EVOLUTION AND DISTRIBUTION OF ANIMALS. 321 



have been long shut off from communication with the great land 

 masses." The rapid multiplication which certain holarctic ani- 

 mals and plants have shown when transported to the Australian 

 realm, demonstrates what might have taken place if impassable 

 barriers had not previously shut them out. 



Each of these great realms may be indefinitely subdivided into 

 provinces and sections, for there is no end to the possibility of 

 analysis. No township or school district has exactly the same 

 animals or plants as any other ; and, finally, in ultimate analysis 

 no two animals or plants are alike. Modification comes with the 

 growth of each new individual, and steadily increases with the 

 individual's separation in time or space from the parent stock. 

 Moreover, we observe apparent anomalies of distribution in every 

 realm : here appears an animal, there a plant, which seems to have 

 a character or a place which it ought not to hold. To the result 

 of unexpected or chance crossing of barriers these apparent anom- 

 alies in geographical distribution are due. Anomalies in distri- 

 bution, like anomalies in evolution, would cease to be such if we 

 knew all the facts and circumstances of their previous history. 

 The present range of the tapir in Farther India and in the north- 

 ern part of South America, two widely separated regions, is at 

 first sight an anomaly of distribution. This anomaly disappears 

 when we know that formerly the tapir ranged over the holarctic 

 realm and became gradually extinct with the changing climate. 

 The bones of a tapir, much like one of the South American species, 

 are found in recent clays in Indiana (Ellettsville), and similar re- 

 mains exist in France, in China, and in Burmah. The isolated, 

 unexterminated colonies are now left at the extremes of the ani- 

 mal's former range, and these colonies at present constitute what 

 we call distinct species. 



The more extended are our studies the fewer are the anomalies 

 which arrest our attention, and the fewer are the distinctive or 

 characteristic forms. There is little foundation for the current 

 belief that each species of animal has originated in the area it 

 now occupies, for in many cases our knowledge of paleontology 

 shows the reverse of this to be true. Even more incorrect is the 

 belief that each species occupies the district or the surroundings 

 best fitted for its habitation. This is manifest in the fact of 

 the extraordinary fertility and persistence shown by many kinds 

 of animals and plants in taking possession of new lands, which 

 have become, through the voluntary or involuntary interference 

 of man, open to their invasion. Facts of this sort are the " enor- 

 mous increase of rabbits and pigs in Australia and New Zealand, 

 of horses and cattle in South America, and of the sparrow in 

 North America, though in none of these cases are the animals 

 natives of the countries in which they thrive so well " ("Wallace). 



