Direktlänk till inlägg 21 maj 2011

high importance

Av debbyhanxu debbyhanxu - 21 maj 2011 07:42

Inasmuch as peculiarities often appear under domestication in one sex and become hereditarily attached to that sex, the same fact probably occurs under nature, and if so, natural selection will be able to modify one sex in its functional relations to the other sex, or in relation to wholly different habits of life in the two sexes, as is sometimes the case with insects. And this leads me to say a few words on what I call Sexual Selection. This depends, not on a struggle for existence, but on a struggle between the males for possession of the females; the result is not death to the unsuccessful competitor, but few or no offspring. Sexual selection is, therefore, less rigorous than natural selection. Generally, the most vigorous males, those which are best fitted for their places in nature, will leave most progeny. But in many cases, victory will depend not on general vigour, but on having special weapons, confined to the male sex. A hornless stag or spurless cock would have a poor chance of leaving offspring. Sexual selection by always allowing the victor to breed might surely give indomitable courage, length to the spur, and strength to the wing to strike in the spurred leg, as well as the brutal cock-fighter, who knows well that he can improve his breed by careful selection of the best cocks. How low in the scale of nature this law of battle descends, I know not; male alligators have been described as fighting, bellowing, and whirling round, like Indians in a war-dance, for the possession of the females; male salmons have been seen fighting all day long; male stag-beetles often bear wounds from the huge mandibles of other males. The war is, perhaps, severest between the males of polygamous animals, and these seem oftenest provided with special weapons. The males of carnivorous animals are already well armed; though to them and to others, special means of defence may be given through means of sexual selection, as the mane to the lion, the shoulder-pad to the boar, and the hooked jaw to the male salmon; for the shield may be as important for victory, as the sword or spear.

You can carry or using a mobile walked in the street.Tory Burch Flip Flops is elegant and trendy, therefore it enables you to to become much more generous and charming, and sporting this sale tory burch, you'll be the main focus arond everyone else.Tory Burch Black Sandals leather ballet flats in distressed nappa leather features the gold metal logo medallion. Spring and summer 2011 is still high color saturation has been welcomed by a comfortable rubber soles will not feel stiff step up, flip the design is more casual, lace embossed on, chain designed to enhance the sweetness index of this pair of Tory Burch Thora . Each piece is stylish yet wearable in its sophisticated aesthetic, blending timeless and classic design elements with modern fashion sensibilitiesU.S Each piece is stylish yet wearable in its sophisticated aesthetic, blending timeless and classic design elements with modern fashion sensibilities.Against the trend of minimalism, popular at the time, was designed Tory Burch Flats Sale its flagship store in downtown New York to feel more like a room in her house in a traditional business.We will supply you the best tory burch flip flops and service. Tory Burch Bootie wanted to create stylish yet wearable clothing and accessories for women of all ages. About the Tory Burch Sandals is the perfect one you should pay attention to.Tory Burch Sophie Wedge is a brand that does not carry Tory Burch Outlet Sale only, but also other products like apparel, bags, and others.So you may also like the Tory Burch sandals and Tory Burch wallets.The Cheap Tory Burch Boots leather upper and sock liner feels soft against the foot, yet is strong and tear resistant, with outstanding breathability.

It may be said that natural selection is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life. We see nothing of these slow changes in progress, until the hand of time has marked the long lapse of ages, and then so imperfect is our view into long past geological ages, that we only see that the forms of life are now different from what they formerly were. Although natural selection can act only through and for the good of each being, yet characters and structures, which we are apt to consider as of very trifling importance, may thus be acted on. When we see leaf-eating insects green, and bark-feeders mottled-grey; the alpine ptarmigan white in winter, the red-grouse the colour of heather, and the black-grouse that of peaty earth, we must believe that these tints are of service to these birds and insects in preserving them from danger. Grouse, if not destroyed at some period of their lives, would increase in countless numbers; they are known to suffer largely from birds of prey; and hawks are guided by eyesight to their prey,--so much so, that on parts of the Continent persons are warned not to keep white pigeons, as being the most liable to destruction. Hence I can see no reason to doubt that natural selection might be most effective in giving the proper colour to each kind of grouse, and in keeping that colour, when once acquired, true and constant. Nor ought we to think that the occasional destruction of an animal of any particular colour would produce little effect: we should remember how essential it is in a flock of white sheep to destroy every lamb with the faintest trace of black. In plants the down on the fruit and the colour of the flesh are considered by botanists as characters of the most trifling importance: yet we hear from an excellent horticulturist, Downing, that in the United States smooth-skinned fruits suffer far more from a beetle, a curculio, than those with down; that purple plums suffer far more from a certain disease than yellow plums; whereas another disease attacks yellow-fleshed peaches far more than those with other coloured flesh. If, with all the aids of art, these slight differences make a great difference in cultivating the several varieties, assuredly, in a state of nature, where the trees would have to struggle with other trees and with a host of enemies, such differences would effectually settle which variety, whether a smooth or downy, a yellow or purple fleshed fruit, should succeed. In looking at many small points of difference between species, which, as far as our ignorance permits us to judge, seem to be quite unimportant, we must not forget that climate, food, etc., probably produce some slight and direct effect. It is, however, far more necessary to bear in mind that there are many unknown laws of correlation of growth, which, when one part of the organisation is modified through variation, and the modifications are accumulated by natural selection for the good of the being, will cause other modifications, often of the most unexpected nature. As we see that those variations which under domestication appear at any particular period of life, tend to reappear in the offspring at the same period;--for instance, in the seeds of the many varieties of our culinary and agricultural plants; in the caterpillar and cocoon stages of the varieties of the silkworm; in the eggs of poultry, and in the colour of the down of their chickens; in the horns of our sheep and cattle when nearly adult;--so in a state of nature, natural selection will be enabled to act on and modify organic beings at any age, by the accumulation of profitable variations at that age, and by their inheritance at a corresponding age. If it profit a plant to have its seeds more and more widely disseminated by the wind, I can see no greater difficulty in this being effected through natural selection, than in the cotton-planter increasing and improving by selection the down in the pods on his cotton-trees. Natural selection may modify and adapt the larva of an insect to a score of contingencies, wholly different from those which concern the mature insect. These modifications will no doubt affect, through the laws of correlation, the structure of the adult; and probably in the case of those insects which live only for a few hours, and which never feed, a large part of their structure is merely the correlated result of successive changes in the structure of their larvae. So, conversely, modifications in the adult will probably often affect the structure of the larva; but in all cases natural selection will ensure that modifications consequent on other modifications at a different period of life, shall not be in the least degree injurious: for if they became so, they would cause the extinction of the species. Natural selection will modify the structure of the young in relation to the parent, and of the parent in relation to the young. In social animals it will adapt the structure of each individual for the benefit of the community; if each in consequence profits by the selected change. What natural selection cannot do, is to modify the structure of one species, without giving it any advantage, for the good of another species; and though statements to this effect may be found in works of natural history, I cannot find one case which will bear investigation. A structure used only once in an animal's whole life, if of high importance to it, might be modified to any extent by natural selection; for instance, the great jaws possessed by certain insects, and used exclusively for opening the cocoon--or the hard tip to the beak of nestling birds, used for breaking the egg. It has been asserted, that of the best short-beaked tumbler-pigeons more perish in the egg than are able to get out of it; so that fanciers assist in the act of hatching. Now, if nature had to make the beak of a full-grown pigeon very short for the bird's own advantage, the process of modification would be very slow, and there would be simultaneously the most rigorous selection of the young birds within the egg, which had the most powerful and hardest beaks, for all with weak beaks would inevitably perish: or, more delicate and more easily broken shells might be selected, the thickness of the shell being known to vary like every other structure.

 
ANNONS

Från
    Kom ihåg mig
URL

Säkerhetskod
   Spamskydd  

Kommentar

Av debbyhanxu debbyhanxu - 26 maj 2011 04:45

I loved New Haven with its cauldron of old-fashioned ethnic politics and student activists. East Haven, next door, was overwhelmingly Italian, while nearby Orange was mostly Irish. The towns farther away from New Haven tended to be wealthier, with th...

Av debbyhanxu debbyhanxu - 26 maj 2011 04:41

However, in 1966 a lot of the white segregationists were still southern Democrats, people like Orval Faubus and Jim Johnson and Governor George Wallace of Alabama. And the Senate was full of them, grand characters like Richard Russell of Georgia and ...

Av debbyhanxu debbyhanxu - 26 maj 2011 04:38

how can it have happened? To faint away at the last moment, when everything was ready; when he was at the very gate! It's like some hideous joke." "I tell you," Martini answered, "the only thing I can think of is that one of these attacks must have c...

Av debbyhanxu debbyhanxu - 26 maj 2011 04:35

Will you not come under shelter, my friend?" the soft voice said. "I am afraid you are chilled." The Gadfly's heart stood still. For a moment he was conscious of nothing but the sickening pressure of the blood that seemed as if it would tear his brea...

Av debbyhanxu debbyhanxu - 25 maj 2011 03:54

Next day, with the courage you find you have when there is nothing more to lose, she got in touch with C. Morris Schrift, and inquired after his mysteri­ous client. "He decided to attend the auction in person," was all Schrift would tell her. "You mi...

Presentation

Fråga mig

0 besvarade frågor

Kalender

Ti On To Fr
           
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20 21
22
23
24
25 26
27
28
29
30
31
<<<
Maj 2011
>>>

Sök i bloggen

Senaste inläggen

Kategorier

Arkiv

RSS

Besöksstatistik

Följ bloggen

Följ debbyhanxu med Blogkeen
Följ debbyhanxu med Bloglovin'

Skaffa en gratis bloggwww.bloggplatsen.se