274 WORK ON 'MAN.' [1867 



est, which makes me forget for some hours every day my 

 accursed stomach." 



The work on Man was interrupted by illness in the early 

 summer of 1868, and he left home on July i6th for Fresh- 

 water, in the Isle of Wight, where he remained with his 

 family until August 2ist. Here he made the acquaintance 

 of Mrs. Cameron. She received the whole family with open- 

 hearted kindness and hospitality, and my father always re- 

 tained a warm feeling of friendship for her. She made an 

 excellent photograph of him, which was published with the 

 inscription written by him : " I like this photograph very 

 much better than any other which has been taken of me." 

 Further interruption occurred in the autumn so that continu- 

 ous work on the ' Descent of Man ' did not begin until 1869. 

 The following letters give some idea of the earlier work in 

 1867 :] 



C. Darwin to A. R. Wallace. 



Down, February 22, [1867?] 



MY DEAR WALLACE, I am hard at work on sexual selec- 

 tion, and am driven half mad by the number of collateral 

 points which require investigation, such as the relative num- 

 ber of the two sexes, and especially on polygamy. Can you 

 aid me with respect to birds which have strongly marked sec- 

 ondary sexual characters, such as birds of paradise, humming- 

 birds, the Rupicola, or any other such cases ? Many gallina- 

 ceous birds certainly are polygamous. I suppose that birds 

 may be known not to be polygamous if they are seen during 

 the whole breeding seasion to associate in pairs, or if the 

 male incubates or aids in feeding the young. Will you have 

 the kindness to turn this in your mind ? But it is a shame 

 to trouble you now that, as I am heartily glad to hear, you are 

 at work on your Malayan travels. I am fearfully puzzled 

 how far to extend your protective views with respect to the 

 females in various classes. The more I work the more im- 

 portant sexual selection apparently comes out. 



