202 EVOLUTION AND GENETICS 



cause, the effects may be to a large extent communi- 

 cated rather than mherited. 



It is quite possible of course that an inherited de- 

 fective dominant character might furnish the start- 

 ing jDoint for these histories, but that the subsequent 

 events are all due to "bad blood" or "defective germ- 

 plasm" remains to be shown. 



"Insanity" is another "psychological trait" that 

 is said to be inherited and the numerous pedigrees 

 that have been collected showing that certain types 

 of insanity occur more frequently in certain fami- 



1 



ii^ 



^T 



Fig. 77. — Chart showing; the inheritance of Huntington's 

 chorea. (After Davenport.) 



lies than in others seem to furnish evidence in sup- 

 port of such a claim. This is particularly the case 

 in Huntington's chorea {fig. 77) a type of insanitj^ 

 often leading ultimately to suicide, that does not 

 appear as a rule until middle life or later. Since it 

 apj)ears to be dominant, its history is more easily 

 followed than in most other cases where the domi- 

 nance or recessiveness is in question. Huntington's 

 chorea has been traced in a limited group of indi- 



