110 A Defence of Mendel's 



mentally not very different from Galton's*. It is an 

 essential part of the Galton-Pearson Law of Ancestral 

 Heredity that in calculating the probable structure of each 

 descendant the structure of each several ancestor must be 

 brought to account. 



Professor Weldon now tells us that these two papers 

 of Gal ton and of Professor Pearson have "given us an 

 expression for the effects of blended inheritance which 

 seems likely to prove generally applicable, though the 

 constants of the equations which express the relation 

 between divergence from the mean in one generation, and 

 that in another, may require modification in special cases. 

 Our knowledge of particulate or mosaic inheritance, and of 

 alternative inheritance, is however still rudimentary, and 

 there is so much contradiction between the results obtained 

 by different observers, that the evidence available is difficult 

 to appreciate." 



But Galton stated (p. 401) in 1897 that his statistical 

 law of heredity "appears to be universally applicable to 

 bi-sexual descent." Pearson in re-formulating the principle 

 in 1898 made no reservation in regard to "alternative" 

 inheritance. On the contrary he writes (p. 393) that "if 

 Mr Galton's law can be firmly established, it is a complete 

 solution, at any rate to a first approximation, of the whole 

 problem of heredity" and again (p. 412) that "it is highly 

 probable that it [this law] is the simple descriptive state- 



* I greatly regret that I have not a precise understanding of the 

 basis of the modification proposed by Pearson. His treatment is in 

 algebraical form and beyond me. Nevertheless I have every confidence 

 that the arguments are good and the conclusion sound. I trust it 

 may not be impossible for him to provide the non-mathematical reader 

 with a paraphrase of his memoir. The arithmetical differences between 

 the original and the modified law are of course clear. 



