Independently of the question of fertility,
in all other respects there is the closest general resemblance between
hybrids and mongrels, in their variability, in their power of absorbing
each other by repeated crosses, and in their inheritance of characters from
both parent-forms. Finally, then, although we are as ignorant of the
precise cause of the sterility of first crosses and of hybrids as we are
why animals and plants removed from their natural conditions become
sterile, yet the facts given in this chapter do not seem to me opposed to
the belief that species aboriginally existed as varieties.
CHAPTER X.
ON THE IMPERFECTION OF THE GEOLOGICAL RECORD.
On the absence of intermediate varieties at the present day -- On the
nature of extinct intermediate varieties; on their number -- On the lapse
of time, as inferred from the rate of denudation and of deposition number
-- On the lapse of time as estimated by years -- On the poorness of our
palaeontological collections -- On the intermittence of geological
formations -- On the denudation of granitic areas -- On the absence of
intermediate varieties in any one formation -- On the sudden appearance of
groups of species -- On their sudden appearance in the lowest known
fossiliferous strata -- Antiquity of the habitable earth.
In the sixth chapter I enumerated the chief objections which might be
justly urged against the views maintained in this volume.
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