HUMAN INHERITANCE 191 



have only brown-eyed children {fig. 72), but a 

 brown-eyed mdividual, one of whose parents had 

 blue eyes, married to a blue-eyed individual has both 

 blue- and brown-eyed children in equal numbers ac- 

 cording to Mendelian expectation. In recent years a 



Pi 



brbf 



Fig. 72. — Diagram to illustrate the inheritance of blue eyes (to 

 the left), and of brown eyes (to the right). 



few cases have been recorded where two blue-eyed 

 parents have had some brown-eyed children, and 

 this has furnished the opponents of Mendelian 

 inheritance with an argument against the general 

 application of Mendel's theory. Such cases are, how- 

 ever, only an argument against an overstatement 

 of that theory as always applying to apparently 

 blue-eyed individuals. It is known that occasionally 

 blue-eyed individuals have only a speck of brown 

 pigment in their eyes. They may then produce some 

 brown-eyed children. In other words, the hybrid 

 brown eye-color is variable in extent, and at one ex- 

 treme shows almost no brown color or possibly none 

 at all, and yet is genetically brown-eyed. That this 

 is the true explanation is shown by the pedigree of 



