As the accumulation of
each formation has often been interrupted, and as long blank intervals
have intervened between successive formations, we ought not to expect
to find, as I attempted to show in the last chapter, in any one or two
formations all the intermediate varieties between the species which
appeared at the commencement and close of these periods; but we ought
to find after intervals, very long as measured by years, but only
moderately long as measured geologically, closely allied forms, or, as
they have been called by some authors, representative species; and
these we assuredly do find. We find, in short, such evidence of the
slow and scarcely sensible mutation of specific forms, as we have a
just right to expect to find.
ON THE STATE OF DEVELOPMENT OF ANCIENT FORMS.
There has been much discussion whether recent forms are more highly
developed than ancient. I will not here enter on this subject, for
naturalists have not as yet defined to each other's satisfaction what
is meant by high and low forms. But in one particular sense the more
recent forms must, on my theory, be higher than the more ancient; for
each new species is formed by having had some advantage in the
struggle for life over other and preceding forms. If under a nearly
similar climate, the eocene inhabitants of one quarter of the world
were put into competition with the existing inhabitants of the same or
some other quarter, the eocene fauna or flora would certainly be
beaten and exterminated; as would a secondary fauna by an eocene, and
a palaeozoic fauna by a secondary fauna.
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