SPECIES AND THEIR DIVISIONS IN DOMESTIC BIRDS
The three general classes of domestic birds include few species but many
varieties, and, outside of the distinct varieties, an indefinite number
of individual types. Where varieties are as numerous as in the fowl,
which has about three hundred, and the pigeon, which has a much greater
number, the differences between them are often very slight. Sometimes
the form of a single small character is the only distinguishing feature.
But, if this is a fixed character, the variety is distinct. Where there
are so many varieties it is hard to make short, appropriate descriptive
names for all, if considered simply as varieties. For such diversity
there must be a more extended classification. Such a classification,
growing gradually with the increase in the number of varieties, will not
be consistent throughout. Hence to understand clearly the relations of
the artificial divisions of species in domestication we must know what a
species is and how these divisions arise.
=Definition of species.= Species are the natural divisions of living
things. Each plant and animal species retains its distinctive character
through long ages because the individuals composing it can produce
perfect offspring only (if asexual) of themselves, or (if bisexual) with
others of their species.
The self-isolation of species is well illustrated when similar plants
grow together, as grasses in the same field and practically on the same
spot; yet year after year all the old kinds are found and no new ones
such as might come from a mixture of two kinds, if they would mix. In
the higher animals, where the parent forms are of different sexes, they
choose mates of their own kind, and so each species remains distinct;
but if in a species there are many different types, such as we find in
domestic fowls, the members of the species, when free to do so, mate as
readily with types quite different from their own as with individuals
exactly like them, and produce offspring of intermediate types with all
the essential characters of the species. In domestication individuals of
distinct yet similar species are sometimes mated and produce offspring
called hybrids, but these are sterile. The mule, which is a hybrid
between the ass and the mare, is the most familiar animal of this kind.
Hybrid, or mule, cage birds are produced by crossing the canary with
several allied species. Among other domestic birds hybrids are almost
unknown.
=Origin of species.= Until near the close of the last century it was
commonly believed that each species had been created in perfect form and
that species were unchangeable; but long before that time some keen
students of the natural sciences and close observers of the changes that
take place in plants and animals in domestication had discovered that
species were not perfectly stable and were changing slowly. Geologists
established the fact that the earth, instead of being only a few
thousand years old, had existed for countless centuries. Among fossil
remains of creatures unlike any now known they had found also other
forms which appeared to be prototypes of existing species. The idea that
the forms of life now on the earth had come from earlier and somewhat
different forms had occurred to several scientists more than a hundred
years ago, but it was not until about 1860 that a satisfactory
explanation of progressive development of forms of life was given to the
world. This mode of creation is called evolution.
The theory of evolution is that partly through their own inherent
tendency to vary and partly through the influence of external things
which affect them, all organisms change slowly; that things of the same
kind, separated and living under different conditions, may in time so
change that they become separate species; and that this process may be
repeated indefinitely, the number of species constantly increasing and
becoming more diversified and more highly developed.
Such a theory would not be entitled to serious consideration unless it
was known that the earth was millions of years old, because we know that
races of fowls separated for over three thousand years (and perhaps
twice as long) and developed into quite different varieties will breed
together as readily as those of the same variety. But when it is certain
that the earth is so old that there has been ample time for changes in
living forms that would require periods of time beyond our
comprehension, some of the relations of varieties and species of birds
have an important bearing on the theory of evolution.
As in the case of fowls just noted, we find that domestic ducks of the
same species, after a separation of several thousand years, breed freely
together. But our domestic ducks are not, like the fowls, all of the
same species, and if individuals of different species are paired they
produce only a few weak hybrids. Our domestic geese are probably
descended from two wild varieties, but races that were not brought
together for thousands of years after they were domesticated are
perfectly fertile together, while when mated with the American Wild
Goose, which is not domesticated but will breed in captivity, they
produce only hybrids. The general resemblance between geese and ducks is
very striking, yet they will not breed together at all.
A comparison of these facts indicates that while three thousand, or even
five or six thousand, years of separation may not be enough to break
down the natural affinity of varieties of the same species, separation
and difference of development will eventually make of varieties distinct
species, a union of which will produce only hybrids, while a longer
separation and further increase of differences makes the break between
the species absolute and they will not breed together at all.
=Natural varieties.= A species having developed as a variety of an
earlier species will continue to develop as one variety or as several
varieties, according to conditions. If a part of a species becomes so
separated from the rest that intercourse ceases, each division of the
species may become a well-defined variety.
=Varieties in domestication.= How a species when domesticated breaks up
into varieties is well illustrated by the case of the fowl. The original
wild species has long disappeared, but there is good reason to suppose
that in size and color it was something between a Brown Pit Game and a
Brown Leghorn. The birds were smaller than most fowls seen in this
country to-day. The prevailing color was a dull brown, because that
color best conceals a small land bird from its enemies. Fowls that were
domesticated and given good care and an abundance of food would usually
grow larger than the wild stock. Thus if any person, or the people
generally in any community, systematically gave their fowls good care, a
variety of unusual size would be developed.
Different colors would also appear in the flocks of fowls, because the
birds of unusual colors would be protected and preserved, instead of
being destroyed as they usually are in the wild state. Other
peculiarities, too, such as large combs, crests, and feathered legs,
would be developed in some lands and neglected in others. This is how it
happened that after thousands of years in domestication the races of
fowls in different parts of the world were quite different in size and
form, but alike in being of many colors.
From a species in this condition modern poultry breeders have made
hundreds of distinct varieties. The easiest method of making a variety
in domestication is to select specimens for breeding as near the desired
type as possible, and to breed only from a few individuals in each
generation which come nearest to the ideal type. In this way a variety
that breeds quite true to the type may be established in from three or
four to eight or ten years, according to the number of characters to be
established as distinctive of the variety. Varieties are also made by
crossing unlike individuals. This process is longer than the other, and
sometimes requires a series of crosses to produce specimens
approximating the ideal sought. After such specimens have been obtained
the method is the same as in the first case. A variety is commonly
considered to be well established when the greater part of the specimens
produced are easily identified as of that variety. But no domestic
variety is ever established in the sense that a species is. All are
artificial, produced by compulsory separation and preserved only as long
as it is continued.
=Classification of domestic varieties of birds.= Domestic varieties of
all kinds of live stock were at first mostly shape-varieties; that is,
the individuals of a variety were alike in shape but of various colors.
This is the case still with some varieties. These shape-varieties are
mostly the common types of certain countries or districts. Thus the
Leghorn fowl is the common fowl of Italy, and the Houdan is a type
common in a small district in France. Such shape-varieties are called
_breeds_. When other types were made by crossing such breeds they also
were called breeds.
When people first began to be interested in the improvement of live
stock, the popular idea of a breed was that it was a domestic species,
and there are still many people who hold this view. This popular
misconception of the nature of a breed is responsible for much of the
inconsistency and confusion in the ordinary classifications of domestic
varieties. To it also is due the use of the term "variety" to apply
especially to color-varieties, which are the principal divisions of
breeds.
In the classification of domestic birds a _variety_ is properly a
color-variety of a breed. Thus in the Plymouth Rock breed there are six
color-varieties--barred, white, buff, partridge, silver-penciled, and
ermine (called Columbian); and in Fantail Pigeons there are six
color-varieties--white, blue, black, red, yellow, and silver. Birds of
the same breed (shape) and the same variety (color) may differ in some
other character, as the form of the comb or the presence or absence of
feathers in certain places. In accordance with such differences
varieties are divided into _subvarieties_. Thus, in Leghorn Fowls the
brown, white, and buff varieties have single-combed and rose-combed
subvarieties.
In any breed, variety, or subvariety certain families are sometimes
distinguished for general or special excellence of form or color. Such a
family is called a _strain_.
=Systematic mixtures of breeds and varieties.= Although so many distinct
varieties have been developed from common domestic stocks, the improved
races do not always displace the mongrels. When the old mongrels
disappear their place is often taken by a new mongrel stock produced by
mixtures of the distinct breeds with each other and with the old mongrel
race. The greater part of such stock is so mixed that its relation to
any established breed could not be determined or expressed, but
systematic mixtures are sometimes made, and to describe these the
following terms are used: _Crossbred_--having parents of different,
distinct breeds, varieties, or subvarieties. A Leghorn male mated with a
Cochin female produces offspring each of which is in blood one half
Leghorn and one half Cochin. _Grade_--having more than half of the blood
of a breed.
If the offspring of a cross such as is described in the preceding
paragraph are mated with birds of one of the parent breeds, the
offspring of this mating will have three fourths of the blood of that
breed. If these in turn are mated to birds of the same pure breed, the
offspring will have seven eighths of the blood of that breed. Animals
bred in this way are called _grades_ until the process has been carried
so far that they are practically pure-bred. Mongrel stock is often
graded up in this way. As a rule stock that is seven eighths pure is not
distinguishable from average pure stock of the same breed.
=Pure-bred, thoroughbred, and standard-bred.= A _pure-bred_ animal is,
strictly speaking, one having the blood only of the variety to which it
belongs. From what has been said of the making of breeds and varieties
it is plain that absolute purity of blood is not a universal attribute
of well-bred domestic birds. A _thoroughbred_ animal is one that is
thoroughly bred for some purpose or to some type. A _standard-bred_
animal is one that is bred especially to conform to requirements agreed
upon by breeders and exhibitors.
A great deal of misapprehension and confusion in the use of these terms
has been caused by the attitude of those who maintain that the term
"thoroughbred," having been used as a name for highly bred running
horses, cannot properly apply to any other kind of live stock, and that
"pure-bred" should apply to all thoroughly bred races. The noun
"Thoroughbred" is the name of a breed of horses. The adjective
"thoroughbred" is common property. Writers on aviculture who wish to be
accurate prefer it in many instances to "pure-bred" because absolute
purity of blood is rare and is not of the importance in breeding that
novices usually suppose. Not only are many new varieties made by
crossing, but in long-established breeds outcrosses are regularly made
to restore or intensify characters.
To illustrate the use of the three terms in application to a single
breed: A stock of Light Brahmas might be kept pure for half a century,
yet at the end of that period might have changed its type entirely. It
might be so deteriorated that it was worth less than common mongrels;
yet it is pure-bred stock. Another stock of the same variety might be
bred for table qualities, egg-production, and the same principal
color-characteristics of the variety, but without attention to the fine
points of fancy breeding. Such a stock is thoroughbred but not
standard-bred.