On the origin of species by means of natural selection ; or, The preservation of favored races in the struggle for lifeD. Appleton and Company, 1875 - Всего страниц: 458 |
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Стр. 236
... sterility of species ; for it seems to make a broad and clear distinction between varieties and species . Degrees of Sterility . - First , for the sterility of species when crossed and of their hybrid offspring . It is impossible to ...
... sterility of species ; for it seems to make a broad and clear distinction between varieties and species . Degrees of Sterility . - First , for the sterility of species when crossed and of their hybrid offspring . It is impossible to ...
Стр. 238
... sterility between distinct species is a universal law of nature . He experimented on some of the very same species as did Gärtner . The difference in their results may , I think , be in part accounted for by Herbert's great ...
... sterility between distinct species is a universal law of nature . He experimented on some of the very same species as did Gärtner . The difference in their results may , I think , be in part accounted for by Herbert's great ...
Стр. 240
... sterility in the hybrids should have gone on increasing . Although I know of hardly any thoroughly well - authenticated cases of perfectly fertile hybrid animals , I have reason to believe that the hybrids from Cervulus vaginalis and ...
... sterility in the hybrids should have gone on increasing . Although I know of hardly any thoroughly well - authenticated cases of perfectly fertile hybrid animals , I have reason to believe that the hybrids from Cervulus vaginalis and ...
Стр. 241
... sterility of species when crossed ; or we must look at this sterility in animals , not as an indelible characteristic , but as one capable of being removed by domestication . Finally , considering all the ascertained facts on the ...
... sterility of species when crossed ; or we must look at this sterility in animals , not as an indelible characteristic , but as one capable of being removed by domestication . Finally , considering all the ascertained facts on the ...
Стр. 244
... the other is used as the father or the mother , there is generally some difference , and occasionally the widest possible difference , in the facility of effecting an union . The hybrids 244 CHAP . IX . Laws governing the Sterility.
... the other is used as the father or the mother , there is generally some difference , and occasionally the widest possible difference , in the facility of effecting an union . The hybrids 244 CHAP . IX . Laws governing the Sterility.
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adapted admit affinities allied species America analogous ancient appear beak become bees believe belonging birds breeds cause cells characters climate closely allied colour continued crossed crustaceans degree developed difficulty distinct species doubt effects eggs embryo existing extinct extremely facts favourable fertilised fertility flowers formations formerly forms fossil Fritz Müller genera genus geological geological period Glacial period gradations greater number groups of species habits Hence hybrids important individuals inhabitants inherited insects instance instincts intercrossing intermediate kind lamellæ larvæ less living male mammals manner Marsupials migration modified descendants natural selection naturalists nearly nest occasionally occur oceanic islands offspring organisation organs parent peculiar perfect pigeon pistil pollen present principle probably produced quadrupeds ranked reciprocal crosses remarked reproductive resemblance rudimentary seeds sexual selection Silurian slight South America stamens sterility structure struggle successive supposed theory tion variability variations varieties vary whilst whole wings young
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Стр. 50 - I should premise that I use this term in a large and metaphorical sense, including dependence of one being on another, and including (which is more important) not only the life of the individual, but success in leaving progeny.
Стр. 63 - It has been said that I speak of natural selection as an active power or Deity; but who objects to an author speaking of the attraction of gravity as ruling the movements of the planets ? Every one knows what is meant and is implied by such metaphorical expressions; and they are almost necessary for brevity.
Стр. 65 - 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 bear the stamp of far higher workmanship...
Стр. 143 - 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. 3 - As many more individuals of each species are born than can possibly survive ; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected.
Стр. 56 - ... there was a large and extremely barren heath, which had never been touched by the hand of man ; but several hundred acres of exactly the same nature had been enclosed twenty-five years previously and planted with Scotch fir. The change in the native vegetation of the planted part of the heath was most remarkable, more than is generally seen in passing from one quite different soil to another ; not only the proportional numbers of the heath-plants were wholly changed, but twelve species of plants...
Стр. 49 - Nothing is easier than to admit in words the truth of the universal struggle for life, or more difficult — at least I have found it so — than constantly to bear this conclusion in mind. Yet unless it be thoroughly engrained in the mind, the whole economy of nature, with every fact on distribution, rarity, abundance, extinction, and variation, will be dimly seen or quite misunderstood.
Стр. 48 - ... we see beautiful adaptations everywhere and in every part of the organic world.
Стр. 69 - 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 depends not so much on general vigor as on having special weapons, confined to the male sex. A hornless stag or spurless cock would have a poor chance of leaving numerous offspring.
Стр. 412 - What limit can be put to this power, acting during long ages and rigidly scrutinising the whole constitution, structure, and habits of each creature, — favouring the good and rejecting the bad ? I can see no limit to this power, in slowly and beautifully adapting each form to the most complex relations of life.