An Introduction to a Biology 



to the callousness, if not disfavour, with which such an 

 attempt is likely to be regarded. Nevertheless I propose 

 to make it. 



§2 



Space forbids me to discuss the question of the advisable- 

 ness of using the term " law " at all as summarising vital 

 phenomena, more than to say that the fact that I use it 

 166 times in this paper demands some apology. 



I use it because, besides possessing the advantage of 

 brevity, it is of all terms in biology the vaguest ; signify- 

 ing as occasion demands either a theory, or a resume, or a 

 hypothesis, or a formula, or a generalisation — to name a 

 few of the more or less legitimate senses in which it is used : 

 and because it shelters, under its wide roof. Laws whose 

 authors aim at explanation, and those whose authors are 

 satisfied with description. And I spell it with a capital L 

 because that is the conventional way of ^^Titing terms the 

 discussion of whose meaning is postponed. 



(a) Pearson's Law 



No one has any excuse for not knowing what the Law of 

 Ancestral Liheritance is ; the essential features of it are 

 outlined by Pearson in the following words : — 



" Taking our stand then on the observed fact that a 

 knowledge neither of parents nor of the whole ancestry 

 will enable us to predict with certainty in a variety of im- 

 portant cases the character of the individual offspring, we 

 ask : What is the correct method of deahng wdth the prob- 

 lem of heredity in such cases ? The causes A, B, C, D, E, 

 . . . which we have as yet succeeded in isolating and 

 defining are not always followed by the effect X, but by any 

 one of the effects U, V, W, X, Y. We are, therefore, not 

 dealing with causation but correlation, and there is there- 

 fore only one method of procedure possible ; we must collect 

 statistics of the frequency with which U, V, W, X, Y, Z 

 respectively follow on A, B, C, D, E. . . , From these 



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