LUTHER BURBANK 



psychiatrists who report that, in cases under ob- 

 servation, where two persons both of whom are 

 insane are mated their offspring all become in- 

 sane. 



It is obvious, then, that the question of selec- 

 tion of marriage partners for persons in whose 

 families there is a strain of insanity is a highly 

 important one. Mendelian heredity explains how 

 it is possible that, in a fraternity whose parents 

 were " mixed dominants " as regards the factors 

 for mental instability, one individual may inherit 

 a perfectly sound and normal nervous system, 

 whereas an own brother or sister of this individ- 

 ual even a twin may inherit a nervous system 

 so unstable as to invite overthrow. 



This must be borne in mind whenever we con- 

 sider the question of persons in whose families 

 there are strains of insanity. 



Unfortunately a recessive trait, in the case of a 

 mixed dominant, may be so completely submerged 

 that it gives no manifestation whatever of its 

 presence. Yet it will come to the surface no less 

 surely if this person marries with another mixed 

 dominant. So the only safe rule in a case where 

 there is known to be insanity in the family heri- 

 tage is to avoid marrying into another family 

 having a like defect. 



It is obvious that cousin marriages under these 

 circumstances would be peculiarly hazardous. 



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