238 GENETICS 



Davenport l lays down the following general eugenic 

 rules for the guidance of those who would produce 

 offspring wisely : "If the negative character is, as in 

 polydactylism and night-blindness, the normal char- 

 acter, the normals should marry normals, and they 

 may be even cousins. If the negative character is 

 abnormal, as imbecility and liability to respiratory dis- 

 eases, then the marriage of two abnormals means prob- 

 ably all children abnormal ; the marriage of two nor- 

 mals from defective strains means about one quarter of 

 the children abnormal ; but the marriage of a normal 

 of the defective strain with one of a normal strain will 

 probably lead to strong children. The worst possible 

 marriage in this class of cases is that of cousins from 

 the defective strain, especially if one or both have 

 the defect. In a word, the consanguineous marriage 

 of persons one or both of whom have the same 

 undesirable defect, is highly unfit, and the mar- 

 riage of even unrelated persons who both belong to 

 strains containing the same undesirable defect is un- 

 fit. Weakness in any characteristic must be mated 

 with strength in that characteristic; and strength 

 may be mated with weakness." 



8. INBREEDING 



The whole matter of inbreeding and the part it 

 plays in emphasizing defects has received a fresh 

 interpretation in the light of Mendelism. 



There is a widespread popular belief that inbreed- 

 ing is injurious and that it is necessary to outcross 



1 Davenport. Rep. of Amer. Breeders Assoc., Vol. VI, p. 431, 1910. 



