Origin of Species Variorum

→ but will have supplanted each other; 1859 1860 1861 1866

of the same species; 1869 1872

→ each variety will have 1859 1860 1861 1866

the same variety will be 1869

the same form will be 1872

→ I believe that during the slow process of modification 1859 1860 1861 1866

OMIT 1869 1872

→ species will have been 1859 1860 1861 1866

same species inhabiting the same area will be 1869 1872

→ will not have been due, 1859 1860 1861 1866

OMIT 1869 1872

→ to 1859 1860 1861 1866

will not be due to 1869 1872

→ facts. 1859 1860 1861 1866 1869

facts. Change of climate must have had a powerful influence on migration. 1872

→ Change of climate must have had a powerful influence on migration: a region when 1859 1860 1861 1866

Change of climate must have had a powerful influence on migration; an impassable region when 1869

A region now impassable to certain organisms from the nature of 1872

→ was different may 1859 1860 1861 1866

was different from what it now is, may 1869

might 1872

→ but now be impassable; 1859 1860 1861 1866

when the climate was different. 1872

OMIT 1869

→but will have supplanted each other; so that, at each successive stage of

modification,

modification

~~and improvement,~~

and improvement,

all the individuals of →each variety will have descended from a single parent. But in the

great majority

majority

of cases, namely, with all organisms which habitually unite for each birth, or which

occasionally

often

intercross, →I believe that during the slow process of modification the individuals of the →species will have been kept nearly uniform by intercrossing; so that many individuals will

have gone

on simultaneously changing, and the whole amount of modification →will not have been due, at each

stage

stage,

→to descent from a single parent. To illustrate what I mean: our English

racehorses

race-horses

differ

~~slightly~~

slightly

from the horses of every other breed; but they do not

own

owe

their

superiority

difference

and

difference

superiority

to descent from any single pair, but to continued care in

the selecting

selecting

and training

of many

many

individuals during

each

many

generation.

generations.

Before discussing the three classes of facts, which I have selected as presenting the greatest amount of difficulty on the theory of

"single

centres of

creation,"

I must say a few words on the means of dispersal.

Means

Dispersal. —

Dispersal .

Dispersal .—

Sir C. Lyell and other authors have ably treated this subject. I can give here only the briefest abstract of the more important →facts. →Change of climate must have had a powerful influence on migration: a region when its

climate,

climate

→was different may have been a high road for

migration;

migration,

→but now be impassable; I shall, however, presently have to discuss this branch of the subject in some detail. Changes of level in the land must also have been highly influential: a narrow isthmus now separates two marine faunas; submerge it, or let it formerly have been submerged, and the two faunas will now blend

together, or

may formerly have

blended.

blended:

Where

where

the sea now extends,