M Database Inspector (cheetah)
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|01 - Variations Under Domestication||01-10 - Methodical and Unconscious Selection||10||
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 of the kind in the country.
But, for our purpose, a form 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 we may infer 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 lifetimes, the forms and qualities of their cattle.
Slow and insensible changes of this kind can never be recognised unless actual measurements or careful drawings of the breeds in question have been made long ago, which may serve for comparison. In some cases, however, unchanged, or but little changed individuals of the same breed exist 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 foxhound; 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. Borrow has not seen, as I am informed by him, any native dog in Spain like our pointer.
|02 - Variations Under Nature||02-01 - Variability||10||
BEFORE applying the principles arrived at in the last chapter to organic beings in a state of nature, we must briefly discuss whether these latter are subject to any variation.
To treat this subject properly, a long catalogue of dry facts ought to be given; but these shall reserve for a future work.
Nor shall I here discuss the various definitions which have been given of the term species.
No one definition has satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of a species.
Generally the term includes the unknown element of a distant act of creation. The term "variety" is almost equally difficult to define; but here community of descent is almost universally implied, though it can rarely be proved.
We have also what are called monstrosities; but they graduate into varieties.
By a monstrosity I presume is meant some considerable deviation of structure, generally injurious, or not useful to the species.
Some authors use the term "variation" in a technical sense, as implying a modification directly due to the physical conditions of life; and "variations" in this sense are supposed not to be inherited; but who can say that the dwarfed condition of shells in the brackish waters of the Baltic, or dwarfed plants on Alpine summits, or the thicker fur of an animal from far northwards, would not in some cases be inherited for at least a few generations?
And in this case I presume that the form would be called a variety.
|03 - Struggle for Existence||03-01 - Bears on Natural Selection||10||
BEFORE entering on the subject of this chapter, I must make a few preliminary remarks, to show how the struggle for existence bears on Natural Selection.
It has been seen in the last chapter that amongst organic beings in a state of nature there is some individual variability: indeed I am not aware that this has ever been disputed.
It is immaterial for us whether a multitude of doubtful forms be alled species or sub-species or varieties; what rank, for instance, the two or three hundred doubtful forms of British plants are entitled to hold, if the existence of any well-marked varieties be admitted.
But the mere existence of individual variability and of some few well-marked varieties, though necessary as the foundation for the work, helps us but little in understanding how species arise in nature. How have all those exquisite adaptations of one part of the organisation to another part, and to the conditions of life, and of one organic being to another being, been perfected?
We see these beautiful co-adaptations most plainly in the woodpecker and the mistletoe; and only a little less plainly in the humblest parasite which clings to the hairs of a quadruped or feathers of a bird; in the structure of the beetle which dives through the water; in the plumed seed which is wafted by the gentlest breeze; in short, we see beautiful adaptations everywhere and in every part of the organic world.
|01 - Variations Under Domestication||01-08 - Breeds of the Domestic Pigeons, their Differences and Origin||10||
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 considerable 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 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 long beak has a very short and 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 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, 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 tailfeathers, instead of twelve or fourteen- the normal number in all the members of the great pigeon family: 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 be specified.