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
... degree of sterility . Kölreuter makes the rule universal ; but then he cuts the knot , for in ten cases in which he found two forms , considered by most authors as distinct species , quite fertile together , he unhesitatingly ranks them ...
... degree of sterility . Kölreuter makes the rule universal ; but then he cuts the knot , for in ten cases in which he found two forms , considered by most authors as distinct species , quite fertile together , he unhesitatingly ranks them ...
Página 255
... degree of sterility could be increased through natural selection to that high degree which is common with so many species , and which is universal with species which have been differentiated to a generic or family rank , will find the ...
... degree of sterility could be increased through natural selection to that high degree which is common with so many species , and which is universal with species which have been differentiated to a generic or family rank , will find the ...
Página 264
... degree of mutual sterility , so that similar differences in the case of varieties would be no sure guide . It is certain that with species the cause lies exclusively in differences in their sexual constitution . Now the varying ...
... degree of mutual sterility , so that similar differences in the case of varieties would be no sure guide . It is certain that with species the cause lies exclusively in differences in their sexual constitution . Now the varying ...
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