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” 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[156]” means “peas probably similar”; when he speaks of Mendel having obtained his results with “a few pairs of plants of known ancestry[157],” he means “a few pairs of known plants” and no more; when he writes that “the law of segregation, like the law of dominance appears to hold only for races of particular ancestry[158],” the statement loses nothing if we write simply “for particular races.” We all know--the Mendelian, best of all--that particular races and particular individuals may, even though indistinguishable by any other test, exhibit peculiarities in heredity. [156] See above, p. 192. [157] See above, p. 187. [158] See above, p. 184. But though on analysis those introductions of the word “ancestry” are found to add nothing, yet we can feel that as used by Professor Weldon they are intended to mean a great deal. Though the appeal may be confessedly to ignorance, the suggestion is implied that if we did know the pedigrees of these various forms we should then have some real light on their present structure or their present behaviour in breeding. Unfortunately there is not the smallest ground for even this hope.