INBREEDING EXPERIMENTS 137 



futile to maintain that there is every reason to suppose 

 wild species should behave exactly as their domestic 

 cousins. Wild types, in general, might not present such 

 an appearance of injury under inbreeding as is often 

 shown by cultivated species. This would not be due to 

 differences in their method of inheritance, however, but 

 because wild species are usually exposed to a more rigor- 

 ous struggle for existence and the individuals are, there- 

 fore, less likely to differ by a large number of hereditary 

 factors. For such reason one should expect experiments 

 on different wild species to give rather varied results, and 

 in the comparatively small number which have been made 

 this is the case. Castle's experiments on the fruit fly gave 

 no markedly unfavorable results. Collins states that self- 

 fertilizing teosinte, a semi-wild relative of maize, causes 

 no loss of vigor. Yet Darwin compared self-fertilized and 

 intercrossed plants of several species which are largely 

 cross-fertilized in the wild with great disadvantage to 

 the former. 



This discussion of the effects of artificial inbreeding 

 in certain plants and animals has been given in some de- 

 tail in order to bring out the many important considera- 

 tions involved. There has even been repetition in order 

 to emphasize the most important points. Details are 

 merely by way of parenthesis, however. Let us now get 

 out of the parenthesis and into the main argument. 



From the preceding observation it can be said that 

 inbreeding has but one demonstrable effect on organisms 

 subjected to its action the isolation of homozygous 

 types. The diversity of the resulting types depends di- 

 rectly upon number of heterozygous hereditary factors 

 present in the individuals with which the process is be- 



