On the Origin of Species by Means of Natural Selection: Or, The Preservation of Favoured Races in the Struggle for LifeEaston Press, 1976 - 470 páginas |
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Página 243
... offspring , is , with reference to my theory , of equal importance with the sterility of species ; for it seems to make a broad and clear distinction between varieties and species . First , for the sterility of species when crossed and ...
... offspring , is , with reference to my theory , of equal importance with the sterility of species ; for it seems to make a broad and clear distinction between varieties and species . First , for the sterility of species when crossed and ...
Página 271
... offspring . The consideration of these facts on dimorphism , as well as of the results of reciprocal crosses , clearly leads to the conclusion that the primary cause of the sterility of crossed species is confined to differences in ...
... offspring . The consideration of these facts on dimorphism , as well as of the results of reciprocal crosses , clearly leads to the conclusion that the primary cause of the sterility of crossed species is confined to differences in ...
Página 421
... offspring . On the one side , there is good reason to believe that slight changes in the conditions of life give vigour and fertility to all organic beings . We know also that a cross between the distinct individuals of the same variety ...
... offspring . On the one side , there is good reason to believe that slight changes in the conditions of life give vigour and fertility to all organic beings . We know also that a cross between the distinct individuals of the same variety ...
Contenido
VARIATION UNDER NATURE | 30 |
STRUGGLE FOR EXISTENCE | 45 |
NATURAL SELECTION | 59 |
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Términos y frases comunes
accumulated adapted admit affinities allied species America ancient appear beak become bees believe belonging birds breeds cause cells characters climate closely allied colour common progenitor continuous crossed crustaceans degree developed difficulty distinct species divergence doubt effects eggs embryo existing exterminated extinct extremely facts favourable fertilised fertility flowers formation forms fossil Fritz Müller genera genus geological geological period gradations greater number groups of species habits Hence hybrids hybrids produced important increase 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 offspring organisation organs Origin of Species parent peculiar perfect pigeons pistil plants pollen present preserved principle probably produced quadrupeds ranked reciprocal crosses remarked resemblance rudimentary seeds slight South America stamens sterility structure struggle successive supposed swimbladder theory variability variations varieties vary whilst whole wings young