Principles of Heredity 197 



extension of Mendel's principle, though we cannot forget 

 that there are other undetected factors at work. 



The value of the appeal to Ancestry. 



But it may be said that Professor Weldon's appeal to 

 ancestry calls for more specific treatment. When he 

 suggests ancestry as "one great reason" for the different 

 properties displayed by different races or individuals, and 

 as providing an account of other special phenomena of 

 heredity, he is perhaps not to be taken to mean any 

 definite ancestry, known or hypothetical. He may, in 

 fact, be using the term "ancestry" merely as a brief 

 equivalent signifying the previous history of the race or 

 individual in question. But if such a plea be put forward, 

 the real utility and value of the appeal to ancestry is 

 even less evident than before. 



Ancestry, as used in the method of Galton and Pearson, 

 means a definite thing. The whole merit of that method 

 lies in the fact that by it a definite accord could be proved 

 to exist between the observed characters and behaviour 

 of specified descendants and the ascertained composition 

 of their pedigree. Professor Weldon in now attributing 

 the observed peculiarities of Telephone &c. to conjectural 

 peculiarities of pedigree if this be his meaning renounces 

 all that had positive value in the reference to ancestry. 

 His is simply an appeal to ignorance. The introduction of 

 the word "ancestry' 1 in this sense contributes nothing. 

 The suggestion that ancestry might explain peculiarities 

 means no more than "we do not know how peculiarities are 

 to be explained." So Professor Weldon's phrase "peas of 

 probably similar ancestral history*" means "peas probably 



* See above, p. 192. 



