MARSH WARBLER 



ment of the female. But it can scarcely be intended in this 

 latter sense, as that would imply that the reactions came into 

 being independently of the utility which the theory suggests. 

 The central fact of the theory appears to be this, that the 

 reactions are the agency by which the mating of the stronger 

 individuals is secured. Let us then carry our minds back to 

 some earlier period, and try to picture the appearance of a 

 variation which possessing greater vitality reflected it in its 

 emotions, stimulated the female, and thus gained an advantage 

 in securing a mate. The weaker members insufficiently 

 endowed with overt expressional movement would gradually 

 disappear and the whole species become transformed. But 

 since, on the average, it would only be those which possessed 

 the power of reflecting their emotions in the highest degree 

 which would attain to reproduction, competition would still 

 continue, and the reactions would slowly increase in intensity 

 pari passu with the selection of the stronger individuals 

 until a level were reached when perhaps further increase 

 might become harmful. This level would then be maintained 

 by the elimination of those that failed to reach the necessary 

 standard. The reactions have accordingly been developed 

 just in so far as they represent increased emotion and thereby 

 increased strength. Now with regard to some of the warblers 

 the facts are as follow : There are ten species which for pur- 

 poses of comparison can be divided into five pairs, the two 

 Whitethroats, Blackcap and Garden Warbler, Grasshopper 

 and Savi's Warbler, Willow Warbler and ChiS- Chaff, and the 

 Eeed and Marsh Warbler. All these pairs are severally very 

 closely allied, but in the case of two of them the relationship 

 is so close that one can only be distinguished from the other 

 with some difficulty, and all may be said to be fairly equally 

 distributed over Western Europe. Eegarding these ten species 

 as a whole we find it difficult to trace any uniformity in the 

 intensity with which they manifest their emotions, and 

 equally difficult to satisfy ourselves of any general resem- 

 blance in the particular form such manifestations take ; 



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