INSANITY 281 



is in some way inherited is obvious, for it occurs much 

 oftener in these families than in the general population, 

 where it is between 1 and 2 per cent. But in these families 

 21 per cent of the offspring of sane parents are insane, and 

 a still higher percentage of the offspring of insane parents 

 are insane. 



The correlation coefficient used as a measure of the 

 strength of the inheritance of insanity lies between .52 and 

 .62. For comparison it may be said that the correlation co- 

 efficient between parent and child in the case of pulmonary 



TABLE 34 

 Data on Inheritance of Insanity (Heron) 



Children 



Parents Insane Sane % Insane 



Both sane 314 1179 21 



One insane 93 299 24 



Both insane 4 4 SO 



tuberculosis was found by Pearson to be about .50; for deaf- 

 mutism ^ it was found to be .54; for stature .50; for intelli- 

 gence between .49 and .58. 



Heron concludes that insanity on the whole is inherited 

 about as strongly as other mental and physical character- 

 istics. 



But insanity cannot be regarded as a simple defect which 

 can accordingly be eliminated from a population altogether, 

 as could albinism. Insanity is a general name for a great 

 variety of conditions of mental lack of balance and many 

 different factors may enter into it. Not every family stock 

 in which it occurs is to be regarded as unsound. But the 

 intermarriage of families in which insanity occurs, and, still 

 more, inbreeding within a family containing insanity is likely 

 to increase the percentage of insane offspring and so should 

 be avoided. 



Two American investigators (Rosanoff and Orr) more 

 friendly than the biometric school to Mendelian theory, have 



1 Dr. Fay's U. S. data. 



