encountered on the theory of descent with modification are
serious serious 1861 1866 1869 1872 | grave 1859 1860 |
enough. All the individuals of the same species, and all the species of the same genus, or even higher group,
must have must have 1859 1860 1861 1866 1869 | are 1872 |
descended from common parents; and therefore, in however distant and isolated parts of the world they
may may 1866 1869 1872 | are 1859 1860 1861 |
now
be found, be found, 1866 1869 1872 | found, 1859 1860 1861 |
they must in the course of successive generations have
travelled travelled 1869 1872 | passed 1859 1860 1861 1866 |
from some one
point point 1866 1869 1872 | part 1859 1860 1861 |
to
all the all the 1866 1869 1872 | the 1859 1860 1861 |
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
form form 1859 1860 1861 1869 1872 | from 1866 |
for very long
periods periods 1866 1869 1872 | periods, 1859 1860 1861 |
of time, immensely of time, immensely 1869 1872 |
enormously 1859 1860 1861 |
of time, enormously 1866 |
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
....... 1866 1869 1872 | of time 1859 1860 1861 |
there will always
be be 1859 1869 | have been 1860 1861 1866 1872 |
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
of of 1859 1860 1861 1866 1869 | as to 1872 |
the full extent of the various climatal and geographical changes which have affected the earth during modern periods; and such changes
may may 1869 | will 1859 1860 1861 1866 1872 |
obviously obviously 1859 1860 1861 1866 1869 | often 1872 |
have
....... 1869 1872 | greatly 1859 1860 1861 1866 |
facilitated migration. As an example, I have attempted to show how potent has been the influence of the Glacial period on the distribution
....... 1869 1872 | both 1859 1860 1861 1866 |
of the same and of
allied allied 1869 1872 | representative 1859 1860 1861 1866 |
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
....... 1866 1869 1872 | very 1859 1860 1861 |
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
the species the species 1866 1869 1872 | species 1859 1860 1861 |
of the same genus is in some degree lessened. |
|
As
according to according to 1869 1872 | on 1859 1860 1861 1866 |
the theory of natural selection an interminable
|