HUMAN EYE COLOUR 45 



relates to the colour of the eye. I mean pure from 

 the point of view of its breeding properties, as opposed 

 to hybrid, in order to distinguish it from the latter. 

 But the question will present itself to the reader : 

 How is a pure duplex to be distinguished from a 

 hybrid one ? The answer has been briefly given at 

 the conclusion of the third chapter. It was there 

 stated that the simplest way, in the case of animals, to 

 distinguish between the pure dominant and the 

 hybrid bearing the dominant character was to mate 

 the individual in question with one bearing the 

 recessive character. The reason that it is simpler to 

 find out whether an individual is hybrid or pure 

 by mating it with a recessive, than by mating it 

 with another hybrid (which was the means adopted 

 in the case of the peas) is that there is no means 

 of finding a hybrid to mate it with, other than 

 by breeding one for the purpose by mating a 

 dominant with a recessive — for this purpose it does 

 not matter whether " the dominant " is pure or 

 hybrid. And even if a hybrid could be found, if 

 the individual to be tested happened to be a pure 

 dominant, the result of mating it with a hybrid 

 would be equal numbers of pure dominants and 

 hybrids, all of which would be alike ; that is to say, 

 it would be the same result, so far as we could see 

 from the characters of the individuals themselves, 

 as that of mating two pure dominants, which would, 

 of course, be nothing but pure dominants. 



The difficulty of distinguishing between pure 

 dominants and hybrids has not presented itself 



