Origin of Species Variorum

→ 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

→ slow modification from 1861 1866

change through the action of 1869

change through 1872

→ as 1861 1866

and its importance in this respect is great, that 1869 1872

→ being 1861 1866 1869

and of their being 1872

→ favours 1861 1866 1869

tends to increase 1872

→ new or changed physical 1861 1866

the 1869

the physical 1872

→ life. 1861 1866 1869

life, in relation to the constitution of each organism. 1872

→ species inhabiting it will be found to be 1866

species inhabiting it, will be found to be 1859 1860 1861

different species inhabiting it is 1869

species inhabiting it is 1872

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.