152 DARWINISM AND HUMAN LIFE 



" We are dealing here with a case in which every 

 possible form of mating has been carried out, and 

 some of the results, at first sight, seem paradoxical. 

 Thus, for instance, the blacks always breed true, 

 whatever their ancestry may have been ; and the 

 same holds good for the whites. The white that 

 is produced by two blues, themselves the product 

 of mating blue with blue over many generations, 

 breeds as true to whiteness as the white of pure 

 white ancestry. A black is pure for blackness and 

 a white is pure for whiteness, whatever the ancestry 

 of the bird may have been. Again, it seems at first 

 sight incongruous that the mating of black with 

 white should give just twice as many blues as two 

 blues mated together. 



" We are dealing with an alternative pair of 

 characters, blackness and whiteness. Every germ- 

 cell, or gamete, whether ovum or spermatozoon, 

 bears a representative of this pair. But it can 

 bear only one representative, viz. either blackness 

 or whiteness. Hence for this pair of characters 

 there are two, and only two, types of gamete : 

 ' black ' gametes and ' white ' gametes. When 

 a black gamete meets a black the result is a black 

 bird ; when a white meets a white the result is a 

 white bird ; but when a white meets a black the 

 resulting zygote 1 contains the representatives or 

 factors for both blackness and whiteness, and 

 develops into a blue bird. Now we must suppose 

 that the gametic representative of a character, 

 the factor, is an unsplittable entity so far as 

 inheritance is concerned. The zygote, being 



1 Gamete is the technical term for a germ-cell, either egg-cell 

 or sperm-cell ; zygote is the technical term for the egg-cell after it 

 has been fertilised by the sperm -cell. 



