RECAPITULA TION 



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As according to the theory of natural selection an 

 interminable number of intermediate forms must have 

 existed, linking together all the species in each group 

 by gradations as fine as are our existing varieties, it may 

 be asked, Why do we not see these linking forms all 

 around us? Why ape not all organic beings blended 

 together in an inextricable chaos? With respect to ex- 

 isting farms7"we sHbuldn-emember that we have no right 

 to expect (excepting in rare cases) to discover jUrecJly 

 connecting links between them, but only between each 

 and some extinct and supplanted form. Even on a wide 

 area, which has during a long period remained continu- 

 ous, and of which the climatic and other condition of life 

 change insensibly in proceeding from a district occupied 

 by one species into another district occupied by a closely 

 allied species, we have no just right to expect often to 

 find intermediate varieties in the intermediate zones. For 

 we have reason to believe that only a few species of a 

 genus ever undergo change; the other species becoming 

 utterly extinct and leaving no modified progeny. Of the'' 

 species which do change, only a few within the same 

 country jchange_ at the same time; and._jall modifications 

 are slowly effected. I have also shown that the inter- 

 mediate varieties which probably at first existed in the 

 intermediate zones would be liable to be supplanted by 

 the allied forms on either hand; for the latter, from ex- 

 isting in greater numbers, would generally be modified 

 and improved at a quicker rate than the intermediate 

 varieties, which existed in lesser numbers; so that the 

 intermediate varieties would, in the long run, be sup- 

 planted and exterminated. 



On this doctrine of the extermination of an infinitude 



V 



