Chap. XV.] CONCLUSION. 293 



I have now recapitulated the facts and considerations 

 which have thoroughly convinced me that species have 

 been modified, during a long course of descent. This 

 has been effected chiefly through the natural selection 

 of numerous successive, slight, favourable variations; 

 aided in an important manner by the inherited effects of 

 the use and disuse of parts; and in an unimportant man- 

 ner, that is in relation to adaptive structures, whether 

 past or present, by the direct action of external condi- 

 tions, and by variations which seem to us in our ignor- 

 ance to arise spontaneously. It appears that I formerly 

 underrated the frequency and value of these latter forms 

 of variation, as leading to permanent modifications of 

 structure independently of natural selection. But as my 

 conclusions have lately been much misrepresented, and 

 it has been stated that I attribute the modification of 

 species exclusively to natural selection, I may be per- 

 mitted to remark that in the first edition of this work, 

 and subsequently, I placed in a most conspicuous posi- 

 tion — namely, at the close of the Introduction — the 

 following words: " I am convinced that natural selection 

 has been the main but not the exclusive means of modi- 

 fication." This has been of no avail. Great is the power 

 of steady misrepresentation; but the history of science 

 shows that fortunately this power does not long endure. 



It can hardly be supposed that a false theory would 

 explain, in so satisfactory a manner as does the theory 

 of natural selection, the several large classes of facts 

 above specified. It has recently been objected that this 

 is an unsafe method of arguing; but it is a method used 

 in judging of the common events of life, and has often 

 been used by the greatest natural philosophers. The 

 undulatory theory of light has thus been arrived at; and 



