BRITISH WARBLERS 



appeal to the biological transmission of acquired modification 

 with little or no evidence to go upon ? It is here that 

 Professor Lloyd Morgan's principle of the " survival of co- 

 incident variations" comes to our aid; and to one who 

 sees — needlessly perhaps — in the psychological aspect of the 

 evolution of behaviour difficulties of interpretation on any 

 known naturalistic hypothesis, acquired modification as the 

 foster-parent of congenital variation seems to be a step in the 

 right direction. I believe it to be an important principle, 

 removing as it does in some measure the difficulties which 

 surround the survival value of incipient variations. 



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