C H A P T E 



R 12 



EVOLUTION AS SEEN IN THE 



GEOGRAPHIC DISTRIBUTION 



OF ANIMALS: CONTINENTS 



Almost everyone knows that if he wishes to hunt lions 

 he should go to Africa, and if tigers are his objective he must travel to 

 India. But of those who know this, how many ever stop to wonder why 

 lions are more common in Africa than they are in India, and why tigers 

 are not found in Africa? As a result of studies by persons who have won- 

 dered about such things, a subdivision of biology known as geographic 

 distribution or zoogeography has developed. 



Zoogeography is concerned with the manner in which animals are dis- 

 tributed over our planet and attempts to explain the observed distribu- 

 tions. We shall commence our discussion of the subject by considering 

 some of the peculiarities encountered in the distribution of animals on the 

 larger land masses of the earth, the continents. 



Africa and South America 



The two large continents crossed by the equator are South America and 

 Africa. Both have extensive tropical regions. Both extend southward into 

 the Temperate Zone. Both have lowland jungles; extensive river systems; 

 broad, dry plains; and high mountains. In short, both present much the 

 same variety of habitats for living things. We might anticipate, therefore, 

 that both continents would be populated with the same, or closely similar, 

 animals. Such an expectation would differ widely from actuality, however. 



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