446 ORIGIN OF SPECIES 



and eggs of most 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 gen- 

 erally 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 ordi- 

 nary view of the independent creation of each species, but 

 are explicable if we admit colonisation from the nearest or 

 readiest source, together w^th the subsequent adaptation of 

 the colonists to their new homes. 



SUMMARY OF THE LAST AND PRESENT CHAPTERS 



In these chapters I have endeavoured to show, that if we 

 make due allowance for our ignorance of the full effects of 

 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 the many curious means 

 of occasional transport, — if we bear in mind, and this is a 

 very important consideration, how often a species may have 

 ranged continuously over a wide area, and then have become 

 extinct in the intermediate tracts, — the difficulty is not insu- 

 perable in believing that all the individuals of the same 

 species, wherever found, are descended from common par- 

 ents. And we are led to this conclusion, which has been ar- 

 rivedatbymany naturalists underthe designation of single cen- 

 tres of creation, by various general considerations, more espe- 

 cially from the importance of barriers of all kinds, and from 

 the analogical distribution of sub-genera, genera, and families. 



With respect to distinct species belonging to the same 



