Descendenz und Hybriden. 643 



The lowest whorl is omitted in (d) because its number of 

 branches appears to be much influenced by surrounding Vege- 

 tation. 



When (()) was corrected for differentiation due to position 

 ihe value of the liomotyposis was found to be very nearly 5. 



These examples show that the subject of differentiation due 

 !o period of growth or position, can be effectively aliowed for. 



Pearson. 



Pearson, Karl, The Law of Ancestral Heredity. (Bio- 

 metrika. Vol. II. 1903. p. 211-229.) 



Examples are given from coat-colour in horses and dogs, 

 and eye-colour in man, to show that two conclusions must be 

 accepted: 



1. that a knov/ledge of the characters of the parents does 

 not accurately define the character of the offspring; 



2. that a knowledge of the whole ancestry, while it cer- 

 tainly limits the ränge of Variation, does not absolutely define 

 the character of the offspring. 



It is stated that nothing corresponding to Mendel's prin- 

 eiples appears in the aforesaid characters in horses, dogs 

 and man. 



It is pointed out that the problem is one of correlation 

 and not of causation, and that statistics must be collected of 

 the frequency with which one set of characters follows on 

 another set. 



The Statistical problem is then stated and the method of 

 procedure given in füll. 



There is overwhelming evidence in favour of the fact that 

 the correlation coefficients between all relatives are positive, 

 and from this it is deduced that the prediction of character in 

 offspring will be closer when all the ancestry is included, than 

 when the parents alone are used. 



Attention is called to the mistake made by biologists 

 in speaking of regression as if it were a persistent retrogressive 

 factor. 



The author states that the Law of Ancestral Heredity im- 

 plies two ideas: 



1. that the proper method of procedure is by multiple 

 correlation; 



2. that a knowledge of the nearer coefficients of correlation 

 will suggest the more distant ones; and results actually obtai- 

 ned for parental, grand-parental, great-grand-parental, and great- 

 great-grand-parental inheritance are given to show that the 

 coefficients of correlation for eye-colour in man and coat-colour 

 in horses are sensibly the same. 



A geometric series fits the result, although this series 

 differs essentially from that originally suggested by Galton. 

 Emphasis is laid on the fact that the Law of Ancestral 



41* 



