| Comparison with 1860 |
|
|
varying, and far-spreading species, which already have
invaded to a certain extent the territories of other species, should be those which would have the best chance of spreading still further, and of giving rise in new countries to new
varieties and species. The process of diffusion may
often be very slow, being
dependent
on climatal and geographical changes, or
on strange accidents, but
in the long run
the dominant forms will
generally succeed in spreading. The diffusion would, it is probable, be slower with the terrestrial inhabitants of distinct continents than with the marine inhabitants of the continuous sea. We might therefore expect to find, as we apparently
do find, a less strict degree of parallel
succession
in the productions
of the land than
of the sea.
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|
| Dominant species spreading from any region might encounter still more dominant species, and then their triumphant course, or even their existence, would cease. We know not at all precisely what are all the conditions most favourable for the multiplication of new
and dominant species; but we can, I think, clearly see that a number of individuals, from giving a better chance of the appearance of favourable variations, and that severe competition with many already existing forms, would be highly favourable, as would be the power of spreading into new territories. A certain amount of isolation, recurring at long intervals of time, would probably be also favourable, as before explained. One quarter of the world may have been most favourable for the production of new and dominant species on the land, and another for those in the waters of the sea. If two great regions had been for a long period favourably circumstanced in an equal degree, whenever their inhabitants met, the battle would be prolonged and severe; and some from one birthplace and some from the other might be victorious. But in the course of time, the
|
varying, and far-spreading species, which
already have | already have 1859 1860 1861 1866 1869 | | have already 1872 |
| new 1859 1860 1861 1866 | | other new 1869 1872 |
| may 1859 1860 1861 1866 | | would 1869 1872 |
| being 1859 1860 1861 1866 | being 1869 1872 |
| dependent 1859 1860 1861 1866 | | depending 1869 1872 |
| or 1859 1860 1861 1866 | or 1869 1872 |
| but 1859 1860 |
| or on the gradual acclimatisation of new species to the various climates through which they must pass, but 1861 |
| or on the gradual acclimatisation of new species to the various climates through which they have to pass, but 1866 |
| and on the gradual acclimatisation of new species to the various climates through which they might have to pass, but 1869 1872 |
| long run 1859 1860 1861 |
| course of time 1866 1869 1872 |
| will 1859 1860 1861 1866 | | would 1869 1872 |
| spreading. 1859 1860 1861 1866 |
| spreading and would ultimately prevail. 1869 1872 |
| apparently 1859 1860 1861 1866 | apparently 1869 1872 |
| parallel 1859 1860 1861 1866 | | parallelism 1869 1872 |
| succession 1859 1860 1861 1866 | succession 1869 1872 |
| productions 1859 1860 1861 1866 | | succession 1869 1872 |
| land than 1859 1860 1861 1866 | | productions 1869 1872 |
| sea. 1859 1860 1861 1866 |
| land than with those of the sea. 1869 1872 |
|
|
Dominant species spreading from any region might encounter still more dominant species, and then their triumphant course, or even their existence, would cease. We know not at all precisely what are all the conditions most favourable for the multiplication of
new | new 1859 1860 1861 |
| any one new 1866 |
|
