46o READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



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

 (brachydactyUsm). Such human abnormahties are inherited. There 





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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 ?, 



