7 6 



VARIATION 



Then there are organs, as the kidneys, whose function is to 

 remove waste products that would otherwise accumulate and 

 destroy the body. There are others, as the udder and various 

 glands, whose function is to manufacture some particular product 

 to be used either within or without the body. There is a system 

 (the muscular) for moving the body as a whole or for the exercise 

 of any of its parts, and a network of nerves forming a ready and 

 rapid. means of communication. There is a heart to drive the 

 blood, and perhaps a bony skeleton to hold the complicated mass 

 together. 



Now the activities or functions of these various parts are by 

 no means constant and invariable from day to day. In other 

 words, there is probably as much deviation in function as in 

 form, and for the purpose of the farmer it is even more 

 important. 



Evolution not a study in morphology only. The mistake is 

 often made of defining evolution as exclusively a study in mor- 

 phology. 1 It means more than that. Living beings are some- 

 thing besides form, and their evolution something more than the 

 development of their form ; indeed, in their service to man both 

 animals and plants are valued less for their structure than for 

 their function, which is what they can do. And so it is that 



1 " The problem of development is an acknowledged morphological problem." 

 C. B. Davenport, Experimental Morphology, Part I, Preface. 



The conception here alluded to is not difficult to account for. The idea of 

 evolution or development as opposed to the older assumption of special crea- 

 tion was first announced at the very close of the eighteenth century, but was not 

 generally before the public until the appearance of the Origin of Species, after the 

 middle of the nineteenth century (1859). At that time biologists were chiefly con- 

 cerned in classification as based upon external structure or form. It is not strange, 

 therefore, that the discussion should have first arisen, and the battles incident to a 

 new, startling, and, in the popular mind, sacrilegious theory have been first fought 

 out, in the field of morphology. 



Gradually, however, biologists began to concern themselves more and more 

 with internal structure (histology), and, quite to their surprise, they found them- 

 selves still within the field of evolution. Then came studies in function (physi- 

 ology)' showing conclusively that this, too, is a matter of development and subject 

 to variation and heredity. It is therefore not only erroneous but for the breeder 

 dangerously misleading to consider the study of evolution as confined to the field 

 of morphology, which is not the exclusive nor to him even the primary manifesta- 

 tion of the great principle of evolution. There is evoluion of function as well as 

 evolution of form. 



