630 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1908. 



to guile. But the drongo-ciickoo is as like the king-crow in appear- 

 ance as one pea is like another. Both are small, glossy, black birds 

 with a longish forked tail. Zoologists, seeing how the cuckoo profits 

 by this resemblance, declare that it mimics the king-crow, and that 

 this resemblance has been brought about by natural selection. The 

 theory sounds very plausible, but close inspection reveals its weak 

 points. The king-crow is no fool, so that in order that the cuckoo 

 may delude him into the belief that it is a fellow king-crow the like- 

 ness must be fairly close. But as the average cuckoo is not in the 

 least like the king-crow in appearance, no small variation in the direc- 

 tion of king-crow appearance would be of any use to it. Hence this 

 remarkable resemblance must in the first place have arisen fortu- 

 itously, or rather, causes similar to those which effected the nigritude 

 of the king-crow must have made the ancestral drongo-cuckoo black. 

 But we are as yet more or less in the dark as to what has caused the 

 king-crow to be black, so that we are not in a position to say how it 

 was that this species of cuckoo came to resemble the drongo in 

 appearance. 



In attempting to account for any characteristic of an organism by 

 means of natural selection we must be able to explain the utility to 

 the organism of the character in question in its initial stage, and at 

 each subsequent stage of its development. It is not sufficient to show 

 that the character in its final and complete stage of use to its pos- 

 sessor. This is an important point which biologists, especially neo- 

 Darwinians, frequently seem to forget. 



The black-and-yellow grosbeak {Pycnorhamjyhits icteroides) , a bird 

 common in many parts of the Himalayas, resembles the black-headed 

 oriole nearly as closely as the drongo-cuckoo does the king-crow. 

 But since the grosbeak does not descend to the plains and the black- 

 headed oriole {Oi'iolus melanocephalus) does not ascend the hills, 

 neither can possibly derive any benefit from the resemblance, which, 

 it should be added, extends only to the cocks. Thus there is here no 

 question of mimicry. 



Another Indian cuckoo, the famous brain-fever bird {Hierococcyx 

 varius)^ displays a remarkable likeness to the shikra {Astur badiits), 

 a sparrow-hawk very common in India. This is said to be a case of 

 mimicry, because the cuckoo is supposed to derive profit from the 

 resemblance. The babblers (Craferopus canorus), which it victim- 

 izes, are said to mistake it for a shikra, flee in terror from it, and so 

 give it the opportunity it requires to gain access to their nests. It is 

 quite likely that the cuckoo does derive benefit from the resemblance. 

 But this is not sufficient to explain a likeness which is so faithful as 

 to extend to the marking of each individual feather. AVlien a bab- 

 bler espies a hawk-like bird, it does not wait to inspect each feather 

 before fleeing in terror; hence all that is necessary to the cuckoo is 



