EVOLUTION OF THE COLORS OF BIRDS. 63 



tions. He says:* "They originate, we know not how, 

 in the nature of the organism. Nor would the state of 

 the case be essentially altered if it were demonstrated, 

 in opposition to Darwin, that every organic modifica- 

 tion was occasioned by some external stimulus. For the 

 change thus set up in the organism in response to the 

 foreign excitation would obviously derive its character 

 from the constitution of the organism, just as, to use 

 Darwin's own example, the peculiarity of a flame is due 

 to the constitution of the combustible materials, and not 

 to the igniting spark. " Prof. Schurman is arguing for 

 a theistic conception of the origin of variations, and 

 hence, of the creation of species, but his conclusion 

 here does not effect the scientific, but only the met- 

 aphysical aspect of the case. As stated in the in- 

 troduction to this chapter, natural law does not explain 

 first cause, with which, indeed, science is not concerned. 

 The ultimate reason for the enlargement of a muscle 

 when exercised, for example, cannot be ascertained, but, 

 nevertheless, if it could be shown why such exercise pro- 

 duced in successive generations variations in the direction 

 of increased dimension, we would have as good an expla- 

 nation of the cause of those particular variations as we 

 have of the cause of the earth's attraction by the sun 

 through gravitation. That variations are conditioned 

 by the reaction of the organism on the influences of the 

 environment, is undeniable, but this does not detract 

 from the validity of an explanation of the origin of 

 variations, so far as science is concerned. An analogy 

 may illustrate this better, perhaps. Certain qualities of 

 the mind are developed by education. It is possible to 

 formulate the exact process by which these mental 

 traits were brought about and it is justifiable to state 



* The Ethical Import of Darwinism, p. 81. 



