Biometry is of value in the determination of general 

 laws relating to various phenomena of heredity in popula- 

 tions or in races as a whole. It furnishes information re- 

 garding the trend of evolution as influenced by operating 

 factors, individually and collectively. 



(b) — Galton's Law of Ancestral Inheritance (1889) 



Galton formulated a law, based on data as to stature 

 and other characteristics in man, and as to coat-color in 

 Basset hounds. It may be stated as follows : 



The parents together contribute one-half the total her- 

 itage; the four grandparents together one-fourth; the eight 

 great-grandparents one-eighth, etc. This law, it should be 

 borne in mind, is only true on an average for a large number 

 of cases. 



Karl Pearson has also investigated this law, and practi- 

 cally substantiates it. Mendelists, however, attempt to 

 show that Galton's and Mendel 's views are not yet in har- 

 mony. It should not be forgotten that one is a "statistical 

 formula applicable to averages of successive generations 

 breeding freely, and the other a physiological formula, 

 applicable to particular sets of cases where parents with con- 

 trasted dominant and recessive characters are crossed, and 

 their hybrid offspring are inbred" (Thomson). 



Statistical methods for the study of inheritance are use- 

 ful in cases which Mendelian analysis cannot solve. There 

 are probably characters which are not inherited according to 

 Mendel 's laws; and there are some somatic characters deter- 

 mined by so large a number of factors, e.g., stature, that 

 their identification may be beyond the range of practical 

 breeding.' 



(c) — Galton's Law of Filial Regression 



Galton and Pearson have also worked out another law 

 of inheritance which may be stated as "the tendency to 

 approximate to the mean or average of the stock." This is 

 called the Law of Filial Regression. Galton's data dealt 

 with the stature, eye-color and artistic faculty of about 150 

 families. Pearson's conclusions are given as follows: 

 "Fathers of a given height have not sons all of a given 

 height, but an array of sons of a mean height different from 

 that of the father, and nearer to the mean height of sons in 

 in general. Thus, take fathers of 72 inches, the mean 



(1) — other complex problems in heredity are the speed of race-horses, 

 milk production in cattle, and the texture of wool when breeds 

 are crossed. 



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