i 5 2 PROBLEMS OF GENETICS 



Sometimes the body plumage is that of C. auratus with the head 

 nearly as in pure cafer, or exactly the reverse may occur. Or we 

 may have the general plumage as in cafer with the throat and 

 crown as in auratus, and the malar stripe either red or black, 

 or mixed red and black, and so on in almost endless variations, 

 it being rare to find, even in birds of the same nest, two indi- 

 viduals alike in all their features of colouration. Usually the 

 first trace of cafer seen in auratus manifests itself as a mixture of 

 red in the black malar stripe, either as a few red feathers, or as a 

 tipping of the black feathers with red, or with merely the basal 

 portion of the feathers red. Sometimes, however, there is a 

 mixture of orange or reddish quills, while the malar stripe remains 

 normal. In C. cafer the traces of auratus are usually shown by a 

 tendency to an incipient nuchal crescent, represented often by 

 merely a few red-tipped feathers on the sides of the nape; at 

 other times by a slight mixture of black in the red malar stripe." 

 Such a state of things accords very imperfectly with expecta- 

 tions under any received theory of Evolution. As in some of 

 the instances discussed in the first chapter we have here two 

 fairly definite forms, nearly allied, which on any evolutionary 

 hypothesis must have been evolved either the one from the other, 

 or both from a third form at a time not very remote from the 

 present, as time must be measured in evolution. Yet though 

 intermediates exist in some quantity, no one can for a moment 

 suggest that they are that definite intermediate from which 

 auratus and cafer descend in common. One cannot imagine that 

 the immediate ancestor of these birds was a mosaic, made up of 

 asymmetrical patches of each sort: but that is what many of the 

 intermediates are. It is not much easier to suppose the ancestor 

 to have been a nondescript, with a compromise between the 

 developed characters of each, with quills buff, malar stripes 

 neither black nor red, with a trace of nuchal crescent, and so on. 

 Such Frankenstein-monsters have played, a considerable part in 

 the imaginations of evolutionary philosophers, but if it were 

 true that there was once a population of these monsters capable 

 of successful existence, surely they should now be found as a 

 population occupying the neutral zone between the two modern 



