1866-1872] SEXUAL SELECTION 93 



protection, or that colour has generally been obtained by Letter 457 

 either sex for purposes of protection. But my view is, as 

 I thought I had made it clear, that the female has (in most 

 cases) been simply prevented from acquiring the gay tints 

 of the male (even when there was a tendency for her to 

 inherit it), because it was hurtful ; and that, when protec- 

 tion is not needed, gay colours are so generally acquired 

 by both sexes as to show that inheritance by both sexes 

 of colour variations is the most usual, when not prevented 

 from acting by Natural Selection. The colour itself may be 

 acquired either by sexual selection or by other unknown 

 causes. 



There are, however, difficulties in the very wide applica- 

 tion you give to sexual selection which at present stagger 

 me, though no one was or is more ready than myself to 

 admit the perfect truth of the principle or the immense 

 importance and great variety of its applications. 



Your chapters on " Man ' are of intense interest but 

 as touching my special heresy, not as yet altogether con- 

 vincing, though, of course, I fully agree with every word 

 and every argument which goes to prove the " evolution " 

 or " development ' of man out of a lower form. My only 

 difficulties are, as to whether you have accounted for every 

 step of the development by ascertained laws. 



I feel sure that the book will keep up and increase 

 your high reputation, and be immensely successful, as it 

 deserves to be. ... 



To G. B. Murdoch. Letter 458 



Down, March I3th, 1871. 



I am much obliged for your valuable letter. 1 I am 

 strongly inclined to think that I have made a great and 



1 We are indebted to Mr. Murdoch for a draft of his letter dated 

 March loth, 1871. It is too long to be quoted at length; the following 

 citations give some idea of its contents : " In your Descent of Man, in 

 treating of the external differences between males and females of the 

 same variety, have you attached sufficient importance to the different 

 amount and kind of energy expended by them in reproduction ? " Mr. 

 Murdoch sums up : " Is it wrong, then, to suppose that extra growth, 

 complicated structure, and activity in one sex exist as escape-valves for 

 surplus vigour, rather than to please or fight with, though they may serve 

 these purposes and be modified by them ?" 



