THE INHERITANCE OF FAMILY TRAITS G7 



mental ability. It has now been dcmonstratctl by the study 

 of scores of families at the Vineland (N. J.) Training School 

 for defectives by Dr. H. H. Goddard. Some pedigrees il- 

 lustrating this law, and those that follow, are given in 

 Figs. 31-35. 



[H-r-O tSISh-r-O 



0- 



-T-(^Oi^(^I^}-r®''H~^ f^ 



r 



I I R 



(N)[N]^(i)[i][t] i^HhISh© b 



N • 



Fig. 31. — Pedigree chart illustrating the law that two defective parents 

 have only defective children. A, Alcoholic; C, criminalistic; D, inf., died in 

 infancy; F, feeble-minded; A'^, normal, T, tubercular. Goddakd, 1910. 



The second law of heredity of mentahty is that, aside 

 from "mongolians," probably no imbecile is born except 

 of parents who, if not mentally defective themselves, both 

 carry mental defect in their germ plasm. Fig. 36 (left side 

 of chart). Many a person of strong mentahty may carry 

 defective germ cells and, whenever two such persons marry, 

 expectation is that one-fourth of their offspring will be 

 defective. If a person that belongs to a strain in which 

 defect is present (and who, consequently, may be carr^-ing 

 the defect in his germ plasm) marry a cousin or other near 

 relative (in whom the chance is large that the same defective 

 germ plasm is carried) the opportunity for two defective 

 germ cells to unite is enhanced. Such consanguineous mar- 

 riages are fraught with grave danger. 



In view of the certainty that all of the children of two 

 feeble-minded parents will be defective how great is the 

 folly, yes, the crime, of letting two such persons marry. It 



