THE DISTINCTION BETWEEN DEVELOPMENT 

 AND HEREDITY IN INBREEDING 



DR. EDWARD M. EAST 

 The Connecticut Agricultural Experiment Station 



There is among animal breeders a tendency to frequent 

 out-crossing as a preventive of a feared deterioration 

 of the breed through inbreeding. This fear is of long 

 standing, probably having arisen contemporary with, or 

 as a result of, the repugnance to incest possessed by so 

 many human tribes. This general state of mind on the 

 ethical question has brought about an unwarranted belief 

 that there is a physiological law opposed to inbreeding 

 per se. Inbreeding undoubtedly results in many cases 

 of deterioration, but the success of the few daring spirits 

 that have inbred superior stock shows that the cases of 

 deterioration were merely made possible by the course 

 pursued, and were not its direct and constant result. 



In the vegetable kingdom a slightly different state of 

 affairs obtains. Some species thrive under inbreeding 

 while others appear to deteriorate. Maize is reduced 

 in vigor in one generation, so that the difference between 

 selfed and crossed plants is noticeable in seedlings two 

 weeks old. Other natural species have evolved intricate 

 mechanisms whereby they are perpetually self -fertilized, 

 and some have even given up sexual reproduction for 

 parthenogenesis (Taraxacum), and yet have survived in 

 competition by their hardiness and prolificacy. Darwin 

 even found that in species that generally appeared to 

 oe injured by inbreeding (Ipomcea purpurea and Mimulus 

 fateus), individuals were occasionally produced that were 

 not affected. 



The classical researches which included the above ob- 

 servations are familiar to all. Direct comparison of 

 crossed and selfed plants, and investigations into the 

 mechanical means by which plants are cross-fertilized, 

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