114 ORGANIC EVOLUTION 



Why the opossums were preserved in spite of the compe- 

 tition of the more perfect higher Mammalia we cannot say, 

 but we do kno\v probably how the marsupials of Australia 

 managed to persist. There is reason to believe that the con- 

 tinent of Australia, or the chain of islands to the north of it, 

 was once connected with the Malay Peninsula, so that the 

 mammals of that time, which we believe were marsupials, 

 could readily pass from one region to the other. At this 

 time apparently much of the earth was peopled by the Afar- 

 snpialia. When, however, Australasia was separated from 

 southeastern Asia by the formation of the deep straits south- 

 east of Sumatra (Fig. 28), communication between the two 

 continents was cut off and the marsupials of Australasia 

 were thus protected from competition with the higher mam- 

 mals which soon arose upon the larger continent. The 

 mammals of the higher type spread over Asia, Europe, 

 Africa, and North and South America, and replaced the 

 marsupial forms. The peculiar distribution of the Mar- 

 supialia, therefore, instead of arguing for the independent 

 origin of the marsupials in two regions, is a beautiful exam- 

 ple of the support given to the theory of evolution by the 

 phenomena of geographical distribution when studied in con- 

 nection with the phenomena of paleontology, geology, and 

 comparative anatomy. Other striking examples might be 

 quoted, but this will suffice to show the general relation of 

 these phenomena of distribution to the theory of evolution. 



The fact that great weight is o;iven by students of zoology 



*::> O O J O./ 



and palaeontology to the phenomena of geographical distri- 

 bution is evidenced by a belief which is becoming more 

 general among paleontologists ; namely, that there was at 

 one time a great Antarctic continent connecting South Africa, 



