Evolution and AdaptationMacmillan, 1903 - Всего страниц: 470 |
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Стр. 4
... actions , and imitation of the old birds at the time of nest - building may , perhaps , also enter into the result . It has been stated that the first nest built by young birds is less perfect than that built by older birds , but this ...
... actions , and imitation of the old birds at the time of nest - building may , perhaps , also enter into the result . It has been stated that the first nest built by young birds is less perfect than that built by older birds , but this ...
Стр. 18
... action of the sense organs , as truly adapta- tions as the special cases that have been selected for illustra- tion . The answer is simply that we are more impressed by those cases of adaptation that are more unusual , as when an animal ...
... action of the sense organs , as truly adapta- tions as the special cases that have been selected for illustra- tion . The answer is simply that we are more impressed by those cases of adaptation that are more unusual , as when an animal ...
Стр. 26
... actions do not assist in preserving its integrity as do some , at least , of the activities of an animal . It is true , of course , that in a mechanical sense every action of the organism leads also to a breaking down of its structure ...
... actions do not assist in preserving its integrity as do some , at least , of the activities of an animal . It is true , of course , that in a mechanical sense every action of the organism leads also to a breaking down of its structure ...
Стр. 82
... action of external and internal factors has brought about considerable changes in the ontogenetic system , and , indeed , in a generally advancing direction , so that in reality a later condition can never correspond to a preceding one ...
... action of external and internal factors has brought about considerable changes in the ontogenetic system , and , indeed , in a generally advancing direction , so that in reality a later condition can never correspond to a preceding one ...
Стр. 95
... action of the environment on the parent or on its reproductive cells . It is the former , i.e. the fluctuating variability , that , according to Darwin , has been used by the breeder to produce most of our domestic In regard to the ...
... action of the environment on the parent or on its reproductive cells . It is the former , i.e. the fluctuating variability , that , according to Darwin , has been used by the breeder to produce most of our domestic In regard to the ...
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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...