Origin of Species Variorum

Comparison with 1869

prevented, so that new places in the polity of each island will have had to be filled up by modifications of the old inhabitants; and time will have been allowed for the varieties in each to become well modified and perfected. When, by renewed elevation, the islands were reconverted into a continental area, there will again have been severe competition: the most favoured or improved varieties will have been enabled to spread: there will have been much extinction of the less improved forms, and the relative proportional numbers of the various inhabitants of the reunited continent will again have been changed; and again there will have been a fair field for natural selection to improve still further the inhabitants, and thus to produce new species.

That natural selection .. acts with extreme slowness I fully admit. The result depends on there being places in the polity of nature, which can be better filled through some of the inhabitants of the country under-going modifications of some kind. The existence of such places will often depend on physical changes, which are generally very slow, and on the immigration of better adapted forms being checked. But the effects of natural selection will probably still oftener depend on some few of the inhabitants becoming slowly modified; the mutual relations of the other inhabitants being thus disturbed. ↑ Although all the individuals of the same species differ in some slight degree from each other, it would often be long before differences of the right nature in various parts of the organisation might occur. The result would often be greatly retarded by free intercrossing. ↑ Many will exclaim that these several causes are amply sufficient .. to neutralise the power of natural selection. I do not believe so. But I do believe that natural selection generally act very slowly in effecting changes, at long intervals of time, and only on .. a .. few of the inhabitants of the same region. .. .. .. .. I further believe that these slow, intermittent

vented, so that new places in the polity of each island will have to be filled up by modifications of the old inhabitants; and time will be allowed for the varieties in each to become well modified and perfected. When, by renewed elevation, the islands shall be re-converted into a continental area, there will again be severe competition: the most favoured or improved varieties will be enabled to spread: there will be much extinction of the less improved forms, and the relative proportional numbers of the various inhabitants of the renewed continent will again be changed; and again there will be a fair field for natural selection to improve still further the inhabitants, and thus produce new species.

That natural selection will always act with extreme slowness, I fully admit. Its action depends on there being places in the polity of nature, which can be better occupied by some of the inhabitants of the country undergoing modification of some kind. The existence of such places will often depend on physical changes, which are generally very slow, and on the immigration of better adapted forms having been checked. ↑ But the action of natural selection will probably still oftener depend on some of the inhabitants becoming slowly modified; the mutual relations of many of the other inhabitants being thus disturbed. Nothing can be effected, unless favourable variations occur, and variation itself is apparently always a very slow process. The process will often be greatly retarded by free intercrossing. Many will exclaim that these several causes are amply sufficient wholly to stop the action of natural selection. I do not believe so. On the other hand, I do believe that natural selection always acts very slowly, often only at long intervals of time, and generally on only a very few of the inhabitants of the same region at the same time. I further believe, that this very slow, intermit- tent