CHAPTER 16 



NATURAL SELECTION IN 



ACTION 



In the preceding chapter we presented a summary of the 

 theory of natural selection, and in the following chapters we shall develop 

 the theory in more detail. At the present time we may ask the question: 

 Granted that natural selection seems logical and probable, can we actually 

 see it in operation? In Chapter 20 we shall describe some experiments in 

 which natural selection was observed to operate in the laboratory. In the 

 present chapter we shall discuss mainly observation of natural selection 

 at work in a state of nature. 



Protection from Predators 



As we have seen, predatory animals constitute one factor in "the strug- 

 gle for existence"; to live and leave offspring, organisms must survive 

 predatory attacks. Some animals survive by running away. Others survive 

 by being inconspicuous: by camouflage or protective coloration. 



By way of example we may cite the common observation that mam- 

 mals (e.g., mice) living on light-colored soils are themselves light colored, 

 while inhabitants of dark-colored soils are dark colored. An example of a 

 hght-colored race of Peromyscus was described above (pp. 322-323). In 

 this case an island of white sand is populated by an almost white race ob- 

 viously descended from darker-colored mice inhabiting neighboring wood- 

 lands. How did the light-colored race arise? We may hypothesize that the 

 light color protects the mice from attack by predators, especially owls. If 



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