- Causes
of Variability
- Effects
of Habit
- Correlation
of Growth
- Inheritance
- Character
of Domestic Varieties
- Difficulty
of distinguishing between
Varieties and Species
- Origin
of Domestic Varieties from
one or more Species
- Domestic
pigeons, their
Differences and Origin
- Principle
of Selection
anciently followed, its Effects
- Methodical
and Unconscious Selection
- Unknown
Origin of our Domestic Productions
- Circumstances
favourable to Man's
power of
Selection
WHEN we look to the individuals
of the same variety or sub-variety
of our older cultivated plants
and animals, one of the first
points which strikes us, is,
that they generally differ much
more from each other, than do
the individuals of any one species
or variety in a state of nature.
When we reflect on the vast diversity
of the plants and animals which
have been cultivated, and which
have varied during all ages under
the most different climates and
treatment, I think we are driven
to conclude that this greater
variability is simply due to
our domestic productions having
been raised under conditions
of life not so uniform as, and
somewhat different from, those
to which the parent-species have
been exposed under nature. There
is, also, I think, some probability
in the view propounded by Andrew
Knight, that this variability
may be partly connected with
excess of food. It seems pretty
clear that organic beings must
be exposed during several generations
to the new conditions of life
to cause any appreciable amount
of variation; and that when the
organisation has once begun to
vary, it generally continues
to vary for many generations.
No case is on record of a variable
being ceasing to be variable
under cultivation. Our oldest
cultivated plants, such as wheat,
still often yield new varieties:
our oldest domesticated animals
are still capable of rapid improvement
or modification.
It has been disputed at what
period of time the causes of
variability, whatever they may
be, generally act; whether during
the early or late period of development
of the embryo, or at the instant
of conception. Geoffroy St Hilaire's
experiments show that unnatural
treatment of the embryo causes
monstrosities; and monstrosities
cannot be separated by any clear
line of distinction from mere
variations. But I am strongly
inclined to suspect that the
most frequent cause of variability
may be attributed to the male
and female reproductive elements
having been affected prior to
the act of conception. Several
reasons make me believe in this;
but the chief one is the remarkable
effect which confinement or cultivation
has on the functions of the reproductive
system; this system appearing
to be far more susceptible than
any other part of the organization,
to the action of any change in
the conditions of life. Nothing
is more easy than to tame an
animal, and few things more difficult
than to get it to breed freely
under confinement, even in the
many cases when the male and
female unite. How many animals
there are which will not breed,
though living long under not
very close confinement in their
native country! This is generally
attributed to vitiated instincts;
but how many cultivated plants
display the utmost vigour, and
yet rarely or never seed! In
some few such cases it has been
found out that very trifling
changes, such as a little more
or less water at some particular
period of growth, will determine
whether or not the plant sets
a seed. I cannot here enter on
the copious details which I have
collected on this curious subject;
but to show how singular the
laws are which determine the
reproduction of animals under
confinement, I may just mention
that carnivorous animals, even
from the tropics, breed in this
country pretty freely under confinement,
with the exception of the plantigrades
or bear family; whereas, carnivorous
birds, with the rarest exceptions,
hardly ever lay fertile eggs.
Many exotic plants have pollen
utterly worthless, in the same
exact condition as in the most
sterile hybrids. When, on the
one hand, we see domesticated
animals and plants, though often
weak and sickly, yet breeding
quite freely under confinement;
and when, on the other hand,
we see individuals, though taken
young from a state of nature,
perfectly tamed, long-lived,
and healthy (of which I could
give numerous instances), yet
having their reproductive system
so seriously affected by unperceived
causes as to fail in acting,
we need not be surprised at this
system, when it does act under
confinement, acting not quite
regularly, and producing offspring
not perfectly like their parents
or variable.
Sterility has been said to
be the bane of horticulture;
but on this view we owe variability
to the same cause which produces
sterility; and variability is
the source of all the choicest
productions of the garden. I
may add, that as some organisms
will breed most freely under
the most unnatural conditions
(for instance, the rabbit and
ferret kept in hutches), showing
that their reproductive system
has not been thus affected; so
will some animals and plants
withstand domestication or cultivation,
and vary very slightly perhaps
hardly more than in a state of
nature.
A long list
could easily be given of 'sporting
plants;' by
this term gardeners mean a single
bud or offset, which suddenly
assumes a new and sometimes very
different character from that
of the rest of the plant. Such
buds can be propagated by grafting, &c.,
and sometimes by seed. These
'sports' are extremely rare under
nature, but far from rare under
cultivation; and in this case
we see that the treatment of
the parent has affected a bud
or offset, and not the ovules
or pollen. But it is the opinion
of most physiologists that there
is no essential difference between
a bud and an ovule in their earliest
stages of formation; so that,
in fact,'sports' support my view,
that variability may be largely
attributed to the ovules or pollen,
or to both, having been affected
by the treatment of the parent
prior to the act of conception.
These cases anyhow show that
variation is not necessarily
connected, as some authors have
supposed, with the act of generation.
Seedlings from
the same fruit, and the young
of the same litter,
sometimes differ considerably
from each other, though both
the young and the parents, as
Muller has remarked, have apparently
been exposed to exactly the same
conditions of life; and this
shows how unimportant the direct
effects of the conditions of
life are in comparison with the
laws of reproduction, and of
growth, and of inheritance; for
had the action of the conditions
been direct, if any of the young
had varied, all would probably
have varied in the same manner.
To judge how much, in the case
of any variation, we should attribute
to the direct action of heat,
moisture, light, food, &c.,
is most difficult: my impression
is, that with animals such agencies
have produced very little direct
effect, though apparently more
in the case of plants. Under
this point of view, Mr Buckman's
recent experiments on plants
seem extremely valuable. When
all or nearly all the individuals
exposed to certain conditions
are affected in the same way,
the change at first appears to
be directly due to such conditions;
but in some cases it can be shown
that quite opposite conditions
produce similar changes of structure.
Nevertheless some slight amount
of change may, I think, be attributed
to the direct action of the conditions
of life as, in some cases, increased
size from amount of food, colour
from particular kinds of food
and from light, and perhaps the
thickness of fur from climate.
Habit also has a deciding influence,
as in the period of flowering
with plants when transported
from one climate to another.
In animals it has a more marked
effect; for instance, I find
in the domestic duck that the
bones of the wing weigh less
and the bones of the leg more,
in proportion to the whole skeleton,
than do the same bones in the
wild-duck; and I presume that
this change may be safely attributed
to the domestic duck flying much
less, and walking more, than
its wild parent. The great and
inherited development of the
udders in cows and goats in countries
where they are habitually milked,
in comparison with the state
of these organs in other countries,
is another instance of the effect
of use. Not a single domestic
animal can be named which has
not in some country drooping
ears; and the view suggested
by some authors, that the drooping
is due to the disuse of the muscles
of the ear, from the animals
not being much alarmed by danger,
seems probable.
There are many laws regulating
variation, some few of which
can be dimly seen, and will be
hereafter briefly mentioned.
I will here only allude to what
may be called correlation of
growth. Any change in the embryo
or larva will almost certainly
entail changes in the mature
animal. In monstrosities, the
correlations between quite distinct
parts are very curious; and many
instances are given in Isidore
Geoffroy St Hilaire's great work
on this subject. Breeders believe
that long limbs are almost always
accompanied by an elongated head.
Some instances of correlation
are quite whimsical; thus cats
with blue eyes are invariably
deaf; colour and constitutional
peculiarities go together, of
which many remarkable cases could
be given amongst animals and
plants. From the facts collected
by Heusinger, it appears that
white sheep and pigs are differently
affected from coloured individuals
by certain vegetable poisons.
Hairless dogs have imperfect
teeth; long-haired and coarse-haired
animals are apt to have, as is
asserted, long or many horns;
pigeons with feathered feet have
skin between their outer toes;
pigeons with short beaks have
small feet, and those with long
beaks large feet. Hence, if man
goes on selecting, and thus augmenting,
any peculiarity, he will almost
certainly unconsciously modify
other parts of the structure,
owing to the mysterious laws
of the correlation of growth.
The result
of the various, quite unknown,
or dimly seen
laws of variation is infinitely
complex and diversified. It is
well worth while carefully to
study the several treatises published
on some of our old cultivated
plants, as on the hyacinth, potato,
even the dahlia, &c.; and
it is really surprising to note
the endless points in structure
and constitution in which the
varieties and sub varieties differ
slightly from each other. The
whole organization seems to have
become plastic, and tends to
depart in some small degree from
that of the parental type.
Any variation
which is not inherited is unimportant
for
us. But the number and diversity
of inheritable deviations of
structure, both those of slight
and those of considerable physiological
importance, is endless. Dr Prosper
Lucas's treatise, in two large
volumes, is the fullest and the
best on this subject. No breeder
doubts how strong is the tendency
to inheritance: like produces
like is his fundamental belief:
doubts have been thrown on this
principle by theoretical writers
alone. When a deviation appears
not unfrequently, and we see
it in the father and child, we
cannot tell whether it may not
be due to the same original cause
acting on both; but when amongst
individuals, apparently exposed
to the same conditions, any very
rare deviation, due to some extraordinary
combination of circumstances,
appears in the parent say, once
amongst several million individuals
and it reappears in the child,
the mere doctrine of chances
almost compels us to attribute
its reappearance to inheritance.
Every one must have heard of
cases of albinism, prickly skin,
hairy bodies, &c. appearing
in several members of the same
family. If strange and rare deviations
of structure are truly inherited,
less strange and commoner deviations
may be freely admitted to be
inheritable. Perhaps the correct
way of viewing the whole subject,
would be, to look at the inheritance
of every character whatever as
the rule, and non-inheritance
as the anomaly.
The laws governing inheritance
are quite unknown; no one can
say why the same peculiarity
in different individuals of the
same species, and in individuals
of different species, is sometimes
inherited and sometimes not so;
why the child often reverts in
certain characters to its grandfather
or grandmother or other much
more remote ancestor; why a peculiarity
is often transmitted from one
sex to both sexes or to one sex
alone, more commonly but not
exclusively to the like sex.
It is a fact of some little importance
to us, that peculiarities appearing
in the males of our domestic
breeds are often transmitted
either exclusively, or in a much
greater degree, to males alone.
A much more important rule, which
I think may be trusted, is that,
at whatever period of life a
peculiarity first appears, it
tends to appear in the offspring
at a corresponding age, though
sometimes earlier. In many cases
this could not be otherwise:
thus the inherited peculiarities
in the horns of cattle could
appear only in the offspring
when nearly mature; peculiarities
in the silkworm are known to
appear at the corresponding caterpillar
or cocoon stage. But hereditary
diseases and some other facts
make me believe that the rule
has a wider extension, and that
when there is no apparent reason
why a peculiarity should appear
at any particular age, yet that
it does tend to appear in the
offspring at the same period
at which it first appeared in
the parent. I believe this rule
to be of the highest importance
in explaining the laws of embryology.
These remarks are of course confined
to the first appearance of
the peculiarity, and not to its
primary cause, which may have
acted on the ovules or male element;
in nearly the same manner as
in the crossed offspring from
a short-horned cow by a long-horned
bull, the greater length of horn,
though appearing late in life,
is clearly due to the male element.
Having alluded to the subject
of reversion, I may here refer
to a statement often made by
naturalists namely, that our
domestic varieties, when run
wild, gradually but certainly
revert in character to their
aboriginal stocks. Hence it has
been argued that no deductions
can be drawn from domestic races
to species in a state of nature.
I have in vain endeavoured to
discover on what decisive facts
the above statement has so often
and so boldly been made. There
would be great difficulty in
proving its truth: we may safely
conclude that very many of the
most strongly-marked domestic
varieties could not possibly
live in a wild state. In many
cases we do not know what the
aboriginal stock was, and so
could not tell whether or not
nearly perfect reversion had
ensued. It would be quite necessary,
in order to prevent the effects
of intercrossing, that only a
single variety should be turned
loose in its new home. Nevertheless,
as our varieties certainly do
occasionally revert in some of
their characters to ancestral
forms, it seems to me not improbable,
that if we could succeed in naturalising,
or were to cultivate, during
many generations, the several
races, for instance, of the cabbage,
in very poor soil (in which case,
however, some effect would have
to be attributed to the direct
action of the poor soil), that
they would to a large extent,
or even wholly, revert to the
wild aboriginal stock. Whether
or not the experiment would succeed,
is not of great importance for
our line of argument; for by
the experiment itself the conditions
of life are changed. If it could
be shown that our domestic varieties
manifested a strong tendency
to reversion, that is, to lose
their acquired characters, whilst
kept under unchanged conditions,
and whilst kept in a considerable
body, so that free intercrossing
might check, by blending together,
any slight deviations of structure,
in such case, I grant that we
could deduce nothing from domestic
varieties in regard to species.
But there is not a shadow of
evidence in favour of this view:
to assert that we could not breed
our cart and race-horses, long
and short-horned cattle and poultry
of various breeds, and esculent
vegetables, for an almost infinite
number of generations, would
be opposed to all experience.
I may add, that when under nature
the conditions of life do change,
variations and reversions of
character probably do occur;
but natural selection, as will
hereafter be explained, will
determine how far the new characters
thus arising shall be preserved.
When we look to the hereditary
varieties or races of our domestic
animals and plants, and compare
them with species closely allied
together, we generally perceive
in each domestic race, as already
remarked, less uniformity of
character than in true species.
Domestic races of the same species,
also, often have a somewhat monstrous
character; by which I mean, that,
although differing from each
other, and from the other species
of the same genus, in several
trifling respects, they often
differ in an extreme degree in
some one part, both when compared
one with another, and more especially
when compared with all the species
in nature to which they are nearest
allied. With these exceptions
(and with that of the perfect
fertility of varieties when crossed,
a subject hereafter to be discussed),
domestic races of the same species
differ from each other in the
same manner as, only in most
cases in a lesser degree than,
do closely-allied species of
the same genus in a state of
nature. I think this must be
admitted, when we find that there
are hardly any domestic races,
either amongst animals or plants,
which have not been ranked by
some competent judges as mere
varieties, and by other competent
judges as the descendants of
aboriginally distinct species.
If any marked distinction existed
between domestic races and species,
this source of doubt could not
so perpetually recur. It has
often been stated that domestic
races do not differ from each
other in characters of generic
value. I think it could be shown
that this statement is hardly
correct; but naturalists differ
most widely in determining what
characters are of generic value;
all such valuations being at
present empirical. Moreover,
on the view of the origin of
genera which I shall presently
give, we have no right to expect
often to meet with generic differences
in our domesticated productions.
When we attempt to estimate
the amount of structural difference
between the domestic races of
the same species, we are soon
involved in doubt, from not knowing
whether they have descended from
one or several parent-species.
This point, if could be cleared
up, would be interesting; if,
for instance, it could be shown
that the greyhound, bloodhound,
terrier, spaniel, and bull-dog,
which we all know propagate their
kind so truly, were the offspring
of any single species, then such
facts would have great weight
in making us doubt about the
immutability of the many very
closely allied and natural species
for instance, of the many foxes
inhabiting different quarters
of the world. I do not believe,
as we shall presently see, that
all our dogs have descended from
any one wild species; but, in
the case of some other domestic
races, there is presumptive,
or even strong, evidence in favour
of this view.
It has often been assumed that
man has chosen for domestication
animals and plants having an
extraordinary inherent tendency
to vary, and likewise to withstand
diverse climates. I do not dispute
that these capacities have added
largely to the value of most
of our domesticated productions;
but how could a savage possibly
know, when he first tamed an
animal, whether it would vary
in succeeding generations, and
whether it would endure other
climates? Has the little variability
of the ass or guinea-fowl, or
the small power of endurance
of warmth by the reindeer, or
of cold by the common camel,
prevented their domestication?
I cannot doubt that if other
animals and plants, equal in
number to our domesticated productions,
and belonging to equally diverse
classes and countries, were taken
from a state of nature, and could
be made to breed for an equal
number of generations under domestication,
they would vary on an average
as largely as the parent species
of our existing domesticated
productions have varied.
In the case of most of our
anciently domesticated animals
and plants, I do not think it
is possible to come to any definite
conclusion, whether they have
descended from one or several
species. The argument mainly
relied on by those who believe
in the multiple origin of our
domestic animals is, that we
find in the most ancient records,
more especially on the monuments
of Egypt, much diversity in the
breeds; and that some of the
breeds closely resemble, perhaps
are identical with, those still
existing. Even if this latter
fact were found more strictly
and generally true than seems
to me to be the case, what does
it show, but that some of our
breeds originated there, four
or five thousand years ago? But
Mr Horner's researches have rendered
it in some degree probable that
man sufficiently civilized to
have manufactured pottery existed
in the valley of the Nile thirteen
or fourteen thousand years ago;
and who will pretend to say how
long before these ancient periods,
savages, like those of Tierra
del Fuego or Australia, who possess
a semi-domestic dog, may not
have existed in Egypt?
The whole subject
must, I think, remain vague;
nevertheless, I
may, without here entering on
any details, state that, from
geographical and other considerations,
I think it highly probable that
our domestic dogs have descended
from several wild species. In
regard to sheep and goats I can
form no opinion. I should think,
from facts communicated to me
by Mr Blyth, on the habits, voice,
and constitution, &c., of
the humped Indian cattle, that
these had descended from a different
aboriginal stock from our European
cattle; and several competent
judges believe that these latter
have had more than one wild parent.
With respect to horses, from
reasons which I cannot give here,
I am doubtfully inclined to believe,
in opposition to several authors,
that all the races have descended
from one wild stock. Mr Blyth,
whose opinion, from his large
and varied stores of knowledge,
I should value more than that
of almost any one, thinks that
all the breeds of poultry have
proceeded from the common wild
Indian fowl (Gallus bankiva).
In regard to ducks and rabbits,
the breeds of which differ considerably
from each other in structure,
I do not doubt that they all
have descended from the common
wild duck and rabbit.
The doctrine
of the origin of our several
domestic races
from several aboriginal stocks,
has been carried to an absurd
extreme by some authors. They
believe that every race which
breeds true, let the distinctive
characters be ever so slight,
has had its wild prototype. At
this rate there must have existed
at least a score of species of
wild cattle, as many sheep, and
several goats in Europe alone,
and several even within Great
Britain. One author believes
that there formerly existed in
Great Britain eleven wild species
of sheep peculiar to it! When
we bear in mind that Britain
has now hardly one peculiar mammal,
and France but few distinct from
those of Germany and conversely,
and so with Hungary, Spain, &c.,
but that each of these kingdoms
possesses several peculiar breeds
of cattle, sheep, &c., we
must admit that many domestic
breeds have originated in Europe;
for whence could they have been
derived, as these several countries
do not possess a number of peculiar
species as distinct parent-stocks?
So it is in India. Even in the
case of the domestic dogs of
the whole world, which I fully
admit have probably descended
from several wild species, I
cannot doubt that there has been
an immense amount of inherited
variation. Who can believe that
animals closely resembling the
Italian greyhound, the bloodhound,
the bull-dog, or Blenheim spaniel, &c.
so unlike all wild Canidae ever
existed freely in a state of
nature? It has often been loosely
said that all our races of dogs
have been produced by the crossing
of a few aboriginal species;
but by crossing we can get only
forms in some degree intermediate
between their parents; and if
we account for our several domestic
races by this process, we must
admit the former existence of
the most extreme forms, as the
Italian greyhound, bloodhound,
bull-dog, &c., in the wild
state. Moreover, the possibility
of making distinct races by crossing
has been greatly exaggerated.
There can be no doubt that a
race may be modified by occasional
crosses, if aided by the careful
selection of those individual
mongrels, which present any desired
character; but that a race could
be obtained nearly intermediate
between two extremely different
races or species, I can hardly
believe. Sir J. Sebright expressly
experimentised for this object,
and failed. The offspring from
the first cross between two pure
breeds is tolerably and sometimes
(as I have found with pigeons)
extremely uniform, and everything
seems simple enough; but when
these mongrels are crossed one
with another for several generations,
hardly two of them will be alike,
and then the extreme difficulty,
or rather utter hopelessness,
of the task becomes apparent.
Certainly, a breed intermediate
between two very distinct breeds
could not be got without extreme
care and long-continued selection;
nor can I find a single case
on record of a permanent race
having been thus formed.
On the Breeds of the Domestic
pigeon.
Believing that it is always
best to study some special group,
I have, after deliberation, taken
up domestic pigeons. I have kept
every breed which I could purchase
or obtain, and have been most
kindly favoured with skins from
several quarters of the world,
more especially by the Hon. W.
Elliot from India, and by the
Hon. C. Murray from Persia. Many
treatises in different languages
have been published on pigeons,
and some of them are very important,
as being of considerably antiquity.
I have associated with several
eminent fanciers, and have been
permitted to join two of the
London Pigeon Clubs. The diversity
of the breeds is something astonishing.
Compare the English carrier and
the short-faced tumbler, and
see the wonderful difference
in their beaks, entailing corresponding
differences in their skulls.
The carrier, more especially
the male bird, is also remarkable
from the wonderful development
of the carunculated skin about
the head, and this is accompanied
by greatly elongated eyelids,
very large external orifices
to the nostrils, and a wide gape
of mouth. The short-faced tumbler
has a beak in outline almost
like that of a finch; and the
common tumbler has the singular
and strictly inherited habit
of flying at a great height in
a compact flock, and tumbling
in the air head over heels. The
runt is a bird of great size,
with long, massive beak and large
feet; some of the sub-breeds
of runts have very long necks,
others very long wings and tails,
others singularly short tails.
The barb is allied to the carrier,
but, instead of a very long beak,
has a very short and very broad
one. The pouter has a much elongated
body, wings, and legs; and its
enormously developed crop, which
it glories in inflating, may
well excite astonishment and
even laughter. The turbit has
a very short and conical beak,
with a line of reversed feathers
down the breast; and it has the
habit of continually expanding
slightly the upper part of the
oesophagus. The Jacobin has the
feathers so much reversed along
the back of the neck that they
form a hood, and it has, proportionally
to its size, much elongated wing
and tail feathers. The trumpeter
and laugher, as their names express,
utter a very different coo from
the other breeds. The fantail
has thirty or even forty tail-feathers,
instead of twelve or fourteen,
the normal number in all members
of the great pigeon family; and
these feathers are kept expanded,
and are carried so erect that
in good birds the head and tail
touch; the oil-gland is quite
aborted. Several other less distinct
breeds might have been specified.
In the skeletons of the several
breeds, the development of the
bones of the face in length and
breadth and curvature differs
enormously. The shape, as well
as the breadth and length of
the ramus of the lower jaw, varies
in a highly remarkable manner.
The number of the caudal and
sacral vertebrae vary; as does
the number of the ribs, together
with their relative breadth and
the presence of processes. The
size and shape of the apertures
in the sternum are highly variable;
so is the degree of divergence
and relative size of the two
arms of the furcula. The proportional
width of the gape of mouth, the
proportional length of the eyelids,
of the orifice of the nostrils,
of the tongue (not always in
strict correlation with the length
of beak), the size of the crop
and of the upper part of the
oesophagus; the development and
abortion of the oil-gland; the
number of the primary wing and
caudal feathers; the relative
length of wing and tail to each
other and to the body; the relative
length of leg and of the feet;
the number of scutellae on the
toes, the development of skin
between the toes, are all points
of structure which are variable.
The period at which the perfect
plumage is acquired varies, as
does the state of the down with
which the nestling birds are
clothed when hatched. The shape
and size of the eggs vary. The
manner of flight differs remarkably;
as does in some breeds the voice
and disposition. Lastly, in certain
breeds, the males and females
have come to differ to a slight
degree from each other.
Altogether at least a score
of pigeons might be chosen, which
if shown to an ornithologist,
and he were told that they were
wild birds, would certainly,
I think, be ranked by him as
well-defined species. Moreover,
I do not believe that any ornithologist
would place the English carrier,
the short-faced tumbler, the
runt, the barb, pouter, and fantail
in the same genus; more especially
as in each of these breeds several
truly-inherited sub-breeds, or
species as he might have called
them, could be shown him.
Great as the differences are
between the breeds of pigeons,
I am fully convinced that the
common opinion of naturalists
is correct, namely, that all
have descended from the rock-pigeon
(Columba livia), including under
this term several geographical
races or sub-species, which differ
from each other in the most trifling
respects. As several of the reasons
which have led me to this belief
are in some degree applicable
in other cases, I will here briefly
give them. If the several breeds
are not varieties, and have not
proceeded from the rock-pigeon,
they must have descended from
at least seven or eight aboriginal
stocks; for it is impossible
to make the present domestic
breeds by the crossing of any
lesser number: how, for instance,
could a pouter be produced by
crossing two breeds unless one
of the parent-stocks possessed
the characteristic enormous crop?
The supposed aboriginal stocks
must all have been rock-pigeons,
that is, not breeding or willingly
perching on trees. But besides
C. livia, with its geographical
sub-species, only two or three
other species of rock-pigeons
are known; and these have not
any of the characters of the
domestic breeds. Hence the supposed
aboriginal stocks must either
still exist in the countries
where they were originally domesticated,
and yet be unknown to ornithologists;
and this, considering their size,
habits, and remarkable characters,
seems very improbable; or they
must have become extinct in the
wild state. But birds breeding
on precipices, and good fliers,
are unlikely to be exterminated;
and the common rock-pigeon, which
has the same habits with the
domestic breeds, has not been
exterminated even on several
of the smaller British islets,
or on the shores of the Mediterranean.
Hence the supposed extermination
of so many species having similar
habits with the rock-pigeon seems
to me a very rash assumption.
Moreover, the several above-named
domesticated breeds have been
transported to all parts of the
world, and, therefore, some of
them must have been carried back
again into their native country;
but not one has ever become wild
or feral, though the dovecot-pigeon,
which is the rock-pigeon in a
very slightly altered state,
has become feral in several places.
Again, all recent experience
shows that it is most difficult
to get any wild animal to breed
freely under domestication; yet
on the hypothesis of the multiple
origin of our pigeons, it must
be assumed that at least seven
or eight species were so thoroughly
domesticated in ancient times
by half-civilized man, as to
be quite prolific under confinement.
An argument, as it seems to
me, of great weight, and applicable
in several other cases, is, that
the above-specified breeds, though
agreeing generally in constitution,
habits, voice, colouring, and
in most parts of their structure,
with the wild rock-pigeon, yet
are certainly highly abnormal
in other parts of their structure:
we may look in vain throughout
the whole great family of Columbidae
for a beak like that of the English
carrier, or that of the short-faced
tumbler, or barb; for reversed
feathers like those of the jacobin;
for a crop like that of the pouter;
for tail-feathers like those
of the fantail. Hence it must
be assumed not only that half-civilized
man succeeded in thoroughly domesticating
several species, but that he
intentionally or by chance picked
out extraordinarily abnormal
species; and further, that these
very species have since all become
extinct or unknown. So many strange
contingencies seem to me improbable
in the highest degree.
Some facts in regard to the
colouring of pigeons well deserve
consideration. The rock-pigeon
is of a slaty-blue, and has a
white rump (the Indian sub-species,
C. intermedia of Strickland,
having it bluish); the tail has
a terminal dark bar, with the
bases of the outer feathers externally
edged with white; the wings have
two black bars: some semi-domestic
breeds and some apparently truly
wild breeds have, besides the
two black bars, the wings chequered
with black. These several marks
do not occur together in any
other species of the whole family.
Now, in every one of the domestic
breeds, taking thoroughly well-bred
birds, all the above marks, even
to the white edging of the outer
tail-feathers, sometimes concur
perfectly developed. Moreover,
when two birds belonging to two
distinct breeds are crossed,
neither of which is blue or has
any of the above-specified marks,
the mongrel offspring are very
apt suddenly to acquire these
characters; for instance, I crossed
some uniformly white fantails
with some uniformly black barbs,
and they produced mottled brown
and black birds; these I again
crossed together, and one grandchild
of the pure white fantail and
pure black barb was of as beautiful
a blue colour, with the white
rump, double black wing-bar,
and barred and white-edged tail-feathers,
as any wild rock-pigeon! We can
understand these facts, on the
well-known principle of reversion
to ancestral characters, if all
the domestic breeds have descended
from the rock-pigeon. But if
we deny this, we must make one
of the two following highly improbable
suppositions. Either, firstly,
that all the several imagined
aboriginal stocks were coloured
and marked like the rock-pigeon,
although no other existing species
is thus coloured and marked,
so that in each separate breed
there might be a tendency to
revert to the very same colours
and markings. Or, secondly, that
each breed, even the purest,
has within a dozen or, at most,
within a score of generations,
been crossed by the rock-pigeon:
I say within a dozen or twenty
generations, for we know of no
fact countenancing the belief
that the child ever reverts to
some one ancestor, removed by
a greater number of generations.
In a breed which has been crossed
only once with some distinct
breed, the tendency to reversion
to any character derived from
such cross will naturally become
less and less, as in each succeeding
generation there will be less
of the foreign blood; but when
there has been no cross with
a distinct breed, and there is
a tendency in both parents to
revert to a character, which
has been lost during some former
generation, this tendency, for
all that we can see to the contrary,
may be transmitted undiminished
for an indefinite number of generations.
These two distinct cases are
often confounded in treatises
on inheritance.
Lastly, the hybrids or mongrels
from between all the domestic
breeds of pigeons are perfectly
fertile. I can state this from
my own observations, purposely
made on the most distinct breeds.
Now, it is difficult, perhaps
impossible, to bring forward
one case of the hybrid offspring
of two animals clearly distinct being
themselves perfectly fertile.
Some authors believe that long-continued
domestication eliminates this
strong tendency to sterility:
from the history of the dog I
think there is some probability
in this hypothesis, if applied
to species closely related together,
though it is unsupported by a
single experiment. But to extend
the hypothesis so far as to suppose
that species, aboriginally as
distinct as carriers, tumblers,
pouters, and fantails now are,
should yield offspring perfectly
fertile, inter se, seems
to me rash in the extreme.
From these several reasons,
namely, the improbability of
man having formerly got seven
or eight supposed species of
pigeons to breed freely under
domestication; these supposed
species being quite unknown in
a wild state, and their becoming
nowhere feral; these species
having very abnormal characters
in certain respects, as compared
with all other Columbidae, though
so like in most other respects
to the rock-pigeon; the blue
colour and various marks occasionally
appearing in all the breeds,
both when kept pure and when
crossed; the mongrel offspring
being perfectly fertile; from
these several reasons, taken
together, I can feel no doubt
that all our domestic breeds
have descended from the Columba
livia with its geographical sub-species.
In favour of this view, I may
add, firstly, that C. livia,
or the rock-pigeon, has been
found capable of domestication
in Europe and in India; and that
it agrees in habits and in a
great number of points of structure
with all the domestic breeds.
Secondly, although an English
carrier or short-faced tumbler
differs immensely in certain
characters from the rock-pigeon,
yet by comparing the several
sub-breeds of these breeds, more
especially those brought from
distant countries, we can make
an almost perfect series between
the extremes of structure. Thirdly,
those characters which are mainly
distinctive of each breed, for
instance the wattle and length
of beak of the carrier, the shortness
of that of the tumbler, and the
number of tail-feathers in the
fantail, are in each breed eminently
variable; and the explanation
of this fact will be obvious
when we come to treat of selection.
Fourthly, pigeons have been watched,
and tended with the utmost care,
and loved by many people. They
have been domesticated for thousands
of years in several quarters
of the world; the earliest known
record of pigeons is in the fifth
Aegyptian dynasty, about 3000
B.C., as was pointed out to me
by Professor Lepsius; but Mr
Birch informs me that pigeons
are given in a bill of fare in
the previous dynasty. In the
time of the Romans, as we hear
from Pliny, immense prices were
given for pigeons; 'nay, they
are come to this pass, that they
can reckon up their pedigree
and race.' Pigeons were much
valued by Akber Khan in India,
about the year 1600; never less
than 20,000 pigeons were taken
with the court. 'The monarchs
of Iran and Turan sent him some
very rare birds;' and, continues
the courtly historian, 'His Majesty
by crossing the breeds, which
method was never practised before,
has improved them astonishingly.'
About this same period the Dutch
were as eager about pigeons as
were the old Romans. The paramount
importance of these considerations
in explaining the immense amount
of variation which pigeons have
undergone, will be obvious when
we treat of Selection. We shall
then, also, see how it is that
the breeds so often have a somewhat
monstrous character. It is also
a most favourable circumstance
for the production of distinct
breeds, that male and female
pigeons can be easily mated for
life; and thus different breeds
can be kept together in the same
aviary.
I have discussed the probable
origin of domestic pigeons at
some, yet quite insufficient,
length; because when I first
kept pigeons and watched the
several kinds, knowing well how
true they bred, I felt fully
as much difficulty in believing
that they could ever have descended
from a common parent, as any
naturalist could in coming to
a similar conclusion in regard
to the many species of finches,
or other large groups of birds,
in nature. One circumstance has
struck me much; namely, that
all the breeders of the various
domestic animals and the cultivators
of plants, with whom I have ever
conversed, or whose treatises
I have read, are firmly convinced
that the several breeds to which
each has attended, are descended
from so many aboriginally distinct
species. Ask, as I have asked,
a celebrated raiser of Hereford
cattle, whether his cattle might
not have descended from long
horns, and he will laugh you
to scorn. I have never met a
pigeon, or poultry, or duck,
or rabbit fancier, who was not
fully convinced that each main
breed was descended from a distinct
species. Van Mons, in his treatise
on pears and apples, shows how
utterly he disbelieves that the
several sorts, for instance a
Ribston-pippin or Codlin-apple,
could ever have proceeded from
the seeds of the same tree. Innumerable
other examples could be given.
The explanation, I think, is
simple: from long-continued study
they are strongly impressed with
the differences between the several
races; and though they well know
that each race varies slightly,
for they win their prizes by
selecting such slight differences,
yet they ignore all general arguments,
and refuse to sum up in their
minds slight differences accumulated
during many successive generations.
May not those naturalists who,
knowing far less of the laws
of inheritance than does the
breeder, and knowing no more
than he does of the intermediate
links in the long lines of descent,
yet admit that many of our domestic
races have descended from the
same parents may they not learn
a lesson of caution, when they
deride the idea of species in
a state of nature being lineal
descendants of other species?
Selection
Let us now briefly consider
the steps by which domestic races
have been produced, either from
one or from several allied species.
Some little effect may, perhaps,
be attributed to the direct action
of the external conditions of
life, and some little to habit;
but he would be a bold man who
would account by such agencies
for the differences of a dray
and race horse, a greyhound and
bloodhound, a carrier and tumbler
pigeon. One of the most remarkable
features in our domesticated
races is that we see in them
adaptation, not indeed to the
animal's or plant's own good,
but to man's use or fancy. Some
variations useful to him have
probably arisen suddenly, or
by one step; many botanists,
for instance, believe that the
fuller's teazle, with its hooks,
which cannot be rivalled by any
mechanical contrivance, is only
a variety of the wild Dipsacus;
and this amount of change may
have suddenly arisen in a seedling.
So it has probably been with
the turnspit dog; and this is
known to have been the case with
the ancon sheep. But when we
compare the dray-horse and race-horse,
the dromedary and camel, the
various breeds of sheep fitted
either for cultivated land or
mountain pasture, with the wool
of one breed good for one purpose,
and that of another breed for
another purpose; when we compare
the many breeds of dogs, each
good for man in very different
ways; when we compare the gamecock,
so pertinacious in battle, with
other breeds so little quarrelsome,
with 'everlasting layers' which
never desire to sit, and with
the bantam so small and elegant;
when we compare the host of agricultural,
culinary, orchard, and flower-garden
races of plants, most useful
to man at different seasons and
for different purposes, or so
beautiful in his eyes, we must,
I think, look further than to
mere variability. We cannot suppose
that all the breeds were suddenly
produced as perfect and as useful
as we now see them; indeed, in
several cases, we know that this
has not been their history. The
key is man's power of accumulative
selection: nature gives successive
variations; man adds them up
in certain directions useful
to him. In this sense he may
be said to make for himself useful
breeds.
The great power of this principle
of selection is not hypothetical.
It is certain that several of
our eminent breeders have, even
within a single lifetime, modified
to a large extent some breeds
of cattle and sheep. In order
fully to realise what they have
done, it is almost necessary
to read several of the many treatises
devoted to this subject, and
to inspect the animals. Breeders
habitually speak of an animal's
organisation as something quite
plastic, which they can model
almost as they please. If I had
space I could quote numerous
passages to this effect from
highly competent authorities.
Youatt, who was probably better
acquainted with the works of
agriculturalists than almost
any other individual, and who
was himself a very good judge
of an animal, speaks of the principle
of selection as 'that which enables
the agriculturist, not only to
modify the character of his flock,
but to change it altogether.
It is the magician's wand, by
means of which he may summon
into life whatever form and mould
he pleases.' Lord Somerville,
speaking of what breeders have
done for sheep, says: 'It would
seem as if they had chalked out
upon a wall a form perfect in
itself, and then had given it
existence.' That most skilful
breeder, Sir John Sebright, used
to say, with respect to pigeons,
that 'he would produce any given
feather in three years, but it
would take him six years to obtain
head and beak.' In Saxony the
importance of the principle of
selection in regard to merino
sheep is so fully recognised,
that men follow it as a trade:
the sheep are placed on a table
and are studied, like a picture
by a connoisseur; this is done
three times at intervals of months,
and the sheep are each time marked
and classed, so that the very
best may ultimately be selected
for breeding.
What English breeders have
actually effected is proved by
the enormous prices given for
animals with a good pedigree;
and these have now been exported
to almost every quarter of the
world. The improvement is by
no means generally due to crossing
different breeds; all the best
breeders are strongly opposed
to this practice, except sometimes
amongst closely allied sub-breeds.
And when a cross has been made,
the closest selection is far
more indispensable even than
in ordinary cases. If selection
consisted merely in separating
some very distinct variety, and
breeding from it, the principle
would be so obvious as hardly
to be worth notice; but its importance
consists in the great effect
produced by the accumulation
in one direction, during successive
generations, of differences absolutely
inappreciable by an uneducated
eye differences which I for one
have vainly attempted to appreciate.
Not one man in a thousand has
accuracy of eye and judgement
sufficient to become an eminent
breeder. If gifted with these
qualities, and he studies his
subject for years, and devotes
his lifetime to it with indomitable
perseverance, he will succeed,
and may make great improvements;
if he wants any of these qualities,
he will assuredly fail. Few would
readily believe in the natural
capacity and years of practice
requisite to become even a skilful
pigeon-fancier.
The same principles are followed
by horticulturists; but the variations
are here often more abrupt. No
one supposes that our choicest
productions have been produced
by a single variation from the
aboriginal stock. We have proofs
that this is not so in some cases,
in which exact records have been
kept; thus, to give a very trifling
instance, the steadily-increasing
size of the common gooseberry
may be quoted. We see an astonishing
improvement in many florists'
flowers, when the flowers of
the present day are compared
with drawings made only twenty
or thirty years ago. When a race
of plants is once pretty well
established, the seed-raisers
do not pick out the best plants,
but merely go over their seed-beds,
and pull up the 'rogues,' as
they call the plants that deviate
from the proper standard. With
animals this kind of selection
is, in fact, also followed; for
hardly any one is so careless
as to allow his worst animals
to breed.
In regard to plants, there
is another means of observing
the accumulated effects of selection
namely, by comparing the diversity
of flowers in the different varieties
of the same species in the flower-garden;
the diversity of leaves, pods,
or tubers, or whatever part is
valued, in the kitchen-garden,
in comparison with the flowers
of the same varieties; and the
diversity of fruit of the same
species in the orchard, in comparison
with the leaves and flowers of
the same set of varieties. See
how different the leaves of the
cabbage are, and how extremely
alike the flowers; how unlike
the flowers of the heartsease
are, and how alike the leaves;
how much the fruit of the different
kinds of gooseberries differ
in size, colour, shape, and hairiness,
and yet the flowers present very
slight differences. It is not
that the varieties which differ
largely in some one point do
not differ at all in other points;
this is hardly ever, perhaps
never, the case. The laws of
correlation of growth, the importance
of which should never be overlooked,
will ensure some differences;
but, as a general rule, I cannot
doubt that the continued selection
of slight variations, either
in the leaves, the flowers, or
the fruit, will produce races
differing from each other chiefly
in these characters.
It may be objected that the
principle of selection has been
reduced to methodical practice
for scarcely more than three-quarters
of a century; it has certainly
been more attended to of late
years, and many treatises have
been published on the subject;
and the result, I may add, has
been, in a corresponding degree,
rapid and important. But it is
very far from true that the principle
is a modern discovery. I could
give several references to the
full acknowledgement of the importance
of the principle in works of
high antiquity. In rude and barbarous
periods of English history choice
animals were often imported,
and laws were passed to prevent
their exportation: the destruction
of horses under a certain size
was ordered, and this may be
compared to the 'roguing' of
plants by nurserymen. The principle
of selection I find distinctly
given in an ancient Chinese encyclopaedia.
Explicit rules are laid down
by some of the Roman classical
writers. From passages in Genesis,
it is clear that the colour of
domestic animals was at that
early period attended to. Savages
now sometimes cross their dogs
with wild canine animals, to
improve the breed, and they formerly
did so, as is attested by passages
in Pliny. The savages in South
Africa match their draught cattle
by colour, as do some of the
Esquimaux their teams of dogs.
Livingstone shows how much good
domestic breeds are valued by
the negroes of the interior of
Africa who have not associated
with Europeans. Some of these
facts do not show actual selection,
but they show that the breeding
of domestic animals was carefully
attended to in ancient times,
and is now attended to by the
lowest savages. It would, indeed,
have been a strange fact, had
attention not been paid to breeding,
for the inheritance of good and
bad qualities is so obvious.
At the present
time, eminent breeders try
by methodical selection,
with a distinct object in view,
to make a new strain or sub-breed,
superior to anything existing
in the country. But, for our
purpose, a kind of Selection,
which may be called Unconscious,
and which results from every
one trying to possess and breed
from the best individual animals,
is more important. Thus, a man
who intends keeping pointers
naturally tries to get as good
dogs as he can, and afterwards
breeds from his own best dogs,
but he has no wish or expectation
of permanently altering the breed.
Nevertheless I cannot doubt that
this process, continued during
centuries, would improve and
modify any breed, in the same
way as Bakewell, Collins, &c.,
by this very same process, only
carried on more methodically,
did greatly modify, even during
their own lifetimes, the forms
and qualities of their cattle.
Slow and insensible changes of
this kind could never be recognised
unless actual measurements or
careful drawings of the breeds
in question had been made long
ago, which might serve for comparison.
In some cases, however, unchanged
or but little changed individuals
of the same breed may be found
in less civilised districts,
where the breed has been less
improved. There is reason to
believe that King Charles's spaniel
has been unconsciously modified
to a large extent since the time
of that monarch. Some highly
competent authorities are convinced
that the setter is directly derived
from the spaniel, and has probably
been slowly altered from it.
It is known that the English
pointer has been greatly changed
within the last century, and
in this case the change has,
it is believed, been chiefly
effected by crosses with the
fox-hound; but what concerns
us is, that the change has been
effected unconsciously and gradually,
and yet so effectually, that,
though the old Spanish pointer
certainly came from Spain, Mr
Barrow has not seen, as I am
informed by him, any native dog
in Spain like our pointer.
By a similar process of selection,
and by careful training, the
whole body of English racehorses
have come to surpass in fleetness
and size the parent Arab stock,
so that the latter, by the regulations
for the Goodwood Races, are favoured
in the weights they carry. Lord
Spencer and others have shown
how the cattle of England have
increased in weight and in early
maturity, compared with the stock
formerly kept in this country.
By comparing the accounts given
in old pigeon treatises of carriers
and tumblers with these breeds
as now existing in Britain, India,
and Persia, we can, I think,
clearly trace the stages through
which they have insensibly passed,
and come to differ so greatly
from the rock-pigeon.
Youatt gives an excellent illustration
of the effects of a course of
selection, which may be considered
as unconsciously followed, in
so far that the breeders could
never have expected or even have
wished to have produced the result
which ensued namely, the production
of two distinct strains. The
two flocks of Leicester sheep
kept by Mr Buckley and Mr Burgess,
as Mr Youatt remarks, 'have been
purely bred from the original
stock of Mr Bakewell for upwards
of fifty years. There is not
a suspicion existing in the mind
of any one at all acquainted
with the subject that the owner
of either of them has deviated
in any one instance from the
pure blood of Mr Bakewell's flock,
and yet the difference between
the sheep possessed by these
two gentlemen is so great that
they have the appearance of being
quite different varieties.'
If there exist savages so barbarous
as never to think of the inherited
character of the offspring of
their domestic animals, yet any
one animal particularly useful
to them, for any special purpose,
would be carefully preserved
during famines and other accidents,
to which savages are so liable,
and such choice animals would
thus generally leave more offspring
than the inferior ones; so that
in this case there would be a
kind of unconscious selection
going on. We see the value set
on animals even by the barbarians
of Tierra del Fuego, by their
killing and devouring their old
women, in times of dearth, as
of less value than their dogs.
In plants the same gradual
process of improvement, through
the occasional preservation of
the best individuals, whether
or not sufficiently distinct
to be ranked at their first appearance
as distinct varieties, and whether
or not two or more species or
races have become blended together
by crossing, may plainly be recognised
in the increased size and beauty
which we now see in the varieties
of the heartsease, rose, pelargonium,
dahlia, and other plants, when
compared with the older varieties
or with their parent-stocks.
No one would ever expect to get
a first-rate heartsease or dahlia
from the seed of a wild plant.
No one would expect to raise
a first-rate melting pear from
the seed of a wild pear, though
he might succeed from a poor
seedling growing wild, if it
had come from a garden-stock.
The pear, though cultivated in
classical times, appears, from
Pliny's description, to have
been a fruit of very inferior
quality. I have seen great surprise
expressed in horticultural works
at the wonderful skill of gardeners,
in having produced such splendid
results from such poor materials;
but the art, I cannot doubt,
has been simple, and, as far
as the final result is concerned,
has been followed almost unconsciously.
It has consisted in always cultivating
the best known variety, sowing
its seeds, and, when a slightly
better variety has chanced to
appear, selecting it, and so
onwards. But the gardeners of
the classical period, who cultivated
the best pear they could procure,
never thought what splendid fruit
we should eat; though we owe
our excellent fruit, in some
small degree, to their having
naturally chosen and preserved
the best varieties they could
anywhere find.
A large amount of change in
our cultivated plants, thus slowly
and unconsciously accumulated,
explains, as I believe, the well-known
fact, that in a vast number of
cases we cannot recognise, and
therefore do not know, the wild
parent-stocks of the plants which
have been longest cultivated
in our flower and kitchen gardens.
If it has taken centuries or
thousands of years to improve
or modify most of our plants
up to their present standard
of usefulness to man, we can
understand how it is that neither
Australia, the Cape of Good Hope,
nor any other region inhabited
by quite uncivilised man, has
afforded us a single plant worth
culture. It is not that these
countries, so rich in species,
do not by a strange chance possess
the aboriginal stocks of any
useful plants, but that the native
plants have not been improved
by continued selection up to
a standard of perfection comparable
with that given to the plants
in countries anciently civilised.
In regard to the domestic animals
kept by uncivilised man, it should
not be overlooked that they almost
always have to struggle for their
own food, at least during certain
seasons. And in two countries
very differently circumstanced,
individuals of the same species,
having slightly different constitutions
or structure, would often succeed
better in the one country than
in the other, and thus by a process
of 'natural selection,' as will
hereafter be more fully explained,
two sub-breeds might be formed.
This, perhaps, partly explains
what has been remarked by some
authors, namely, that the varieties
kept by savages have more of
the character of species than
the varieties kept in civilised
countries.
On the view here given of the
all-important part which selection
by man has played, it becomes
at once obvious, how it is that
our domestic races show adaptation
in their structure or in their
habits to man's wants or fancies.
We can, I think, further understand
the frequently abnormal character
of our domestic races, and likewise
their differences being so great
in external characters and relatively
so slight in internal parts or
organs. Man can hardly select,
or only with much difficulty,
any deviation of structure excepting
such as is externally visible;
and indeed he rarely cares for
what is internal. He can never
act by selection, excepting on
variations which are first given
to him in some slight degree
by nature. No man would ever
try to make a fantail, till he
saw a pigeon with a tail developed
in some slight degree in an unusual
manner, or a pouter till he saw
a pigeon with a crop of somewhat
unusual size; and the more abnormal
or unusual any character was
when it first appeared, the more
likely it would be to catch his
attention. But to use such an
expression as trying to make
a fantail, is, I have no doubt,
in most cases, utterly incorrect.
The man who first selected a
pigeon with a slightly larger
tail, never dreamed what the
descendants of that pigeon would
become through long-continued,
partly unconscious and partly
methodical selection. Perhaps
the parent bird of all fantails
had only fourteen tail-feathers
somewhat expanded, like the present
Java fantail, or like individuals
of other and distinct breeds,
in which as many as seventeen
tail-feathers have been counted.
Perhaps the first pouter-pigeon
did not inflate its crop much
more than the turbit now does
the upper part of its oesophagus,
a habit which is disregarded
by all fanciers, as it is not
one of the points of the breed.
Nor let it be thought that
some great deviation of structure
would be necessary to catch the
fancier's eye: he perceives extremely
small differences, and it is
in human nature to value any
novelty, however slight, in one's
own possession. Nor must the
value which would formerly be
set on any slight differences
in the individuals of the same
species, be judged of by the
value which would now be set
on them, after several breeds
have once fairly been established.
Many slight differences might,
and indeed do now, arise amongst
pigeons, which are rejected as
faults or deviations from the
standard of perfection of each
breed. The common goose has not
given rise to any marked varieties;
hence the Thoulouse and the common
breed, which differ only in colour,
that most fleeting of characters,
have lately been exhibited as
distinct at our poultry-shows.
I think these views further
explain what has sometimes been
noticed namely that we know nothing
about the origin or history of
any of our domestic breeds. But,
in fact, a breed, like a dialect
of a language, can hardly be
said to have had a definite origin.
A man preserves and breeds from
an individual with some slight
deviation of structure, or takes
more care than usual in matching
his best animals and thus improves
them, and the improved individuals
slowly spread in the immediate
neighbourhood. But as yet they
will hardly have a distinct name,
and from being only slightly
valued, their history will be
disregarded. When further improved
by the same slow and gradual
process, they will spread more
widely, and will get recognised
as something distinct and valuable,
and will then probably first
receive a provincial name. In
semi-civilised countries, with
little free communication, the
spreading and knowledge of any
new sub-breed will be a slow
process. As soon as the points
of value of the new sub-breed
are once fully acknowledged,
the principle, as I have called
it, of unconscious selection
will always tend, perhaps more
at one period than at another,
as the breed rises or falls in
fashion, perhaps more in one
district than in another, according
to the state of civilisation
of the inhabitants slowly to
add to the characteristic features
of the breed, whatever they may
be. But the chance will be infinitely
small of any record having been
preserved of such slow, varying,
and insensible changes.
I must now say a few words
on the circumstances, favourable,
or the reverse, to man's power
of selection. A high degree of
variability is obviously favourable,
as freely giving the materials
for selection to work on; not
that mere individual differences
are not amply sufficient, with
extreme care, to allow of the
accumulation of a large amount
of modification in almost any
desired direction. But as variations
manifestly useful or pleasing
to man appear only occasionally,
the chance of their appearance
will be much increased by a large
number of individuals being kept;
and hence this comes to be of
the highest importance to success.
On this principle Marshall has
remarked, with respect to the
sheep of parts of Yorkshire,
that 'as they generally belong
to poor people, and are mostly in
small lots, they never can
be improved.' On the other hand,
nurserymen, from raising large
stocks of the same plants, are
generally far more successful
than amateurs in getting new
and valuable varieties. The keeping
of a large number of individuals
of a species in any country requires
that the species should be placed
under favourable conditions of
life, so as to breed freely in
that country. When the individuals
of any species are scanty, all
the individuals, whatever their
quality may be, will generally
be allowed to breed, and this
will effectually prevent selection.
But probably the most important
point of all, is, that the animal
or plant should be so highly
useful to man, or so much valued
by him, that the closest attention
should be paid to even the slightest
deviation in the qualities or
structure of each individual.
Unless such attention be paid
nothing can be effected. I have
seen it gravely remarked, that
it was most fortunate that the
strawberry began to vary just
when gardeners began to attend
closely to this plant. No doubt
the strawberry had always varied
since it was cultivated, but
the slight varieties had been
neglected. As soon, however,
as gardeners picked out individual
plants with slightly larger,
earlier, or better fruit, and
raised seedlings from them, and
again picked out the best seedlings
and bred from them, then, there
appeared (aided by some crossing
with distinct species) those
many admirable varieties of the
strawberry which have been raised
during the last thirty or forty
years.
In the case
of animals with separate sexes,
facility in preventing
crosses is an important element
of success in the formation of
new races, at least, in a country
which is already stocked with
other races. In this respect
enclosure of the land plays a
part. Wandering savages or the
inhabitants of open plains rarely
possess more than one breed of
the same species. Pigeons can
be mated for life, and this is
a great convenience to the fancier,
for thus many races may be kept
true, though mingled in the same
aviary; and this circumstance
must have largely favoured the
improvement and formation of
new breeds. Pigeons, I may add,
can be propagated in great numbers
and at a very quick rate, and
inferior birds may be freely
rejected, as when killed they
serve for food. On the other
hand, cats, from their nocturnal
rambling habits, cannot be matched,
and, although so much valued
by women and children, we hardly
ever see a distinct breed kept
up; such breeds as we do sometimes
see are almost always imported
from some other country, often
from islands. Although I do not
doubt that some domestic animals
vary less than others, yet the
rarity or absence of distinct
breeds of the cat, the donkey,
peacock, goose, &c., may
be attributed in main part to
selection not having been brought
into play: in cats, from the
difficulty in pairing them; in
donkeys, from only a few being
kept by poor people, and little
attention paid to their breeding;
in peacocks, from not being very
easily reared and a large stock
not kept; in geese, from being
valuable only for two purposes,
food and feathers, and more especially
from no pleasure having been
felt in the display of distinct
breeds.
To sum up on
the origin of our Domestic
Races of animals
and plants. I believe that the
conditions of life, from their
action on the reproductive system,
are so far of the highest importance
as causing variability. I do
not believe that variability
is an inherent and necessary
contingency, under all circumstances,
with all organic beings, as some
authors have thought. The effects
of variability are modified by
various degrees of inheritance
and of reversion. Variability
is governed by many unknown laws,
more especially by that of correlation
of growth. Something may be attributed
to the direct action of the conditions
of life. Something must be attributed
to use and disuse. The final
result is thus rendered infinitely
complex. In some cases, I do
not doubt that the intercrossing
of species, aboriginally distinct,
has played an important part
in the origin of our domestic
productions. When in any country
several domestic breeds have
once been established, their
occasional intercrossing, with
the aid of selection, has, no
doubt, largely aided in the formation
of new sub-breeds; but the importance
of the crossing of varieties
has, I believe, been greatly
exaggerated, both in regard to
animals and to those plants which
are propagated by seed. In plants
which are temporarily propagated
by cuttings, buds, &c., the
importance of the crossing both
of distinct species and of varieties
is immense; for the cultivator
here quite disregards the extreme
variability both of hybrids and
mongrels, and the frequent sterility
of hybrids; but the cases of
plants not propagated by seed
are of little importance to us,
for their endurance is only temporary.
Over all these causes of Change
I am convinced that the accumulative
action of Selection, whether
applied methodically and more
quickly, or unconsciously and
more slowly, but more efficiently,
is by far the predominant power. |