| ↑ 1 blocks not present in 1869 1872; present in 1859 1860 1861 1866 |
| I am far from thinking
that the most divergent varieties will
invariably prevail and multiply:
a medium form may often long endure, and may or may not produce more than one modified descendant; for natural selection will always act according to the nature of the places which are either unoccupied or not perfectly occupied by other beings; and this will depend on infinitely complex relations.
|
|
| → no doubt 1872 |
| I do not doubt that 1859 1860 1861 1866 1869 |
|
| → augmented. 1872 |
| increased in the successive generations. 1859 1860 1861 1866 1869 |
|
| →
a
10
.
1859 1861 1866 1869 1872 |
|
a
10
.
1860 |
|
| →
a
10
,
1859 1861 1866 1869 1872 |
|
a
10
1860 |
|
| →
f
10
1872 |
|
f
10
,
1859 1861 1866 1869 |
|
,
f
10
,
1860 |
|
| →
m
10
,
1859 1861 1866 1869 1872 |
|
m
10
1860 |
|
| → OMIT 1869 1872 |
| or they may have arrived at the doubtful category of sub-species; 1859 1860 1861 1866 |
|
|
that the most divergent varieties are invariably
a medium form may often long endure, and may or may not produce more than one modified descendant; for natural selection will always act according to the nature of the places which are either unoccupied or not perfectly occupied by other beings; and this will depend on infinitely complex relations. ↑
But as a general rule, the more diversified in structure the descendants from any one species can be rendered, the more places they will be enabled to seize on, and the more their modified progeny will
In our diagram the line of succession is broken at regular intervals by small numbered letters marking the successive forms which have become sufficiently distinct to be recorded as varieties. But these breaks are imaginary, and might have been inserted
after intervals long enough to
the accumulation of a considerable amount of divergent variation. |
|
| As all the modified descendants from a common and widely-diffused species, belonging to a large genus, will tend to partake of the same advantages which made their parent successful in life, they will generally go on multiplying in number as well as diverging in character: this is represented in the diagram by the several divergent branches proceeding from (A). The modified offspring from the later and more highly improved branches in the lines of descent, will, it is probable, often take the place of, and so destroy, the earlier and less improved branches: this is represented in the diagram by some of the lower branches not reaching to the upper horizontal lines. In some cases
→no doubt
the process of modification will be confined to a single line of descent, and the number of
descendants will not be increased; although the amount of divergent modification may have been
→augmented. This case would be represented in the diagram, if all the lines proceeding from (A) were removed, excepting that from
a
1
to
→
a
10
.
In the same
the English race-horse and English pointer have apparently both gone on slowly diverging in character from their original stocks, without either having given off any fresh branches or races. |
|
| After ten thousand generations, species (A) is supposed to have produced three forms,
→
a
10
,
→
f
10
and
→
m
10
,
from having diverged in character during the successive generations, will have come to differ largely, but perhaps unequally, from each other and from their common parent. If we suppose the amount of change between each horizontal line in our diagram to be excessively small, these three forms may still be only well-marked varieties;
→OMIT
but we have only to suppose the steps in the process of modification to be
|
