86 MAN [CHAP. VIII 



Letter 449 makes me constantly distrust myself. I fear we shall never 

 quite understand each other. I value the cases of bright- 

 coloured, incubating male fisher, and brilliant female butter- 

 flies, solely as showing that one sex may be made brilliant 

 without any necessary transference of beauty to the other 

 sex ; for in these cases I cannot suppose that beauty in the 

 other sex was checked by selection. 



I fear this letter will trouble you to read it. A very short 

 answer about your belief in regard to the female finches and 

 Gallinacese would suffice. 



Letter 450 A. R. Wallace to C. Darwin. 



9, St. Mark's Crescent, N.W., Sept. 27th, 1868. 



Your view seems to be that variations occurring in one 

 sex are transmitted either to that sex exclusively or to both 

 sexes equally, or more rarely partially transferred. But we 

 have every gradation of sexual colours, from total dissimilarity 

 to perfect identity. If this is explained solely by the laws 

 of inheritance, then the colours of one or other sex will be 

 always (in relation to the environment) a matter of chance. 

 I cannot think this. I think selection more powerful than 

 laws of inheritance, of which it makes use, as shown by cases 

 of two, three or four forms of female butterflies, all of which 

 have, I have little doubt, been specialised for protection. 



To answer your first question is most difficult, if not 

 impossible, because we have no sufficient evidence in indi- 

 vidual cases of slight sexual difference, to determine whether 

 the male alone has acquired his superior brightness by sexual 

 selection, or the female been made duller by need of protec- 

 tion, or whether the two causes have acted. Many of the 

 sexual differences of existing species may be inherited dif- 

 ferences from parent forms, which existed under different 

 conditions and had greater or less need of protection. 



I think I admitted before, the general tendency (probably) 

 of males to acquire brighter tints. Yet this cannot be universal, 

 for many female birds and quadrupeds have equally bright 

 tints. 



To your second question I can reply more decidedly. I 

 do think the females of the Gallinaceae you mention have 

 been modified or been prevented from acquiring the brighter 

 plumage of the male, by need of protection. I know that the 



