An Introduction to a Biology 



and black eyes were to produce an (extracted) albino — 

 which, if the Law of Contribution were true, they could 

 not do : the Mendelian prediction about the offspring of 

 a pair of such albinos is that they will be all albinos ; the 

 expectation based on the Law of Contribution is that a 

 quarter of the coat of each individual child will be grey — 

 supposing the proportions for individuals in which each 

 progenitor contributes, according to that Law, to be the 

 same as that demanded for populations by Galton's. The 

 Mendehan prediction is right. ^ In fact, the Law of Con- 

 tribution is so utterly invalid that every case of alternative 

 inheritance is a contradiction of it. It may apply to some 

 cases of blended inheritance. But the reason that I have 

 formulated it and given it a name is not that it may perhaps 

 apply to one or two cases, but because, unless it is definitely 

 enunciated, it will not be reckoned as having any claims 

 to recognition, and because, the sooner it is widely recognised, 

 the easier will it be to put an end to its confusion with Galton's 

 Law. 



§4 



{a) Statistical Laws, " descriptive " : Physiological 



Laws, " explanatory " 



The remark might be made about the Law of Contribu- 

 tion that it is Galton's Law made appUcable to the individual ; 

 and this in a sense is true, but there is a profound differ- 

 ence between the two, for whilst the Law of Contribution 

 is an attempt to picture the way in which characters are 

 represented in the germ-cells of individuals, Galton's Law 

 is merely a statement that the characters of the ancestry 

 of a population reappear in certain definite proportions in 

 that population. It is only concerned with that which 

 is above the horizontal line AB in the figure on p. 182. 

 Moreover, it is only true of the aggregate of adults, 

 and not of the individuals which compose that aggregate. 



iDarbishire, :04a, p. 23. 

 i8o 



