42 HEREDITY 



large pedigree stock of Basset hounds (dwarf blood- 

 hounds) belonging to Sir Everett Millais. He found 

 that the human and canine data, widely various as they 

 were, could yet be expressed in an exceedingly simple 

 generalisation which he called the law of ancestral 

 inheritance. In all probability this law may prove 

 to be universally true of bi-parental reproduction. 

 There is a quite valid sense in which we regard 

 inheritance as dual, half- paternal, half- maternal. 

 But it is plain that the same applies to the inherit- 

 ance of each parent, and so on ad infinitnin. Hence 

 the inheritance of each individual is not dual but 

 multiple, and Mr. Galton has proved that it is 

 actually capable of exact mathematical expression. 

 But before we see what this is it is necessary to state, 

 as clearly as may be, that Galton's Law deals with 

 races and generations, not with individuals. In the 

 discussion of the principles of heredity, or indeed of 

 any biological generalisation, it seems impossible to 

 bring home to some people the idea that they are 

 generalisations, 710^ " particularisations." The objec- 

 tions of such people imply a confusion of thought 

 such as that which would suppose the statement of 

 a cricketer's batting average as twenty to mean that 

 whenever he went to the wickets he made twenty 

 runs, never more, never less. The law about to be 

 stated is an average, and much less to be disproved 

 by the quotation of single instances than the state- 

 ment of the batsman's average is disproved by the 

 observation that on such and such an occasion he 

 made a " duck " or a " century." 



Galton's Law may thus be stated : — " The two 

 parents between them contribute on the average 



