| Comparison with 1860 |
|
in their structure and constitution. Lastly, isolation,
by checking immigration and consequently competition,
will give time for any
new variety to be slowly
improved;
and
this may sometimes be of importance in the production of new species. If, however, an isolated area be very small, either from being surrounded by barriers, or from having very peculiar physical conditions, the total number of the individuals supported on it will necessarily be very
small; and fewness of individuals will greatly
retard the production of new species through natural selection, by decreasing the chance
of the appearance of
favourable variations.
↑| 4 blocks not present in 1859 1860; present in 1861 1866 1869 1872 | | The mere lapse of time by itself does nothing
either for or against natural selection.
I state this because it has been erroneously asserted that the element of time is
assumed by me to play an all-important part in natural selection,
as if all species
were necessarily undergoing
slow modification from
some innate law.
Lapse of time is only so far highly
important, as
it gives a better chance of beneficial variations arising, being
selected, accumulated,
and fixed,
in relation to the slowly changing organic and inorganic conditions of life. It likewise favours
the
direct action of new or changed physical
conditions of life.
|
|
|
| If we turn to nature to test the truth of these remarks, and look at any small isolated area, such as an oceanic island, although the total
number of the
species inhabiting it, will be found to be
small, as we shall see in our chapter on geographical
distribution;
yet of these
species a very large proportion are endemic,— that is, have been produced there, and nowhere else. Hence an oceanic island at first sight seems to have been highly favourable for the production of new species. But we may thus greatly
deceive ourselves, for to ascertain whether a small isolated area, or a large open area like a continent, has been most favourable for the production of new organic forms, we ought to make the comparison within equal times; and this we are incapable of doing. |
|
| Although I do not doubt that
isolation is of considerable
importance in the production of new species, on the whole I am inclined to believe that largeness of area is of
more importance,
more
especially in
the production of species,
which will
prove capable of enduring for a long period, and of spreading widely. Throughout a great and open area, not only will there be a better chance of favourable variations
arising from the large number of individuals of the same species
|
in their structure and constitution. Lastly,
isolation, | isolation, 1859 1860 1861 1866 | | isolation 1869 1872 |
| by checking immigration and consequently competition, 1859 1860 1861 1866 |
| OMIT 1869 1872 |
| any 1859 1860 1861 1866 | | a 1869 1872 |
| slowly 1859 1860 1861 1866 1869 | slowly 1872 |
| improved; 1859 1860 1861 1866 1869 | | improved 1872 |
| and 1859 1860 1861 1866 1869 |
| at a slow rate; and 1872 |
| importance in the production of new species. 1859 1860 1861 1866 1869 |
| much importance. 1872 |
| individuals supported on it will necessarily be very 1859 1860 1861 1866 |
| inhabitants will be 1869 1872 |
| fewness of individuals will greatly 1859 1860 1861 1866 |
| this will 1869 1872 |
| chance 1859 1860 1861 1866 | | chances 1869 1872 |
| the appearance of 1859 1860 1861 1866 1869 |
| OMIT 1872 |
| variations. 1859 1860 1861 1866 | | individual differences. 1869 | | variations arising. 1872 |
| 4 blocks not present in 1859 1860; present in 1861 1866 1869 1872 | | The mere lapse of time by itself does nothing
either for or against natural selection.
I state this because it has been erroneously asserted that the element of time is
assumed by me to play an all-important part in natural selection,
as if all species
were necessarily undergoing
slow modification from
some innate law.
Lapse of time is only so far highly
important, as
it gives a better chance of beneficial variations arising, being
selected, accumulated,
and fixed,
in relation to the slowly changing organic and inorganic conditions of life. It likewise favours
the
direct action of new or changed physical
conditions of life.
|
|
|
If we turn to nature to test the truth of these remarks, and look at any small isolated area, such as an oceanic island, although the
total | total 1859 1860 1861 1866 | total 1869 1872 |
| the 1859 1860 1861 1866 1869 | the 1872 |
| species inhabiting it, will be found to be 1859 1860 1861 |
| species inhabiting it will be found to be 1866 |
| different species inhabiting it is 1869 |
| species inhabiting it is 1872 |
| geographical 1859 1860 | | Geographical 1861 1866 1869 1872 |
| distribution; 1859 1860 | | Distribution; 1861 1866 1869 1872 |
| these 1859 1860 1861 1866 1872 | | the 1869 |
| else. 1859 1860 1861 1866 |
| else in the world. 1869 1872 |
| greatly 1859 1860 1861 1866 | greatly 1869 1872 |
|
|
Although
I do not doubt that | I do not doubt that 1859 1860 |
| OMIT 1861 1866 1869 1872 |
| considerable 1859 1860 1861 1866 | | great 1869 1872 |
| of 1859 1860 1861 1866 | | still 1869 1872 |
| importance, 1859 1860 1861 1866 | | important, 1869 1872 |
| more 1859 1860 | more 1861 1866 1869 1872 |
| in 1859 1860 1861 1866 | | for 1869 1872 |
| species, 1859 1860 1861 1866 1869 | | species 1872 |
| will 1859 1860 1861 1866 | | shall 1869 1872 |
| variations 1859 1860 1861 1866 1869 | | variations, 1872 |
|
