206 MENDELISM 



more rapid in the early stages because the cross-breds 

 will themselves exhibit the new character. In this 

 case, even if the new type has a very marked advantage 

 over the parent form, the process of completely sup- 

 planting the latter will be delayed, because the old 

 type of character can survive concealed in heterozygote 

 individuals. 



Let us pause, for a moment to sum up the novel ideas 

 which have so far been presented in this and the 

 preceding chapter. 



We found in the first place that from the point 

 of view of heredity we must look upon an animal or 

 a plant as a composite being, made up of a great 

 number of unit characters, each capable of separate 

 description, and all inherited independently of one 

 another. 



When a pair of nearly-related animals or plants 

 are mated together, when, in fact, like is bred with 

 like, and with still greater certainty in cases of self- 

 fertilization such as are not uncommon among plants, 

 every unit character born by one gamete finds a 

 corresponding mate among the characters born by the 

 second gamete. It naturally follows that a series of 

 characters similar to those of the parent or parents 

 make their appearance in the offspring. 



When a pair of individuals belonging to distinct 

 varieties or races are mated together, the result is the 

 same in the case of the majority of characters exhibited 

 by each of them. For separate varieties of the same 

 species differ from one another in a small number of 

 units only, and organisms which differ in more than a 



