648 THE DESCENT OF MAN 



to that lately given of albino birds not pairing from being 

 rejected by their comrades. 



In various parts of the northern seas a remarkable vari- 

 ety of the common Guillemot (Jlria troile) is found; and in 

 Feroe, one out of every five birds, according to Q-raba's esti- 

 mation, presents this variation. It is characterized" by a 

 pure white ring round the eye, with a curved narrow white 

 line, an inch and a half in length, extending back from the 

 ring. This conspicuous character has caused the bird to be 

 ranked by several ornithologists as a distinct species under 

 the name of H, lacrymans, but it is now known to be merely 

 a variety. It often pairs with the common kind, yet inter- 

 mediate gradations have never been seen; nor is this sur- 

 prising, for variations which appear suddenly are often, as 

 I have elsewhere shown," transmitted either unaltered or 

 not at all. We thus see that two distinct forms of the 

 same species may coexist in the same district, and we can- 

 not doubt that if the one had possessed any advantage over 

 the other, it would soon have been multiplied to the exclu- 

 sion of the latter. If, for instance, the male pied ravens, 

 instead of being persecuted by their comrades, had been 

 highly attractive (like the above pied peacock) to the black 

 female ravens, their numbers would have rapidly increased. 

 And this would have been a case of sexual selection. 



With respect to the slight individual differences which 

 are common, in a greater or less degree, to all the members 

 of the same species, we have every reason to believe that 

 they are by far the most important for the work of selection. 

 Secondary sexual characters are eminently liable to vary, 

 both with animals in a state of nature and" under domestica- 

 tion." There is also reason to believe, as we have seen in 

 our eighth chapter, that variations are more apt to occur 

 in the male than in the female sex. All these contingencies 



* Grabs, ibid., s. 54. Macgillivray, ibid., vol. v. p. 327. 

 *• "Variation of Animals and Plants under Domestication," vol. ii. p. 92. 

 ^ On these points see also "Variation of Animals and Plants under Domes- 

 ticartiou," roL i. p. 2S3; vol. ii pp. 73, 76. 



