WONDERFUL NATURE OF INHERITANCE—PEDIGREES OF OUR DOMESTICATED
ANIMALS—INHERITANCE NOT DUE TO CHANCE—TRIFLING CHARACTERS
INHERITED—DISEASES INHERITED—PECULIARITIES IN THE EYE
INHERITED—DISEASES IN THE HORSE—LONGEVITY AND VIGOUR—ASYMMETRICAL
DEVIATIONS OF STRUCTURE—POLYDACTYLISM AND REGROWTH OF SUPERNUMERARY
DIGITS AFTER AMPUTATION—CASES OF SEVERAL CHILDREN SIMILARLY AFFECTED
FROM NON-AFFECTED PARENTS—WEAK AND FLUCTUATING INHERITANCE: IN WEEPING
TREES, IN DWARFNESS, COLOUR OF FRUIT AND FLOWERS—COLOUR OF
HORSES—NON-INHERITANCE IN CERTAIN CASES—INHERITANCE OF STRUCTURE AND
HABITS OVERBORNE BY HOSTILE CONDITIONS OF LIFE, BY INCESSANTLY
RECURRING VARIABILITY, AND BY REVERSION—CONCLUSION.
The subject of inheritance is an immense one, and has been treated by
many authors. One work alone, ‘De l’Hérédité Naturelle’ by Dr. Prosper
Lucas, runs to the length of 1562 pages. We must confine ourselves to
certain points which have an important bearing on the general subject
of variation, both with domestic and natural productions. It is obvious
that a variation which is not inherited throws no light on the
derivation of species, nor is of any service to man, except in the case
of perennial plants, which can be propagated by buds.
If animals and plants had never been domesticated, and wild ones alone
had been observed, we should probably never have heard the saying, that
“like begets like.” The proposition would have been as self-evident as
that all the buds on the same tree are alike, though neither
proposition is strictly true. For, as has often been remarked, probably
no two individuals are identically the same. All wild animals recognise
each other, which shows that there is some difference between them; and
when the eye is well practised, the shepherd knows each sheep, and man
can distinguish a fellow-man out of millions on millions of other men.
Some authors have gone so far as to maintain that the production of
slight differences is as much a necessary function of the powers of
generation, as the production of offspring like their parents. This
view, as we shall see in a future chapter, is not theoretically
probable, though practically it holds good. The saying that “like
begets like” has, in fact, arisen from the perfect confidence felt by
breeders, that a superior or inferior animal will generally reproduce
its kind; but this very superiority or inferiority shows that the
individual in question has departed slightly from its type.
The whole subject of inheritance is wonderful. When a new character
arises, whatever its nature may be, it generally tends to be inherited,
at least in a temporary and sometimes in a most persistent manner. What
can be more wonderful than that some trifling peculiarity, not
primordially attached to the species, should be transmitted through the
male or female sexual cells, which are so minute as not to be visible
to the naked eye, and afterwards through the incessant changes of a
long course of development, undergone either in the womb or in the egg,
and ultimately appear in the offspring when mature, or even when quite
old, as in the case of certain diseases? Or again, what can be more
wonderful than the well-ascertained fact that the minute ovule of a
good milking cow will produce a male, from whom a cell, in union with
an ovule, will produce a female, and she, when mature, will have large
mammary glands, yielding an abundant supply of milk, and even milk of a
particular quality? Nevertheless, the real subject of surprise is, as
Sir H. Holland has well remarked,[1] not that a character should be
inherited, but that any should ever fail to be inherited. In a future
chapter, devoted to an hypothesis which I have termed pangenesis, an
attempt will be made to show the means by which characters of all kinds
are transmitted from generation to generation.
Some writers,[2] who have not attended to natural history, have
attempted to show that the force of inheritance has been much
exaggerated. The breeders of animals would smile at such simplicity;
and if they condescended to make any answer, might ask what would be
the chance of winning a prize if two inferior animals were paired
together? They might ask whether the half-wild Arabs were led by
theoretical notions to keep pedigrees of their horses? Why have
pedigrees been scrupulously kept and published of the Shorthorn cattle,
and more recently of the Hereford breed? Is it an illusion that these
recently improved animals safely transmit their excellent qualities
even when crossed with other breeds? have the Shorthorns, without good
reason, been purchased at immense prices and exported to almost every
quarter of the globe, a thousand guineas having been given for a bull?
With greyhounds pedigrees have likewise been kept, and the names of
such dogs, as Snowball, Major, etc., are as well known to coursers as
those of Eclipse and Herod on the turf. Even with the Gamecock,
pedigrees of famous strains were formerly kept, and extended back for a
century. With pigs, the Yorkshire and Cumberland breeders “preserve and
print pedigrees;” and to show how such highly-bred animals are valued,
I may mention that Mr. Brown, who won all the first prizes for small
breeds at Birmingham in 1850, sold a young sow and boar of his breed to
Lord Ducie for 43 guineas; the sow alone was afterwards sold to the
Rev. F. Thursby for 65 guineas; who writes, “She paid me very well,
having sold her produce for 300 pounds, and having now four breeding
sows from her.”[3] Hard cash paid down, over and over again, is an
excellent test of inherited superiority. In fact, the whole art of
breeding, from which such great results have been attained during the
present century, depends on the inheritance of each small detail of
structure. But inheritance is not certain; for if it were, the
breeder’s art[4] would be reduced to a certainty, and there would be
little scope left for that wonderful skill and perseverance shown by
the men who have left an enduring monument of their success in the
present state of our domesticated animals.
It is hardly possible, within a moderate compass, to impress on the
mind of those who have not attended to the subject, the full conviction
of the force of inheritance which is slowly acquired by rearing
animals, by studying the many treatises which have been published on
the various domestic animals, and by conversing with breeders. I will
select a few facts of the kind, which, as far as I can judge, have most
influenced my own mind. With man and the domestic animals, certain
peculiarities have appeared in an individual, at rare intervals, or
only once or twice in the history of the world, but have reappeared in
several of the children and grandchildren. Thus Lambert, “the
porcupine-man,” whose skin was thickly covered with warty projections,
which were periodically moulted, had all his six children and two
grandsons similarly affected.[5] The face and body being covered with
long hair, accompanied by deficient teeth (to which I shall hereafter
refer), occurred in three successive generations in a Siamese family;
but this case is not unique, as a woman[6] with a completely hairy face
who was exhibited in London in 1663, and another instance has recently
occurred. Colonel Hallam[7] has described a race of two-legged pigs,
“the hinder extremities being entirely wanting;” and this deficiency
was transmitted through three generations. In fact, all races
presenting any remarkable peculiarity, such as solid-hoofed swine,
Mauchamp sheep, niata cattle, etc., are instances of the long-continued
inheritance of rare deviations of structure.
When we reflect that certain extraordinary peculiarities have thus
appeared in a single individual out of many millions, all exposed in
the same country to the same general conditions of life, and, again,
that the same extraordinary peculiarity has sometimes appeared in
individuals living under widely different conditions of life, we are
driven to conclude that such peculiarities are not directly due to the
action of the surrounding conditions, but to unknown laws acting on the
organisation or constitution of the individual;—that their production
stands in hardly closer relation to the conditions of life than does
life itself. If this be so, and the occurrence of the same unusual
character in the child and parent cannot be attributed to both having
been exposed to the same unusual conditions, then the following problem
is worth consideration, as showing that the result cannot be due, as
some authors have supposed, to mere coincidence, but must be consequent
on the members of the same family inheriting something in common in
their constitution. Let it be assumed that, in a large population, a
particular affection occurs on an average in one out of a million, so
that the _à priori_ chance that an individual taken at random will be
so affected is only one in a million. Let the population consist of
sixty millions, composed, we will assume, of ten million families, each
containing six members. On these data, Professor Stokes has calculated
for me that the odds will be no less than 8333 millions to 1 that in
the ten million families there will not be even a single family in
which one parent and two children will be affected by the peculiarity
in question. But numerous instances could be given, in which several
children have been affected by the same rare peculiarity with one of
their parents; and in this case, more especially if the grandchildren
be included in the calculation, the odds against mere coincidence
become something prodigious, almost beyond enumeration.
In some respects the evidence of inheritance is more striking when we
consider the reappearance of trifling peculiarities. Dr. Hodgkin
formerly told me of an English family in which, for many generations,
some members had a single lock differently coloured from the rest of
the hair. I knew an Irish gentleman, who, on the right side of his
head, had a small white lock in the midst of his dark hair: he assured
me that his grandmother had a similar lock on the same side, and his
mother on the opposite side. But it is superfluous to give instances;
every shade of expression, which may often be seen alike in parents and
children, tells the same story. On what a curious combination of
corporeal structure, mental character, and training, handwriting
depends! yet every one must have noted the occasional close similarity
of the handwriting in father and son, although the father had not
taught his son. A great collector of autographs assured me that in his
collection there were several signatures of father and son hardly
distinguishable except by their dates. Hofacker, in Germany, remarks on
the inheritance of handwriting; and it has even been asserted that
English boys when taught to write in France naturally cling to their
English manner of writing; but for so extraordinary a statement more
evidence is requisite.[8] Gait, gestures, voice, and general bearing
are all inherited, as the illustrious Hunter and Sir A. Carlisle have
insisted.[9] My father communicated to me some striking instances, in
one of which a man died during the early infancy of his son, and my
father, who did not see this son until grown up and out of health,
declared that it seemed to him as if his old friend had risen from the
grave, with all his highly peculiar habits and manners. Peculiar
manners pass into tricks, and several instances could be given of their
inheritance; as in the case, often quoted, of the father who generally
slept on his back, with his right leg crossed over the left, and whose
daughter, whilst an infant in the cradle, followed exactly the same
habit, though an attempt was made to cure her.[10] I will give one
instance which has fallen under my own observation, and which is
curious from being a trick associated with a peculiar state of mind,
namely, pleasureable emotion. A boy had the singular habit, when
pleased, of rapidly moving his fingers parallel to each other, and,
when much excited, of raising both hands, with the fingers still
moving, to the sides of his face on a level with the eyes; when this
boy was almost an old man, he could still hardly resist this trick when
much pleased, but from its absurdity concealed it. He had eight
children. Of these, a girl, when pleased, at the age of four and a half
years, moved her fingers in exactly the same way, and what is still
odder, when much excited, she raised both her hands, with her fingers
still moving, to the sides of her face, in exactly the same manner as
her father had done, and sometimes even still continued to do so when
alone. I never heard of any one, excepting this one man and his little
daughter, who had this strange habit; and certainly imitation was in
this instance out of the question.
Some writers have doubted whether those complex mental attributes, on
which genius and talent depend, are inherited, even when both parents
are thus endowed. But he who will study Mr. Galton’s able work on
‘Hereditary Genius’ will have its doubts allayed.
Unfortunately it matters not, as far as inheritance is concerned, how
injurious a quality or structure may be if compatible with life. No one
can read the many treatises[11] on hereditary disease and doubt this.
The ancients were strongly of this opinion, or, as Ranchin expresses
it, _Omnes Grœci, Arabes, et Latini in eo consentiunt._ A long
catalogue could be given of all sorts of inherited malformations and of
predisposition to various diseases. With gout, fifty per cent of the
cases observed in hospital practice are, according to Dr. Garrod,
inherited, and a greater percentage in private practice. Every one
knows how often insanity runs in families, and some of the cases given
by Mr. Sedgwick are awful,—as of a surgeon, whose brother, father, and
four paternal uncles were all insane, the latter dying by suicide; of a
Jew, whose father, mother, and six brothers and sisters were all mad;
and in some other cases several members of the same family, during
three or four successive generations, have committed suicide. Striking
instances have been recorded of epilepsy, consumption, asthma, stone in
the bladder, cancer, profuse bleeding from the slightest injuries, of
the mother not giving milk, and of bad parturition being inherited. In
this latter respect I may mention an odd case given by a good
observer,[12] in which the fault lay in the offspring, and not in the
mother: in a part of Yorkshire the farmers continued to select cattle
with large hind-quarters, until they made a strain called
“Dutch-buttocked,” and “the monstrous size of the buttocks of the calf
was frequently fatal to the cow, and numbers of cows were annually lost
in calving.”
Instead of giving numerous details on various inherited malformations
and diseases, I will confine myself to one organ, that which is the
most complex, delicate, and probably best-known in the human frame,
namely, the eye, with its accessory parts.[13] To begin with the
latter: I have received an account of a family in which one parent and
the children are affected by drooping eyelids, in so peculiar a manner,
that they cannot see without throwing their heads backwards. Mr. Wade,
of Wakefield, has given me an analogous case of a man who had not his
eyelids thus affected at birth, nor owed their state, as far as was
known, to inheritance, but they began to droop whilst he was an infant
after suffering from fits, and he has transmitted the affection to two
out of his three children, as was evident in the photographs of the
whole family sent to me together with this account. Sir A. Carlisle[14]
specifies a pendulous fold to the eyelids, as inherited. “In a family,”
says Sir H. Holland,[15] “where the father had a singular elongation of
the upper eyelid, seven or eight children were born with the same
deformity; two or three other children having it not.” Many persons, as
I hear from Sir J. Paget, have two or three hairs in their eyebrows
much longer than the others; and even so trifling a peculiarity as this
certainly runs in families.
With respect to the eye itself, the highest authority in England, Mr.
Bowman, has been so kind as to give me the following remarks on certain
inherited imperfections. First, hypermetropia, or morbidly long sight:
in this affection, the organ, instead of being spherical, is too flat
from front to back, and is often altogether too small, so that the
retina is brought too forward for the focus of the humours;
consequently a convex glass is required for clear vision of near
objects, and frequently even of distant ones. This state occurs
congenitally, or at a very early age, often in several children of the
same family, where one of the parents has presented it.[16] Secondly,
myopia, or short-sight, in which the eye is egg-shaped and too long
from front to back; the retina in this case lies behind the focus, and
is therefore fitted to see distinctly only very near objects. This
condition is not commonly congenital, but comes on in youth, the
liability to it being well known to be transmissible from parent to
child. The change from the spherical to the ovoidal shape seems the
immediate consequence of something like inflammation of the coats,
under which they yield, and there is ground for believing that it may
often originate in causes acting on the individual affected,[17] and
may thenceforward become transmissible. When both parents are myopic
Mr. Bowman has observed the hereditary tendency in this direction to be
heightened, and some of the children to be myopic at an earlier age or
in a higher degree than their parents. Thirdly, squinting is a familiar
example of hereditary transmission: it is frequently a result of such
optical defects as have been above mentioned; but the more primary and
uncomplicated forms of it are also sometimes in a marked degree
transmitted in a family. Fourthly, _Cataract,_ or opacity of the
crystalline lens, is commonly observed in persons whose parents have
been similarly affected, and often at an earlier age in the children
than in the parents. Occasionally more than one child in a family is
thus afflicted, one of whose parents or other relations, presents the
senile form of the complaint. When cataract affects several members of
a family in the same generation, it is often seen to commence at about
the same age in each: _e.g.,_ in one family several infants or young
persons may suffer from it; in another, several persons of middle age.
Mr. Bowman also informs me that he has occasionally seen, in several
members of the same family, various defects in either the right or left
eye; and Mr. White Cooper has often seen peculiarities of vision
confined to one eye reappearing in the same eye in the offspring.[18]
The following cases are taken from an able paper by Mr. W. Sedgwick,
and from Dr. Prosper Lucas.[19] Amaurosis, either congenital or coming
on late in life, and causing total blindness, is often inherited; it
has been observed in three successive generations. Congenital absence
of the iris has likewise been transmitted for three generations, a
cleft-iris for four generations, being limited in this latter case to
the males of the family. Opacity of the cornea and congenital smallness
of the eyes have been inherited. Portal records a curious case, in
which a father and two sons were rendered blind, whenever the head was
bent downwards, apparently owing to the crystalline lens, with its
capsule, slipping through an unusually large pupil into the anterior
chamber of the eye. Day-blindness, or imperfect vision under a bright
light, is inherited, as is night-blindness, or an incapacity to see
except under a strong light: a case has been recorded, by M. Cunier, of
this latter defect having affected eighty-five members of the same
family during six generations. The singular incapacity of
distinguishing colours, which has been called _Daltonism,_ is
notoriously hereditary, and has been traced through five generations,
in which it was confined to the female sex.
With respect to the colour of the iris: deficiency of colouring matter
is well known to be hereditary in albinoes. The iris of one eye being
of different colour from that of the other, and the iris being spotted,
are cases which have been inherited. Mr. Sedgwick gives, in addition,
on the authority of Dr. Osborne,[20] the following curious instance of
strong inheritance: a family of sixteen sons and five daughters all had
eyes “resembling in miniature the markings on the back of a
tortoiseshell cat.” The mother of this large family had three sisters
and a brother all similarly marked, and they derived this peculiarity
from their mother, who belonged to a family notorious for transmitting
it to their posterity.
Finally, Dr. Lucas emphatically remarks that there is not one single
faculty of the eye which is not subject to anomalies; and not one which
is not subjected to the principle of inheritance. Mr. Bowman agrees
with the general truth of this proposition; which of course does not
imply that all malformations are necessarily inherited; this would not
even follow if both parents were affected by an anomaly which in most
cases was transmissible.
Even if no single fact had been known with respect to the inheritance
of disease and malformations by man, the evidence would have been ample
in the case of the horse. And this might have been expected, as horses
breed much quicker than man, are matched with care, and are highly
valued. I have consulted many works, and the unanimity of the belief by
veterinaries of all nations in the transmission of various morbid
tendencies is surprising. Authors who have had wide experience give in
detail many singular cases, and assert that contracted feet, with the
numerous contingent evils, of ring-bones, curbs, splints, spavin,
founder and weakness of the front legs, roaring or broken and thick
wind, melanosis, specific ophthalmia, and blindness (the great French
veterinary Huzard going so far as to say that a blind race could soon
be formed), crib-biting, jibbing and ill-temper, are all plainly
hereditary. Youatt sums up by saying “there is scarcely a malady to
which the horse is subject which is not hereditary;” and M. Bernard
adds that the doctrine “that there is scarcely a disease which does not
run in the stock, is gaining new advocates every day.”[21] So it is in
regard to cattle, with consumption, good and bad teeth, fine skin, etc.
etc. But enough, and more than enough, has been said on disease. Andrew
Knight, from his own experience, asserts that disease is hereditary
with plants; and this assertion is endorsed by Lindley.[22]
Seeing how hereditary evil qualities are, it is fortunate that good
health, vigour, and longevity are equally inherited. It was formerly a
well-known practice, when annuities were purchased to be received
during the life-time of a nominee, to search out a person belonging to
a family of which many members had lived to extreme old age. As to the
inheritance of vigour and endurance, the English race-horse offers an
excellent instance. Eclipse begot 334, and King Herod 497 winners. A
“cock-tail” is a horse not purely bred, but with only one-eighth, or
one-sixteenth impure blood in his veins, yet very few instances have
ever occurred of such horses having won a great race. They are
sometimes as fleet for short distances as thoroughbreds, but as Mr.
Robson, the great trainer, asserts, they are deficient in wind, and
cannot keep up the pace. Mr. Lawrence also remarks, “perhaps no
instance has ever occurred of a three-part-bred horse saving his _
‘distance’_ in running two miles with thoroughbred racers.” It has been
stated by Cecil, that when unknown horses, whose parents were not
celebrated, have unexpectedly won great races, as in the case of Priam,
they can always be proved to be descended, on both sides, through many
generations, from first-rate ancestors. On the Continent, Baron
Cameronn challenges, in a German veterinary periodical, the opponents
of the English race-horse to name one good horse on the Continent,
which has not some English race-blood in his veins.[23]
With respect to the transmission of the many slight, but infinitely
diversified characters, by which the domestic races of animals and
plants are distinguished, nothing need be said; for the very existence
of persistent races proclaims the power of inheritance.
A few special cases, however, deserve some consideration. It might have
been anticipated, that deviations from the law of symmetry would not
have been inherited. But Anderson[24] states that a rabbit produced in
a litter a young animal having only one ear; and from this animal a
breed was formed which steadily produced one-eared rabbits. He also
mentions a bitch with a single leg deficient, and she produced several
puppies with the same deficiency. From Hofacker’s account,[25] it
appears that a one-horned stag was seen in 1781 in a forest in Germany,
in 1788 two, and afterwards, from year to year, many were observed with
only one horn on the right side of the head. A cow lost a horn by
suppuration,[26] and she produced three calves which had on the same
side of the head, instead of a horn, a small bony lump attached merely
to the skin; but we here encroach on the subject of inherited
mutilations. A man who is left-handed, and a shell in which the spire
turns in the wrong directions, are departures from the normal
asymmetrical condition, and they are well-known to be inherited.
_Polydactylism._—Supernumerary fingers and toes are eminently liable,
as various authors have insisted, to be inherited. Polydactylism
graduates[27] by multifarious steps from a mere cutaneous appendage,
not including any bone, to a double hand. But an additional digit,
supported on a metacarpal bone, and furnished with all the proper
muscles, nerves, and vessels, is sometimes so perfect, that it escapes
detection, unless the fingers are actually counted. Occasionally there
are several supernumerary digits; but usually only one, making the
total number six. This one may be attached to the inner or outer margin
of the hand, representing either a thumb or little finger, the latter
being the more frequent. Generally, through the law of correlation,
both hands and both feet are similarly affected. Dr. Burt Wilder has
tabulated[28] a large number of cases, and finds that supernumerary
digits are more common on the hands than on the feet, and that men are
affected oftener than women. Both these facts can be explained on two
principles which seem generally to hold good; firstly, that of two
parts, the more specialised one is the more variable, and the arm is
more highly specialised than the leg; and secondly that male animals
are more variable than females.
The presence of a greater number of digits than five is a great
anomaly, for this number is not normally exceeded by any existing
mammal, bird, or reptile. Nevertheless, supernumerary digits are
strongly inherited; they have been transmitted through five
generations; and in some cases, after disappearing for one, two, or
even three generations, have reappeared through reversion. These facts
are rendered, as Professor Huxley has observed, more remarkable from
its being known in most cases that the affected person has not married
one similarly affected. In such cases the child of the fifth generation
would have only 1-32nd part of the blood of his first sedigitated
ancestor. Other cases are rendered remarkable by the affection
gathering force, as Dr. Struthers has shown, in each generation, though
in each the affected person married one not affected; moreover, such
additional digits are often amputated soon after birth, and can seldom
have been strengthened by use. Dr. Struthers gives the following
instance: in the first generation an additional digit appeared on one
hand; in the second, on both hands; in the third, three brothers had
both hands, and one of the brothers a foot affected; and in the fourth
generation all four limbs were affected. Yet we must not over-estimate
the force of inheritance. Dr. Struthers asserts that cases of
non-inheritance and of the first appearance of additional digits in
unaffected families are much more frequent than cases of inheritance.
Many other deviations of structure, of a nature almost as anomalous as
supernumerary digits, such as deficient phalanges,[29] thickened
joints, crooked fingers, etc., are, in like manner, strongly inherited,
and are equally subject to intermission, together with reversion,
though in such cases there is no reason to suppose that both parents
had been similarly affected.[30]
Additional digits have been observed in negroes as well as in other
races of man, and in several of the lower animals, and have been
inherited. Six toes have been described on the hind feet of the newt
(_Salamandra cristata_), and are said to have occurred with the frog.
It deserves notice, that the six-toed newt, though adult, preserved
some of its larval characters; for part of the hyoidal apparatus, which
is properly absorbed during the act of metamorphosis, was retained. It
is also remarkable that in the case of man various structures in an
embryonic or arrested state of development, such as a cleft-palate,
bifid uterus, etc., are often accompanied by polydactylism.[31] Six
toes on the hinder feet are known to have been inherited for three
generations of cats. In several breeds of the fowl the hinder toe is
double, and is generally transmitted truly, as is well shown when
Dorkings are crossed with common four-toed breeds.[32] With animals
which have properly less than five digits, the number is sometimes
increased to five, especially on the front legs, though rarely carried
beyond that number; but this is due to the development of a digit
already existing in a more or less rudimentary state. Thus, the dog has
properly four toes behind, but in the larger breeds a fifth toe is
commonly, though not perfectly, developed. Horses, which properly have
one toe alone fully developed with rudiments of the others, have been
described with each foot bearing two or three small separate hoofs:
analogous facts have been noticed with cows, sheep, goats, and
pigs.[33]
There is a famous case described by Mr. White of a child, three years
old, with a thumb double from the first joint. He removed the lesser
thumb, which was furnished with a nail; but to his astonishment it grew
again and reproduced a nail. The child was then taken to an eminent
London surgeon, and the newly-grown thumb was removed by its
socket-joint, but again it grew and reproduced a nail. Dr. Struthers
mentions a case of the partial regrowth of an additional thumb,
amputated when a child was three months old; and the late Dr. Falconer
communicated to me an analogous instance. In the last edition of this
work I also gave a case of the regrowth of a supernumerary
little-finger after amputation; but having been informed by Dr.
Bachmaier that several eminent surgeons expressed, at a meeting of the
Anthropological Society of Munich, great doubt about my statements, I
have made more particular inquiries. The full information thus gained,
together with a tracing of the hand in its present state, has been laid
before Sir J. Paget, and he has come to the conclusion that the degree
of regrowth in this case is not greater than sometimes occurs with
normal bones, especially with the humerus, when amputated at an early
age. He further does not feel fully satisfied about the facts recorded
by Mr. White. This being so, it is necessary for me to withdraw the
view which I formerly advanced, with much hesitation, chiefly on the
ground of the supposed regrowth of additional digits, namely, that
their occasional development in man is a case of reversion to a lowly,
organised progenitor provided with more than five digits.
I may here allude to a class of facts closely allied to, but somewhat
different from, ordinary cases of inheritance. Sir H. Holland[34]
states that brothers and sisters of the same family are frequently
affected, often at about the same age, by the same peculiar disease,
not known to have previously occurred in the family. He specifies the
occurrence of diabetes in three brothers under ten years old; he also
remarks that children of the same family often exhibit in common
infantile diseases, the same peculiar symptoms. My father mentioned to
me the case of four brothers who died between the ages of sixty and
seventy, in the same highly peculiar comatose state. An instance has
already been given of supernumerary digits appearing in four children
out of six in a previously unaffected family. Dr. Devay states[35] that
two brothers married two sisters, their first-cousins, none of the four
nor any relation being an albino; but the seven children produced from
this double marriage were all perfect albinoes. Some of these cases, as
Mr. Sedgwick[36] has shown, are probably the result of reversion to a
remote ancestor, of whom no record had been preserved; and all these
cases are so far directly connected with inheritance that no doubt the
children inherited a similar constitution from their parents, and, from
being exposed to nearly similar conditions of life, it is not
surprising that they should be affected in the same manner and at the
same period of life.
Most of the facts hitherto given have served to illustrate the force of
inheritance, but we must now consider cases grouped as well as the
subject allows into classes, showing how feeble, capricious, or
deficient the power of inheritance sometimes is. When a new peculiarity
first appears, we can never predict whether it will be inherited. If
both parents from their birth present the same peculiarity, the
probability is strong that it will be transmitted to at least some of
their offspring. We have seen that variegation is transmitted much more
feebly by seed, taken from a branch which had become variegated through
bud-variation, than from plants which were variegated as seedlings.
With most plants the power of transmission notoriously depends on some
innate capacity in the individual: thus Vilmorin[37] raised from a
peculiarly coloured balsam some seedlings, which all resembled their
parent; but of these seedlings some failed to transmit the new
character, whilst others transmitted it to all their descendants during
several successive generations. So again with a variety of the rose,
two plants alone out of six were found by Vilmorin to be capable of
transmitting the desired character; numerous analogous cases could be
given.
The weeping or pendulous growth of trees is strongly inherited in some
cases, and, without any assignable reason, feebly in other cases. I
have selected this character as an instance of capricious inheritance,
because it is certainly not proper to the parent-species, and because,
both sexes being borne on the same tree, both tend to transmit the same
character. Even supposing that there may have been in some instances
crossing with adjoining trees of the same species, it is not probable
that all the seedlings would have been thus affected. At Moccas Court
there is a famous weeping oak; many of its branches “are 30 feet long,
and no thicker in any part of this length than a common rope:” this
tree transmits its weeping character, in a greater or less degree, to
all its seedlings; some of the young oaks being so flexible that they
have to be supported by props; others not showing the weeping tendency
till about twenty years old.[38] Mr. Rivers fertilised, as he informs
me, the flowers of a new Belgian weeping thorn (_Cratægus oxyacantha_)
with pollen from a crimson not-weeping variety, and three young trees,
“now six or seven years old, show a decided tendency to be pendulous,
but as yet are not so much so as the mother-plant.” According to Mr.
MacNab,[39] seedlings from a magnificent weeping birch (_Betula alba_),
in the Botanic Garden at Edinburgh, grew for the first ten or fifteen
years upright, but then all became weepers like their parent. A peach
with pendulous branches, like those of the weeping willow, has been
found capable of propagation by seed.[40] Lastly, a weeping or rather a
prostrate yew (_Taxus baccata_) was found in a hedge in Shropshire; it
was a male, but one branch bore female flowers, and produced berries;
these, being sown, produced seventeen trees all of which had exactly
the same peculiar habit with the parent-tree.[41]
These facts, it might have been thought, would have been sufficient to
render it probable that a pendulous habit would in all cases be
strictly inherited. But let us look to the other side. Mr. MacNab[42]
sowed seeds of the weeping beech (_Fagus sylvatica_), but succeeded in
raising only common beeches. Mr. Rivers, at my request, raised a number
of seedlings from three distinct varieties of weeping elm; and at least
one of the parent-trees was so situated that it could not have been
crossed by any other elm; but none of the young trees, now about a foot
or two in height, show the least signs of weeping. Mr. Rivers formerly
sowed above twenty thousand seeds of the weeping ash (_Fraxinus
excelsior_), and not a single seedling was in the least degree
pendulous: in Germany, M. Borchmeyer raised a thousand seedlings, with
the same result. Nevertheless, Mr. Anderson, of the Chelsea Botanic
Garden, by sowing seed from a weeping ash, which was found before the
year 1780, in Cambridgeshire, raised several pendulous trees.[43]
Professor Henslow also informs me that some seedlings from a female
weeping ash in the Botanic Garden at Cambridge were at first a little
pendulous, but afterwards became quite upright: it is probable that
this latter tree, which transmits to a certain extent its pendulous
habit, was derived by a bud from the same original Cambridgeshire
stock; whilst other weeping ashes may have had a distinct origin. But
the crowning case, communicated to me by Mr. Rivers, which shows how
capricious is the inheritance of a pendulous habit, is that a variety
of another species of ash (_F. lentiscifolia_), now about twenty years
old, which was formerly pendulous, “has long lost this habit, every
shoot being remarkably erect; but seedlings formerly raised from it
were perfectly prostrate, the stems not rising more than two inches
above the ground.” Thus the weeping variety of the common ash, which
has been extensively propagated by buds during a long period, did not
with Mr. Rivers, transmit its character to one seedling out of above
twenty thousand; whereas the weeping variety of a second species of
ash, which could not, whilst grown in the same garden, retain its own
weeping character, transmitted to its character the pendulous habit in
excess!
Many analogous facts could be given, showing how apparently capricious
is the principle of inheritance. All the seedlings from a variety of
the Barberry (_B. vulgaris_) with red leaves inherited the same
character; only about one-third of the seedlings of the copper Beech
(_Fagus sylvatica_) had purple leaves. Not one out of a hundred
seedlings of a variety of the _Cerasus padus,_ with yellow fruit, bore
yellow fruit: one-twelfth of the seedlings of the variety of _Cornus
mascula,_ with yellow fruit, came true:[44] and lastly, all the trees
raised by my father from a yellow-berried holly (_Ilex aquifolium_),
found wild, produced yellow berries. Vilmorin[45] observed in a bed of
_Saponaria calabrica_ an extremely dwarf variety, and raised from it a
large number of seedlings; some of these partially resembled their
parent, and he selected their seed; but the grandchildren were not in
the least dwarfed: on the other hand, he observed a stunted and bushy
variety of _Tagetes signata_ growing in the midst of the common
varieties by which it was probably crossed; for most of the seedlings
raised from this plant were intermediate in character, only two
perfectly resembling their parent; but seed saved from these two plants
reproduced the new variety so truly, that hardly any selection has
since been necessary.
Flowers transmit their colour truly, or most capriciously. Many annuals
come true: thus I purchased German seeds of thirty-four named
sub-varieties of one _race_ of ten-week stocks (_Matthiola annua_), and
raised a hundred and forty plants, all of which, with the exception of
a single plant, came true. In saying this, however, it must be
understood that I could distinguish only twenty kinds out of the
thirty-four named sub-varieties; nor did the colour of the flower
always correspond with the name affixed to the packet; but I say that
they came true, because in each of the thirty-six short rows every
plant was absolutely alike, with the one single exception. Again, I
procured packets of German seed of twenty-five named varieties of
common and quilled asters, and raised a hundred and twenty-four plants;
of these, all except ten were true in the above limited sense; and I
considered even a wrong shade of colour as false.
It is a singular circumstance that white varieties generally transmit
their colour much more truly than any other variety. This fact probably
stands in close relation with one observed by Verlot,[46] namely, that
flowers which are normally white rarely vary into any other colour. I
have found that the white varieties of _Delphinium consolida_ and of
the Stock are the truest. It is, indeed, sufficient to look through a
nurseryman’s seed-list, to see the large number of white varieties
which can be propagated by seed. The several coloured varieties of the
sweet-pea (_Lathyrus odoratus_) are very true; but I hear from Mr.
Masters, of Canterbury, who has particularly attended to this plant,
that the white variety is the truest. The hyacinth, when propagated by
seed, is extremely inconstant in colour, but “white hyacinths almost
always give by seed white-flowered plants;”[47] and Mr. Masters informs
me that the yellow varieties also reproduce their colour, but of
different shades. On the other hand, pink and blue varieties, the
latter being the natural colour, are not nearly so true: hence, as Mr.
Masters has remarked to me, “we see that a garden variety may acquire a
more permanent habit than a natural species;” but it should have been
added, that this occurs under cultivation, and therefore under changed
conditions.
With many flowers, especially perennials, nothing can be more
fluctuating than the colour of the seedlings, as is notoriously the
case with verbenas, carnations, dahlias, cinerarias, and others.[48] I
sowed seed of twelve named varieties of Snapdragon (_Antirrhinum
majus_), and utter confusion was the result. In most cases the
extremely fluctuating colour of seedling plants is probably in chief
part due to crosses between differently-coloured varieties during
previous generations. It is almost certain that this is the case with
the polyanthus and coloured primrose (_Primula veris_ and _vulgaris_),
from their reciprocally dimorphic structure;[49] and these are plants
which florists speak of as never coming true by seed: but if care be
taken to prevent crossing, neither species is by any means very
inconstant, in colour; thus I raised twenty-three plants from a purple
primrose, fertilised by Mr. J. Scott with its pollen, and eighteen came
up purple of different shades, and only five reverted to the ordinary
yellow colour: again, I raised twenty plants from a bright-red cowslip,
similarly treated by Mr. Scott, and every one perfectly resembled its
parent in colour, as likewise did, with the exception of a single
plant, 72 grandchildren. Even with the most variable flowers, it is
probable that each delicate shade of colour might be permanently fixed
so as to be transmitted by seed, by cultivation in the same soil, by
long-continued selection, and especially by the prevention of crosses.
I infer this from certain annual larkspurs (_Delphinium consolida_ and
_ajacis_), of which common seedlings present a greater diversity of
colour than any other plant known to me; yet on procuring seed of five
named German varieties of _D. consolida,_ only nine plants out of
ninety-four were false; and the seedlings of six varieties of _D.
ajacis_ were true in the same manner and degree as with the stocks
above described. A distinguished botanist maintains that the annual
species of Delphinium are always self-fertilised; therefore I may
mention that thirty-two flowers on a branch of _ D. consolida,_
enclosed in a net, yielded twenty-seven capsules, with an average of
17·2 seed in each; whilst five flowers, under the same net, which were
artificially fertilised, in the same manner as must be effected by bees
during their incessant visits, yielded five capsules with an average of
35·2 fine seed; and this shows that the agency of insects is necessary
for the full fertility of this plant. Analogous facts could be given
with respect to the crossing of many other flowers, such as carnations,
etc., of which the varieties fluctuate much in colour.
As with flowers, so with our domesticated animals, no character is more
variable than colour, and probably in no animal more so than with the
horse. Yet, with a little care in breeding, it appears that races of
any colour might soon be formed. Hofacker gives the result of matching
two hundred and sixteen mares of four different colours with
like-coloured stallions, without regard to the colour of their
ancestors; and of the two hundred and sixteen colts born, eleven alone
failed to inherit the colour of their parents: Autenrieth and Ammon
assert that, after two generations, colts of a uniform colour are
produced with certainty.[50]
In a few rare cases peculiarities fail to be inherited, apparently from
the force of inheritance being too strong. I have been assured by
breeders of the canary-bird that to get a good jonquil-coloured bird it
does not answer to pair two jonquils, as the colour then comes out too
strong, or is even brown; but this statement is disputed by other
breeders. So again, if two crested canaries are paired, the young birds
rarely inherit this character:[51] for in crested birds a narrow space
of bare skin is left on the back of the head, where the feathers are
up-turned to form the crest, and, when both parents are thus
characterised, the bareness becomes excessive, and the crest itself
fails to be developed. Mr. Hewitt, speaking of Laced Sebright Bantams,
says[52] that, “why this should be so I know not, but I am confident
that those that are best laced frequently produce offspring very far
from perfect in their markings, whilst those exhibited by myself, which
have so often proved successful, were bred from the union of
heavily-laced birds with those that were scarcely sufficiently laced.”
It is a singular fact that, although several deaf-mutes often occur in
the same family, and though their cousins and other relations are often
in the same condition, yet their parents are rarely deaf-mutes. To give
a single instance: not one scholar out of 148, who were at the same
time in the London Institution, was the child of parents similarly
affected. So again, when a male or female deaf-mute marries a sound
person, their children are most rarely affected: in Ireland, out of 203
children thus produced one alone was mute. Even when both parents have
been deaf-mutes, as in the case of forty-one marriages in the United
States and of six in Ireland, only two deaf and dumb children were
produced. Mr. Sedgwick,[53] in commenting on this remarkable and
fortunate failure in the power of transmission in the direct line,
remarks that it may possibly be owing to “excess having reversed the
action of some natural law in development.” But it is safer in the
present state of our knowledge to look at the whole case as simply
unintelligible.
Although many congenital monstrosities are inherited, of which examples
have already been given, and to which may be added the lately recorded
case of the transmission during a century of hare-lip with a
cleft-palate in the writer’s own family,[54] yet other malformations
are rarely or never inherited. Of these latter cases, many are probably
due to injuries in the womb or egg, and would come under the head of
non-inherited injuries or mutilations. With plants, a long catalogue of
inherited monstrosities of the most serious and diversified nature
could easily be given; and with plants, there is no reason to suppose
that monstrosities are caused by direct injuries to the seed or embryo.
With respect to the inheritance of structures mutilated by injuries or
altered by disease, it was until lately difficult to come to any
definite conclusion. Some mutilations have been practised for a vast
number of generations without any inherited result. Godron remarks[55]
that different races of man have from time immemorial knocked out their
upper incisors, cut off joints of their fingers, made holes of immense
size through the lobes of their ears or through their nostrils, tatooed
themselves, made deep gashes in various parts of their bodies, and
there is no reason to suppose that these mutilations have ever been
inherited.[56] Adhesions due to inflammation and pits from the
small-pox (and formerly many consecutive generations must have been
thus pitted) are not inherited. With respect to Jews, I have been
assured by three medical men of the Jewish faith that circumcision,
which has been practised for so many ages, has produced no inherited
effect. Blumenbach, however, asserts[57] that Jews are often born in
Germany in a condition rendering circumcision difficult, so that a name
is given them signifying “born circumcised;” and Professor Preyer
informs me that this is the case in Bonn, such children being
considered the special favourites of Jehovah. I have also heard from
Dr. A. Newman, of Guy’s Hospital, of the grandson of a circumcised Jew,
the father not having been circumcised, in a similar condition. But it
is possible that all these cases may be accidental coincidence, for Sir
J. Paget has seen five sons of a lady and one son of her sister with
adherent prepuces; and one of these boys was affected in a manner
“which might be considered like that commonly produced by
circumcision;” yet there was no suspicion of Jewish blood in the family
of these two sisters. Circumcision is practised by Mahomedans, but at a
much later age than by Jews; and Dr. Riedel, Assistant Resident in
North Celebes, writes to me that the boys there go naked until from six
to ten years old; and he has observed that many of them, though not
all, have their prepuces much reduced in length, and this he attributes
to the inherited effects of the operation. In the vegetable kingdom
oaks and other trees have borne galls from primeval times, yet they do
not produce inherited excrescences; and many other such facts could be
adduced.
Notwithstanding the above several negative cases, we now possess
conclusive evidence that the effects of operations are sometimes
inherited. Dr. Brown-Séquard[58] gives the following summary of his
observations on guinea-pigs; and this summary is so important that I
will quote the whole:—
“1st. Appearance of epilepsy in animals born of parents having been
rendered epileptic by an injury to the spinal cord.
“2nd. Appearance of epilepsy also in animals born of parents having
been rendered epileptic by the section of the sciatic nerve.
“3rd. A change in the shape of the ear in animals born of parents in
which such a change was the effect of a division of the cervical
sympathetic nerve.
“4th. Partial closure of the eyelids in animals born of parents in
which that state of the eyelids had been caused either by the section
of the cervical sympathetic nerve or the removal of the superior
cervical ganglion.
“5th. Exophthalmia in animals born of parents in which an injury to the
restiform body had produced that protrusion of the eyeball. This
interesting fact I have witnessed a good many times, and I have seen
the transmission of the morbid state of the eye continue through four
generations. In these animals, modified by heredity, the two eyes
generally protruded, although in the parents usually only one showed
exophthalmia, the lesion having been made in most cases only on one of
the corpora restiformia.
“6th. Hæmatoma and dry gangrene of the ears in animals born of parents
in which these ear-alterations had been caused by an injury to the
restiform body near the nib of the calamus.
“7th. Absence of two toes out of the three of the hind leg, and
sometimes of the three, in animals whose parents had eaten up their
hind-leg toes which had become anæsthetic from a section of the sciatic
nerve alone, or of that nerve and also of the crural. Sometimes,
instead of complete absence of the toes, only a part of one or two or
three was missing in the young, although in the parent not only the
toes but the whole foot was absent (partly eaten off, partly destroyed
by inflammation, ulceration, or gangrene).
“8th. Appearance of various morbid states of the skin and hair of the
neck and face in animals born of parents having had similar alterations
in the same parts, as effects of an injury to the sciatic nerve.”
It should be especially observed that Brown-Séquard has bred during
thirty years many thousand guinea-pigs from animals which had not been
operated upon, and not one of these manifested the epileptic tendency.
Nor has he ever seen a guinea-pig born without toes, which was not the
offspring of parents which had gnawed off their own toes owing to the
sciatic nerve having been divided. Of this latter fact thirteen
instances were carefully recorded, and a greater number were seen; yet
Brown-Séquard speaks of such cases as one of the rarer forms of
inheritance. It is a still more interesting fact—
“That the sciatic nerve in the congenitally toeless animal has
inherited the power of passing through all the different morbid states
which have occurred in one of its parents from the time of the division
till after its reunion with the peripheric end. It is not therefore
simply the power of performing an action which is inherited, but the
power of performing a whole series of actions, in a certain order.”
In most of the cases of inheritance recorded by Brown-Séquard only one
of the two parents had been operated upon and was affected. He
concludes by expressing his belief that “what is transmitted is the
morbid state of the nervous system,” due to the operation performed on
the parents.
With the lower animals Dr. Prosper Lucas has collected a long list of
inherited injuries. A few instances will suffice. A cow lost a horn
from an accident with consequent suppuration, and she produced three
calves which were hornless on the same side of the head. With the
horse, there seems hardly a doubt that exostoses on the legs, caused by
too much travelling on hard roads, are inherited. Blumenbach records
the case of a man who had his little finger on the right hand almost
cut off, and which in consequence grew crooked, and his sons had the
same finger on the same hand similarly crooked. A soldier, fifteen
years before his marriage, lost his left eye from purulent ophthalmia,
and his two sons were microphthalmic on the same side.[59] In all cases
in which a parent has had an organ injured on one side, and two or more
of the offspring are born with the same organ affected on the same
side, the chances against mere coincidence are almost infinitely great.
Even when only a single child is born having exactly the same part of
the body affected as that of his injured parent, the chances against
coincidence are great; and Professor Rolleston has given me two such
cases which have fallen under his own observation,—namely of two men,
one of whom had his knee and the other his cheek severely cut, and both
had children born with exactly the same spot marked or scarred. Many
instances have been recorded of cats, dogs, and horses, which have had
their tails, legs, etc., amputated or injured, producing offspring with
the same parts ill-formed; but as it is not very rare for similar
malformations to appear spontaneously, all such cases may be due to
coincidence. It is, however, an argument on the other side that “under
the old excise laws the shepherd-dog was only exempt from tax when
without a tail, and for this reason it was always removed;”[60] and
there still exist breeds of the shepherd-dog which are always born
destitute of a tail. Finally, it must be admitted, more especially
since the publication of Brown-Séquard’s observations, that the effects
of injuries, especially when followed by disease, or perhaps
exclusively when thus followed, are occasionally inherited.[61]
_Causes of Non-inheritance._
A large number of cases of non-inheritance are intelligible on the
principle, that a strong tendency to inheritance does exist, but that
it is overborne by hostile or unfavourable conditions of life. No one
would expect that our improved pigs, if forced during several
generations to travel about and root in the ground for their own
subsistence, would transmit, as truly as they now do their short
muzzles and legs, and their tendency to fatten. Dray-horses assuredly
would not long transmit their great size and massive limbs, if
compelled to live on a cold, damp mountainous region; we have indeed
evidence of such deterioration in the horses which have run wild on the
Falkland Islands. European dogs in India often fail to transmit their
true character. Our sheep in tropical countries lose their wool in a
few generations. There seems also to be a close relation between
certain peculiar pastures and the inheritance of an enlarged tail in
fat-tailed sheep, which form one of the most ancient breeds in the
world. With plants, we have seen that tropical varieties of maize lose
their proper character in the course of two or three generations, when
cultivated in Europe; and conversely so it is with European varieties
cultivated in Brazil. Our cabbages, which here come so true by seed,
cannot form heads in hot countries. According to Carrière,[62] the
purple-leafed beech and barberry transmit their character by seed far
less truly in certain districts than in others. Under changed
circumstances, periodical habits of life soon fail to be transmitted,
as the period of maturity in summer and winter wheat, barley, and
vetches. So it is with animals: for instance, a person, whose statement
I can trust, procured eggs of Aylesbury ducks from that town, where
they are kept in houses and are reared as early as possible for the
London market; the ducks bred from these eggs in a distant part of
England, hatched their first brood on January 24th, whilst common
ducks, kept in the same yard and treated in the same manner, did not
hatch till the end of March; and this shows that the period of hatching
was inherited. But the grandchildren of these Aylesbury ducks
completely lost their habit of early incubation, and hatched their eggs
at the same time with the common ducks of the same place.
Many cases of non-inheritance apparently result from the conditions of
life continually inducing fresh variability. We have seen that when the
seeds of pears, plums, apples, etc., are sown, the seedlings generally
inherit some degree of family likeness. Mingled with these seedlings, a
few, and sometimes many, worthless, wild-looking plants commonly
appear, and their appearance may be attributed to the principle of
reversion. But scarcely a single seedling will be found perfectly to
resemble the parent-form; and thus may be accounted for by constantly
recurring variability induced by the conditions of life. I believe in
this, because it has been observed that certain fruit-trees truly
propagate their kind whilst growing on their own roots; but when
grafted on other stocks, and by this process their natural state is
manifestly affected, they produce seedlings which vary greatly,
departing from the parental type in many characters.[63] Metzger, as
stated in the ninth chapter, found that certain kinds of wheat brought
from Spain and cultivated in Germany, failed during many years to
reproduce themselves truly; but at last, when accustomed to their new
conditions, they ceased to be variable,—that is, they became amenable
to the power of inheritance. Nearly all the plants which cannot be
propagated with any approach to certainty by seed, are kinds which have
been long propagated by buds, cuttings, offsets, tubers, etc., and have
in consequence been frequently exposed during what may be called their
individual lives to widely diversified conditions of life. Plants thus
propagated become so variable, that they are subject, as we have seen
in the last chapter, even to bud-variation. Our domesticated animals,
on the other hand, are not commonly exposed during the life of the
individual to such extremely diversified conditions, and are not liable
to such extreme variability; therefore they do not lose the power of
transmitting most of their characteristic features. In the foregoing
remarks on non-inheritance, crossed breeds are of course excluded, as
their diversity mainly depends on the unequal development of character
derived from either parent or their ancestors.
_Conclusion._
It has been shown in the early part of this chapter how commonly new
characters of the most diversified nature, whether normal or abnormal,
injurious or beneficial, whether affecting organs of the highest or
most trifling importance, are inherited. It is often sufficient for the
inheritance of some peculiar character, that one parent alone should
possess it, as in most cases in which the rarer anomalies have been
transmitted. But the power of transmission is extremely variable. In a
number of individuals descended from the same parents, and treated in
the same manner, some display this power in a perfect manner, and in
some it is quite deficient; and for this difference no reason can be
assigned. The effects of injuries or mutilations are occasionally
inherited; and we shall see in a future chapter that the long-continued
use and disuse of parts produces an inherited effect. Even those
characters which are considered the most fluctuating, such as colour,
are with rare exceptions transmitted much more forcibly than is
generally supposed. The wonder, indeed, in all cases is not that any
character should be transmitted, but that the power of inheritance
should ever fail. The checks to inheritance, as far as we know them,
are, firstly, circumstances hostile to the particular character in
question; secondly, conditions of life incessantly inducing fresh
variability; and lastly, the crossing of distinct varieties during some
previous generation, together with reversion or atavism-that is, the
tendency in the child to resemble its grand-parents or more remote
ancestors instead of its immediate parents. This latter subject will be
discussed in the following chapter.
REFERENCES
[1] ‘Medical Notes and Reflections,’ 3rd edit., 1855, p. 267.
[2] Mr. Buckle, in his ‘History of Civilisation,’ expresses doubts on
the subject, owing to the want of statistics. _See also_ Mr. Bowen,
Professor of Moral Philosophy, in ‘Proc. American Acad. of Sciences,’
vol. v. p. 102.
[3] For greyhounds, _see_ Low’s ‘Domestic Animals of the British
Islands,’ 1845, p. 721. For game-fowls, _see_ ‘The Poultry Book,’ by
Mr. Tegetmeier, 1866, p. 123. For pigs, _ see_ Mr. Sidney’s edition of
‘Youatt on the Pig,’ 1860, pp. 11, 22.
[4] ‘The Stud Farm,’ by Cecil, p. 39.
[5] ‘Philosophical Transactions,’ 1755, p. 23. I have seen only
second-hand accounts of the two grandsons. Mr. Sedgwick, in a paper to
which I shall hereafter often refer, states that _ four_ generations
were affected, and in each the males alone.
[6] Barbara Van Beck, figured, as I am informed by the Rev. W.D. Fox,
in Woodburn’s ‘Gallery of Rare Portraits,’ 1816, vol. ii.
[7] ‘Proc. Zoolog. Soc.,’ 1833, p. 16.
[8] Hofacker ‘Ueber die Eigenschaften,’ etc., 1828, s. 34. With
respect to France, Report by Pariset in ‘Comptes Rendus,’ 1847, p.
592.
[9] Hunter, as quoted in Harlan’s ‘Med. Researches,’ p. 530. Sir A.
Carlisle, ‘Phil. Transact.,’ 1814, p. 94.
[10] Girou de Buzareingues, ‘De la Génération,’ p. 282. I have given
an analogous case in my book on ‘The Expression of the Emotions.’
[11] The works which I have read and found most useful are Dr. Prosper
Lucas’s great work, ‘Traité de l’Hérédité Naturelle,’ 1847; Mr. W.
Sedgwick, in ‘British and Foreign Medico-Chirurg. Review,’ April and
July, 1861, and April and July, 1863: Dr. Garrod on Gout is quoted in
these articles. Sir Henry Holland, ‘Medical Notes and Reflections,’
3rd edit., 1855. Piorry, ‘De l’Hérédité dans les Maladies,’ 1840.
Adams, ‘A Philosophical Treatise on Hereditary Peculiarities,’ 2nd
edit., 1815. Essay on ‘Hereditary Diseases,’ by Dr. J. Steinan, 1843.
_See_ Paget in ‘Medical Times,’ 1857, p. 192, on the Inheritance of
Cancer; Dr. Gould, in ‘Proc. of American Acad. of Sciences,’ Nov. 8th,
1853, gives a curious case of hereditary bleeding in four generations.
Harlan, ‘Medical Researches,’ p. 593.
[12] Marshall, quoted by Youatt in his work on Cattle, p. 284.
[13] Almost any other organ might have been selected. For instance Mr.
J. Tomes, ‘System of Dental Surgery,’ 2nd edit., 1873, p. 114, gives
many instances with teeth, and others have been communicated to me.
[14] ‘Philosoph. Transact.,’ 1814, p. 94.
[15] ‘Medical Notes and Reflections,’ 3rd edit., p. 33.
[16] This affection, as I hear from Mr. Bowman, has been ably
described and spoken of as hereditary by Dr. Donders of Utrecht, whose
work was published in English by the Sydenham Society in 1864.
[17] M. Giraud-Teulon has recently collected abundant statistical
evidence, ‘Revue des Cours Scientifiques,’ Sept., 1870, p. 625,
showing that short sight is due to the habit of viewing objects from a
short distance, _c’est le travail assidu, de près._
[18] Quoted by Mr. Herbert Spencer, ‘Principles of Biology,’ vol. i.
p. 244.
[19] ‘British and Foreign Medico-Chirurg. Review,’ April, 1861, pp.
482-6; ‘L’Héréd. Nat.,’ tom. i. pp. 391-408.
[20] Dr. Osborne, Pres. of Royal College of Phys. in Ireland,
published this case in the ‘Dublin Medical Journal,’ for 1835.
[21] These various statements are taken from the following works and
papers:—Youatt on ‘The Horse,’ pp. 35, 220. Lawrence, ‘The Horse,’ p.
30. Karkeek, in an excellent paper in ‘Gard. Chronicle,’ 1853, p. 92.
Mr. Burke, in ‘Journal of R. Agricul. Soc. of England,’ vol. v. p.
511. ‘Encyclop. of Rural Sports,’ p. 279. Girou de Buzareingues,
‘Philosoph. Phys.,’ p. 215. _ See_ following papers in ‘The
Veterinary;’ Roberts in vol. ii. p. 144; M. Marrimpoey vol. ii. p.
387; Mr. Karkeek, vol. iv. p. 5; Youatt on Goitre in Dogs, vol. v. p.
483: Youatt in vol. vi. pp. 66, 348, 412; M. Bernard, vol. xi. p. 539;
Dr. Samesreuther, on Cattle, in vol. xii. p. 181; Percivall, in vol.
xiii. p. 47. With respect to blindness in horses _see also_ a whole
row of authorities in Dr. P. Lucas’s great work, tom. i. p. 399. Mr.
Baker in ‘The Veterinary,’ vol. xiii. p. 721, gives a strong case of
hereditary imperfect vision and of jibbing.
[22] Knight on ‘The Culture of the Apple and Pear,’ p. 34. Lindley’s
‘Horticulture,’ p. 180.
[23] These statements are taken from the following works in
order:—Youatt on ‘The Horse,’ p. 48; Mr. Darvill, in ‘The Veterinary,’
vol. viii. p. 50. With respect to Robson, _see_ ‘The Veterinary,’ vol.
iii. p. 580; Mr. Lawrence on ‘The Horse,’ 1829, p. 9; ‘The Stud Farm,’
by Cecil, 1851; Baron Cameronn, quoted in ‘The Veterinary,’ vol. x. p.
500.
[24] ‘Recreations in Agriculture and Nat. Hist.,’ vol. i. p. 68.
[25] ‘Ueber die Eigenschaften,’ etc., 1828, s. 107.
[26] Bronn’s ‘Geschichte der Natur,’ Band ii. 2 s. 132.
[27] Vrolik has discussed this point at full length in a work
published in Dutch, from which Sir J. Paget has kindly translated for
me passages. _See, also,_ Isidore Geoffroy St. Hilaire’s ‘Hist. des
Anomalies,’ 1832, tom. i. p. 684.
[28] ‘Massachusetts Medical Society,’ vol. ii. No. 3; and ‘Proc.
Boston Soc. of Nat. Hist.,’ vol. xiv. 1871, p. 154.
[29] Dr. J. W. Ogle gives a case of the inheritance of deficient
phalanges during four generations. He adds references to various
recent papers on inheritance, ‘Brit. and For. Med.-Chirurg. Review,’
April 1872.
[30] For these several statements, _see_ Dr. Struthers ‘Edinburgh New
Phil. Journal,’ July, 1863, especially on intermissions in the line of
descent. Prof. Huxley, ‘Lectures on our Knowledge of Organic Nature,’
1863, p. 97. With respect to inheritance, _see_ Dr. Prosper Lucas,
‘L’Hérédité Nat.,’ tom. i. p. 325. Isid. Geoffroy, ‘Anom.,’ tom. i. p.
701. Sir A. Carlisle, in ‘Phil. Transact.,’ 1814, p. 94. A. Walker, on
‘Intermarriage,’ 1838, p. 140, gives a case of five generations; as
does Mr. Sedgwick in ‘Brit. and Foreign Medico-Chirurg. Review,’
April, 1863, p. 462. On the inheritance of other anomalies in the
extremities _see_ Dr. H. Dobell, in vol. xlvi. of ‘Medico-Chirurg.
Transactions,’ 1863; also Mr. Sedgwick in op. cit., April, 1863, p.
460. With respect to additional digits in the negro _see_ Prichard,
‘Physical History of Mankind.’ Dr. Dieffenbach (‘Jour. Royal Geograph.
Soc.,’ 1841, p. 208) says this anomaly is not uncommon with the
Polynesians of the Chatham Islands; and I have heard of several cases
with Hindus and Arabs.
[31] Meckel and Isid G. St. Hilaire insist on this fact. _See also_ M.
A. Roujou, ‘Sur quelques Analogies du Type Humain,’ p. 61; published,
I believe, in the ‘Journal of the Anthropolog. Soc. of Paris,’ Jan.
1872.
[32] ‘The Poultry Chronicle,’ 1854, p. 559.
[33] The statements in this paragraph are taken from Isidore Geoffroy
St. Hilaire, ‘Hist. des Anomalies,’ tom. i. pp. 688-693. Mr. Goodman
gives, ‘Phil. Soc. of Cambridge,’ Nov. 25th, 1872, the case of a cow
with three well developed toes on each hind limb, besides the ordinary
rudiments; and her calf by an ordinary bull had extra digits. This
calf also bore two calves having extra digits.
[34] ‘Medical Notes and Reflections,’ 1839, pp. 24, 34. _See also_ Dr.
P. Lucas, ‘L’Héréd. Nat.,’ tom. ii. p. 33.
[35] ‘Du Danger des Mariages Consanguins,’ 2nd edit., 1862, p. 103.
[36] ‘British and Foreign Medico-Chirurg. Review,’ July, 1863, pp.
183, 189.
[37] Verlot ‘La Product. des Variétés,’ 1865, p. 32.
[38] Loudon’s ‘Gardener’s Mag.,’ vol. xii. 1836, p. 368.
[39] Verlot, ‘La Product. des Variétés,’ 1865, p. 94.
[40] Bronn’s ‘Geschichte der Natur,’ B. ii. s. 121. Mr. Meehan makes a
similar statement in ‘Proc. Nat. of Philadelphia,’ 1872, p. 235.
[41] Rev. W. A. Leighton, ‘Flora of Shropshire,’ p. 497; and
Charlesworth, ‘Mag. of Nat. Hist.,’ vol. i. 1837, p. 30. I possess
prostrate trees produced from these seeds.
[42] Verlot, op. cit., p. 93.
[43] For these several statements, _see_ Loudon’s ‘Gard. Magazine,’
vol. x. 1834, pp. 408, 180; and vol. ix. 1833, p. 597.
[44] These statements are taken from Alph. De Candolle, ‘Bot.
Géograph.,’ p. 1083.
[45] Verlot, op. cit., p. 38.
[46] Op. cit., p. 59.
[47] Alph. De Candolle, ‘Géograph. Bot.,’ p. 1082.
[48] _See_ ‘Cottage Gardener,’ April 10th, 1860, p. 18, and Sept.
10th, 1861, p. 456; ‘Gardener’s Chronicle,’ 1845, p. 102.
[49] Darwin in ‘Journal of Proc. Linn. Soc. Bot.,’ 1862, p. 94.
[50] Hofacker, ‘Ueber die Eigenschaften,’ etc., s. 10.
[51] Bechstein, ‘Naturgesch. Deutschlands,’ B. iv. s. 462. Mr. Brent,
a great breeder of canaries, informs me that he believes that these
statements are correct.
[52] ‘The Poultry Book,’ by W. B. Tegetmeier, 1866, p. 245.
[53] ‘British and Foreign Med.-Chirurg. Review,’ July, 1861, pp.
200-204. Mr. Sedgwick has given such full details on this subject,
with ample references, that I need refer to no other authorities.
[54] Mr. Sproule, in ‘British Medical Journal,’ April 18th, 1863.
[55] ‘De l’Espèce,’ tom. ii. 1859, p. 299.
[56] Nevertheless Mr. Wetherell states, ‘Nature,’ Dec. 1870, p. 168,
that when he visited fifteen years ago the Sioux Indians, he was
informed “by a physician, who has passed much of his time with these
tribes, that sometimes a child was born with these marks. This was
confirmed by the U.S. Government Indian Agent.”
[57] ‘Philosoph. Mag.,’ vol. iv. 1799, p. 5.
[58] ‘Proc. Royal Soc.,’ vol. x. p. 297. ‘Communication to the Brit.
Assoc.,’ 1870. ‘The Lancet,’ Jan. 1875, p. 7. The extracts are from
this last paper. It appears that Obersteiner, ‘Stricker’s Med.
Jahrbücher,’ 1875, No. 2, has confirmed Brown-Séquard’s observations.
[59] This last case is quoted by Mr. Sedgwick in ‘British and Foreign
Medico-Chirurg. Review,’ April, 1861, p. 484. For Blumenbach, _see_
above-cited paper. _See also_ Dr. P. Lucas, ‘Traité de l’Héréd. Nat.,’
tom. ii. p. 492. Also, ‘Transact. Linn. Soc.,’ vol. ix. p. 323. Some
curious cases are given by Mr. Baker in the ‘Veterinary,’ vol. xiii.
p. 723. Another curious case is given in the ‘Annales des Scienc.
Nat.,’ 1st series, tom. xi. p. 324.
[60] ‘The Dog,’ by Stonehenge, 1867, p. 118.
[61] The Mot-mot habitually bites the barbs off the middle part of the
two central tail-feathers, and as the barbs are congenitally somewhat
reduced on the same part of these feathers, it seems extremely
probable, as Mr. Salvin remarks (‘Proc. Zoolog. Soc.’ 1873, p. 429),
that this is due to the inherited effects of long-continued
mutilation.
[62] ‘Production et Fixation des Variétés,’ 1865, p. 72.
[63] Downing, ‘Fruits of America,’ p. 5: Sageret, ‘Pom. Phys.,’ pp.
43, 72.