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are our present 1866 1869
our present 1859 1860 1861
are our existing 1872

of a genus ever 1861 1866 1869 1872
are 1859 1860

the other species becoming utterly extinct and leaving no modified progeny. 1861 1866 1869 1872
at any one period; and all changes are slowly effected. 1859 1860

number of intermediate forms must have existed, linking together all the species in each group by
gradations
graduations
as fine as are our present varieties, it may be asked, Why do we not see these linking forms all around us? Why are not all organic beings blended together in an inextricable chaos? With respect to existing forms, we should remember that we have no right to expect (excepting in rare cases) to discover directly connecting links between them, but only between each and some extinct and supplanted form. Even on a wide area, which has during a long period remained continuous, and of which the
climatic
climate
and other conditions of life change insensibly in
proceeding
going
from a district occupied by one species into another district occupied by a closely allied species, we have no just right to expect often to find intermediate varieties in the intermediate
zones.
zone.
For we have reason to believe that only a few species of a genus ever
undergoing
undergo
change
change;
the other species becoming utterly extinct and leaving no modified progeny. Of the species which do change, only a few within the same country change at the same time; and all modifications are slowly effected. I have also shown that the intermediate varieties which
probably
will
at first
probably
probably
existed
exist
in the intermediate zones,
would
will
be liable to be supplanted by the allied forms on either hand;
for
and
the latter, from existing in greater numbers,
would
will
generally be modified and improved at a quicker rate than the intermediate varieties, which
existed
exist
in lesser numbers; so that the intermediate varieties
would,
will,
in the long run, be supplanted and exterminated.
On this doctrine of the extermination of an infinitude of connecting links, between the living and extinct inhabitants of the world, and at each successive period between the extinct and still older species, why is not every geological formation charged with such links?