212 THE FACTORIAL HYPOTHESIS 



does not assume that any one factor produces a 

 particular character directly and by itself, but only 

 that a character in one organism may differ from a 

 character in another because the sets of factors in the 

 two organisms have one difference. This point is 

 not likely to be misunderstood by any one who grasps 

 the meaning of the factorial hypothesis. The ''or- 

 ganism-as-a- whole " argument, so long as it is not a 

 vague and mystical sentiment incapable of clear 

 expression, has no terrors for the factorial hypothesis, 

 for this hypothesis disclaims any intention of making 

 one unit character the sole product of one factor of 

 the germ. 



2. No one disputes that characters vary, but it has 

 become necessary to explain what we mean by this 

 statement. Many populations have been shown to 

 be mixtures of different genetic types. This means 

 that many of the individuals have different germ 

 plasms. In man, for instance, there are blue-eyed, 

 brown-eyed, black-eyed and pink-eyed individuals, 

 and these variations of eye color have been shown 

 by Hurst, the Davenports, Holmes and others to 

 depend on different factorial constitutions. It has 

 been shown in several cases, notably in corn, by 

 Shull, and by East and Hayes, that populations may 

 contain differences in many factors that have 

 similar effects on the same character. In this case 

 too the different factors that affect a part in the same 

 w^ay are shown to separate and recombine in succes- 

 sive generations. The result is variability, but 

 variabiUty of a sort that is compatible with the 



