BRITISH WARBLERS 



movements visible to an external observer may be absent in 

 slight, and sometimes in intense emotions. May not this be 

 true of the emotion of a bird, and may not the relation between 

 the strength of the emotion and the intensity of the expres- 

 sional movement, which is here assumed, be open to question ? 

 Circumstances at least seem to show that such may be the 

 case. For do we not observe in bird life numberless degrees 

 of emotional reaction, ranging from almost imperceptible 

 movements up to extravagant actions, corresponding to a 

 sexual instinct the strength of which cannot well be differ- 

 entiated in x y z and all the rest. 



The proposition, as I understand it, is somewhat as 

 follows : Not all the males are of equal strength ; the stronger 

 individuals are capable of greater sexual emotion. This 

 emotion must somehow express itself, and does so in many 

 cases by what are known as motor reactions. These reactions 

 excite the female. The stronger the male the stronger the 

 reaction and the greater chance that male will have of over- 

 coming the reluctance of the female, pairing, and transmitting 

 'its greater strength to descendants, and the greater scope 

 will there be for the development of secondary sexual 

 characters, which will naturally result from greater strength 

 and possibly contribute to a more effective pairing situation. 

 And at first sight this would appear to be a reasonable 

 interpretation of all the peculiar attitudes, antics, and vocal 

 extravagances which are the subject of our investigation ; but 

 when we attempt to bring it into accord with the phenomena 

 which we actually observe, the task is not altogether an easy 

 one. Certain essential features of the theory are not very 

 clear to me ; for instance, there is no very definite expression 

 of opinion as to whether the theory is one to explain the 

 evolution of antics from movements that at some earlier 

 period were not so pronounced, by ' the selection of variations 

 all tending in the direction of greater activity ; or whether 

 it only claims to show how, having once arisen, they may 

 now have a meaning in relation to something in the environ- 



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