Epilogue: What Comes of Studying Vertebrates 813 



to be destined to play the leading role in the next act of the drama. 

 Where will that next act take us? 



The old saying, "History repeats itself," is exemplified in the 

 history of the vertebrates. In the early days of Amphibia, the group 

 began to radiate along several and various lines of specialization, but 

 retaining in all of them the essential characteristics of amphibians. 

 Many of the resulting groups became extinct; a few have survived to 

 the present. But along another line amphibian characteristics were 

 replaced by those of reptiles. In the early days of Reptilia, diversifica- 

 tion set in and produced a temporarily dominant reptilian fauna, of 

 which only a feeble remnant survives. But along one line reptilian 

 characteristics were replaced by those of mammals. In both instances, 

 the origin of reptiles and that of mammals, the new type of animal 

 was superior to the old in its ability to extend the range of its habitat 

 and attain a variety of modes of effective living. Then, in the early 

 days of Mammalia, specialization set in along the many lines leading 

 to the numerous and highly diverse mammalian Orders, of which some 

 became extinct and many survive to constitute an important part of 

 the world's present vertebrate life. But, along one line, mammals of an 

 ancient and primitive type persisted even down to the present without 

 undergoing any conspicuous anatomic specialization except for such 

 sporadic instances as the burrowing adaptations of moles or the spines 

 of hedgehogs. Then, in comparatively recent times, certain descendants 

 of these lowly insectivores acquired a new trick of adaptation — adapta- 

 tion of the environment to meet the needs of a relatively unspecialized 

 body. Along this novel line came the now dominant human primate. 



There is no reason to think that evolution has stopped or that man 

 is its finished and final product. His ever-increasing command of his 

 environment is a biologic evolution as truly as any change of bodily 

 structure. The type of evolution peculiar to man — i.e., evolution of 

 ideas which become embodied in environmental mechanisms and struc- 

 tures or otherwise imprinted upon the environment — is obviously 

 progressing at a rapid and accelerating rate. The present human 

 population of the world exhibits the characteristics of a group at an 

 early stage of evolution, a stage of progressive change and of diversi- 

 fication. Numerous races have already been differentiated, distin- 

 guished by differences in pigmentation of skin and by small anatomic 

 differences. There is a very wide range in degree and types of human 

 intelligence. Some existing individuals could hardly be expected to 

 poke something with a stick unless shown how. At the upper extreme 

 are brains which give us higher mathematics and a knowledge of the 

 atom and the Milky Way. Much more significant than the physical 

 differentiation of races is the diversification of ideas, because differences 



