V 



On the Difference between Physiological and 

 Statistical Laws of Heredity 



(Manchester Memoirs, Vol. L, 1906, No. 11.) 



§ 1, Introductory. — § 2. Statistical Laws : (a) Pearson's Law ; (6) Gal- 

 ton's Law ; (c) The difference between the two. — § 3. Physiological 

 Laws : (a) The Law of Diminishing Individual Contribution ; (6) 

 Mendel' s Law ; (c) The difference between the two. — § 4. The 

 difference between statistical and physiological Laws: (a) The 

 former " descriptive" : the latter " explanatory " ; (6) Mendel's 

 Law true of units : Pearson's of masses ; (c) Examples of the 

 confusion between physiological and statistical Laws ; (d) De- 

 scription of a method of dealing with the material of a breeding 

 experiment in such a way that the data obtained may be used 

 to test the validity both of Mendel's and of Pearson's Law ; 

 (e) Why do white sheep eat more than black ones ? 



§1 



There are those who maintain that it is not the part of 

 the biologist to argue, to discuss, and to explain ; and who 

 assert that he is transgressing his proper limits when he 

 ceases to confine himself to the description of observations 

 and experiments, and to drawdng from them certain obvious 

 conclusions. 



I do not hold this opinion : because I am convinced 

 that if as much (I do not say more) trouble were taken to 

 understand the meaning of a term as is spent in establish- 

 ing the authenticity of a fact, the progress of our know- 

 ledge of fundamental natural processes — heredity, variation, 

 the determination of sex, to name a few — would be more 

 rapid than it is at present. For it seems to me to be evident 



167 



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