28 PROBLEMS OF GENETICS 



and nowhere else throughout its distribution, that therefore we 

 may suggest that there is some difference in the condition of 

 life at Digne which makes the continuance of Honoratii there 

 possible and beneficial. 



A polymorphism offering a parallel to that of the variable 

 moths is afforded by the breeding plumage of the Ruff, the 

 male of Machetes pugnax. The variety of plumage which these 

 cocks exhibit is such that the statement that no two can be 

 found alike is only a venial exaggeration. Newton remarks 16 

 ''that all this wonderful 'show' is the consequence of the poly- 

 gamous habit of the Ruff can scarcely be doubtful"; but even if 

 it be conceded that the great external differentiation of the 

 cocks may be a result of sexual selection, the problem of their 

 polymorphism remains unsolved, for, as we are well aware, 

 polygamy is not usually associated with polymorphism of the 

 male. The Black Cock (Tetrao tetrix), for example, is as polyga- 

 mous as the Ruff, but in that and countless other cases, both 

 sexes are constant to one type of plumage. 



When we thus compare the polymorphism of one species with 

 the fixity of another, and attempt to determine the causes which 

 have led to these extraordinary contrasts, two distinct lines of 

 argument are open to us. We may ascribe the difference either 

 to causes external to the organisms, primarily, that is to say, 

 to a difference in the exigencies of Adaptation under Natural 

 Selection; or on the other hand we may conceive the difference 

 as due to innate distinctions in the chemical and physiological 

 constitutions of the fixed and the variable respectively. There 

 is truth undoubtedly in both conceptions. If the mole were 

 physiologically incapable of producing an albino that variety 

 would not have come into being, and if the albino were totally 

 incapable of getting its living it would not be able to hold its 



16 Diet, of Birds, p. 800. It would be interesting and profitable to attempt in 

 a long series of Ruffs to determine the Mendelian factors which by their combinations 

 give r?se to this complex assemblage of varietal forms. A few such factors both of 

 colour and pattern can be at once distinguished, and it is noticeable that some of 

 the resulting types of barring, spangling and penciling show a perceptible corre- 

 spondence with some of the types of colouration found in the breeds of domestic 

 fowls. 



