THE EVOLUTION OF ANIMAL FUNCTION 



By KEITH LUCAS 



Fellow of Trinity College, Cambridge 



PART I 



No serious student of biological thought can have failed to 

 observe how small a part the hypothesis of evolution has played 

 in the development of animal physiology. In every other 

 department of biology the publication of the Origin of Species 

 marks a profound change in the direction of research and an 

 altered interpretation of facts already known. To the study 

 of animal structure, for example, Darwin's work brought a 

 vigour and activity such as had never before been experienced. 

 Morphologists found a new meaning in their work. They ceased 

 to toil at a classification whose basis was mere caprice, tracing 

 instead the sequence of a course of development which bound 

 together the whole animal kingdom by the tie of common 

 blood. But with the study of animal function it was otherwise. 

 There is no break in the history of physiology to mark the 

 pre-Darwinian from the post-Darwinian period. Questions of 

 function have never been called in to help in tracing the course 

 of evolution, and the idea of evolution has given no aid in the 

 interpretation of the known facts of function. If the hypothesis 

 of evolution were to-morrow to be proved untenable, physiologists 

 would scarcely be concerned. 



We naturally inquire for the cause by which two sciences 

 so closely related have been led into such diverse paths. And 

 it is not far to seek. Many years before Darwin wrote, the 

 study of morphology had taken upon itself the duty of clas- 

 sifying animals, pronouncing definitely against the claim of 

 physiology to a share in the enterprise. And it followed in the 

 regular course of things that the criteria of classification afforded 

 the material by which the developmental relationships of animals 

 were afterwards determined. In this historical fact there lies, as 

 I believe, the key to that indifference which physiologists still 

 display towards the evolution of those functions which form the 



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