INTRODUCTION. 5 



my essay had been written, I should probably never 

 have completed it. Almost all the conclusions at which 

 I have arrived I find confirmed by this naturalist, whose 

 knowledge on many points is much fuller than mine. 

 Wherever I have added any fact or view from Prof. 

 Hackel's writings, I give his authority in the text, other 

 statements I leave as they originally stood in my manu- 

 script, occasionally giving in the foot-notes references 

 to his works, as a confirmation of the more doubtful or 

 interesting points. 



During many years it has seemed to me highly 

 probable that sexual selection has played an important 

 part in differentiating the races of man ; but in- my 

 1 Origin of Species ' (first edition, p. 199) I contented 

 myself by merely alluding to this belief. "When I came 

 to apply this view to man, I found it indispensable to 

 treat the whole subject in full detail. 3 Consequently 

 the second part of the present work, treating of sexual 

 selection, has extended to an inordinate length, com- 

 pared with the first part; but this could not be 

 avoided. 



I had intended adding to the present volumes an 

 essay on the expression of the various emotions by man 

 and the lower animals. My attention was called to this 

 subject many years ago by Sir Charles Bell's admirable 



9 Prof. Hackel is the sole author who, since the publication of the 

 • Origin,' has discussed, in his various works, in a very able manner, the 

 subject of sexual selection, and has seen its full importance. 



