368 FOUNDATIONS OF BIOLOGY 



almost as constant as the structural similarities of the blood 

 vessels, or, in evolutionary terms, "a common property has 

 persisted in the bloods of certain groups of animals through- 

 out the ages which have elapsed during their evolution from 

 a common ancestor." Blood relationship is a fact. 



6. Distribution 



Every one recognizes that the fauna and flora are not the 

 same in all regions of the Earth. There is a characteristic 

 life on mountain, plain, and seashore, and in the sea as well 

 as in pond and puddle and also in the Arctic, Temperate, 

 and Torrid zones. But the problem of animal and plant 

 distribution is by no means so simple as this statement 

 might seem to imply, because the study involves the in- 

 vestigation of both the relations of the various organisms to 

 the general environing conditions, and also the interrelations 

 of the species with each other. It forms a part of the sciences 

 of plant and animal ECOLOGY. 



Confining attention merely to the geographical distribu- 

 tion of animals which forms the science of ZOOGEOG- 

 RAPHY let us take a couple of clear-cut examples and see 

 whether special creation or evolution is the more reasonable 

 explanation of the facts. 



At the present time a characteristic family of Mammals, 

 known as the Tapirs, is represented by distinct species in two 

 widely separated regions, Central and South America and 

 Southern Asia and adjacent islands. But paleontological 

 studies show that in the Pliocene period Tapirs were distrib- 

 uted over nearly all of North America, Europe, and Northern 

 Asia, and thereafter gradually became extinct so that by the 

 close of the Pleistocene period the remnants were distributed 

 as we find them to-day. In brief, the present discontinuous 

 distribution represents the remnants of a world-wide Tapir 



