the males
resemble the females in all respects except in their combs, wattles, spurs,
and instincts; hence it might have been expected that the diseased hen would
have assumed only those masculine characters which are proper to the breed,
but she acquired, in addition, well-arched tail sickle-feathers quite a foot
in length, saddle-feathers on the loins, and hackles on the neck,--ornaments
which, as Mr. Hewitt remarks, "would be held as abominable in this breed." The
Sebright bantam is known (13/65. 'The Poultry Book' by Mr. Tegetmeier 1866
page 241.) to have originated about the year 1800 from a cross between a
common bantam and a Polish fowl, recrossed by a hen-tailed bantam, and
carefully selected; hence there can hardly be a doubt that the sickle-feathers
and hackles which appeared in the old hen were derived from the Polish fowl or
common bantam; and we thus see that not only certain masculine characters
proper to the Sebright bantam, but other masculine characters derived from the
first progenitors of the breed, removed by a period of above sixty years, were
lying latent in this henbird, ready to be evolved as soon as her ovaria became
diseased.

From these several facts it must be admitted that certain characters,
capacities, and instincts, may lie latent in an individual, and even in a
succession of individuals, without our being able to detect the least sign of
their presence. When fowls, pigeons, or cattle of different colours are
crossed, and their offspring change colour as they grow old, or when the
crossed turbit acquired the characteristic frill after its third moult, or
when rarely-bred bantams partially assume the red plumage of their prototype,
we cannot doubt that these qualities were from the first present, though
latent, in the individual animal, like the characters of a moth in the
caterpillar. Now, if these animals had produced offspring before they had
acquired with advancing age their new characters, nothing is more probable
than that they would have transmitted them to some of their offspring, who in
this case would in appearance have received such characters from their grand-
parents or more distant progenitors. We should then have had a case of
reversion, that is, of the reappearance in the child of an ancestral
character, actually present, though during youth completely latent, in the
parent; and this we may safely conclude is what occurs in all reversions to
progenitors, however remote.

This view of the latency in each generation of all the characters which appear
through reversion, is also supported by their actual presence in some cases
during early youth alone, or by their more frequent appearance and greater
distinctness at this age than during maturity. We have seen that this is often
the case with the stripes on the legs and faces of the several species of the
horse genus. The Himalayan rabbit, when crossed, sometimes produces offspring
which revert to the parent silver-grey breed, and we have seen that in purely
bred animals pale-grey fur occasionally reappears during early youth. Black
cats, we may feel assured, would occasionally produce by reversion tabbies;
and on young black kittens, with a pedigree (13/66. Carl Vogt 'Lectures on
Man' English translation 1864 page 411.) known to have been long pure, faint
traces of stripes may almost always be seen which afterwards disappear.
Hornless Suffolk cattle occasionally produce by reversion horned animals; and
Youatt (13/67. 'On Cattle' page 174.) asserts that even in hornless
individuals "the rudiment of a horn may be often felt at an early age."

No doubt it appears at first sight in the highest degree improbable that in
every horse of every generation there should be a latent capacity and tendency
to produce stripes, though these may not appear once in a thousand
generations; that in every white, black, or other coloured pigeon, which may
have transmitted its proper colour during centuries, there should be a latent
capacity in the plumage to become blue and to be marked with certain
characteristic bars; that in every child in a six-fingered family there should
be the capacity for the production of an additional digit; and so in other
cases. Nevertheless, there is no more inherent improbability in this being the
case than in a useless and rudimentary organ, or even in only a tendency to
the production of a rudimentary organ, being inherited during millions of
generations, as is well known to occur with a multitude of organic beings.
There is no more inherent improbability in each domestic pig, during a
thousand generations, retaining the capacity and tendency to develop great
tusks under fitting conditions, than in the young calf having retained, for an
indefinite number of generations rudimentary incisor teeth, which never
protrude through the gums.

I shall give at the end of the next chapter a summary of the three preceding
chapters; but as isolated and striking cases of reversion have here been
chiefly insisted on, I wish to guard the reader against supposing that
reversion is due to some rare or accidental combination of circumstances. When
a character, lost during hundreds of generations, suddenly reappears, no doubt
some such combination must occur; but reversions, to the immediately preceding
generations may be constantly observed, at least, in the offspring of most
unions. This has been universally recognised in the case of hybrids and
mongrels, but it has been recognised simply from the difference between the
united forms rendering the resemblance of the offspring to their grandparents
or more remote progenitors of easy detection. Reversion is likewise almost
invariably the rule, as Mr. Sedgwick has shown, with certain diseases. Hence
we must conclude that a tendency to this peculiar form of transmission is an
integral part of the general law of inheritance.

MONSTROSITIES.

A large number of monstrous growths and of lesser anomalies are admitted by
every one to be due to an arrest of development, that is, to the persistence
of an embryonic condition. But many monstrosities cannot be thus explained;
for parts of which no trace can be detected in the embryo, but which occur in
other members of the same class of animals occasionally appear, and these may
probably with truth be attributed to reversion. As, however, I have treated
this subject as fully as I could in my 'Descent of Man' (ch. 1 2nd edition), I
will not here recur to it.

[When flowers which have normally an irregular structure become regular or
peloric, the change is generally looked at by botanists as a return to the
primitive state. But Dr. Maxwell Masters (13/68. 'Natural Hist. Review' April
1863 page 258. See also his Lecture, Royal Institution, March 16, 1860. On
same subject see Moquin-Tandon 'Elements de Teratologie' 1841 pages 184, 352.
Dr. Peyritsch has collected a large number of very interesting cases 'Sitzb.
d. k. Akad. d. Wissensch.' Wien b. 60 and especially b. 66 1872 page 125.),
who has ably discussed this subject, remarks that when, for instance, all the
sepals of a Tropaeolum become green and of the same shape, instead of being
coloured with one prolonged into a spur, or when all the petals of a Linaria
become simple and regular, such cases may be due merely to an arrest of
development; for in these flowers all the organs during their earliest
condition are symmetrical, and, if arrested at this stage of growth, they
would not become irregular. If, moreover, the arrest were to take place at a
still earlier period of development, the result would be a simple tuft of
green leaves; and no one probably would call this a case of reversion. Dr.
Masters designates the cases first alluded to as regular peloria; and others,
in which all the corresponding parts assume a similar form of irregularity, as
when all the petals in a Linaria become spurred, as irregular peloria. We have
no right to attribute these latter cases to reversion, until it can be shown
that the parent-form, for instance, of the genus Linaria had had all its
petals spurred; for a chance of this nature might result from the spreading of
an anomalous structure, in accordance with the law, to be discussed in a
future chapter, of homologous parts tending to vary in the same manner. But as
both forms of peloria frequently occur on the same individual plant of the
Linaria (13/69. Verlot 'Des Varietes' 1865 page 89; Naudin 'Nouvelles Archives
du Museum' tome 1 page 137.), they probably stand in some close relation to
one another. On the doctrine that peloria is simply the result of an arrest of
development, it is difficult to understand how an organ arrested at a very
early period of growth should acquire its full functional perfection;--how a
petal, supposed to be thus arrested, should acquire its brilliant colours, and
serve as an envelope to the flower, or a stamen produce efficient pollen; yet
this occurs with many peloric flowers. That pelorism is not due to mere chance
variability, but either to an arrest of development or to reversion, we may
infer from an observation made by Ch. Morren (13/70. In his discussion on some
curious peloric Calceolarias quoted in 'Journal of Horticulture' February 24,
1863 page 152.) namely, that families which have irregular flowers often
"return by these monstrous growths to their regular form; whilst we never see
a regular flower realise the structure of an irregular one."

Some flowers have almost certainly become more or less completely peloric
through reversion, as the following interesting case shows. Corydalis tuberosa
properly has one of its two nectaries colourless, destitute of nectar, only
half the size of the other, and therefore, to a certain extent, in a
rudimentary state; the pistil is curved towards the perfect nectary, and the
hood, formed of the inner petals, slips off the pistil and stamen in one
direction alone, so that, when a bee sucks the perfect nectary, the stigma and
stamens are exposed and rubbed against the insect's body. In several closely
allied genera, as in Dielytra, etc., there are two perfect nectaries, the
pistil is straight, and the hood slips off on either side, according as the
bee sucks either nectary. Now, I have examined several flowers of Corydalis
tuberosa, in which both nectaries were equally developed and contained nectar;
in this we see only the redevelopment of a partially aborted organ; but with
this redevelopment the pistil becomes straight, and the hood slips off in
either direction, so that these flowers have acquired the perfect structure,
so well adapted for insect agency, of Dielytra and its allies. We cannot
attribute these coadapted modifications to chance, or to correlated
variability; we must attribute them to reversion to a primordial condition of
the species.

The peloric flowers of Pelargonium have their five petals in all respects
alike, and there is no nectary so that they resemble the symmetrical flowers
of the closely allied genus Geranium; but the alternate stamens are also
sometimes destitute of anthers, the shortened filaments being left as
rudiments, and in this respect they resemble the symmetrical flowers of the
closely allied genus Erodium. Hence we may look at the peloric flowers of
Pelargonium as having reverted to the state of some primordial form, the
progenitor of the three closely related genera of Pelargonium, Geranium, and
Erodium.

In the peloric form of Antirrhinum majus, appropriately called the" Wonder,"
the tubular and elongated flowers differ wonderfully from those of the common
snapdragon; the calyx and the mouth of the corolla consist of six equal lobes,
and include six equal instead of four unequal stamens. One of the two
additional stamens is manifestly formed by the development of a
microscopically minute papilla, which may be found at the base of the upper
lip of the flower of the common snapdragons in the nineteen plants examined by
me. That this papilla is a rudiment of a stamen was well shown by its various
degrees of development in crossed plants between the common and the peloric
Antirrhinum. Again, a peloric Galeobdolon luteum, growing in my garden, had
five equal petals, all striped like the ordinary lower lip, and included five
equal instead of four unequal stamens; but Mr. R. Keeley, who sent me this
plant, informs me that the flowers vary greatly, having from four to six lobes
to the corolla, and from three to six stamens. (13/71. For other cases of six
divisions in peloric flowers of the Labiatae and Scrophulariaceae see Moquin-
Tandon 'Teratologie' page 192.) Now, as the members of the two great families
to which the Antirrhinum and Galeobdolon belong are properly pentamerous, with
some of the parts confluent and others suppressed, we ought not to look at the
sixth stamen and the sixth lobe to the corolla in either case as due to
reversion, any more than the additional petals in double flowers in these same
two families. But the case is different with the fifth stamen in the peloric
Antirrhinum, which is produced by the redevelopment of a rudiment always
present, and which probably reveals to us the state of the flower, as far as
the stamens are concerned, at some ancient epoch. It is also difficult to
believe that the other four stamens and the petals, after an arrest of
development at a very early embryonic age, would have come to full perfection
in colour, structure, and function, unless these organs had at some former
period normally passed through a similar course of growth. Hence it appears to
me probable that the progenitor of the genus Antirrhinum must at some remote
epoch have included five stamens and borne flowers in some degree resembling
those now produced by the peloric form. The conclusion that peloria is not a
mere monstrosity, irrespective of any former state of the species, is
supported by the fact that this structure is often strongly inherited, as in
the case of the peloric Antirrhinum and Gloxinia and sometimes in that of the
peloric Corydalis solida. (13/72. Godron reprinted from the 'Memoires de
l'Acad. de Stanislas' 1868.)

Lastly I may add that many instances have been recorded of flowers, not
generally considered as peloric, in which certain organs are abnormally
augmented in number. As an increase of parts cannot be looked at as an arrest
of development, nor as due to the redevelopment of rudiments, for no rudiments
are present, and as these additional parts bring the plant into closer
relationship with its natural allies, they ought probably to be viewed as
reversions to a primordial condition.]

These several facts show us in an interesting manner how intimately certain
abnormal states are connected together; namely, arrests of development causing
parts to become rudimentary or to be wholly suppressed,--the redevelopment of
parts now in a more or less rudimentary condition,--the reappearance of organs
of which not a vestige can be detected,--and to these may be added, in the
case of animals, the presence during youth, and subsequent disappearance, of
certain characters which occasionally are retained throughout life. Some
naturalists look at all such abnormal structures as a return to the ideal
state of the group to which the affected being belongs; but it is difficult to
conceive what is meant to be conveyed by this expression. Other naturalists
maintain, with greater probability and distinctness of view, that the common
bond of connection between the several foregoing cases is an actual, though
partial, return to the structure of the ancient progenitor of the group. If
this view be correct, we must believe that a vast number of characters,
capable of evolution, lie hidden in every organic being. But it would be a
mistake to suppose that the number is equally great in all beings. We know,
for instance, that plants of many orders occasionally become peloric; but many
more cases have been observed in the Labiatae and Scrophulariaceae than in any
other order; and in one genus of the Scrophulariaceae, namely Linaria, no less
than thirteen species have been described in this condition (13/73. Moquin-
Tandon 'Teratologie' page 186.) On this view of the nature of peloric flowers,
and bearing in mind certain monstrosities in the animal kingdom, we must
conclude that the progenitors of most plants and animals have left an
impression, capable of redevelopment, on the germs of their descendants,
although these have since been profoundly modified.

The fertilised germ of one of the higher animals, subjected as it is to so
vast a series of changes from the germinal cell to old age,--incessantly
agitated by what Quatrefages well calls the tourbillon vital,--is perhaps the
most wonderful object in nature. It is probable that hardly a change of any
kind affects either parent, without some mark being left on the germ. But on
the doctrine of reversion, as given in this chapter, the germ becomes a far
more marvellous object, for, besides the visible changes which it undergoes,
we must believe that it is crowded with invisible characters, proper to both
sexes, to both the right and left side of the body, and to a long line of male
and female ancestors separated by hundreds or even thousands of generations
from the present time: and these characters, like those written on paper with
invisible ink, lie ready to be evolved whenever the organisation is disturbed
by certain known or unknown conditions.

CHAPTER 2.XIV.

INHERITANCE continued.--FIXEDNESS OF CHARACTER--PREPOTENCY--SEXUAL LIMITATION
--CORRESPONDENCE OF AGE.

FIXEDNESS OF CHARACTER APPARENTLY NOT DUE TO ANTIQUITY OF INHERITANCE.
PREPOTENCY OF TRANSMISSION IN INDIVIDUALS OF THE SAME FAMILY, IN CROSSED
BREEDS AND SPECIES; OFTEN STRONGER IN ONE SEX THAN THE OTHER; SOMETIMES DUE TO
THE SAME CHARACTER BEING PRESENT AND VISIBLE IN ONE BREED AND LATENT IN THE
OTHER.
INHERITANCE AS LIMITED BY SEX.
NEWLY-ACQUIRED CHARACTERS IN OUR DOMESTICATED ANIMALS OFTEN TRANSMITTED BY ONE
SEX ALONE, SOMETIMES LOST BY ONE SEX ALONE.
INHERITANCE AT CORRESPONDING PERIODS OF LIFE.
THE IMPORTANCE OF THE PRINCIPLE WITH RESPECT TO EMBRYOLOGY; AS EXHIBITED IN
DOMESTICATED ANIMALS: AS EXHIBITED IN THE APPEARANCE AND DISAPPEARANCE OF
INHERITED DISEASES; SOMETIMES SUPERVENING EARLIER IN THE CHILD THAN IN
THE PARENT.
SUMMARY OF THE THREE PRECEDING CHAPTERS.

In the last two chapters the nature and force of Inheritance, the
circumstances which interfere with its power, and the tendency to Reversion,
with its many remarkable contingencies, were discussed. In the present chapter
some other related phenomena will be treated of, as fully as my materials
permit.

FIXEDNESS OF CHARACTER.

It is a general belief amongst breeders that the longer any character has been
transmitted by a breed, the more fully it will continue to be transmitted. I
do not wish to dispute the truth of the proposition that inheritance gains
strength simply through long continuance, but I doubt whether it can be
proved. In one sense the proposition is little better than a truism; if any
character has remained constant during many generations, it will be likely to
continue so, if the conditions of life remain the same. So, again, in
improving a breed, if care be taken for a length of time to exclude all
inferior individuals, the breed will obviously tend to become truer, as it
will not have been crossed during many generations by an inferior animal. We
have previously seen, but without being able to assign any cause, that, when a
new character appears, it is occasionally from the first constant, or
fluctuates much, or wholly fails to be transmitted. So it is with the
aggregate of slight differences which characterise a new variety, for some
propagate their kind from the first much truer than others. Even with plants
multiplied by bulbs, layers, etc., which may in one sense be said to form
parts of the same individual, it is well known that certain varieties retain
and transmit through successive bud-generations their newly-acquired
characters more truly than others. In none of these, nor in the following
cases, does there appear to be any relation between the force with which a
character is transmitted and the length of time during which it has been
transmitted. Some varieties, such as white and yellow hyacinths and white
sweet-peas, transmit their colours more faithfully than do the varieties which
have retained their natural colour. In the Irish family, mentioned in the
twelfth chapter, the peculiar tortoiseshell-like colouring of the eyes was
transmitted far more faithfully than any ordinary colour. Ancon and Mauchamp
sheep and niata cattle, which are all comparatively modern breeds, exhibit
remarkably strong powers of inheritance. Many similar cases could be adduced.

As all domesticated animals and cultivated plants have varied, and yet are
descended from aboriginally wild forms, which no doubt had retained the same
character from an immensely remote epoch, we see that scarcely any degree of
antiquity ensures a character being transmitted perfectly true. In this case,
however, it may be said that changed conditions of life induce certain
modifications, and not that the power of inheritance fails; but in every case
of failure, some cause, either internal or external, must interfere. It will
generally be found that the organs or parts which in our domesticated
productions have varied, or which still continue to vary,--that is, which fail
to retain their former state,--are the same with the parts which differ in the
natural species of the same genus. As, on the theory of descent with
modification, the species of the same genus have been modified since they
branched off from a common progenitor, it follows that the characters by which
they differ from one another have varied, whilst other parts of the
organisation have remained unchanged; and it might be argued that these same
characters now vary under domestication, or fail to be inherited, from their
lesser antiquity. But variation in a state of nature seems to stand in some
close relation with changed conditions of life, and characters which have
already varied under such conditions would be apt to vary under the still
greater changes consequent on domestication, independently of their greater or
less antiquity.

Fixedness of character, or the strength of inheritance, has often been judged
of by the preponderance of certain characters in the crossed offspring between
distinct races; but prepotency of transmission here comes into play, and this,
as we shall immediately see, is a very different consideration from the
strength or weakness of inheritance. (14/1. See 'Youatt on Cattle' pages 92,
69, 78, 88, 163; and 'Youatt on Sheep' page 325. Also Dr. Lucas 'L'Hered.
Nat.' tome 2 page 310.) It has often been observed that breeds of animals
inhabiting wild and mountainous countries cannot be permanently modified by
our improved breeds; and as these latter are of modern origin, it has been
thought that the greater antiquity of the wilder breeds has been the cause of
their resistance to improvement by crossing; but it is more probably due to
their structure and constitution being better adapted to the surrounding
conditions. When plants are first subjected to culture, it has been found
that, during several generations, they transmit their characters truly, that
is, do not vary, and this has been attributed to ancient characters being
strongly inherited: but it may with equal or greater probability be consequent
on changed conditions of life requiring a long time for their cumulative
action. Notwithstanding these considerations, it would perhaps be rash to deny
that characters become more strongly fixed the longer they are transmitted;
but I believe that the proposition resolves itself into this,--that characters
of all kinds, whether new or old, tend to be inherited, and that those which
have already withstood all counteracting influences and been truly
transmitted, will, as a general rule, continue to withstand them, and
consequently be faithfully inherited.

PREPOTENCY IN THE TRANSMISSION OF CHARACTER.

When individuals, belonging to the same family, but distinct enough to be
recognised, or when two well-marked races, or two species, are crossed, the
usual result, as stated in the previous chapter, is, that the offspring in the
first generation are intermediate between their parents, or resemble one
parent in one part and the other parent in another part. But this is by no
means the invariable rule; for in many cases it is found that certain
individuals, races, and species, are prepotent in transmitting their likeness.
This subject has been ably discussed by Prosper Lucas (14/2. 'Hered. Nat.'
tome 2 pages 112-120.), but is rendered extremely complex by the prepotency
sometimes running equally in both sexes, and sometimes more strongly in one
sex than in the other; it is likewise complicated by the presence of secondary
sexual characters, which render the comparison of crossed breeds with their
parents difficult.

It would appear that in certain families some one ancestor, and after him
others in the same family, have had great power in transmitting their likeness
through the male line; for we cannot otherwise understand how the same
features should so often be transmitted after marriages with many females, as
in the case of the Austrian Emperors; and so it was, according to Niebuhr,
with the mental qualities of certain Roman families. (14/3. Sir H. Holland
'Chapters on Mental Physiology' 1852 page 234.) The famous bull Favourite is
believed (14/4. 'Gardener's Chronicle' 1860 page 270.) to have had a prepotent
influence on the shorthorn race. It has also been observed (14/5. Mr. N.H.
Smith 'Observations on Breeding' quoted in 'Encyclop. of Rural Sports' page
278.) with English racehorses that certain mares have generally transmitted
their own character, whilst other mares of equally pure blood have allowed the
character of the sire to prevail. A famous black greyhound, Bedlamite, as I
hear from Mr. C.M. Brown "invariably got all his puppies black, no matter what
was the colour of the bitch;" but then Bedlamite "had a preponderance of black
in his blood, both on the sire and dam side."

[The truth of the principle of prepotency comes out more clearly when distinct
races are crossed. The improved Shorthorns, notwithstanding that the breed is
comparatively modern, are generally acknowledged to possess great power in
impressing their likeness on all other breeds; and it is chiefly in
consequence of this power that they are so highly valued for exportation.
(14/6. Quoted by Bronn 'Geshichte der Natur' b. 2 s. 170. See Sturm 'Ueber
Racen' 1825 s. 104-107. For the niata cattle see my 'Journal of Researches'
1845 page 146.) Godine has given a curious case of a ram of a goat-like breed
of sheep from the Cape of Good Hope, which produced offspring hardly to be
distinguished from himself, when crossed with ewes of twelve other breeds. But
two of these half-bred ewes, when put to a merino ram, produced lambs closely
resembling the merino breed. Girou de Buzareingues (14/7. Lucas 'L'Heredite
Nat.' tome 2 page 112.) found that of two races of French sheep the ewes of
one, when crossed during successive generations with merino rams, yielded up
their character far sooner than the ewes of the other race. Sturm and Girou
have given analogous cases with other breeds of sheep and with cattle, the
prepotency running in these cases through the male side; but I was assured on
good authority in South America, that when niata cattle are crossed with
common cattle, though the niata breed is prepotent whether males or females
are used, yet that the prepotency is strongest through the female line. The
Manx cat is tailless and has long hind legs; Dr. Wilson crossed a male Manx
with common cats, and, out of twenty-three kittens, seventeen were destitute
of tails; but when the female Manx was crossed by common male cats all the
kittens had tails, though they were generally short and imperfect. (14/8. Mr.
Orton 'Physiology of Breeding' 1855 page 9.)

In making reciprocal crosses between pouter and fantail pigeons, the pouter-
race seemed to be prepotent through both sexes over the fantail. But this is
probably due to weak power in the fantail rather than to any unusually strong
power in the pouter, for I have observed that barbs also preponderate over
fantails. This weakness of transmission in the fantail, though the breed is an
ancient one, is said (14/9. Boitard and Corbie 'Les Pigeons' 1824 page 224.)
to be general; but I have observed one exception to the rule, namely, in a
cross between a fantail and laugher. The most curious instance known to me of
weak power in both sexes is in the trumpeter pigeon. This breed has been well
known for at least 130 years: it breeds perfectly true, as I have been assured
by those who have long kept many birds: it is characterised by a peculiar tuft
of feathers over the beak, by a crest on the head, by a singular coo quite
unlike that of any other breed, and by much-feathered feet. I have crossed
both sexes with turbits of two sub-breeds, with almond tumblers, spots, and
runts, and reared many mongrels and recrossed them; and though the crest on
the head and feathered feet were inherited (as is generally the case with most
breeds), I have never seen a vestige of the tuft over the beak or heard the
peculiar coo. Boitard and Corbie (14/10. 'Les Pigeons' pages 168, 198.) assert
that this is the invariable result of crossing trumpeters with other breeds:
Neumeister (14/11. 'Das Ganze' etc. 1837 s. 39.), however, states that in
Germany mongrels have been obtained, though very rarely, which were furnished
with the tuft and would trumpet: but a pair of these mongrels with a tuft,
which I imported, never trumpeted. Mr. Brent states (14/12. 'The Pigeon Book'
page 46.) that the crossed offspring of a trumpeter were crossed with
trumpeters for three generations, by which time the mongrels had 7/8ths of
this blood in their veins, yet the tuft over the beak did not appear. At the
fourth generation the tuft appeared, but the birds though now having 15-16ths
trumpeter's blood still did not trumpet. This case well shows the wide
difference between inheritance and prepotency; for here we have a well-
established old race which transmits its characters faithfully, but which,
when crossed with any other race, has the feeblest power of transmitting its
two chief characteristic qualities.

I will give one other instance with fowls and pigeons of weakness and strength
in the transmission of the same character to their crossed offspring. The Silk
fowl breeds true, and there is reason to believe is a very ancient race; but
when I reared a large number of mongrels from a Silk hen by a Spanish cock,
not one exhibited even a trace of the so-called silkiness. Mr. Hewitt also
asserts that in no instance are the silky feathers transmitted by this breed
when crossed with any other variety. But three birds out of many raised by Mr.
Orton from a cross between a silk cock and a bantam hen had silky feathers.
(14/13. 'Physiology of Breeding' page 22; Mr. Hewitt in 'The Poultry Book' by
Tegetmeier 1866 page 224.) So that it is certain that this breed very seldom
has the power of transmitting its peculiar plumage to its crossed progeny. On
the other hand, there is a silk sub-variety of the fantail pigeon, which has
its feathers in nearly the same state as in the Silk fowl: now we have already
seen that fantails, when crossed, possess singularly weak power in
transmitting their general qualities; but the silk sub-variety when crossed
with any other small-sized race invariably transmits its silky feathers!
(14/14. Boitard and Corbie 'Les Pigeons' 1824 page 226.)

The well-known horticulturist, Mr. Paul, informs me that he fertilised the
Black Prince hollyhock with pollen of the White Globe and the Lemonade and
Black Prince hollyhocks reciprocally; but not one seedling from these three
crosses inherited the black colour of the Black Prince. So, again, Mr. Laxton,
who has had such great experience in crossing peas, writes to me that
"whenever a cross has been effected between a white-blossomed and a purple-
blossomed pea, or between a white-seeded and a purple-spotted, brown or maple-
seeded pea, the offspring seems to lose nearly all the characteristics of the
white-flowered and white-seeded varieties; and this result follows whether
these varieties have been used as the pollen-bearing or seed-producing
parents."

The law of prepotency comes into action when species are crossed, as with
races and individuals. Gartner has unequivocally shown (14/15.
'Bastarderzeugung' s. 256, 290, etc. Naudin 'Nouvelles Archives du Museum'
tome 1 page 149 gives a striking instance of prepotency in Datura stramonium
when crossed with two other species.) that this is the case with plants. To
give one instance: when Nicotiana paniculata and vincaeflora are crossed, the
character of N. paniculata is almost completely lost in the hybrid; but if N.
quadrivalvis be crossed with N. vincaeflora, this latter species, which was
before so prepotent, now in its turn almost disappears under the power of N.
quadrivalvis. It is remarkable that the prepotency of one species over another
in transmission is quite independent, as shown by Gartner, of the greater or
less facility with which the one fertilises the other.

With animals, the jackal is prepotent over the dog, as is stated by Flourens,
who made many crosses between these animals; and this was likewise the case
with a hybrid which I once saw between a jackal and a terrier. I cannot doubt,
from the observations of Colin and others, that the ass is prepotent over the
horse; the prepotency in this instance running more strongly through the male
than through the female ass; so that the mule resembles the ass more closely
than does the hinny. (14/16. Flourens 'Longevite Humaine' page 144 on crossed
jackals. With respect to the difference between the mule and the hinny I am
aware that this has generally been attributed to the sire and dam transmitting
their characters differently; but Colin, who has given in his 'Traite Phys.
Comp.' tome 2 pages 537-539, the fullest description which I have met with of
these reciprocal hybrids, is strongly of opinion that the ass preponderates in
both crosses, but in an unequal degree. This is likewise the conclusion of
Flourens, and of Bechstein in his 'Naturgeschichte Deutschlands' b. 1 s. 294.
The tail of the hinny is much more like that of the horse than is the tail of
the mule, and this is generally accounted for by the males of both species
transmitting with greater power this part of their structure; but a compound
hybrid which I saw in the Zoological Gardens, from a mare by a hybrid ass-
zebra, closely resembled its mother in its tail.) The male pheasant, judging
from Mr. Hewitt's descriptions (14/17. Mr. Hewitt who has had such great
experience in raising these hybrids says ('Poultry Book' by Mr. Tegetmeier
1866 pages 165-167) that in all, the head was destitute of wattles, comb, and
ear-lappets; and all closely resembled the pheasant in the shape of the tail
and general contour of the body. These hybrids were raised from hens of
several breeds by a cock-pheasant; but another hybrid, described by Mr.
Hewitt, was raised from a hen-pheasant, by a silver-laced Bantam cock, and
this possessed a rudimental comb and wattles.), and from the hybrids which I
have seen, preponderates over the domestic fowl; but the latter, as far as
colour is concerned, has considerable power of transmission, for hybrids
raised from five differently coloured hens differed greatly in plumage. I
formerly examined some curious hybrids in the Zoological Gardens, between the
Penguin variety of the common duck and the Egyptian goose (Anser aegyptiacus);
and although I will not assert that the domesticated variety preponderated
over the natural species, yet it had strongly impressed its unnatural upright
figure on these hybrids.

I am aware that such cases as the foregoing have been ascribed by various
authors, not to one species, race, or individual being prepotent over the
other in impressing its character on its crossed offspring, but to such rules
as that the father influences the external characters and the mother the
internal or vital organs. But the great diversity of the rules given by
various authors almost proves their falseness. Dr. Prosper Lucas has fully
discussed this point, and has shown (14/18. 'L'Hered. Nat.' tome 2 book 2
chapter 1.) that none of the rules (and I could add others to those quoted by
him) apply to all animals. Similar rules have been announced for plants, and
have been proved by Gartner (14/19. 'Bastarderzeugung' s. 264-266. Naudin
'Nouvelles Archives du Museum' tome 1 page 148 has arrived at a similar
conclusion.) to be all erroneous. If we confine our view to the domesticated
races of a single species, or perhaps even to the species of the same genus,
some such rules may hold good; for instance, it seems that in reciprocally
crossing various breeds of fowls the male generally gives colour (14/20.
'Cottage Gardener' 1856 pages 101, 137.); but conspicuous exceptions have
passed under my own eyes. It seems that the ram usually gives its peculiar
horns and fleece to its crossed offspring, and the bull the presence or
absence of horns.

In the following chapter on Crossing I shall have occasion to show that
certain characters are rarely or never blended by crossing, but are
transmitted in an unmodified state from either parent-form; I refer to this
fact here because it is sometimes accompanied on the one side by prepotency,
which thus acquires the false appearance of unusual strength. In the same
chapter I shall show that the rate at which a species or breed absorbs and
obliterates another by repeated crosses, depends in chief part on prepotency
in transmission.]

In conclusion, some of the cases above given,--for instance, that of the
trumpeter pigeon,--prove that there is a wide difference between mere
inheritance and prepotency. This latter power seems to us, in our ignorance,
to act in most cases quite capriciously. The very same character, even though
it be an abnormal or monstrous one, such as silky feathers, may be transmitted
by different species, when crossed, either with prepotent force or singular
feebleness. It is obvious, that a purely-bred form of either sex, in all cases
in which prepotency does not run more strongly in one sex than the other, will
transmit its character with prepotent force over a mongrelised and already
variable form. (14/21. See some remarks on this head with respect to sheep by
Mr. Wilson in 'Gardener's Chronicle' 1863 page 15. Many striking instances of
this result are given by M. Malingie-Nouel 'Journ. R. Agricult. Soc.' volume
14 1853 page 220 with respect to crosses between English and French sheep. He
found that he obtained the desired influence of the English breeds by crossing
intentionally mongrelised French breeds with pure English breeds.) From
several of the above-given cases we may conclude that mere antiquity of
character does not by any means necessarily make it prepotent. In some cases
prepotency apparently depends on the same character being present and visible
in one of the two breeds which are crossed, and latent or invisible in the
other breed; and in this case it is natural that the character which is
potentially present in both breeds should be prepotent. Thus, we have reason
to believe that there is a latent tendency in all horses to be dun-coloured
and striped; and when a horse of this kind is crossed with one of any other
colour, it is said that the offspring are almost sure to be striped. Sheep
have a similar latent tendency to become dark-coloured, and we have seen with
what prepotent force a ram with a few black spots, when crossed with white
sheep of various breeds, coloured its offspring. All pigeons have a latent
tendency to become slaty-blue, with certain characteristic marks, and it is
known that, when a bird thus coloured is crossed with one of any other colour,
it is most difficult afterwards to eradicate the blue tint. A nearly parallel
case is offered by those black bantams which, as they grow old, develop a
latent tendency to acquire red feathers. But there are exceptions to the rule:
hornless breeds of cattle possess a latent capacity to reproduce horns, yet
when crossed with horned breeds they do not invariably produce offspring
bearing horns.

We meet with analogous cases with plants. Striped flowers, though they can be
propagated truly by seed, have a latent tendency to become uniformly coloured,
but when once crossed by a uniformly coloured variety, they ever afterwards
fail to produce striped seedlings. (14/22. Verlot 'Des Varietes' 1865 page
66.) Another case is in some respects more curious: plants bearing peloric
flowers have so strong a latent tendency to reproduce their normally irregular
flowers, that this often occurs by buds when a plant is transplanted into
poorer or richer soil. (14/23. Moquin-Tandon 'Teratologie' page 191.) Now I
crossed the peloric snapdragon (Antirrhinum majus), described in the last
chapter, with pollen of the common form; and the latter, reciprocally, with
peloric pollen. I thus raised two great beds of seedlings, and not one was
peloric. Naudin (14/24. 'Nouvelles Archives du Museum' tome 1 page 137.)
obtained the same result from crossing a peloric Linaria with the common form.
I carefully examined the flowers of ninety plants of the crossed Antirrhinum
in the two beds, and their structure had not been in the least affected by the
cross, except that in a few instances the minute rudiment of the fifth stamen,
which is always present, was more fully or even completely developed. It must
not be supposed that this entire obliteration of the peloric structure in the
crossed plants can be accounted for by any incapacity of transmission; for I
raised a large bed of plants from the peloric Antirrhinum, artificially
fertilised by its own pollen, and sixteen plants, which alone survived the
winter, were all as perfectly peloric as the parent-plant. Here we have a good
instance of the wide difference between the inheritance of a character and the
power of transmitting it to crossed offspring. The crossed plants, which
perfectly resembled the common snapdragon, were allowed to sow themselves, and
out of a hundred and twenty-seven seedlings, eighty-eight proved to be common
snapdragons, two were in an intermediate condition between the peloric and
normal state, and thirty-seven were perfectly peloric, having reverted to the
structure of their one grand-parent. This case seems at first sight to offer
an exception to the rule just given, namely, that a character which is present
in one form and latent in the other is generally transmitted with prepotent
force when the two forms are crossed. For in all the Scrophulariaceae, and
especially in the genera Antirrhinum and Linaria, there is, as was shown in
the last chapter, a strong latent tendency to become peloric; but there is
also, as we have seen, a still stronger tendency in all peloric plants to
reacquire their normal irregular structure. So that we have two opposed latent
tendencies in the same plants. Now, with the crossed Antirrhinums the tendency
to produce normal or irregular flowers, like those of the common Snapdragon,
prevailed in the first generation; whilst the tendency to pelorism, appearing
to gain strength by the intermission of a generation, prevailed to a large
extent in the second set of seedlings. How it is possible for a character to
gain strength by the intermission of a generation, will be considered in the
chapter on pangenesis.

On the whole, the subject of prepotency is extremely intricate,--from its
varying so much in strength, even in regard to the same character, in
different animals,--from its running either equally in both sexes, or, as
frequently is the case with animals, but not with plants, much stronger in one
sex than the other,--from the existence of secondary sexual characters,--from
the transmission of certain characters being limited, as we shall immediately
see, by sex,--from certain characters not blending together,--and, perhaps,
occasionally from the effects of a previous fertilisation on the mother. It is
therefore not surprising that no one has hitherto succeeded in drawing up
general rules on the subject of prepotency.

INHERITANCE AS LIMITED BY SEX.

New characters often appear in one sex, and are afterwards transmitted to the
same sex, either exclusively or in a much greater degree than to the other.
This subject is important, because with animals of many kinds in a state of
nature, both high and low in the scale, secondary sexual characters, not
directly connected with the organs of reproduction, are conspicuously present.
With our domesticated animals, characters of this kind often differ widely
from those distinguishing the two sexes of the parent species; and the
principle of inheritance, as limited by sex, explains how this is possible.

[Dr. P. Lucas has shown (14/25. 'L'Hered. Nat.' tome 2 pages 137-165. See also
Mr. Sedgwick's four memoirs, immediately to be referred to.) that when a
peculiarity, in no manner connected with the reproductive organs, appears in
either parent, it is often transmitted exclusively to the offspring of the
same sex, or to a much greater number of them than of the opposite sex. Thus,
in the family of Lambert, the horn-like projections on the skin were
transmitted from the father to his sons and grandsons alone; so it has been
with other cases of ichthyosis, with supernumerary digits, with a deficiency
of digits and phalanges, and in a lesser degree with various diseases,
especially with colour-blindness and the haemorrhagic diathesis, that is, an
extreme liability to profuse and uncontrollable bleeding from trifling wounds.
On the other hand, mothers have transmitted, during several generations, to
their daughters alone, supernumerary and deficient digits, colour-blindness
and other peculiarities. So that the very same peculiarity may become attached
to either sex, and be long inherited by that sex alone; but the attachment in
certain cases is much more frequent to one than the other sex. The same
peculiarities also may be promiscuously transmitted to either sex. Dr. Lucas
gives other cases, showing that the male occasionally transmits his
peculiarities to his daughters alone, and the mother to her sons alone; but
even in this case we see that inheritance is to a certain extent, though
inversely, regulated by sex. Dr. Lucas, after weighing the whole evidence,
comes to the conclusion that every peculiarity tends to be transmitted in a
greater or lesser degree to that sex in which it first appears. But a more
definite rule, as I have elsewhere shown (14/26. 'Descent of Man' 2nd edition
page 32.) generally holds good, namely, that variations which first appear in
either sex at a late period of life, when the reproductive functions are
active, tend to be developed in that sex alone; whilst variations which first
appear early in life in either sex are commonly transmitted to both sexes. I
am, however, far from supposing that this is the sole determining cause.

A few details from the many cases collected by Mr. Sedgwick (14/27. On Sexual
Limitation in Hereditary Diseases 'Brit. and For. Med.-Chirurg. Review' April
1861 page 477; July page 198; April 1863 page 445; and July page 159. Also in
1867 'On the influence of Age in Hereditary Disease.'), may be here given.
Colour-blindness, from some unknown cause, shows itself much oftener in males
than in females; in upwards of two hundred cases collected by Mr. Sedgwick,
nine-tenths related to men; but it is eminently liable to be transmitted
through women. In the case given by Dr. Earle, members of eight related
families were affected during five generations: these families consisted of
sixty-one individuals, namely, of thirty-two males, of whom nine-sixteenths
were incapable of distinguishing colour, and of twenty-nine females, of whom
only one-fifteenth were thus affected. Although colour-blindness thus
generally clings to the male sex, nevertheless, in one instance in which it
first appeared in a female, it was transmitted during five generations to
thirteen individuals, all of whom were females. The haemorrhagic diathesis,
often accompanied by rheumatism, has been known to affect the males alone
during five generations, being transmitted, however, through the females. It
is said that deficient phalanges in the fingers have been inherited by the
females alone during ten generations. In another case, a man thus deficient in
both hands and feet, transmitted the peculiarity to his two sons and one
daughter; but in the third generation,--out of nineteen grandchildren, twelve
sons had the family defect, whilst the seven daughters were free. In ordinary
cases of sexual limitation, the sons or daughters inherit the peculiarity,
whatever it may be, from their father or mother, and transmit it to their
children of the same sex; but generally with the haemorrhagic diathesis, and
often with colour-blindness, and in some other cases, the sons never inherit
the peculiarity directly from their fathers, but the daughters alone transmit
the latent tendency, so that the sons of the daughters alone exhibit it. Thus
the father, grandson, and great-great-grandson will exhibit a peculiarity,--
the grandmother, daughter, and great-grand-daughter having transmitted it in a
latent state. Hence we have, as Mr. Sedgwick remarks, a double kind of atavism
or reversion; each grandson apparently receiving and developing the
peculiarity from his grandfather, and each daughter apparently receiving the
latent tendency from her grandmother.

From the various facts recorded by Dr. Prosper Lucas, Mr. Sedgwick, and
others, there can be no doubt that peculiarities first appearing in either
sex, though not in any way necessarily or invariably connected with that sex,
strongly tend to be inherited by the offspring of the same sex, but are often
transmitted in a latent state through the opposite sex.

Turning now to domesticated animals, we find that certain characters not
proper to the parent species are often confined to, and inherited by, one sex

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