1 6 DarbiSHIRE, Laws of Heredity. 



individual : and this in a sense is true : but there is a pro- 

 found difference between the two ; for, whilst the Law of 

 Contribution is an attempt to picture the way in which 

 characters are represented in the germ cells of individuals, 

 Galton's Law is merely a statement that the characters of 

 the ancestry of a population reappe'ar in certain definite 

 proportions in that population. It is only concerned 

 with that which is above the horizontal line AB \x\. the 

 figure on the next page. Moreover it is only true of the 

 aggregate of adults, and not of the individuals which 

 compose that aggregate. The Law of Contribution, on 

 the other hand, deals with that which is below as well as 

 with that which is above the horizontal line, and it is true 

 of the individuals. 



Now, although Galton's Law is true of the mass but 

 not of the component individuals, the Law of Contribution 

 is true of the individuals and of the mass as well : because 

 according to it all the individuals are contributed to, in 

 the same degree. 



The widespread belief in the existence of a Law which 

 is true both of mass and individual is the result of the 

 interaction of two outstanding characters of the human 

 mind, (i.) an inability to distinguish between truths about 

 masses and truths about individuals — and (ii.) a passion for 

 explaining things ; for possessing a formula for familiar 

 phenomena ; in the case of heredity for seeing below the 

 line in the diagram opposite. 



Man has observed that on the whole Galton's Law is 

 true of masses — though he has not expressed himself in 

 these words. Feature No. (i.) had led him to think that the 

 truth is of individuals, and has thus satisfied No. (ii.) and 

 supplied him with a brief formula, a simple picture of the 

 way in which characters are inherited — a picture of what 

 is below the line AB in the diagram. 



