| → OMIT 1869 1872 |
| the course of ages chanced to arise, and which in 1859 1860 1861 1866 |
|
| → give a tendency to 1872 |
| by specially acting on the reproductive system, causes or 1859 1860 1861 1866 |
| cause or 1869 |
|
| → increased variability; 1872 |
| increases variability; 1859 1860 1861 1866 |
| excite a tendency to vary; 1869 |
|
| → have 1872 |
| of life are supposed to have undergone a 1859 1860 1861 1866 |
| are supposed to have 1869 |
|
| → the occurrence of 1872 |
| profitable variations occurring; and unless 1859 1860 1861 1866 1869 |
|
| ↑ 1 blocks not present in 1869 1872; present in 1859 1860 1861 1866 |
| Not that,
as I believe,
any extreme amount of variability is necessary; as man can certainly produce great results by adding up in any given direction mere individual differences, so could Nature,
but far more easily, from having incomparably longer time at her disposal.
|
|
| → in order that 1872 |
| to produce 1859 1860 1861 1866 1869 |
|
| → should be left, for 1872 |
| for 1859 1860 1861 1866 1869 |
|
|
inhabitants
almost immediately undergo a change, and some species
become extinct. We may conclude, from what we have seen of the intimate and complex manner in which the inhabitants of each country are bound together, that any change in the numerical proportions of
the inhabitants, independently of the change of climate itself, would
seriously affect
the others. If the country were open on its borders, new forms would certainly immigrate, and this
would
disturb the relations of some of the former inhabitants. Let it be remembered how powerful the influence of a single introduced tree or mammal has been shown to be. But in the case of an island, or of a country partly surrounded by barriers, into which new and better adapted forms could not freely enter, we should then have places in the economy of nature which would assuredly be better filled up, if some of the original inhabitants were in some manner modified; for, had the area been open to immigration, these same places would have been seized
by intruders. In such
slight
which in
→OMIT
any way favoured the individuals of any
species, by better adapting them to their altered conditions, would tend to be preserved; and natural selection would
have free scope for the work of improvement. |
|
| We have
to believe, as
in the first chapter, that
in the conditions of
→give a tendency to
→increased variability;
and in the foregoing
the conditions
→have
and this would manifestly be favourable to natural selection, by
a better chance of
→the occurrence of
occur, natural selection can do nothing. Under the term of "variations," it must never be forgotten that mere individual differences are
included. As man can
produce a great result with his domestic animals and plants by adding up in any given direction individual differences, so could natural selection, but far more easily, from having incomparably longer time for action. ↑
Nor do I believe that any great physical change, as of climate, or any unusual degree of isolation to check
is
necessary
→in order that
new and unoccupied places
→should be left, for
natural selection to fill up by
improving some of the varying inhabitants. For as all the inhabitants of each country are struggling together with nicely balanced forces, extremely slight modifications in the structure or habits of one
would often give it an advantage over others; and still further modifications of the same kind would often still further increase the
as long as the
continued under the same conditions of life and profited by similar means of subsistence and defence. No country can be named in which all
|
