Origin of Species Variorum

→ process of 1859 1860 1861 1866

changes effected through 1869

modification of 1872

→ natural 1859 1860 1861 1866 1869

species through natural 1872

→ in a great degree 1859 1860 1861 1866

almost 1869 1872

→ individuals of a varying species throughout the area 1859 1860 1861 1866

varying individuals of the same species 1869 1872

→ same species, which otherwise would have inhabited the surrounding and differently circumstanced 1859 1860 1861

same species, which othewise would have inhabited the surrounding and differently circumstanced 1866

surrounding 1869 1872

→ be 1859 1860 1861 1866

also, be 1869

also, be thus 1872

↑ 3 blocks not present in 1859 1860 1861 1866; present in 1869 1872

Moritz Wagner has lately published an interesting essay on this subject, and has shown that the service rendered by isolation in preventing crosses between newly formed varieties is probably greater even than I have supposed. But from reasons already assigned I can by no means agree with this naturalist, that migration and isolation are necessary for the formation of new species. The importance of isolation is likewise great in preventing, after any physical change in the conditions, such as of climate, elevation of the land, &c., the immigration of better adapted organisms; and thus new places in the natural economy of the district are left open for the old inhabitants to struggle for and become adapted to.

→ by checking immigration and consequently competition, 1859 1860 1861 1866

OMIT 1869 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

→ the appearance of 1859 1860 1861 1866 1869

OMIT 1872

→ species 1861 1866

the forms of life 1872

OMIT 1869

the

their

modified offspring, solely by natural selection preserving

similar

the same

favourable variations.

Isolation, also, is an important element in the →process of →natural selection. In a confined or isolated area, if not very large, the organic and inorganic conditions of life will generally be →in a great degree uniform; so that natural selection will tend to modify all the →individuals of a varying species throughout the area in the same

manner.

~~relation~~

~~the~~

~~same~~

~~conditions.~~

Intercrossing

~~also,~~

with the

inhabitants

individuals

of the →same species, which otherwise would have inhabited the surrounding and differently circumstanced

districts

districts,

will,

will

→be prevented. ↑ But isolation probably acts more efficiently in checking the immigration of better adapted organisms, after any physical change, such as of climate or elevation of the land, &c.; and thus new places in the natural economy of the country are left open for the old inhabitants to struggle

for

for,

and become adapted to, through

modifica- tions

modifications

in their structure and constitution. Lastly,

isolation

isolation,

→by checking immigration and consequently competition, will give time for

any

new variety to be

~~slowly~~

slowly

improved

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

chances

chance

of →the appearance of favourable

individual differences.

variations arising.

variations.

The mere lapse of time by itself does

nothing,

nothing

either for or against natural selection. I state this because it has been erroneously asserted that the element of time

has been

assumed by me to play an all-important part in

modifying species,

natural selection,

as if all →species were necessarily

under- going

undergoing