M Database Inspector (cheetah)
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|OriginOfSpecies - 475 Rows|
|03 - Struggle for Existence||03-05 - Nature of the Checks to Increase||10||
In looking at Nature, it is most necessary to keep the foregoing considerations always in mind- never to forget that every single organic being may be said to be striving to the utmost to increase in numbers; that each lives by a struggle at some period of its life; that heavy destruction inevitably falls either on the young or old, during each generation or at recurrent intervals. Lighten any cheek, mitigate the destruction ever so little, and the number of the species will
almost instantaneously increase to any amount.
|04 - Natural Selection||04-03 - Its Power on Characters of Trifling Importance||20||In looking at many small points of difference between species, which, as far as our ignorance permits us to judge, seem quite unimportant, we must not forget that climate, food, &c., have no doubt produced some direct effect. It is also necessary to bear in mind that, owing to the law of correlation, when one part varies, and the variations are accumulated through natural selection, other modifications, often of the most unexpected nature, will ensue.|
|01 - Variations Under Domestication||01-08 - Breeds of the Domestic Pigeons, their Differences and Origin||80||
In favour of this view, I may add, firstly, that the wild C. livia 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, that, although an English carrier or a short-faced tumbler differs immensely in certain characters from the rock-pigeon, yet that, by comparing the several sub-breeds of these two races, more especially those brought from distant countries, we can make, between them and the rock-pigeon, an almost perfect series; so we can in some other cases, but not with all the breeds.
Thirdly, those characters which are mainly distinctive of each breed are in each eminently variable, for instance the wattle and length of beak of the carrier, the shortness of that of the tumbler, and the number of tailfeathers in the fantail; and the explanation of this fact will be obvious when we 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 Egyptian 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 90,000 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 likewise be obvious when we treat of Selection. We shall then, also, see how it is that the several 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.
|06 - Difficutiles in Theory||06-08 - Means of Transition||50||
In considering transitions of organs, it is so important to bear in mind the probability of conversion from one function to another, that I will give another instance.
Pedunculated cirripedes have two minute folds of skin, called by me the ovigerous frena, which serve, through the means of a sticky secretion, to retain the eggs until they are hatched within the sack.
These cirripedes have no branchiae, the whole surface of the body and of the sack, together with the small frena, serving for respiration.
The Balanidae or sessile cirripedes, on the other hand, have no ovigerous frena, the eggs lying loose at the bottom of the sack, within the well-enclosed shell; but they have, in the same relative position with the frena, large, much-folded membranes, which freely communicate with the circulatory lacunae of the sack and body, and which have been considered by all naturalists to act as branchiae.
Now I think no one will dispute that the ovigerous frena in the one family are strictly homologous with the branchiae of the other family; indeed, they graduate into each other.
Therefore it need not be doubted that the two little folds of skin, which originally served as ovigerous frena, but which, likewise, very slightly aided in the act of respiration, have been gradually converted by natural selection into branchiae simply through an increase in their size and the obliteration of their adhesive glands.
If all pedunculated cirripedes had become extinct, and they have suffered far more extinction than have sessile cirripedes, who would ever have imagined that the branchiae in this latter family had originally existed as organs for preventing the ova from being washed out of the sack?