GENERAL SUMMARY AND CONCLUDING REMARKS 



and Chiff-chaff, for instance, are closely related, live under the 

 influence of a similar environment, require similar food and 

 construct similar nests, yet the former builds upon the ground, 

 the latter in some suitable undergrowth a foot or so above it. 

 Can we then say that the ground leads to success in the one 

 case but brings disaster in the other ? Surely not when we 

 bear in mind the identity of the conditions of existence of the 

 two species. Or again, of the numberless channels into which 

 sexual behaviour has been guided, can we say that each has 

 some definite value attached to it ? Can we even say that it is 

 strictly correlated with something which has utility ? Grant- 

 ing for the moment that emotional manifestation does play a 

 part, granting that attitudes and antics create on the whole a 

 more effective pairing situation, that beautiful plumage adds 

 to the effect and that song contributes to an increased 

 emotional tone — granting all of this, can anyone seriously 

 suggest that wings raised a little more or a little less, slowly 

 flapped or quickly fluttered, partially or fully expanded, a tail 

 waved with a sidelong or an up-and-down motion, a song- 

 produced as the bird ascends or descends in the air, and a host 

 of other trifling but specific forms of behaviour, depend for 

 their usefulness on being cast in just this or that particular 

 mould. If the life behaviour as a whole has utility, does it 

 follow that every detail is independently useful ? 



In much of the behaviour which centres round the securing 

 and defence of a territory, the building of a nest, and the care 

 of the young, wherein a psychical accompaniment seems 

 to be required as a contributory factor, one cannot help being 

 impressed with the difficulties of evolutionary interpretation in 

 terms of fluctuating variation or mutation only. How can we 

 appeal to the slow accumulation of fluctuating variations only 

 in a case where a definite organic structure in A depends 

 for its success on a definite psychical factor in B ? How can 

 we appeal to variations of definite origin in explanation of the 

 guidance of behaviour which is accommodating the organism 

 to new and changed conditions of existence ? How can we 



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