Barrier would further act in preventing species formed in one part migrating to another part.
[{131}] «The following notes occur on the back of the page.» Number of species not related to capabilities of the country: furthermore not always those best adapted, perhaps explained by creationists by changes and progress. «See [p. 34, note 1].»
Although creationists can, by help of geology, explain much, how can he explain the marked relation of past and present in same area, the varying relation in other cases, between past and present, the relation of different parts of same great area. If island, to adjoining continent, if quite different, on mountain summits,—the number of individuals not being related to capabilities, or how &c.—our theory, I believe, can throw much light and all facts accord.
[{132}] See Origin, Ed. i. p. 390, vi. p. 543.
[{133}] On oscillation see Origin, Ed. i. p. 291, vi. p. 426.
[{134}] «From the back of MS.» Effect of climate on stationary island and on continent, but continent once island. Moreover repeated oscillations fresh diffusion when non-united, then isolation, when rising again immigration prevented, new habitats formed, new species, when united free immigration, hence uniform characters. Hence more forms «on?» the island. Mountain summits. Why not true species. First let us recall in Part I, conditions of variation: change of conditions during several generations, and if frequently altered so much better [perhaps excess of food]. Secondly, continued selection [while in wild state]. Thirdly, isolation in all or nearly all,—as well to recall advantages of.
[In continent, if we look to terrestrial animal, long continued change might go on, which would only cause change in numerical number «? proportions»: if continued long enough might ultimately affect all, though to most continents «there is» chance of immigration. Some few of whole body of species must be long affected and entire selection working same way. But here isolation absent, without barrier, cut off such «illegible». We can see advantage of isolation. But let us take case of island thrown up by volcanic agency at some distances, here we should have occasional visitants, only in few numbers and exposed to new conditions and «illegible» more important,—a quite new grouping of organic beings, which would open out new sources of subsistence, or «would» control «?» old ones. The number would be few, can old have the very best opportunity. «The conquest of the indigenes by introduced organisms shows that the indigenes were not perfectly adapted, see Origin, Ed. i. p. 390.» Moreover as the island continued changing,—continued slow changes, river, marshes, lakes, mountains &c. &c., new races as successively formed and a fresh occasional visitant.
If island formed continent, some species would emerge and immigrate. Everyone admits continents. We can see why Galapagos and C. Verde differ «see Origin, Ed. i. p. 398»], depressed and raised. We can see from this repeated action and the time required for a continent, why many more forms than in New Zealand «see Origin, Ed. i. p. 389 for a comparison between New Zealand and the Cape» no mammals or other classes «see however, Origin, Ed. i. p. 393 for the case of the frog». We can at once see how it comes when there has been an old channel of migration,—Cordilleras; we can see why Indian Asiatic Flora,—[why species] having a wide range gives better chance of some arriving at new points and being selected, and adapted to new ends. I need hardly remark no necessity for change.
Finally, as continent (most extinction «?» during formation of continent) is formed after repeated elevation and depression, and interchange of species we might foretell much extinction, and that the survivor would belong to same type, as the extinct, in same manner as different part of same continent, which were once separated by space as they are by time «see Origin, Ed. i. pp. 339 and 349».
As all mammals have descended from one stock, we ought to expect that every continent has been at some time connected, hence obliteration of present ranges. I do not mean that the fossil mammifers found in S. America are the lineal successors «ancestors» of the present forms of S. America: for it is highly improbable that more than one or two cases (who will say how many races after Plata bones) should be found. I believe this from numbers, who have lived,—mere «?» chance of fewness. Moreover in every case from very existence of genera and species only few at one time will leave progeny, under form of new species, to distant ages; and the more distant the ages the fewer the progenitors. An observation may be here appended, bad chance of preservation on rising island, the nurseries of new species, appeal to experience «see Origin, Ed. i. p. 292». This observation may be extended, that in all cases, subsiding land must be, in early stages, less favourable to formation of new species; but it will isolate them, and then if land recommences rising how favourable. As preoccupation is bar to diffusion to species, so would it be to a selected variety. But it would not be if that variety was better fitted to some not fully occupied station; so during elevation or the formation of new stations, is scene for new species. But during elevation not favourable to preservation of fossil (except in caverns «?»); when subsidence highly favourable in early stages to preservation of fossils; when subsidence, less sediment. So that our strata, as general rule will be the tomb of old species (not undergoing any change) when rising land the nursery. But if there be vestige will generally be preserved to future ages, the new ones will not be entombed till fresh subsidence supervenes. In this long gap we shall have no record: so that wonderful if we should get transitional forms. I do not mean every stage, for we cannot expect that, as before shown, until geologists will be prepared to say that although under unnaturally favourable condition we can trace in future ages short-horn and Herefordshire «see [note 2, p. 26]».