in the
direction required by the theory; but to this latter subject I shall have to return in the following direction required by the theory; but to this latter subject I shall have to return in the following 1869 |
following 1859 1860 |
direction required by my theory; but to this latter subject I shall have to return in the following 1861 1866 |
direction required by the theory; but to this latter subject I shall return in the following 1872 |
chapter. |
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...OMIT 1866 1869 1872 |
One other consideration is worth notice: 1859 1860 1861 |
With With 1866 1869 1872 | with 1859 1860 1861 |
animals and plants that
....... 1866 1869 1872 | can 1859 1860 1861 |
propagate rapidly and
do do 1866 1869 1872 | are 1859 1860 1861 |
not
wander much, wander much, 1866 1869 1872 | highly locomotive, 1859 1860 1861 |
there is reason to suspect, as we have formerly seen, that their varieties are generally at first local; and that such local varieties do not spread widely and supplant their parent-forms until they have been modified and perfected in some considerable degree. According to this view, the chance of discovering in a formation in any one country all the early stages of transition between any two
such forms, such forms, 1866 1869 | forms, 1859 1860 1861 1872 |
is small, for the successive changes are supposed to have been local or confined to some one spot. Most marine animals have a wide range; and we have seen that with plants it is those which have the widest range, that oftenest present varieties; so
that, that, 1866 1869 1872 | that 1859 1860 1861 |
with shells and other marine animals, it is
probable probable 1869 1872 |
probably 1859 1860 |
highly probable that 1861 1866 |
that those which have that those which have 1869 |
those which have 1859 1860 1861 1866 |
that those which 1872 |
had the widest range, far exceeding the limits of the known geological formations of Europe,
....... 1861 1866 1869 1872 | which 1859 1860 |
have oftenest given rise, first to local varieties and ultimately to new species; and this again would greatly lessen the chance of our being able to trace the stages of transition in any
one one 1859 1860 1866 1869 1872 | ony 1861 |
geological formation. |
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It is a more important consideration,
....... 1869 1872 | clearly 1866 |
leading to the same result, as lately insisted on by Dr. Falconer, namely, that the
period period 1869 1872 | periods 1866 |
during which
each species underwent each species underwent 1869 1872 |
species have been undergoing 1866 |
modification, though
..
long as measured by years,
was, from the reasons lately assigned, probably was, from the reasons lately assigned, probably 1869 |
have probably been 1866 |
was probably 1872 |
short in comparison with
that that 1869 1872 | the periods 1866 |
during which
it it 1869 1872 |
these same species 1866 |
remained without undergoing any change. ↑2 blocks not present in 1859 1860 1861 1869 1872; present in 1866 | We may infer that this has been the case, from there being no inherent tendency in organic beings to become modified or to progress in structure, and from all modifications depending, firstly on long-continued variability, and secondly on changes in the physical conditions of life, or on changes in the habits and structure of competing species, or on the immigration of new forms; and such contingencies will supervene in most cases only after long intervals of time and at a slow rate.
These changes, moreover, in the organic and inorganic conditions of life will affect only a limited number of the inhabitants of any one area or country.
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It should not be forgotten, that at the present day, with perfect specimens for examination, two forms can seldom be connected by intermediate
varieties, varieties, 1861 1866 1869 1872 | varieties 1859 1860 |
and thus proved to be the same species, until many specimens
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