INHERITANCE IN MANKIND 39 



way that some of the children of the marriage of a 

 person showing the character with a person without it 

 manifest the character clearly and some not at all, we 

 may suspect Mendelian dominance. If, in a long pedi- 

 gree, these two types of children be on the average 

 nearly equal in number, and if the character be trans- 

 mitted only through those persons who show it openly, 

 our suspicion may become a certainty. A recessive 

 character may appear in the offspring of a person not 

 showing it, but a dominant character, if present at all, 

 must be apparent. If a person have it not, he cannot 

 transmit it. 



Let us compare these theoretical results with those 

 actually found by Hurst in the population of a Leices- 

 tershire village. 1 Parents with no brown pigment in 

 their eyes produced exclusively children without it. 

 Brown-eyed parents, on the other hand, might be either 

 pure-bred or half-bred with respect to that character, 

 and the relative numbers of their brown-eyed and grey- 

 eyed children were very nearly those of the theoretical 

 Mendelian results. 



As we cannot tell by inspection if an individual be 

 pure or half-bred with regard to a dominant character, 

 we will represent all brown-eyed persons by the symbol 

 0, whether they be of the type DD or DR. 



1 For details of this and other investigations on Mendelian phenomena reference 

 is made to Prof. Bateson's recent book on Mendelism. Other instances of inherit- 

 ance in this chapter are taken from The Treasury of Human Inheritance, edited by 

 Prof. Karl Pearson. 



