88 BIOLOGY AND SOCIAL PROBLEMS 



tics together with the principle of dominance, 

 we shall find it easy to understand the condi- 

 tions just mentioned for the guinea-pig. 



In the original pair of animals for such a 

 series of breeding experiments as have been 

 briefly mentioned, it makes no difference how 

 the sexes are combined ; the male may be 

 white or black, the outcome will be the same. 

 But for simplicity we may assume that the 

 male is black and the female white. As each 

 individual comes from a pure stock, the male 

 will produce sperm cells, all of which will carry 

 the black characteristic, and the female, for 

 the same reason, will produce egg cells, all 

 of which will carry the white characteristic. 

 Their offspring, then, will be the product of 

 a white egg, so to speak, fertilized by a black 

 sperm. Such animals, as is well known, are al- 

 ways black in color. But as already indicated 

 they possess within them the recessive white 

 characteristic. If we assume, now, that their 

 reproductive elements are pure like those of 

 their parents, then we should expect each male 

 of this stock to produce, not one kind of sperm, 

 but two, one with the white characteristic and 

 the other with the black, and that these ele- 

 ments would be present in equal numbers. The 



