OSBORN, REVIEW OF THE PLEISTOCENE 



243 



cycles of environment and of life which have never prevailed before and 

 will never recur even if the world were to enter a fifth glacial stage, for 

 besides the extraordinary geographic and climatic changes which have 

 been outlined in the previous pages there was the prodigal profusion of 

 life which survived from Pliocene times and has since become extinct. 



The result of these complex conditions was the assemblage in Europe 

 of animals indigenous to every continent on the globe except South 



Fig. 6. — Five chief zoogeographic regions of Europe, Asia and northern Africa from which 

 the mammals migrated into westerti Europe during the Pleistocene 



America and Australia, and adapted to every climatic life-zone from the 

 warm and dry plains of southern Asia and northern Africa to the tem- 

 perate forests and meadows of Eurasia, from the alpine heights of the 

 Alps, Pyrenees and Altai Mountains to the high, dry steppes of central 

 Asia with their alternating heat of summer and cold of winter, from the 

 tundras or barren grounds of Scandinavia, northern Europe and Siberia 

 to the mild climate of southern Europe. All these animals had been 

 evolving during the Pliocene Epoch in these various habitats and thev 



