430 CONCLUSION. Chap. XIV. 



been, or cjin bo, (hawn between species and well-marked varie- 

 ties. It cannot be maintained that species when intercrossed 

 are invariably sterile, and varieties invariably fertile ; or that 

 sterility is a special endowment and sign of creation. The be- 

 lief tliat species were immutable productions was almost una- 

 voidable ;is lon;!^ as the history of the world was thought to be 

 of shoct duration ; and now that we have acquired some idea 

 of the lapse of time, Ave are too apt to assume, without proof, 

 that the geological record is so perfect that it would have 

 alforded us plain evidence of the mutation of species, if they 

 had undergone nmtation. 



But the chief cause of oin- natural unwillingness to admit 

 that one species has given birth to other and distinct species, 

 is, that we are always slow in admitting any great change of 

 which we do not see the steps. The difficulty is the same as 

 that felt by so many geologists, Avhen Lyell first insisted that 

 long lines of inland cliffs had been formed, and great valleys 

 excavated, by the agencies Avhich we see still at Avork. The 

 mind cannot possibly grasp the full meaning of the term of 

 even ten million years ; it cannot add up and perceive the full 

 effects of many slight A'ariations, accumulated during an almost 

 hillnite number of generations. 



Although I am fully convinced of the truth of the A'ieAVS 

 giA'en in this Aolume under the fonn of an abstract, I by no 

 means expect to convince experienced naturalists Avhose minds 

 are stocked Avitli a multitude of facts all A'iewed, during a long 

 course of years, from a point of vicAV directly opposite to mine. 

 It is so easy to hide our ignorance under such expressions as 

 the " plan of creation," " unity of design," etc., and to think 

 that Ave giA'e an ex2:)lanation Avhen Ave only restate a fact ! 

 Any one Avhose disposition leads him to attach more Aveight 

 to unexjilained difficulties than to the explanation of a certain 

 numl)er of facts, Avill certainly reject the theory. A fcAV natu- 

 ralists, endoAA'ed Avith much flexibility of mind, and Avho liaA'e 

 already begun to doubt the immutability of species, may be 

 induouced by this volume ; but I look Avith confidence to the 

 future, to young and rising naturalists, Avho Avill be able to 

 view both sides of the question Avith impartiality, ^^'hoeve^ 

 is led to bclicA'e that species are mutable Avill do good service 

 by conscientiously expressing his conA'iction ; for thus only 

 can tlie load of prejudice by Avhich this subject is overwhelmed 

 be removed. 



Several eminent naturalists have of late published tluir 



