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1859
1860
1861
1866
1869
1872

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1860
1861
1866
1869
1872

z 14 , 1859 1861 1866 1869 1872
z 14 1860

In each genus, the species, 1859 1860
The species of a genus 1861 1866
In any genus, the species 1869 1872

will 1859 1860 1861 1866
from each other, will 1869 1872

period continue transmitting 1859
period continue to transmit 1860 1861 1866
but unequal periods continue to transmit 1869 1872

between
tween
the horizontal lines. After fourteen thousand generations, six new species, marked by the letters n 14 to z 14 ,
, are
are
supposed to have been produced. In each genus, the species, which are already
very
extremely
different in
character
character,
will generally tend to produce the greatest number of modified descendants; for
they
these
will have the best chance of
seizing on
filling
new and widely different places in the polity of nature: hence in the diagram I have chosen the extreme species (A), and the nearly extreme species (I), as those which have largely varied, and have given rise to new varieties and species. The other nine species (marked by capital letters) of our original genus, may for
a
a
long period continue transmitting unaltered
descendants:
descendants;
and this is shown in the diagram by the dotted lines
unequally
not
prolonged
far
far
upwards.
upwards
from
from
want
want
of
of
space.
space.
But during the process of modification, represented in the diagram, another of our principles, namely that of extinction, will have played an important part. As in each fully stocked country natural selection necessarily acts by the selected form having some advantage in the struggle for life over other forms, there will be a constant tendency in the improved descendants of any one species to supplant and exterminate in each stage of descent their predecessors and their original
progenitor.
parent.
For it should be remembered that the competition will generally be most severe between those forms which are most nearly related to each other in habits, constitution, and structure. Hence all the intermediate forms between the earlier and later states, that is between the less and more improved
states
state
of
the same
a
species, as well as the original parent-species itself, will generally tend to become extinct. So it probably will be with many whole collateral lines of descent, which will be conquered by later and improved
lines.
lines
of
of
descent.
descent.
If, however, the