| → because new varieties are very slowly formed, for variation 1866 |
| variation 1859 1860 1861 1869 1872 |
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| → variations chance to 1859 1861 1866 |
| varia- tions chance to 1860 |
| individual differences or variations 1869 1872 |
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in smaller numbers in a narrow and intermediate zone. For forms existing in larger numbers will
have a better chance, within any given period, of presenting further favourable variations for natural selection to seize on, than will the rarer forms which exist in lesser numbers. Hence, the more common forms, in the race for life, will tend to beat and supplant the less common forms, for these will be more slowly modified and improved. It is the same principle which, as I believe, accounts for the common species in each country, as shown in the second chapter, presenting on an average a greater number of well-marked varieties than do the rarer species. I may illustrate what I mean by supposing three varieties of sheep to be kept, one adapted to an extensive mountainous region; a second to a comparatively narrow, hilly tract; and a third to
plains at the base; and that the inhabitants are all trying with equal steadiness and skill to improve their stocks by selection; the chances in this case will be strongly in favour of the great holders on the mountains or on the
improving their breeds more quickly than the small holders on the intermediate narrow, hilly tract; and consequently the improved mountain or plain breed will soon take the place of the less improved hill breed; and thus the two breeds, which originally existed in greater numbers, will come into close contact with each other, without the interposition of the supplanted, intermediate
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| To sum up, I believe that species come to be tolerably well-defined objects, and do not at any one period present an inextricable chaos of varying and intermediate links:
because new varieties are very slowly formed, for
→because new varieties are very slowly formed, for variation
is a
slow process, and natural selection can do nothing until favourable
→variations chance to
occur, and until a place in
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