| → will 1859 1860 1861 1866 |
| from each other, will 1869 1872 |
|
| → period continue to transmit 1860 1861 1866 |
| period continue transmitting 1859 |
| but unequal periods continue to transmit 1869 1872 |
|
|
→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
→period 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 quite new station, in which
and
do not come into competition, both may continue to exist.
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