M Database Inspector (cheetah)
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|OriginOfSpecies - 475 Rows|
|01 - Variations Under Domestication||01-08 - Breeds of the Domestic Pigeons, their Differences and Origin||20||
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 caudal and sacral vertebrae vary in number; 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 the wing and tail to each other and to the body; the relative length of the leg and foot; 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, and in some breeds the voice and disposition, differ remarkably.
Lastly, in certain breeds, the males and females have come to differ in a slight degree from each other.
|09 - On the Imperfection of the Geological Record||09-01 -On the absence of intermediate varieties at the present day||10||
IN the sixth chapter I enumerated the chief objections which might be justly urged against the views maintained in this volume.
Most of them have now been discussed.
One, namely the distinctness of specific forms, and their not being blended together by innumerable transitional links, is a very obvious difficulty.
I assigned reasons why such links do not commonly occur at the present day, under the circumstances apparently most favourable for their presence, namely on an extensive and continuous area with graduated physical conditions.
I endeavoured to show, that the life of each species depends in a more important manner on the presence of other already defined organic forms, than on climate; and, therefore, that the really governing conditions of life do not graduate away quite insensibly like heat or moisture.
I endeavoured, also, to show that intermediate varieties, from existing in lesser numbers than the forms which they connect, will generally be beaten out and exterminated during the course of further modification and improvement.
The main cause, however, of innumerable intermediate links not now occurring everywhere throughout nature depends on the very process of natural selection, through which new varieties continually take the places of and exterminate their parent-forms.
But just in proportion as this process of extermination has acted on an enormous scale, so must the number of intermediate varieties, which have formerly existed on the earth, be truly enormous.
Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the most obvious and gravest objection which can be urged against my theory.
The explanation lies, as I believe, in the extreme imperfection of the geological record.
In the first place it should always be borne in mind what sort of intermediate forms must, on my theory, have formerly existed.
I have found it difficult, when looking at any two species, to avoid picturing to myself, forms directly intermediate between them.
But this is a wholly false view; we should always look for forms intermediate between each species and a common but unknown progenitor; and the progenitor will generally have differed in some respects from all its modified descendants.
To give a simple illustration: the fantail and pouter pigeons have both descended from the rock-pigeon; if we possessed all the intermediate varieties which have ever existed, we should have an extremely close series between both and the rock-pigeon; but we should have no varieties directly intermediate between the fantail and pouter; none, for instance, combining a tail somewhat expanded with a crop somewhat enlarged, the characteristic features of these two breeds.
These two breeds, moreover, have become so much modified, that if we had no historical or indirect evidence regarding their origin, it would not have been possible to have determined from a mere comparison of their structure with that of the rock-pigeon, whether they had descended from this species or from some other allied species, such as C. oenas.
|06 - Difficutiles in Theory||06-11 - Organs of Small Importance||40||
In the second place, we may easily err in attributing importance to characters, and in believing that they have been developed through natural selection.
We must by no means overlook the effects of the definite action of changed conditions of life,- of so-called spontaneous variations, which seem to depend in a quite subordinate degree on the nature of the conditions,- of the tendency to reversion to long-lost characters,- of the complex laws of growth, such as of correlation, compensation, of the pressure of one part on another, &c.,- and finally of sexual selection, by which characters of use to one sex are often gained and then transmitted more or less perfectly to the other sex, though of no use to this sex.
But structures thus indirectly gained, although at first of no advantage to a species, may subsequently have been taken advantage of by its modified descendants, under new conditions of life and newly acquired habits.
|05 - Laws of Variation||05-12 - Reversion to Long Lost Characters||60||
In the north-west part of India the kattywar breed of horses is so generally striped, that, as I hear from Colonel Poole, who examined this breed for the Indian Government, a horse without stripes is not considered as purely-bred.
The spine is always striped; the legs are generally barred; and the shoulder-stripe, which is sometimes double and sometimes treble, is common; the side of the face, moreover, is sometimes striped.
The stripes are often plainest in the foal; and sometimes quite disappear in old horses.
Colonel Poole has seen both gray and bay kattywar horses striped when first foaled. I have also reason to suspect, from information given me by Mr. W. W. Edwards, that with the English race-horse the spinal stripe is much commoner in the foal than in the fullgrown animal.
I have myself recently bred a foal from a bay mare (offspring of a Turkoman horse and a Flemish mare) by a bay English race-horse; this foal when a week old was marked on its hinder quarters and on its forehead with numerous, very narrow, dark, zebra-like bars, and its legs were feebly striped: all the stripes soon disappeared completely.
Without here entering on further details, I may state that I have collected cases of leg and shoulder stripes in horses of very different breeds in various countries from Britain to eastern China; and from Norway in the north to the Malay Archipelago in the south. In all parts of the world these stripes occur far oftenest in duns and mouse-duns; by the term dun a large range of colour is included, from one between brown and black to a close approach to