The Origin of Species by Means of Natural Selection; Or, the Preservation of Favored Races in the Struggle for Life ...A.L. Burt, 1890 - 538페이지 |
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37 페이지
... variability , both by acting directly on the organization , and indirectly by affecting the reproductive system . It is not probable that variability is an inherent and necessary contingent , under all circum- stances . The greater or ...
... variability , both by acting directly on the organization , and indirectly by affecting the reproductive system . It is not probable that variability is an inherent and necessary contingent , under all circum- stances . The greater or ...
144 페이지
... variability in the parts undergoing modi- fication may always be expected . Now let us turn to nature . When a part ... variability , which has continually been accumulated by natural selection for the benefit of the species . But as the ...
... variability in the parts undergoing modi- fication may always be expected . Now let us turn to nature . When a part ... variability , which has continually been accumulated by natural selection for the benefit of the species . But as the ...
306 페이지
... variability graduates away . When mongrels and the more fertile hybrids are propagated for several generations , an extreme amount of variability in the offspring in both cases is notorious ; but some few instances of both hybrids and ...
... variability graduates away . When mongrels and the more fertile hybrids are propagated for several generations , an extreme amount of variability in the offspring in both cases is notorious ; but some few instances of both hybrids and ...
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adapted admit affinities allied species America ancient appear Asa Gray beak become bees believe belonging birds breeds cause cells characters climate closely allied color continued crossed crustaceans degree developed difficulty distinct species divergence domestic doubt effects eggs embryo existing extinct extremely facts favorable fertility flowers formation forms fossil Fritz Müller genera genus geological geological period Glacial period gradations greater number groups of species habits Hence hybrids hybrids produced important individuals inhabitants inherited insects instance instincts intercrossing intermediate intervals kind lamellæ larvæ less living male mammals manner marsupials migration modified descendants natural selection naturalists nearly nest occasionally oceanic islands offspring organs parent peculiar perfect pigeons pistil pollen present principle probably produced quadrupeds ranked remarked resemblance rudimentary seeds sexual selection Silurian slight South America stamens sterility structure successive suppose tend theory tion variability variations varieties vary whole widely different wings young