142 MENDELISM chap. 



fulfilled to start with the population remains in 

 equilibrium. If the condition is not fulfilled to start 

 with, Hardy showed that a position of equilibrium 

 becomes established after a single generation, and 

 that this position is thereafter maintained. The 

 proportions of the three classes which satisfy the 

 equation (f =pr are exceedingly numerous, and 

 populations in which they existed in the proportions 

 shown in the appended table would remain in stable 

 equilibrium generation after generation : — 



/. 2,q. r. 



2 I 



4 4 



6 9 



8 i6 



20,000 100,000,000 



2t 



.,2 



This, of course, assumes that all three classes are 

 equally fertile, and that no form of selection is 

 taking place to the benefit of one class more than 

 of another. Moreover, it makes no difference 

 whether / represents the homozygous dominants or 

 whether it stands for the recessives. A population 

 containing a very small proportion of dominants 

 and one containing a similar proportion of recessives 

 are equally stable. The term dominant is in some 

 respects apt to be misleading, for a dominant 

 character cannot in virtue of its dominance establish 

 itself at the expense of a recessive one. Brown 

 eyes in man are dominant to blue, but there is no 

 reason to suppose that as years go on the population 

 of these islands will become increasingly brown eyed. 

 Given equality of conditions both are on an equal 



