VARIATION AND HEREDITY 215 



type," and in most cases, except in those in which 

 a marked alternation of generations has been de- 

 veloped, the resemblance is closest between the 

 progeny and its immediate ancestors. This fact 

 of resemblance between relatives is called Heredity. 

 It has been defined as " the genetic relation between 

 successive generations." In popular writing we 

 often read of " The Law of Heredity." In the sense 

 of an external constraining influence that creates 

 or compels such a resemblance, there is no such 

 thing, of course. Laws of that sort do not exist 

 in the world of Nature. As a matter of fact, He- 

 redity implies merely a comparison between related 

 organisms and is not a " thing in itself." 



It will be recalled at once that such resemblance 

 may be specific ; that is, a particularly long nose or a 

 certain cast of feature may be the common posses- 

 sion of both father and son. Such physical traits, 

 by an easy-going analogy, are naturally classed in 

 the same category with material heritage such as 

 property and lands, which descend from father to 

 son. It must be kept in mind, however, that this 

 is an analogy only. The physical features of the 

 individual are the result of development from a rela- 

 tively undifferentiated germ-cell. They were non- 

 existent in the zygote. On the other hand, these 

 characteristics, as we shall see later, may be passed 

 on without even appearing in visible form, to re- 

 appear in a subsequent generation. For this and 

 many other reasons it is difficult not to believe that 

 the characteristics of the individual inhere in some 



