Origin of Species Variorum

→ to be filled up by the modification of 1872

for 1869

↑ 1 blocks not present in 1869 1872; present in 1859 1860 1861 1866

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, and become adapted to, through modifica- tions in their structure and constitution.

→ OMIT 1869 1872

by checking immigration and consequently competition, 1859 1860 1861 1866

→ at a slow rate; and 1872

and 1859 1860 1861 1866 1869

→ much importance. 1872

importance in the production of new species. 1859 1860 1861 1866 1869

→ inhabitants will be 1869 1872

individuals supported on it will necessarily be very 1859 1860 1861 1866

→ this will 1869 1872

fewness of individuals will greatly 1859 1860 1861 1866

→ OMIT 1872

the appearance of 1859 1860 1861 1866 1869

→ the forms of life 1872

species 1861 1866

OMIT 1869

→ change through 1872

slow modification from 1861 1866

change through the action of 1869

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

as 1861 1866

→ and of their being 1872

being 1861 1866 1869

→ tends to increase 1872

favours 1861 1866 1869

→ the physical 1872

new or changed physical 1861 1866

the 1869

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

life. 1861 1866 1869

→ species inhabiting it is 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

→ else in the world. 1869 1872

else. 1859 1860 1861 1866

→ OMIT 1861 1866 1869 1872

I do not doubt that 1859 1860

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

elements for

the formation of new species. The importance of isolation is likewise great in preventing, after any physical change in the

conditions,

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

will be

left open →to be filled up by the modification of the old

inhabitants

struggle

for

and

become

adapted

to.

↑ Lastly,

isolation,

isolation

→OMIT will give time for

any

new variety to be

slowly

....

improved;

improved

→at a slow rate; and this may sometimes be of →much importance. 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 →inhabitants will be small; and →this will retard the production of new species through natural selection, by decreasing the

chance

chances

of →OMIT favourable

variations.

individual differences.

variations arising.

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

natural selection,

modifying species,

as if all →the forms of life were necessarily

under- going

undergoing

→change through some innate law. Lapse of time is only so far

highly

....

important, →and its importance in this respect is great, that it gives a better chance of beneficial variations arising, →and of their being selected,

increased,

accumulated,

and

fixed,

relation

the

slowly

changing

organic

and

inorganic

conditions

life.

It likewise →tends to increase the

direct

definite

direct

action of →the physical conditions of →life, in relation to the constitution of each organism.

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 is small, as we shall see in our chapter on

geographical

Geographical

distribution;

Distribution;

yet of

the

these

species a very large proportion are endemic,— that is, have been produced there, and nowhere →else in the world. 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 →OMIT isolation is of

considerable

great

importance in the production of new species, on the whole I am inclined to believe that largeness of area is

importance,

especially

the production of

species,

species

which

will

shall

prove capable of enduring for a long period, and of spreading widely. Throughout a great and open area, not only will there be a