The Origin of Species by Means of Natural Selection, Or, The Preservation of Favored Races in the Struggle for Life, 1-2권D. Appleton, 1917 |
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... fertility has been di- minished in nearly all these cases by an independent cause , namely , by too close interbreeding . I have made so many experiments and collected so many facts , show- ing on the one hand that an occasional cross ...
... fertility has been di- minished in nearly all these cases by an independent cause , namely , by too close interbreeding . I have made so many experiments and collected so many facts , show- ing on the one hand that an occasional cross ...
13 페이지
... fertility , both of first crosses and of hybrids , is more easily affected by unfavourable conditions , than is that of pure species . But the fertility of first crosses is likewise innately variable ; for it is not always the same in ...
... fertility , both of first crosses and of hybrids , is more easily affected by unfavourable conditions , than is that of pure species . But the fertility of first crosses is likewise innately variable ; for it is not always the same in ...
16 페이지
... fertility . These facts show how completely the fertility of a hybrid may be independent of its external resemblance to either pure parent . Considering the several rules now given , which govern the fertility of first crosses and of ...
... fertility . These facts show how completely the fertility of a hybrid may be independent of its external resemblance to either pure parent . Considering the several rules now given , which govern the fertility of first crosses and of ...
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adapted affinity allied species ancient animals appear Archipelago beak become believe belonging birds breeds Cambrian cause characters climate closely allied colour common continent crossed crustaceans degree developed difficulty distinct species domestic doubt eggs embryo Europe existing extinct extremely facts favourable fertilised fertility fish flowers formation formerly forms fossil Fritz Müller Gärtner genera genus geological geological period Glacial period gradations groups of species habits Hence hybrids hybrids produced important individuals inhabitants inherited insects instance instincts intercrossing intermediate land larvæ less living male mammals manner Marsupials migration modified descendants natural selection naturalists nearly occur oceanic islands offspring organisation parent peculiar perfect pigeon pistil plants pollen present probably produced progenitor quadrupeds ranked reciprocal crosses remarked resemblance seeds Silurian slight South America stage stamens sterility structure successive suppose theory tion variability variations varieties vary whilst whole widely different wings