An Introduction to a Biology 



difference that exists between a physiological Law like 

 Mendel's, which is true of units, and a statistical one like 

 the Law of Ancestral Inheritance, which is true of masses. 

 All intending students of heredity should be asked this riddle ; 

 and if they cannot detect the fallacy in it they should be 

 declared unfit for their intended task. 



The similarity between the impression made on the 

 mind by asking the question and Mendelism, and that 

 between the idea conveyed by the answer and the Law 

 of Ancestral Inheritance does not lie only in the fact 

 that while the question and Mendelism deal with indi- 

 viduals, the answer and the Law of Ancestral Inheritance 

 refer to masses. The idea implied in the question is like 

 Mendelism, because it suggests what Mendelism effects, 

 the discovery of a hitherto unsuspected order in familiar 

 phenomena ; while the truth conveyed in the answer is 

 like the biometric treatment of heredity, because it is the 

 accurate statement of a relationship that you already know 

 to exist. Everyone knows that the sum-total of children 

 are more or less like the sum-total of their parents; the 

 biometrician accurately measures the degree of this resem- 

 blance. 



The answer you expect is physiological. The answer 

 you get is statistical. 



APPENDIX A to p. 190 



It is interesting to inquire what Galton himself said, 

 when he formulated his Law, on the subject of its applicability 

 to individual cases. He said ('97, p. 403) : "It should be 

 noted that nothing in this statistical law contradicts the 

 generally accepted view that the chief, if not the sole, line 

 of descent runs from germ to germ and not from person to 

 person. The person may be accepted on the whole as a 

 fair representative of the germ, and, being so, the statistical 

 laws which apply to the persons would apply to the germs 

 also, though with less precision in individual cases. Now 

 this law is strictly consonant with the observed binary sub- 



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