RECAPITULATION AND CONCLUSION 503 



With respect to existing forms, we should remember that we 

 have no right to expect (excepting in rare cases) to discover 

 directly connecting Hnks between them, but only between 

 each and some extinct and supplanted form. Even on a wide 

 area, which has during a long period remained continuous, 

 and of which the climatic and other conditions 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 inter- 

 mediate 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 change at the 

 same time; and all modifications are slowly effected. I have 

 also shown that the intermediate 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 existing in greater numbers, would generally be modi- 

 fied and improved at a quicker rate than the intermediate vari- 

 eties, which existed in lesser numbers; so that the inter- 

 mediate varieties would, in the long run, be supplanted and 

 exterminated. 



On this doctrine of the extermination of an infinitude of 

 connecting links, between the living and extinct inhabitants 

 of the world, and at each successive period between the 

 extinct and still older species, why is not every geological 

 formation charged with such links? Why does not every col- 

 lection of fossil remains afford plain evidence of the grada- 

 tion and mutation of the forms of life? Although geological 

 research has undoubtedly revealed the former existence of 

 many links, bringing numerous forms of life much closer to- 

 gether, it does not yield the infinitely many fine gradations 

 between past and present species required on the theory ; and 

 this is the most obvious of the many objections which may 

 be urged against it. Why, again, do whole groups of allied 

 species appear, though this appearance is often false, to have 

 come in suddenly on the successive geological stages? Al- 

 though we now know that organic beings appeared on this 

 globe, at a period incalculably remote, long before the lowest 



