NATURAL SELECTION. 95 



These facts can be explained on the belief of their de- 

 scent from a common form ; therefore it may be safely 

 admitted that all the members of the same class are 

 descended from one progenitor. But as the members 

 of quite distinct classes have something in common in 

 structure and much in common in constitution, analogy 

 would lead us one step further, and to infer as probable 

 that aU living creatures are descended from a single pro- 

 totype. 



Descent of Thus a large yet undefined extension may 



Man, part I., gafely be given to the direct and indirect re- 

 ''"^^ ■ suits of natural selection ; but I now admit, 

 after reading the essay by Nageli on plants, and the re- 

 marks by Tarious authors with respect to animals, more 

 especially those recently made by Professor Broca, that in 

 the earlier editions of my " Origin of Species " I perhaps 

 attributed too much to the action of natural 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 ; but I am convinced, from the light 

 gained during even the last few years, that very many 

 structures which now appear to us useless will here- 

 after be proved to be useful, and will therefore come 

 within the range of natural selection. Nevertheless, I 

 did not formerly consider suflBciently the existence of 

 structures, which, as far as we can at present judge, are 

 neither beneficial 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 distinct objects in view : firstly, to show that species 

 had not been separately created ; and, secondly, that natu- 

 ral selection had been the chief agent of change, though 

 largely aided by the inherited effects of habit, and slightly 



