448 ORIGIN OF SPECIES 



certain forms and not others to enter, either in greater or 

 lesser numbers; according or not, as those which entered 

 happened to come into more or less direct competition with 

 each other and with the aborigines : and according as the im- 

 migrants were capable of varying more or less rapidly, there 

 would ensue in the two or more regions, independently of 

 their physical conditions, infinitely diversified conditions of 

 life, — there would be an almost endless amount of organic 

 action and reaction, — and we should find some groups of 

 beings greatly, and some only slightly modified, — some de- 

 veloped in great force, some existing in scanty numbers — 

 and this we do find in the several great geographical prov- 

 inces of the world. 



On these same principles we can understand, as I have 

 endeavoured to show, why oceanic islands should have few 

 inhabitants, but that of these, a large proportion should be 

 endemic or peculiar; and why, in relation to the means of 

 migration, one group of beings should have all its species pe- 

 culiar, and another group, even within the same class, should 

 have all its species the same with those in an adjoining 

 quarter of the world. We can see why whole groups of or- 

 ganisms, as batrachians and terrestrial mammals, should be 

 absent from oceanic islands, whilst the most isolated islands 

 should possess their own peculiar species of aerial mammals 

 or bats. We can see why, in islands, there should be some 

 relation between the presence of mammals, in a more or less 

 modified condition, and the depth of the sea between such 

 islands and the mainland. We can clearly see why all the 

 inhabitants of an archipelago, though specifically distinct on 

 the several islets, should be closely related to each other; 

 and should likewise be related, but less closely, to those of 

 the nearest continent, or other source whence immigrants 

 might have been derived. We can see why, if there exist 

 very closely allied or representative species in two^ areas, 

 however distant from each other, some identical species will 

 almost always there be found. 



As the late Edward Forbes often insisted, there is a strik- 

 ing parallelism in the laws of life throughout time and 

 space; the laws governing the succession of forms in past 

 times being nearly the same with those governing at the 



