510 TRANSMISSION 



Distinctions between inheritance and development. There is 

 still another reason why the true nature of an individual cannot 

 always be detected by appearances, and this is found in the 

 relative development of inherited characters. 



For example, suppose that in the illustration given on page 

 506 B and R represent size instead of color. If B represents 

 great size and R extreme smallness, then, by all the principles 

 of inheritance, the 28 B 6 ^? 2 of the scheme previously discussed 

 are born for something above the mean size, which would be 

 represented by the 70 B^R^. 



Suppose, however, that through insufficient feed many of 

 these individuals fail to develop the full size which is their birth- 

 right. Such individuals then appear small, like the B^R*, or 

 perhaps even the R*. 



So it comes about that these twenty-eight individuals, though 

 born alike as to tendencies with respect to size, and each repre- 

 sented by formula B^R*, are yet very different when examined 

 after development, which of necessity depends upon the condi- 

 tions of life. And so it is that, owing to differences in develop- 

 ment, relative quality as we infer it from the appearance of the 

 adult is but a rough and often misleading indication of the char- 

 acters actually present through inheritance. Relative strength 

 of characters as inherited may be known with certainty only 

 through an intimate knowledge of pedigrees. Thus a buyer of 

 an adult animal would have great difficulty in selecting, from 

 appearances only, the individual born with greatest tendency to 

 develop unusual size. 



The mathematical nature of descent not due entirely to bisexual 

 reproduction. The truth of this statement we deduce from the 

 fact that offspring asexually produced vary on the same plan as 

 do individuals that are bisexually produced. It is to be inferred 

 also from the further fact, already alluded to, that successive 

 offspring of the same parents are not alike, but form a distribution 

 of the same general outlines as that of the total population. 



This shows that the mathematical element in reproduction is 

 to be sought not only in bisexual union, but farther back also 

 in the facts of cell division and the splitting of the chromosomes, 

 if not indeed in their very constitution. 



