Natural Selection 



103 



10 



20 



30 

 Distance in miles 



Fig. 41. The relative frequencies (symbolized by the dimensions of the 

 squares) of three different types of chromosomes in populations of Drosophila 

 pseudoobscura which live at different elevations in the Sierra Nevada in or 

 near Yosemite Park, California. Stippled, white, and shaded squares represent 

 three . different kinds of chromosomes. (From Dobzhansky, Evolution, Genetics 

 and Man, John Wiley & Sons, Inc.) 



(a) 



(b) 



(c) 



(d) 



Fig. 42. Mimicry in the beetle family Cerambycidae. Two flower-visiting 

 species of beetles (a) Sphecomorpha murina and (c) Acyphoderes odijneroides 

 mimic two wasps which visit the same flowers in their respective localities 

 (b) Polybia nigra and (d) Polybia liliacea. (From Linsley.) 



