Origin of Species Variorum

Comparison with 1869

of our imaginary Glacial period, the arctic productions were as uniform round the polar regions as they are at the present day. But it is necessary also to include many sub-arctic and .. some few .. temperate forms, for some of these are the same on the lower mountains and on the plains of North America and Europe; and it may be reasonably asked how I account for the necessary degree of uniformity of the sub-arctic and northern temperate forms round the world, at the commencement of the real Glacial period. At the present day, the sub-arctic and northern temperate productions of the Old and New Worlds are separated from each other by the Atlantic Ocean and by the extreme northern part of the Pacific. During the Glacial period, when the in- habitants of the Old and New Worlds lived further southwards than at present, they must have been still more completely separated by wider spaces of ocean; so that it may well be asked how the same species could have entered the two continents then so widely separated. The explanation, I believe, lies in the nature of the climate before the commencement of the Glacial period. At this, the newer Pliocene period, .. the majority of the inhabitants of the world were specifically the same as now, and we have good reason to believe that the climate was warmer than at the present day. ↑ Hence we may suppose that the organisms which now live under latitude 60°, lived during the Pliocene period farther north under the Polar Circle, in latitude 66°-67°; and that the strictly arctic productions then lived on the broken land still nearer to the pole. Now if we look at a terrestrial globe, we see under the Polar Circle that there is almost continuous land from western Europe, through Siberia, to eastern America. And .. this continuity of the circumpolar land, with the consequent

the arctic productions were as uniform round the polar regions as they are at the present day. But the foregoing remarks on distribution apply not only to strictly arctic forms, but also to many sub-arctic and to some few northern temperate forms, for some of these are the same on the lower mountain-slopes and on the plains of North America and Europe; and it may be .. asked how I account for this degree of uniformity in the sub-arctic and .. temperate forms round the world, at the commencement of the Glacial period. At the present day, the sub-arctic and northern temperate productions of the Old and New Worlds are separated from each other by the whole Atlantic Ocean and by the .. northern part of the Pacific. During the Glacial period, when the .. inhabitants of the Old and New Worlds lived farther southwards than they do at present, they must have been still more completely separated from each other by wider spaces of ocean; so that it may well be asked how the same species could have entered two regions then so widely separated. 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. ↑ Hence we may suppose that the organisms which now live under latitude 60°, during the Pliocene period lived father north under the Polar Circle, in latitude 66°-67°; and that the present arctic productions then lived on the broken land still nearer to the pole. Now, if we look at a terrestrial globe, we see that under the Polar Circle there is almost continuous land from western Europe, through Siberia, to eastern America. And to this continuity of the circumpolar land, and to the consequent