464 DIRECTIVE FACTORS IN EVOLUTION: 



To Groos and to Julian S. Huxley we owe two luminous 

 suggestions. In his Play of Ammals (Eng. Trans., 1898, 

 p. 242), Groos suggests that " in order to preserve the 

 species the discharge of the sexual function must be ren- 

 dered difficult, since the impulse to it is so powerful that 

 without some such arrest it might easily become prejudicial 

 to that end ". " This very strength of impulse is itself 

 necessary to the preservation of the species; but, on the 

 other hand, dams must be opposed to the impetuous stream, 

 lest the impulse expend itself before it is made effectual, 

 or the mothers of the race be robbed of their strength, to the 

 detriment of their offspring." . . . " The most important 

 factor in maintaining this necessary check is the coyness 

 of the female; coquetry is the conflict between natural im- 

 pulse and coyness, and the male's part is to overcome the 

 latter" (op. cit., p. 243). 



!NTot less interesting is the suggestion developed by Julian 

 S. Huxley in his remarkable study of the courtship-habits 

 of the Great Crested Grebe, Podiceps cristatus (Proc. 

 Zool. Soc. London, 1914, pp. 491-562). In the Great 

 Crested Grebe the two sexes are practically alike in plumage, 

 colour, and habits; but the courtship is extraordinarily elab- 

 orate a self-exhausting ritual, " not leading up to or con- 

 nected with coition ". Mr. Huxley believes that " the court- 

 ship ceremonies serve to keep the two birds of a pair together, 

 and to keep them constant to each other ". " Birds have obvi- 

 ously got to a pitch where their psychological states play 

 an important part in their lives. Thus, if a method is to 

 be devised for keeping two birds together, provision will have 

 to be made for an interplay of consciousness or emotion 

 between them." The courtship is justified by the strength 

 of the emotional bond it establishes. There is a " Mutual 



