158 Huxley, Bird-watching and Biological Science. [April 



(as in the Grebe); in Display Courtships, to drop the second (as 

 in the Warblers). As a special development of the Display Court- 

 ships we get courtships like those of the Blackcock. 



It is interesting to note the relation of Darwinian Sexual Selec- 

 tion to these various categories. 



Darwinian Sexual Selection obviously does not operate in primi- 

 tive display courtships like that of the Warblers, nor in Mutual 

 Courtships. On the other hand, Selous' work shows that it does 

 operate, with almost diagrammatic clearness, in the Blackcock. 

 In the case of monogamous birds in which the males only have 

 brilliant colors, I should like to reserve judgment. But there is 

 another point; all courtship, it is here maintained (as also by E. 

 Howard and by Pycraft) has had its origin in posturings and 

 actions that are merely the direct outcome of sexual excitement, 

 so that one finds birds without any special sexual structures or 

 colors going through actions that are of the nature of courtship, 

 be it mutual or be \t Darwinian (take as example the Gulls on one 

 side and the Sylviidfe on the other). Then it is clear that the 

 development of special colors and structures employed in court- 

 ship must be a later addition, due to some separate influence, and 

 this holds true both of structures (like the Grebe's crest) used in 

 mutual courtship, or those (like the crest of the Ruby-crowned 

 Kinglet) used in display courtship. These latter, as I say, may 

 perhaps owe their origin to Darwinian Sexual Selection. The 

 former cannot, so we must revise our theories in the light of this 

 new conception of Mutual Courtship. 



Mr. Selous has a very interesting chapter on this subject. 

 (Selous, '05. "Inter-sexual Selection," pp. 261-283), to which, 

 however, my attention has only just been drawn. My own con- 

 clusions, though similar in many ways, were reached entirely 

 independently (Huxley, '14, pp. 523-525). 



It is necessary to observe that in most birds, as in Man himself, 

 the two forms of Courtship are inextricably interwoven. Man is 

 one of the most complicated of all, for while much is absolutely 

 reciprocal, yet there is much that is not mutual, and it is almost 

 impossible not to believe that here at least there has been a double 

 action of Darwinian Selection, the ancestral appearance of both 

 man and woman having been modified in different ways through- 

 its agency. 



