422 CONCLUSION. [Chap. XV. 



.attraction of gravity, was also attacked by Leibnitz, "as sub- 

 versive of natural, and inferential ly of revealed, religion." A cele- 

 brated author and divine has written to me that " he has gradually 

 "learnt to see that it is just as noble a conception of the Deity to 

 "believe that He created a few original forms capable of self- 

 " development into other and needful forms, as to believe that He 

 " required a fresh act of creation to supply the voids caused by the 

 " action of His laws." 



Why, it may be asked, until recently did nearly all the most 

 eminent living naturalists and geologists disbelieve in the muta- 

 bility of species. It cannot be asserted that organic beings in a 

 state of nature are subject to no variation ; it cannot be proved 

 that the amount of variation in the course of long ages is a limited 

 quantity ; no clear distinction has been, or can be, drawn between 

 species and well-marked varieties. It cannot be maintained that 

 species when intercrossed are invariably sterile, and varieties in- 

 variably fertile ; or that sterility is a special endowment and sign 

 of creation. The belief that species were immutable productions 

 was almost unavoidable as long as the history of the world was 

 thought to be of short duration ; and now that we have acquired 

 some idea of the lapse of time, we are too apt to assume, without 

 proof, that the geological record is so perfect that it would have 

 afforded us plain evidence of the mutation of species, if they had 

 undergone mutation. 



But the chief cause of our natural unwillingness to admit that 

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

 are always slow in admitting great changes of which we do not see 

 the steps. The difficulty is the same as that felt by so many geo- 

 logists, when Lyell first insisted that long lines of inland cliffs had 

 been formed, and great valleys excavated, by the agencies which 

 we see still at work. The mind cannot possibly grasp the full 

 meaning of the term of even a million years ; it cannot add up and 

 perceive the full effects of many slight variations, accumulated 

 d uring an almost infinite number of generations. 



Although I am fully convinced of the truth of the views given in 

 this volume under the form of an abstract, I by no means expect 

 to convince experienced naturalists whose minds are stocked with 

 a multitude of facts all viewed, during a long course of years, from 

 a point of view directly opposite to mine. It is so easy to hide our 

 ignorance under such expressions as the " plan of creation," " unity 

 of design," &c, and to think that we give an explanation when we 

 only re-state a fact. Anyone whose disposition leads him to attach 

 more weight to unexplained difficulties than to the explanation of 



