TYPE AND VARIABILITY 



425 



Here we have a third valuation for type (8.83), represent- 

 ing the average, as distinct from 9 of the highest frequency, 

 or most usual length, and both distinct from the 10 inches of 

 the ear planted. 



Practical use of the mean. The mean gives a good average 

 value of the character, and establishes the practical or com- 

 mercial value of a race or variety, for it shows what it will do 

 on the average. It is not always, however, a good index of the 

 prevailing type, for, as often happens, the variety with the 

 higher mean may have the lower mode. Neither is the mean 

 always a good index of conditions ; for example, in a population 

 of one thousand paupers and one millionaire the mean wealth 

 is fair, but the type is clearly that of the pauper. 



Here are three separate and very definite conceptions of 

 type: (i) the ideal, which is used in selecting the parentage; 

 (2) the prevailing type as represented by the highest frequency 

 or most usual length (the mode) ; and (3) the average length as 

 represented by the mean." 



These three conceptions of type the ideal type of the 

 parent, the prevailing type of the offspring, and the general 

 average of the offspring have distinct applications to the 

 practical affairs of breeding. 1 The breeder of pedigreed stock 

 is interested primarily in the ideal and in the mode, or highest 

 frequency, while the general farmer who multiplies or raises it 

 for the open market is most interested in its mean, or average 

 production. 



SECTION II VARIABILITY, OR DEVIATION 

 FROM TYPE 



Having established definite distinctions as to type, the student 

 of transmission should next form equally clear conceptions as to 

 deviation from type, commonly known as variability. 2 



distribution," representing an entire race, spoken of as the "population." The 

 heading fV means the products of the values (lengths) multiplied by the corre- 

 sponding frequencies. 



1 It is to be noted that the generation to which the selected parent belonged 

 had also its own mode and mean, which may have been quite different from those 

 of the offspring. 



2 The term " variability " should not be understood as expressing departure 

 in the sense of wandering from a fixed standard. Students sometimes gain the 



