Evolution and AdaptationMacmillan, 1903 - Всего страниц: 470 |
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Стр. 12
... advantage to the animal , except possibly in sav- ing a certain amount of food , but since the same change will take place when an abundance of food is consumed , the result is , under these conditions , of no use . The thickening of ...
... advantage to the animal , except possibly in sav- ing a certain amount of food , but since the same change will take place when an abundance of food is consumed , the result is , under these conditions , of no use . The thickening of ...
Стр. 21
... to attract insects , and their presence is one of the means by which in- sects find the flowers . This also is of advantage to the race . ORGANS OF LITTLE USE TO THE INDIVIDUAL In every organism The Problem of Adaptation 21.
... to attract insects , and their presence is one of the means by which in- sects find the flowers . This also is of advantage to the race . ORGANS OF LITTLE USE TO THE INDIVIDUAL In every organism The Problem of Adaptation 21.
Стр. 24
... advantage to the plant to have attracted the attention of the fruit - eating birds . On the other hand one of the most brilliantly colored seeds , the acorn , is too large to pass through the digestive tracts of birds , and is , in fact ...
... advantage to the plant to have attracted the attention of the fruit - eating birds . On the other hand one of the most brilliantly colored seeds , the acorn , is too large to pass through the digestive tracts of birds , and is , in fact ...
Стр. 28
... advantage to the river to straighten its course . Again , a glacier moulds itself to its bed , and gradually moves around obstacles to a lower level , but this adaptation of the glacier to the form of its surroundings cannot be said to ...
... advantage to the river to straighten its course . Again , a glacier moulds itself to its bed , and gradually moves around obstacles to a lower level , but this adaptation of the glacier to the form of its surroundings cannot be said to ...
Стр. 29
... advantage is it to the crystal whether it is complete or incomplete ? In the case of an animal it is of some importance to be able to complete itself after injury , because it can then better obtain the food necessary to keep it alive ...
... advantage is it to the crystal whether it is complete or incomplete ? In the case of an animal it is of some importance to be able to complete itself after injury , because it can then better obtain the food necessary to keep it alive ...
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acquired characters adaptation adult advantage amongst animals and plants aphids appear arisen artificial selection assume become believe birds breed butterflies caterpillars causes cells chromosomes color connection crawl crustaceans Darwin Darwinian degeneration degrees descendants determined direction elementary species embryo environment evidence evolution examine exist experiments explain fact fertilized eggs flowers fluctuating variations gemmules geotropic germ-cells give heliotropic hybrid hypothesis important individuals inheritance of acquired insects instance instinct kinds Lamarck Lamarckian large number larvæ later leaves less light living long-styled male and female mammals ment moths mutation theory Nägeli natural selection nest offspring organs origin outcome pangenesis parent form parthenogenetic polar body pollen probable produced question race reproduction resemblance response result rotifers seeds sexual reproduction sexual selection shown side sort spermatozoon stages stamens structure supposed surface takes place tion tropisms tube variability varieties Vries Weismann wings young
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Стр. 117 - If such do occur, can we doubt (remembering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating their kind ? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favourable individual differences and variations, and the destruction of those which are injurious, I have called Natural...
Стр. 131 - To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree.
Стр. 116 - When we reflect on this struggle, we may console ourselves with the full belief, that the war of nature is not incessant, that no fear is felt, that death is generally prompt, and that the vigorous, the healthy, and the happy survive and multiply.
Стр. 116 - Can the principle of selection, which we have seen is so potent in the hands of man, apply under nature? I think we shall see that it can act most efficiently. Let the endless number of slight variations and individual differences occurring in our domestic productions, and, in a lesser degree, in those under nature, be borne in mind ; as well as the strength of the hereditary tendency.
Стр. 113 - The amount of food for each species of course gives the extreme limit to which each can increase ; but very frequently it is not the obtaining food, but the serving as prey to other animals, which determines the average numbers of a species.
Стр. 119 - ... be, compared with those accumulated by nature during whole geological periods. Can we wonder, then, that nature's productions should be far "truer" in character than man's productions; that they should be infinitely better adapted to the most complex conditions of life, and should plainly...
Стр. 129 - LONG before the reader has arrived at this part of my work, a crowd of difficulties will have occurred to him. Some of them are so serious that to this day I can hardly reflect on them without being in some degree staggered...
Стр. 117 - Variations neither useful nor injurious would not be affected by natural selection, and would be left either a fluctuating element, as perhaps we see in certain polymorphic species, or would ultimately become fixed, owing to the nature of the organism and the nature of the conditions.
Стр. 116 - Can it, then, be thought improbable, seeing that variations useful to man have undoubtedly occurred, that other variations, useful in some way to each being in the great and complex battle of life, should occur in the course of many successive generations ? If such do occur, can we doubt (remembering that many more...
Стр. 108 - Again, it may be asked, how is it that varieties, which I have called incipient species, become ultimately converted into good and distinct species, which in most cases obviously differ from each other far more than do the varieties of the same species...