| → doubtful or at last into well-defined 1872 |
| well-defined 1859 1860 1861 1866 |
| doubtful or at last well-defined 1869 |
|
| →
m
14
,
1859 1861 1866 1869 1872 |
|
m
14
1860 |
|
| →
z
10
)
1859 1861 1866 1869 1872 |
|
z
10
1860 |
|
| →
z
14
,
1859 1861 1866 1869 1872 |
|
z
14
1860 |
|
| → In any genus, the species 1869 1872 |
| In each genus, the species, 1859 1860 |
| The species of a genus 1861 1866 |
|
| → from each other, will 1869 1872 |
| will 1859 1860 1861 1866 |
|
| → but unequal periods continue to transmit 1869 1872 |
| period continue transmitting 1859 |
| period continue to transmit 1860 1861 1866 |
|
|
more numerous or greater in amount, to convert these three forms into
→doubtful or at last into well-defined
the diagram illustrates the steps by which the small differences distinguishing varieties are increased into the larger differences distinguishing species. By continuing the same process for a greater number of generations (as shown in the diagram in a condensed and simplified manner), we get eight species, marked by the letters between
a
14
and
→
m
14
,
descended from (A). Thus, as I believe, species are multiplied and genera are formed. |
|
| In a large genus it is probable that more than one species would vary. In the diagram I have assumed that a second species (I) has produced, by analogous steps, after ten thousand generations, either two well-marked varieties
(
w
10
and
→
z
10
)
two species, according to the amount of change supposed to be represented
the horizontal lines. After fourteen thousand generations, six new species, marked by the letters
n
14
to
→
z
14
,
supposed to have been produced.
→In any genus, the species
which are already
different in
→from each other, will
generally tend to produce the greatest number of modified descendants; for
will have the best chance of
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
long
→but unequal periods continue to transmit
unaltered
and this is shown in the diagram by the dotted lines
prolonged
|
|
| 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
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
of
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
If, however, the modified offspring of a species get into some distinct country, or become quickly adapted to some
|
