352 Darwin, and after Darwin, 



be regarded as intentionally preparatory to the 

 various uses which they subsequently acquire. 



Now this argument, forcible as it appears at first 

 sight, is really at fault both in its premiss and in its 

 conclusion. By which I mean that, in the first place 

 the premiss is not true, and, in the next place, that 

 even if it were, the conclusion would not necessarily 

 follow. The premiss is, "that every modification of 

 structure must have been functionless at first, when it 

 began to appear ; " and the conclusion is, that, qua 

 functionless, such a modification cannot have been 

 caused by natural selection. I will consider these two 

 points separately. 



First as to the premiss, it is not true that every 

 modification of structure must necessarily be function- 

 less when it first begins to appear. There are two 

 very good reasons why such should not be the case in 

 all instances, even if it should be the case in some. 

 For, as a matter of observable fact, a very large 

 proportional number of incipient organs are useful 

 from the very moment of their inception. Take, for 

 example, what is perhaps the most wonderful instance 

 of refined mechanism in nature the eye of a verte- 

 brated animal. Comparative anatomy and embryology 

 combine to testify that this organ had its origin in 

 modifications of the endings of the ordinary nerves 

 of the skin. Now it is evident that from the very 

 first any modification of a cutaneous nerve whereby it 

 was rendered able, in however small a degree, to be 

 differently affected by light and by darkness would be 

 of benefit to the creature presenting it ; for the 

 creature would thus be able to seek the one and shun 

 the other according to the requirements of its life. 



