Origin of Species Variorum

... within each great class the lower organisms change at a slower rate than the higher; .. consequently they .. will have had a better chance of ranging widely and of still retaining the same specific character. This fact, together with the seeds and eggs of almost all lowly organised forms being very minute and better fitted for distant transportal, probably accounts for a law which has long been observed, and which has lately been .. discussed by Alph. de Candolle in regard to plants, namely, that the lower any group of organisms stands, the more widely it ... ranges.

The relations just discussed,— namely, lower organisms ranging more widely than the higher,— some of the species of widely-ranging genera themselves ranging widely,— such facts, as alpine, lacustrine, and marsh productions being generally related to those which live on the surrounding low lands and dry lands,— the striking relationship between the inhabitants of islands and those of the nearest mainland— the still closer relationship of the distinct inhabitants of the islands in the same archipelago— are inexplicable on the ordinary view of the ... independent creation of each species, but are explicable if we admit colonisation from the nearest or readiest source, together with the subsequent ... adaptation of the colonists to their new homes.

Summary of the last and present Chapter .

In these chapters I have endeavoured to show, that if we make due allowance for our ignorance of the full effects of the changes of climate and of the level of the land, which have certainly occurred within the recent period, and of other .. changes which .. have probably occurred,— if we remember how .. ignorant we are with respect to