14G THE DESCENT OF MAX. [Part I. 



as Isidore GeolFroy has shown in the case of man, many 

 stranfije deviations of structure are tied together. Inde- 

 pendently of correlation, a change in one part often leads, 

 through the increased or decreased use of other parts, to 

 other changes of a quite unexpected nature. It is also 

 well to reflect on such facts, as the wondei-ful growth of 

 galls on plants caused by the poison of an insect, and on 

 the remarkable changes of color in the plumage of parrots 

 when fed on certain fishes, or inoculated with the poison 

 of toads ; *" for we can thus see that the fluids of the 

 system, if altered for some special purpose, might induce 

 other strange changes. We should especially bear in 

 mind that modifications acquired and continually used 

 during past ages for some useful purpose would probably 

 become firmly fixed and might be long inherited. 



Thus a very large yet undefined extension may safely 

 be given to the direct and indirect results of natural selec- 

 tion ; but I now admit, after reading the essay by Xilgeli 

 on j^lants, and the remarks by various authors with respect 

 to animals, more especially those recently made by Prof. 

 Bi'oca, that in the earlier editions of my ' Origin of Spe- 

 cies ' I j)robably attributed too much to the action of natu- 

 ral selection or the survival of the fittest. I have altered 

 the fifth edition of the Origin so as to confine my remarks 

 to adaptive changes of structure. I had not formerly 

 sufficiently considered the existence of many structures 

 which appear to be, as far as we can judge, neither bene- 

 ficial nor injurious ; and this I believe to be one of the 

 greatest oversights as yet detected in my work. I may 

 be permitted to say, as some excuse, that I had two dis- 

 tinct objects in view, firstly, to show that sj^ecies had not 

 been separately created, and secondly, that natural selec- 

 tion had been the chief agent of change, though largely 



*" ' The Variation of Animals and Plants under Domestication,' vol. iu 

 pp. 280, 282. 



