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of time, immensely 1869 1872
enormously 1859 1860 1861
of time, enormously 1866

encountered on the theory of descent with modification are
grave
serious
enough. All the individuals of the same species, and all the species of the same genus, or even higher group,
are
must have
descended from common parents; and therefore, in however distant and isolated parts of the world they
are
may
now
found,
be found,
they must in the course of successive generations have
passed
travelled
from some one
part
point
to
the
all the
others. We are often wholly unable even to conjecture how this could have been effected. Yet, as we have reason to believe that some species have retained the same specific
from
form
for very long
periods,
periods
of time, immensely long as measured by years, too much stress ought not to be laid on the occasional wide diffusion of the same species; for during very long periods
of time
....
there will always
have been
be
a good chance for wide migration by many means. A broken or interrupted range may often be accounted for by the extinction of the species in the intermediate regions. It cannot be denied that we are as yet very ignorant
as to
of
the full extent of the various climatal and geographical changes which have affected the earth during modern periods; and such changes
will
may
often
obviously
have
greatly
....
facilitated migration. As an example, I have attempted to show how potent has been the influence of the Glacial period on the distribution
both
....
of the same and of
representative
allied
species throughout the world. We are as yet profoundly ignorant of the many occasional means of transport. With respect to distinct species of the same genus inhabiting
very
....
distant and isolated regions, as the process of modification has necessarily been slow, all the means of migration will have been possible during a very long period; and consequently the difficulty of the wide diffusion of
species
the species
of the same genus is in some degree lessened.
As
on
according to
the theory of natural selection an interminable