DISPLAY OF THE MALLARD IN RELATION TO PAIRING 85 



in the second ; and the spectacle may be witnessed of a duck 

 courting, and persisting in the courtship of a non-displaying 

 male amongst a crowd of displaying ones. Moreover, specific 

 courtship is frequently initiated in absence of preliminary 

 display. It is therefore doubtful if display is a necessary 

 antecedent to courtship or pairing. It may be regarded as in 

 essence and origin no more than the bodily expression of 

 emotional overflow. But although it may not be in an 

 absolute sense the product of sexual selection (supposing the 

 latter a factor in evolution), it may yet conceivably be a 

 correlate of such selection. While primarily merely an 

 accompaniment of the pairing instinct, it may serve as an 

 additional stimulus to further development. But apart 

 from the question of origin, and granted selection on the 

 part of the female, the practical point is : does display, 

 in its present form, really count in the drake as a 

 qualification or advantage in the securing of a mate? In 

 birds in general, Groos holds that display is a necessary 

 antecedent to pairing. But without assuming its necessity, 

 it remains conceivable that display may count. The 

 pairing instinct in birds is a seasonal phenomenon of gradual 

 growth, spontaneous in the individual, but responsive to, 

 and possibly accelerated by, environmental factors. If we 

 take a female in which the pairing instinct is on the verge of 

 final achievement, it seems not unreasonable, in view of the 

 undoubted intersexual sensitiveness to display, that the dis- 

 play of a particular drake may be the final stimulus the 

 straw which turns the balance. If in this sense display 

 is of value to the drake, then display is a factor 

 in sexual selection ; and so far as sexual selection has 

 modified or expanded it, it is a product of sexual selection, 

 whatever its origin. The missing link in the argument is 

 that there is no evidence that such a stimulus, due to a 

 particular male, necessarily results in his being chosen. The 

 impression one receives, in fact, is otherwise. Nevertheless, 

 in view of the difficulty or impossibility of accurate observa- 

 tion on such a nice point, it would be unjustifiable to deny 

 its occurrence. 



3. It is safe to assume that the apparent close similarity 



