An Introduction to a Biology 



For whilst the way in which I made that error was by lift- 

 ing Mendel's Law from the level of a would-be explanatory 

 to that of a purely descriptive Law, he made it by lowering 

 Galton's from the level of a purely descriptive to that of a 

 would-be explanatory one. And the reason that I dis- 

 covered my mistake before he did was that it is easier to see 

 that Mendel's Law is something more than a purely descrip- 

 tive one, than it is to see that Galton's is not a would-be 

 explanatory one. And the reason again of this is that 

 Galton's Law is confused with another one which resembles 

 it in one respect, but differs from it in being would-be ex- 

 planatory. The remarkable thing about this Law is that 

 whilst it is characteristic of most Laws to be enunciated and 

 receive a name first and then become widely believed in after- 

 wards, the reverse is the case with this one ; for it is believed 

 in by all biologists who are not Mendelians, by all breeders 

 of animals or plants, and by all persons not belonging to 

 these classes who think about heredity at all. 



But it has not yet received a name. I propose to call it 

 the Law of Diminishing Individual Contribution. 



According to it : the germ plasm of an individual contains 

 contributions from all of its progenitors : the amount of the 

 contribution being large in proportion as the progenitor is 

 near, i.e. large in the case of the parents, smaller in the case 

 of the grandparents, and so forth. 



It is ^ very good type of biological Law : it has the 

 advantage of simplicity : it is also, except in a few cases, 

 untrue. 



I will now give three cases to show how widespread 

 belief in this Law is. 



The first that I give is that of the result of crossing a 

 yellow and white pink-eyed Japanese waltzing mouse with 

 a pink-eyed white mouse that is, an albino. The result is, 

 usually, a black-eyed grey mouse. 1 And to anyone not 

 familiar with it, the result is most astounding : it is quite the 



1 Darbishire, :04a, p. 7. 

 174 



