CHAPTER 



13 



EVOLUTION AS SEEN IN THE 



GEOGRAPHIC DISTRIBUTION 



OF ANIMALS: OCEANIC 



ISLANDS 



Animal distribution on continents is highly complex. 

 The situation observed at present is the result of long series of changing 

 events stretching back through the dim vistas of geologic time. Continents 

 present a multiplicity of varied habitats open to animals capable of occupy- / 

 ing them. Periods of isolation of continents, or portions of continents, re- 

 sulting from submergence of intervening land, alternate with periods of 

 connection, when the intervening land is again above sea level. Changing 

 climates over great portions of the earth, extinction of previous inhabi- 

 tants, appearance of new forms — these and many other factors operating 

 through the ages have rendered the continental zoogeographic record in- 

 tricate and difficult to decipher. Accordingly, zoogeographers turn to 

 oce anic islands ^S-Ejagans^oLstudying factors operating in evolution and 

 distri bution .und£g-si-fflfile^-cond44icais. Oceanic islands^ may be thought of 

 as affording the zoogeographer an approach to laboratory experimentation. 

 Unfortunately biologists were not on hand to record the birth and subse- 

 quent population of the oceanic islands upon which we must depend at 

 present for most of our knowledge of the subject. Consequently inferences 



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