i8o MENDELISM chap. 



2q heterozygotes. Hardy pointed out that, other 

 things being equal, such a population would be in 

 equilibrium for this particular factor so long as the 

 condition q- =pr was fulfilled. If the condition is 

 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 : ' 



/. Iq. r. 



12 I 



I 4 4 



I 6 9 



I 8 i6 



I 2O,O00 100,000,000- 



I 2« n^ 



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 



