iv PREFACE. 



tributed to the inherited effects of use and disuse, with re- 

 spect both to the body and mind. I also attributed some 

 amount of modification to the direct and prolonged action 

 of changed conditions of life. Some allowance, too, must 

 be made for occasional reversions of structure; nor must we 

 forget what I have called "correlated" growth, meaning 

 thereby that various parts of the organization are in some 

 unknown manner so connected, that when one part varies 

 so do others; and if variations in the one are accumulated 

 by selection other parts will be modified. Again, it has 

 been said by several critics that when I found that many 

 details of structure in man could not be explained through 

 natural selection, I invented sexual selection; I gave, how- 

 ever, a tolerably clear sketch of this principle in the first 

 edition of the " Origin of Species," and I there stated that 

 it was applicable to man. This subject of sexual selection 

 has been treated at full length in the present work, simply 

 because an opportunity was here first afforded me. I have 

 been struck with the likeness of many of the half -favorable 

 criticisms on sexual selection, with those which appeared 

 at first on natural selection; such as, that it would explain 

 some few details, but certainly was not applicable to the 

 extent to which I have employed it. My conviction of the 

 power of sexual selection remains unshaken ; but it is 

 probable, or almost certain, that several of my conclusions 

 will hereafter be found erroneous; this can hardly fail to 

 be the case in the first treatment of a subject. When 

 naturalists have become familiar with the idea of sexual 

 selection, it will, as I believe, be much more largely ac- 

 cepted; and it has already been fully and favorably re- 

 ceived by several capable judges. 



DOWN, BECKENHAM, KENT, September, 1874 



