On the Origin of Species by Means of Natural Selection, Or, The Preservation of Favoured Races in the Struggle for Life |
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Page 210
CHAPTER VIII HYBRIDISM Distinction between the sterility of first crosses and of hybrids— Sterility various in degree , not universal , affected by close interbreeding , removed by domestication — Laws governing the sterility of hybrids ...
CHAPTER VIII HYBRIDISM Distinction between the sterility of first crosses and of hybrids— Sterility various in degree , not universal , affected by close interbreeding , removed by domestication — Laws governing the sterility of hybrids ...
Page 227
... sterility ensues . So it is with hybrids , for hybrids in successive generations are eminently liable to vary , as every experimentalist has observed . Thus we see that when organic beings are placed under new and unnatural conditions ...
... sterility ensues . So it is with hybrids , for hybrids in successive generations are eminently liable to vary , as every experimentalist has observed . Thus we see that when organic beings are placed under new and unnatural conditions ...
Page 236
... sterility does not strictly follow systematic affinity , but is governed by several curious and complex laws . It is gener- ally different , and sometimes widely different , in reciprocal crosses between the same two species . It is not ...
... sterility does not strictly follow systematic affinity , but is governed by several curious and complex laws . It is gener- ally different , and sometimes widely different , in reciprocal crosses between the same two species . It is not ...
Contents
VARIATION UNDER DOMESTICATION | 6 |
VARIATION UNDER NATURE | 38 |
STRUGGLE FOR EXISTENCE | 52 |
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accumulated adapted affinities allied species amount analogous ancient animals appear archipelago become bees believe birds breeds cause cells characters cirripedes climate closely allied colour common parent continuous crossed crustaceans degree difficulty distant distinct species divergence domestic doubt eggs embryo endemic Europe existing exterminated extinct extremely facts favourable fertility flower formations forms fossil Gärtner genera genus geological geological period Glacial period gradations greater number groups of species habits Hence hermaphrodites hybrids hybrids produced important increase in number individuals inhabitants inherited insects instance instincts intercrossing land larvæ less living male mammals manner migration modification modified descendants natural selection naturalists nearly nest occasionally oceanic islands offspring perfect pigeons pistil plants pollen present probably produced progenitor ranked reciprocal crosses remarked resemblance seeds sexual selection Silurian slight South America sterility structure struggle successive suppose swimbladder theory tion trees variability variations vary whole widely