388 EXPERIMENTAL STUDY OF INHERITANCE 



result that " inbreeding probably reduces very slightly the 

 productiveness of Drosophila, but the productiveness may be 

 fully maintained under constant inbreeding (brother and sister) 

 if selection be made from the more productive families." 



Castle (191 1 ) also reports that a polydactylous race of guinea- 

 pigs all descended from one individual remained exceedingly 

 vigorous for ten years and then showed no hint of diminishing 

 fertility. 



While it seems certain that prolonged and close inbreeding 

 may afford opportunity for an inherent taint to show itself, to 

 spread, and to accumulate, it is not the consanguinity that is 

 to blame for the taint. The same consequences would probably 

 result if matings took place among unrelated organisms with the 

 same kind of taint. The idea that there can be any objection 

 to the marriage of two healthy cousins who fall in love with 

 one another is preposterous. 



Some variations are from the first so stable that their per- 

 sistence is certain without any precautions of inbreeding. But, 

 in other cases, it appears to be the experience of breeders that 

 a period of inbreeding, with elimination of any " weeds " that 

 may crop up, serves to fix characters, developing " prepotency " 

 in regard to the desired qualities. Crossing may then be resorted 

 to without any fear of the excellence being lost, and with the 

 expectation of an increased stimulus to vigour. 



It seems well established that some stable and important 

 breeds of cattle — e.g. polled Angus — have arisen under conditions 

 involving in the early stages extremely close inbreeding, and it 

 is well known in horse-breeding that very valuable results have 

 been reached by using the same stallion repeatedly on successive 

 generations. 



Thus, if we take the pedigree of the short-horn bull " Courtier," 

 calved January 6th, 1896, owned by the Iowa Agricultural 

 College, we find from the tabulation given by Mr. R. W. Barclay 

 that " Champion of England " (17526) appears in the pedigree 



