Origin of Species Variorum

Comparison with 1866

Text in this page (from paragraph 4210, sentence 100, word 17 to paragraph 4210, sentence 200, word 107) is not present in 1866

I am very far from supposing that all difficulties are removed on the view here given in regard to the range and affinities of the allied species which live in the northern and southern tem- perate zones and on the mountains of the intertropical regions, are removed on the views above given. It is extremely difficult to understand how a vast number of peculiar forms confined to the tropics could have been therein preserved during the coldest part of the Glacial period. The number of forms in Australia, which are related to European temperate forms, but which differ so greatly that it is impossible to believe that they could have been modified since the Glacial period, perhaps indicates some much more ancient cold period, even as far back as the miocene age, in accordance with the recent speculations of certain geologists. So again, as I am informed by Mr. Bates, the strongly marked character of several species of Carabus, inhabiting the southern parts of America, indicates that their common progenitor must have been introduced at some early period; and other analogous facts could be given. The exact lines and means of migration during the recent Glacial period cannot be indicated; nor the reason why certain species and not others have migrated; why certain species have been modified and have given rise to new groups of forms, and others have remained unaltered. ↑ We cannot hope to explain such facts, until we can say why one species and not another becomes naturalised by man's agency in a foreign land; why one ranges twice or thrice as far, and is twice or thrice as common, as another species within their own homes. ↑

I have said that many difficulties remain to be solved: some of the most remarkable are stated with admirable clearness by Dr. Hooker in his botanical works on the antarctic regions. These cannot be here discussed. I will only say that as far as regards the occurrence of identical species at points so enormously remote as Kerguelen Land, New Zealand, and Fuegia, I believe that towards the close of the Glacial period, icebergs, as suggested by Lyell, have been largely concerned in their dispersal. But the existence of several quite distinct species, belonging to genera exclusively confined to the south,

northern and southern temperate zones, and on the intertropical mountains. When during the height of the Glacial period the ocean-currents were widely different to what they now are, some of the inhabitants of the temperate seas might have reached the equator; of these a few would perhaps at once be able to migrate southward, by keeping to the cooler currents, whilst others might remain and survive in the cooler depths, until the southern hemisphere was in its turn subjected to a glacial climate and permitted of their further progress; in nearly the same manner as, according to Forbes, isolated spaces inhabited by Arctic productions exist to the present day in the deeper parts of the temperate seas.

I am far from supposing that all difficulties in regard to the distribution and affinities of the identical and allied species, which now live so widely separated in the north and south, and sometimes on the intermediate mountain-ranges, are removed on the views above given. ↑ The exact lines .. of migration ... cannot be indicated. ... .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ... .. .. .. .. ↑ We cannot say why certain species and not others have migrated; why certain species have been modified and have given rise to new forms, whilst others have remained unaltered. We cannot hope to explain such facts, until we can say why one species and not another becomes naturalised by mans agency in a foreign land; why one species ranges twice or thrice as far, and is twice or thrice as common, as another species within their own homes.

Various special difficulties also remain to be solved: for instance, the occurrence, as shown by Dr. Hooker, of the same plants at points so enormously remote as Kerguelen Land, New Zealand, and Fuegia; but icebergs, as suggested by Lyell, may have been concerned in their dispersal. The existence,