Origin of Species Variorum

Comparison with 1872

of the ... independent creation of each species, but are explicable if we admit colonisation from the nearest and readiest source, together with 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 insuperable in believing that all the individuals of the same species, wherever found, are descended from common parents. And we are led to this conclusion, which has been arrived at by many naturalists under the designation of single centres of creation, by various general considerations, more especially 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 genus, which on our theory .. have spread from one parent-source; if we make the same allowances as before for our ignorance, and remember that some forms of life have changed very slowly, enormous periods of time having been thus granted for their migration, ... the

of the nearest mainland,— are, I think, utterly inexplicable on the ordinary view of the independent creation of each species, but are explicable on the view of colonisation from the nearest or readiest source, together with the subsequent modification and better adaptation of the colonists to their new homes.

Summary of 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 all the changes of climate and of the level of the land, which have certainly occurred within the recent period, and of other similar changes which may have occurred within the same period; if we remember how profoundly ignorant we are with respect to the many and curious means of occasional transport,— a subject which has hardly ever been properly experimented on; if we bear in mind how often a species may have ranged continuously over a wide area, and then have become extinct in the intermediate tracts, the difficulties in believing that all the individuals of the same species, wherever located, have descended from the same parents, are not insuperable. And we are led to this conclusion, which has been arrived at by many naturalists under the designation of single centres of creation, by some general considerations, more especially from the importance of barriers and from the analogical distribution of sub-genera, genera, and families.

With respect to the distinct species of the same genus, which on my theory must have spread from one parent-source; if we make the same allowances as before for our ignorance, and remember that some forms of life change most slowly, enormous periods of time being thus granted for their migration, I do not think that the