i6 4 THE DARWINIAN THEORY 



The Difficulty with Regard to the Earliest 

 Commencement of Organs. 



/ This difficulty is a very serious one, for Natural 

 Selection can only act on an organ after it has 

 already attained sufficient size to be of practical 

 importance and utility. Natural Selection accounts 

 for any amount of modification in an organ when 

 once established ; modification in any direction, 

 either of increase or decrease, but does not offer any 

 explanation of the first appearance of such an organ. 

 This is best understood by a few examples, showing 

 the continuous preservation of a series of very minute 

 variations. 



i. The wing of the Bat, a flying mammal, is 

 clearly a modified arm with great elongation of 

 the fingers and webbing of the skin, which also 

 extends from the side of the body and involves 

 the hind-legs and tail (Fig. 28). It is easy to 

 see that, when once established as a flying organ, 

 Natural Selection would cause survival of those with 

 the best wings, and so lead to gradual improvement 

 and perfection of the wing. But how does the wing 

 first commence ? 



Bats are a specialised group of mammals which 

 must have been descended from non-flying ancestors. 

 If the first commencement of the wing was a slight 

 accidental elongation of the fingers, and a slight 

 increase in the webbing, this would not give the 

 power of flight, and would be of no use as a wing 

 until it had attained a considerable size. In other 

 words, such an organ as a wing would in its earliest 



