| → on the earth, 1859 1860 1861 1866 |
| OMIT 1869 1872 |
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course of further modification and improvement. The main cause, however, of innumerable intermediate links not now occurring everywhere throughout
on the very process of natural selection, through which new varieties continually take the places of and
their parent-forms. But just in proportion as this process of extermination has acted on an enormous scale, so must the number of intermediate varieties, which have formerly
→on the earth,
be truly enormous. Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such
organic chain; and
perhaps, is the most obvious and
objection which can be urged against
The explanation lies, as I believe, in the extreme imperfection of the geological record. |
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| In the first
it should always be borne in mind what sort of intermediate forms must, on
theory, have formerly existed. I have found it difficult, when looking at any two species, to avoid picturing to
forms
intermediate between them. But this is a wholly false view; we should always look for forms intermediate between each species and a common but unknown progenitor; and the progenitor will generally have differed in some respects from all its modified descendants. To give a simple illustration: the fantail and pouter pigeons
both descended from the rock-pigeon; if we possessed all the intermediate varieties which have ever existed, we should have an extremely close series between both and the rock-pigeon; but we should have no varieties directly intermediate between the fantail and pouter; none, for instance, combining a tail somewhat expanded with a crop somewhat enlarged, the characteristic features of these two breeds. These
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