386 EXPERIMENTAL STUDY OF INHERITANCE 



distinguished in a general view " (Natural Inheritance, 1889, 

 chap. ii.). 



Sometimes, as in mules, the hybrid offspring are sterile. This 

 may show itself (1) in atrophy of the reproductive organs, (2) in 

 abnormalities in the reproductive ducts ; or (3) in more obscure 

 conditions in regard to which we can only shroud our ignorance 

 with the words, " constitutional incapacity." 



§ 8. Consanguinity 



Consanguinity. — In many peoples — Jewish and Mohammedan, 

 Indian and Roman — laws against the marriage of near kin go 

 back to remote antiquity, but it seems probable that the basis 

 of these was social rather than biological. In other peoples — 

 Persian, Phoenician, Arab, and even Greek — consanguineous 

 marriages were permitted and sometimes encouraged. The 

 idea that the marriage of near kin is a cause of degeneracy seems 

 to be relatively modern, and is probably based in large measure 

 on the observed degeneracy in closely intermarried noble 

 families. In certain closely inbred communities, moreover, a 

 large percentage of deaf-mutes and weak-minded has been often 

 observed. But it is not difficult to find counter-instances — e.g. 

 in the Norfolk Islanders and in the people of Batz on the lower 

 Loire — where close inbreeding has not been followed by ill-effects. 

 Mr. George H. Darwin has made out a strong case in support of 

 the position that consanguineous marriages are not in themselves 

 causes of degeneration or of diminished fertility. 



Biologically it seems certain that close inbreeding can go far 

 without any ill effects, but further in some types than others. 

 Many plants, such as garden-peas, wheat, and oats are habitually 

 self-fertilising ; the same is true of a few of the hermaphrodite 

 animals, e.g. the parasitic flukes and tape-worms. But these 

 are cases which have become adapted to this sort of (auto- 



