1869.] SEXUAL SELECTION. Ill 



if a layman had delivered the same address, he would have 

 done good service in spreading what, as I hope and believe, is 

 to a large extent the truth ; but a clergyman in delivering such 

 an address does, as it appears to me, much more good by his 

 power to shake ignorant prejudices, and by setting, if I may 

 be permitted to say so, an admirable example of liberality. 

 With sincere respect, I beg leave to remain, 



Dear Sir, yours faithfully and obliged, 



Charles Darwin. 



[The references to the subject of expression in the following 

 letter are explained by the fact, that my father's original 

 intention was to give his essay on this subject as a chapter 

 in the ' Descent of Man,' which in its turn grew, as we have 

 seen, out of a proposed chapter in ' Animals and Plants : '] 



C. Darwin to F. Miiller. 



Down, February 22, [1869?] 



. . . Although you have aided me to so great an extent in 

 many ways, I am going to beg for any information on two other 

 subjects. I am preparing a discussion on " Sexual Selection," 

 and I want much to know how low down in the animal scale 

 sexual selection of a particular kind extends. Do you know 

 of any lowly organised animals, in which the sexes are 

 separated, and in which the male differs from the female in 

 arms of offence, like the horns and tusks of male mammals, or 

 in gaudy plumage and ornaments, as with birds and butter- 

 flies ? I do not refer to secondary sexual characters, by which 

 the male is able to discover the female, like the plumed 

 antennae of moths, or by which the male is enabled to seize 

 the female, like the curious pincers described by you in some 

 of the lower Crustaceans. But what I want to know is, how 

 low in the scale sexual differences occur which require some 

 degree of self-consciousness in the males, as weapons by 



