CHAPTER XIII. INHERITANCE _continued_—REVERSION OF 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-Arrière_; and by the German _Rückschlag,_ or

_Rückschritt._ 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.”[1] 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.[2]

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.[3] 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.[4] This

occurs still more frequently with the less improved breeds, such as the

Norfolks.[5] 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[6] 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;”[7] 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[8] 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;[9] 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.[10] 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[11] 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[12] 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] 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[14] has strongly insisted

on what slight evidence the common belief in their reversion to a

primitive state rests. Godron[15] 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[16] 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[17]

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.[18] 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 Kölreuter to the present day,

has insisted on this tendency. Gärtner has recorded some good

instances; but no one has given more striking ones than Naudin.[19] 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.”[20]

_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[21] 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[22]

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 Tropæolum, 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[23] 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[24] 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.[25] 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.”[26] 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.[27] 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,[28] 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[29] 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 tæniopus_ of

Abyssinia,[30] 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,[31]

and remarks that mules are particularly liable to be thus striped on

their legs. In South America, according to Roulin,[32] such stripes are

more frequent and conspicuous in the mule than in the ass. In the

United States, Mr. Gosse,[33] 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,[34] 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[35] 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_[36] 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[37] 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[38] 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[39] 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.[40] 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.”[41] 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”;[42] but I have myself seen

one exception to this rule. Mr. S. J. Salter[43] who raised a large

number of hybrids from a bantam-hen by _Gallus sonneratii,_ states that

“all were exceedingly wild.” Mr. Waterton[44] 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[45] 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[46] 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.[47] 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.”[48] 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.[49] 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[50]

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.

Gärtner 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

Gärtner himself, than hybrids.[51]

Gärtner 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[52] 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.[53]

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.[54] A duck ten years old has been known to assume both the

perfect winter and summer plumage of the drake.[55] Waterton,[56] 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.”[57] That admirable observer Reaumur[58] 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[59] 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.[60] 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 Achatinellæ[61] are

as often sinistral as dextral. I will give an analogous case in the

great articulate kingdom: the two sides of Verruca[62] 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[63] 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[64] 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[65] 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[66] 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[67] 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,[68] who has ably

discussed this subject, remarks that when, for instance, all the sepals

of a Tropæolum 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,[69] 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[70]

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.[71] 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_.[72]

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 Labiatæ and Scrophulariaceæ

than in any other order; and in one genus of the Scrophulariaceæ,

namely Linaria, no less than thirteen species have been described in

this condition.[73] 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.

REFERENCES

[1] Youatt on Sheep, pp. 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.

[2] Youatt on Cattle, pp. 155, 174.

[3] Youatt on Sheep, 1838, pp. 17, 145.

[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, p. 395.

[5] Youatt, pp. 19, 234.

[6] ‘The Poultry Book,’ by Mr. Tegetmeier, 1866, p. 231.

[7] Loudon’s ‘Gardener’s Mag.,’ vol. x., 1834, p. 396: a nurseryman,

with much experience on this subject, has likewise assured me that

this sometimes occurs.

[8] ‘Gardener’s Chronicle,’ 1855, p. 777.

[9] Ibid., 1862, p. 721.

[10] Mr. Boner speaks (‘Chamois-hunting,’ 2nd edit., 1860, p. 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.

[11] _See_ some excellent remarks on this subject by Mr. Wallace

‘Journal Proc. Linn. Soc.,’ 1858, vol. iii. p. 60.

[12] Dureau de la Malle ‘Comptes Rendus,’ tom. xli., 1855, p. 807.

From the statements above given, the author concludes that the wild

pigs of Louisiana are not descended from the European _Sus scrofa._

[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,’ tom. xli., 1855, p. 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.

[14] ‘Flora of Australia,’ 1859, Introduct., p. ix.

[15] ‘De l’Espèce,’ tom. ii. pp. 54, 58, 60.

[16] Mr. Sedgwick gives many instances in the ‘British and Foreign

Med.-Chirurg. Review,’ April and July, 1863, pp. 448, 188.

[17] In his edit. of ‘Youatt on the Pig,’ 1860, p. 27.

[18] Dr. P. Lucas, ‘Héréd. Nat.,’ tom. ii. pp. 314, 892: _see_ a good

practical article on the subject in ‘Gard. Chronicle,’ 1856, p. 620. I

could add a vast number of references, but they would be superfluous.

[19] Kölreuter gives curious cases in his ‘Dritte Fortsetzung,’ 1766,

ss. 53, 59; and in his well-known ‘Memoirs on Lavatera and Jalapa.’

Gärtner, ‘Bastarderzeugung,’ ss. 437, 441, etc. Naudin in his

“Recherches sur l’Hybridité,” ‘Nouvelles Archives du Muséum,’ tom. i.

p. 25.

[20] Quoted by Mr. Sedgwick in ‘Med.-Chirurg. Review,’ April, 1861, p.

485. Dr. H. Dobell in ‘Med.-Chirurg. Transactions,’ vol. xlvi., 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.

[21] Verlot ‘Des Variétés,’ 1865, p. 63.

[22] ‘Nouvelles Archives du Muséum,’ tom. i. p. 25. Alex. Braun (in

his ‘Rejuvenescence,’ Ray Soc., 1853, p. 315) apparently holds a

similar opinion.

[23] Mr. Teebay in ‘The Poultry Book,’ by Mr. Tegetmeier, 1866, p. 72.

[24] Quoted by Hofacker ‘Ueber die Eigenschaften,’ etc., s. 98.

[25] Azara, ‘Essais Hist. Nat. de Paraguay,’ tom. ii. 1801, p. 372.

[26] These facts are given on the high authority of Mr. Hewitt, in

‘The Poultry Book,’ by Mr. Tegetmeier, 1866, p. 248.

[27] ‘The Poultry Book,’ by Tegetmeier, 1866, p. 97.

[28] ‘Gardener’s Chron. and Agricultural Gazette,’ 1866, p. 528.

[29] Ibid., 1860, p. 343. I am glad to find that so experienced a

breeder of cattle as Mr. Willoughby Wood, (‘Gard. Chron.’ 1869, p.

1216), admits my principle of a cross giving a tendency to reversion.

[30] Sclater in ‘Proc. Zoolog. Soc.,’ 1862, p. 163.

[31] ‘History of the Horse,’ p. 212.

[32] ‘Mém. présentés par divers Savans à l’Acad. Royale,’ tom. vi.

1835, p. 338.

[33] ‘Letters from Alabama,’ 1859, p. 280.

[34] ‘Hist. Nat. des Mammiferes,’ 1820, tom. i.

[35] ‘Philosoph. Transact.,’ 1821, p. 20.

[36] Sclater, in ‘Proc. Zoolog. Soc.,’ 1862, p. 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,’ vol. xviii., 1860, p. 229.

[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, p. 320: and Col. Hamilton Smith in ‘Nat. Library,

Horses,’ p. 318; and ‘Dict. Class. d’Hist. Nat.,’ tom. iii. p. 563.

[38] Figured in the ‘Gleanings from the Knowsley Menageries,’ by Dr.

J. E. Gray.

[39] ‘Darwin’sche Theorie und ihre Stellung zu Moral und Religion,’ p.

85.

[40] Cases of both Spanish and Polish hens sitting are given in the

‘Poultry Chronicle,’ 1855, vol. iii. p. 477.

[41] ‘The Poultry Book,’ by Mr. Tegetmeier, 1866, pp. 119, 163. The

author, who remarks on the two negatives (‘Journ. of Hort.,’ 1862, p.

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, p. 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,’ vol. iii. p. 13, as an “exemplary mother.”

On the other hand, an exceptional case is given in the ‘Cottage

Gardener,’ 1860, p. 388, of a hen raised from a Spanish cock and black

Polish hen which did not incubate.

[42] ‘The Poultry Book,’ by Tegetmeier, 1866, pp. 165, 167.

[43] ‘Natural History Review,’ 1863, April, p. 277.

[44] ‘Essays on Natural History,’ p. 917.

[45] As stated by Mr. Orton, in his ‘Physiology of Breeding,’ p. 12.

[46] M. E. de Selys-Longchamps refers (‘Bulletin Acad. Roy. de

Bruxelles,’ tom. xii. No. 10) to more than seven of these hybrids shot

in Switzerland and France. M. Deby asserts (‘Zoologist,’ vol. v.,

1845-46, p. 1254) that several have been shot in various parts of

Belgium and Northern France. Audubon (‘Ornitholog. Biography,’ vol.

iii. p. 168), speaking of these hybrids, says that, in North America,

they “now and then wander off and become quite wild.”

[47] ‘Journal of Researches,’ 1845, p. 71.

[48] ‘Expedition to the Zambesi,’ 1865, pp. 25, 150.

[49] Dr. P. Broca, on ‘Hybridity in the Genus Homo,’ Eng. translat.,

1864, p. 39.

[50] ‘Nouvelles Archives du Muséum,’ tom. i. p. 151.

[51] ‘Bastarderzeugung,’ s. 582, 438, etc.

[52] ‘Die Bastardbefruchtung . . . der Weiden,’ 1865, s. 23. For

Gärtner’s remarks on this head, _see_ ‘Bastarderzeugung,’ s. 474, 582.

[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,’ pp. 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.

[54] Yarrell, ‘Phil. Transact.,’ 1827, p. 268; Dr. Hamilton, in ‘Proc.

Zoolog. Soc.,’ 1862, p. 23.

[55] ‘Archiv. Skand. Beiträge zur Naturgesch.’ viii. s. 397-413.

[56] In his ‘Essays on Nat. Hist.,’ 1838, Mr. Hewitt gives analogous

cases with hen-pheasants in ‘Journal of Horticulture,’ July 12, 1864,

p. 37. Isidore Geoffroy Saint-Hilaire, in his ‘Essais de Zoolog. Gen.’

(‘suites a Buffon,’ 1842, pp. 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 p. 513.

[57] ‘Cottage Gardener,’ 1860, p. 379.

[58] ‘Art de faire Eclore,’ etc., 1749, tom. ii. p. 8.

[59] Sir H. Holland, ‘Medical Notes and Reflections,’ 3rd edit., 1855,

p. 31.

[60] _See_ Steenstrup on the ‘Obliquity of Flounders’: in ‘Annals and

Mag. of Nat. Hist.’ May, 1865, p. 361. I have given an abstract of

Malm’s explanation of this wonderful phenomenon in the ‘Origin of

Species’ 6th Edit. p. 186.

[61] Dr. E. von Martens, in ‘Annals and Mag. of Nat. Hist.’ March,

1866, p. 209.

[62] Darwin, ‘Balanidæ,’ Ray Soc., 1854, p. 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.

[63] Mormodes ignea: Darwin, ‘Fertilisation of Orchids,’ 1862, p. 251.

[64] ‘Journal of Horticulture,’ July, 1864, p. 38. I have had the

opportunity of examining these remarkable feathers through the

kindness of Mr. Tegetmeier.

[65] ‘The Poultry Book,’ by Mr. Tegetmeier, 1866, p. 241.

[66] Carl Vogt, ‘Lectures on Man,’ Eng. translat., 1864, p. 411.

[67] ‘On Cattle,’ p. 174.

[68] ‘Natural Hist. Review,’ April, 1863, p. 258. _See also_ his

Lecture, Royal Institution, March 16, 1860. On same subject see

Moquin-Tandon, ‘Eléments de Tératologie,’ 1841, pp. 184, 352. Dr.

Peyritsch has collected a large number of very interesting cases,

Sitzb. d. k. Akad. d. Wissensch.: Wien. b. LX. and especially b.

LXVI., 1872, p. 125.

[69] Verlot, ‘Des Variétés,’ 1865, p. 89; Naudin, ‘Nouvelles Archives

du Museum,’ tom. i. p. 137.

[70] In his discussion on some curious peloric Calceolarias, quoted in

‘Journal of Horticulture,’ Feb. 24, 1863, p. 152.

[71] For other cases of six divisions in peloric flowers of the

Labiatæ and Scrophulariaceæ, _see_ Moquin-Tandon, ‘Tératologie,’ p.

192.

[72] Godron, reprinted from the ‘Mémoires de l’Acad. de Stanislas,’

1868.

[73] Moquin-Tandon, ‘Tératologie,’ p. 186.