460 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



two joints instead of three and a thumb with one joint in place of two 

 (brachydactylism). Such human abnormalities are inherited. There 



is given on this page a chart (Fig. 96) of a family tree in which 

 brachydactylism is very common; it is based on a study made by 

 Drinkwater. Males in the chart are represented by 6, females by ?, 



