Origin of Species Variorum

→ at 1859 1860 1861

they do at 1866 1869 1872

→ by 1859 1860 1861

from each other by 1866 1869 1872

→ ocean. 1859 1860 1861

ocean; so that it may well be asked how the same species could have entered two regions then so widely separated. 1866

ocean; so that it may well be asked how the same species could have entered the two continents then so widely separated. 1869

ocean; so that it may well be asked how the same species could then or previously have entered the two continents. 1872

↑ 2 blocks not present in 1859 1860 1861; present in 1866 1869 1872

The explanation, I believe, lies in the nature of the climate before the commencement of the Glacial period. During this, the newer Pliocene period, when the majority of the inhabitants of the world were specifically the same as now, we have good reason to believe that the climate was warmer than at the present day.

→ now living under the climate of latitude 60°, 1859 1860 1861

which now live under latitude 60°, 1866

which now live under latitude 60°, lived 1869

which now live under latitude 60°, 1872

→ during the Pliocene period lived 1859 1860 1861 1866

during the Pliocene period 1869

lived during the Pliocene period 1872

→ globe, we shall see that 1859 1860 1861

terrestrial globe, we see that 1866

terrestrial globe, we see 1869 1872

→ for intermigration under a more favourable climate, 1859 1860 1861

under a more favourable climate for intermigration, 1866

under a more favourable climate 1869 1872

→ I attribute the necessary amount of uniformity in 1859 1860 1861

I attribute a considerable degree of uniformity in 1866

for intermigration, will account for the supposed uniformity of 1869 1872

→ large, but partial 1859 1860 1861 1866 1869

great 1872

and northern temperate productions of the Old and New Worlds are separated from each other by the

whole Atlantic

Atlantic

Ocean and by the

~~extreme~~

extreme

northern part of the Pacific. During the Glacial period, when the

in-

....

habitants

inhabitants

of the Old and New Worlds lived

further

farther

southwards than →at present, they must have been still more completely separated →by wider spaces of →ocean. ↑ I believe the above difficulty may be surmounted by looking to still earlier changes of climate of an opposite nature. We have good reason to believe that during the newer Pliocene period, before the Glacial epoch, and whilst the majority of the inhabitants of the world were specifically the same as now, the climate was warmer than at the present day. Hence we may suppose that the organisms →now living under the climate of latitude 60°, →during the Pliocene period lived

further

father

farther

north under the Polar Circle, in latitude

66°-67°;

and that the

present

strictly

arctic productions then lived on the broken land still nearer to the pole.

Now,

Now

if we look at a →globe, we shall see that under the Polar Circle

that there

there

is almost continuous land from western Europe, through Siberia, to eastern America. And

this continuity of the circumpolar land,

with

and to

the consequent freedom →for intermigration under a more favourable climate, →I attribute the necessary amount of uniformity in the sub-arctic and

~~northern~~

northern

temperate productions of the Old and New Worlds, at a period anterior to the Glacial epoch.

Believing, from reasons before alluded to, that our continents have long remained in nearly the same relative position, though subjected to →large, but partial oscillations of level, I am strongly inclined to extend the above view, and to infer that during some

still earlier

earlier

and still warmer period, such as the older Pliocene period, a large number of the same plants and animals