266 BOMBAY DUCKS 



in form, yet both are equally successful in obtaining 

 food, and both secure it in the same manner. More- 

 over, the young male has a tail four inches in length, 

 but, later on, he grows one sixteen inches long, yet he 

 continues to obtain food in the same manner. Thus 

 a difference of twelve inches in the length of his tail 

 does not appreciably affect his ability to find food. 



Even if we could demonstrate that each species takes 

 the shape best suited to its mode of life, if we could 

 prove, for example, that the Nilgiri blue flycatcher 

 would be greatly handicapped in the search for food 

 were his shape that of the grey-headed flycatcher, this 

 would not be sufficient. If natural selection alone is 

 responsible for the shape of an organism, we must 

 prove that every step in the transition from the common 

 ancestral form to that of the present species was a 

 distinct gain to the species. This point is often lost sight 

 of by those who invoke the aid of natural selection to 

 explain every zoological difficulty. It seems to me that 

 the great diversity in shape exhibited by birds having 

 similar habits merely shows that there are several 

 equally good methods of accomplishing an object. 



If Nature desires to call into existence a number of 

 flycatching birds, she is not obliged to cast all in exactly 

 the same mould ; she is able to create many different 

 forms of organism, all well adapted to the work before 

 them. The general shape is of course determined by 

 natural selection, especially in the case of highly 

 specialized birds, such as woodpeckers, kingfishers, and 

 swifts. But, even in such cases, considerable diversity 

 of form is permitted. The less specialized the habits 



