The Factors of Evolution 



247 



evolution in the potato beetle. The same experiment has been 

 performed in Nature 's laboratory by transferring beetles from 

 the relatively cool, moist climate of Chicago to the hot arid 

 air of Tucson, Arizona. As a result of this transfer not only 

 are morphological (color) changes induced, but physiological 

 ones as well. The beetles gradually acquire the power to re- 



MUTATIONS IN THE POTATO BEETLE 



2 represents a type derived experimentally from 1 by the use of high 

 temperature. 5 was derived from 4 by using high temperature and 

 relative humidity and 7 from 8 by high temperature and low humidity. 

 From Tower, ' ' Evolution in Chrysomelid Beetles, ' ' Carnegie Institution, 

 Publication No. 48. 



tain more water in their tissues during hibernation, and 

 thereby to resist the effects of the dry climate. They show 

 also certain changes in their responses to stimuli. These 

 changes moreover are not reversible, but persist when the 

 beetles are returned to their original home at Chicago. They 



