From this cause alone the
intermediate varieties will be liable to accidental extermination; and
during the process of further modification through natural selection, they
will almost certainly be beaten and supplanted by the forms which they
connect; for these, from existing in greater numbers will, in the
aggregate, present more varieties, and thus be further improved through
natural selection and gain further advantages.
Lastly, looking not to any one time, but at all time, if my theory be true,
numberless intermediate varieties, linking closely together all the species
of the same group, must assuredly have existed; but the very process of
natural selection constantly tends, as has been so often remarked, to
exterminate the parent forms and the intermediate links. Consequently
evidence of their former existence could be found only among fossil remains,
which are preserved, as we shall attempt to show in a future chapter, in an
extremely imperfect and intermittent record.
ON THE ORIGIN AND TRANSITION OF ORGANIC BEINGS WITH PECULIAR HABITS AND
STRUCTURE.
It has been asked by the opponents of such views as I hold, how, for
instance, could a land carnivorous animal have been converted into one with
aquatic habits; for how could the animal in its transitional state have
subsisted? It would be easy to show that there now exist carnivorous
animals presenting close intermediate grades from strictly terrestrial to
aquatic habits; and as each exists by a struggle for life, it is clear that
each must be well adapted to its place in nature.
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