THE ORIGIN AND HISTORY OF ANIMAL LIFE 



611 



RUNNING (Deer) 



FLYING (Bat) 



SWIMMING (Seal) 



HANGING (Sloth) 



Figure 431. Adaptive radiation or divergent evolution. The various mammals have evolved 

 from a common ancestor, the five-toed land mammal shown at the center of the diagram. Note 

 how the structure of the limbs has been modified (specialized) to adapt them to a wide variety 

 of environments. 



Classification 



One hundred years before organic evolu- 

 tion was generally recognized, biologists 

 had classified animals according to their de- 

 grees of similarity into phyla, classes, orders, 

 etc. Linnaeus (1707-1778), who introduced 

 our present system of classification, was a 

 firm believer in special creation. For the 



most part, the groups into which Linnaeus 

 and others divided the animal kingdom con- 

 tain animals that are actually closely related 

 genetically. Also, the order adopted, begin- 

 ning with the protozoans and proceeding to 

 the more and more complex groups, is what 

 one would expect if species arose from pre- 

 existing species. The careful taxonomic 

 studies of recent years, furthermore, have 



