210 THE FACTORIAL HYPOTHESIS 



product of the activity of the germ cell may be 

 different. All sorts of characters might be affected 

 by the change, but certain parts might be more con- 

 spicuously changed than are others. It is these more 

 obvious effects that we seize upon and call unit 

 characters. It is the custom of most writers to speak 

 of the most affected part as a ^^unit character/' and 

 to disregard minor or less obvious changes in other 

 parts. They frequently speak of a unit character as 

 the result of a unit factor, forgetting that the unit 

 character may be only one effect of the factor. 



Failure to realize the importance of these two 

 points, namely, that a single factor may have sev- 

 eral effects, and that a single character may depend 

 on many factors, has led to much confusion between 

 factors and characters, and at times to the abuse of 

 the term ^'unit character.'' It can not, therefore, 

 be too strongly insisted upon that the real unit in 

 heredity is the factor, while the character is the prod- 

 uct of a number of genetic factors and of environ- 

 mental conditions. The character behaves as a unit 

 only when the contrasted individuals differ in regard 

 to a single genetic factor, and only in this case may 

 it be called a unit character. As soon as the indi- 

 viduals differ by two or more genetic factors that 

 affect the same character the latter can be no longer 

 considered a unit. So much misunderstanding has 

 arisen among geneticists themselves through the 

 careless use of the term ^^unit character" that 

 the term deserves the disrepute into which it is 

 falling. 



