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CHAPTER 29 



FIGURE 29-1. Distribution of inversion types in D. pseudoobscura collected 

 in the Southwestern United States. {After Th. Dobzhansky and C. Epling.) 



in the different areas. By a process of elimi- 

 nation, therefore, we conclude that the pri- 

 mary reason for these population differences 

 lies in the different adaptive values which 

 these different inversion types confer in dif- 

 ferent territories. In support of this view are 

 laboratory tests which demonstrate that, 

 despite the lack of any obvious morphological 

 effects, these inversions have such different 

 physiological effects that each type is dif- 

 ferent from the others in being more adapted 

 to certain experimental environments than 

 it is to others. It is reasonably certain, 



therefore, that in nature, too, these different 

 gene arrangements are adaptive, the differ- 

 ences among the three types of populations, 

 which we may define as three different races, 

 being the result of natural selection. 



Similar results have been obtained with 

 three California races of the cinquefoil plant 

 species, Potentilla glandulosa, which live at 

 sea level, mid-elevation, and the alpine zone, 

 respectively. The sea level race is killed 

 when grown in the alpine environment. The 

 alpine race grown at lower elevations proves 

 less resistant to rust fungi than the lower ele- 



