THE THEORY OF CHANGE OF FUNCTION 57 



small bud arising from the surface of the body and 

 is absolutely useless for any of the purposes to 

 which we put our arms. If this represents the 

 primitive condition, why should such an organ 

 have been preserved at all ? Again, a more striking 

 example and one yet not thoroughly explained is 

 found in the wing of the bat. This is a great fold 

 of skin connecting together the much elongated 

 fingers, and also connecting these with the sides of 

 the body extending downwards so as to involve 

 the legs as well. This constitutes as we know 

 a very efficient flying apparatus. The theory 

 of evolution undoubtedly requires that bats 

 should be descended from, should have had as 

 ancestors, mammals possessing fingers of normal 

 length and devoid of the lateral expansion of the 

 skin. The theory of Natural Selection demands 

 further that the various steps in the transformations 

 of this ancestral form to the existing bat should 

 have been slow and gradual. Now it is obvious 

 that a very slight lengthening of the fingers, coupled 

 with a very slight increase in the extent to which 

 they were webbed, would in no way enable the 

 ancestral mammal to fly ; and hence that such 

 accidental variations could never have been pre- 

 served and perpetuated because of their utility as 

 flying organs. 



Cases such as these have long been felt to offer 

 very serious difficulty and to throw serious doubt, 

 not on the reality of Natural Selection, but on its 

 sufficiency. Darwin himself suggested a possible 

 solution of the difficulty, at any rate in certain cases, 



