286 THE SPREAD OF EVOLUTION. [ch. xiv. 



The letter from Darwin to Wallace goes on : " The rea- 

 son of my being so much interested just at present about 

 sexual selection is, that I have almost resolved to publish 

 a little essay on the origin of Mankind, and I still strongly 

 think (though I failed to convince you, and this, to me, is 

 the heaviest blow possible) that sexual selection has been 

 the main agent in forming the races of man. 



" By the way, there is another subject which I shall in- 

 troduce in my essay, namely, expression of countenance. 

 Now, do you happen to know by any odd chance a very 

 good-natured and acute observer in the Malay Archipelago, 

 who you think would make a few easy observations for me 

 on the expression of the Malays when excited by various 

 emotions ?" 



The reference to the subject of expression in the above 

 letter is explained by the fact, that my father's original in- 

 tention 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. 



He got much valuable help from Dr. Giinther, of the 

 Natural History Museum, to whom he wrote in May 1870 : 



" As I crawl on with the successive classes I am aston- 

 ished to find how similar the rules are about the nuptial or 

 ' wedding dress ' of all animals. The subject has begun to 

 interest me in an extraordinary degree ; but I must try not 

 to fall into my common error of being too speculative. But 

 a drunkard might as well say he would drink a little and 

 not too much ! My essay, as far as fishes, batrachians and 

 reptiles are concerned, will be in fact yours, only written by 

 me." 



The last revise of the Descent of Man was corrected on 

 January 15th, 1871, so that the book occupied him for about 

 three years. He wrote to Sir J. Hooker : " I finished the 

 last proofs of my book a few days ago ; the work half-killed 

 me, and I have not the most remote idea whether the book 

 is worth publishing." 



He also wrote to Dr. Gray : 



" I have finished my book on the Descent of Man, &c, 

 and its publication is delayed only by the Index : when pub- 

 lished, I will send you a copy, but I do not know that you 

 will care about it. Parts, as on the moral sense, will, I dare 

 say, aggravate you, and if I hear from you, I shall probably 

 receive a few stabs from your polished stiletto of a pen." 



