330 Geographical Distribution of Animals 



the generalised results applicable to the whole animal kingdom. 

 But the premises are wrong. Whatever regions we may seek to 

 establish applicable to all classes, we are necessarily mixing up several 

 principles, namely geological, historical, i.e. evolutionary, with present 

 day statistical facts. We might as well attempt one compound 

 picture representing a chick's growth into an adult bird and a child's 

 growth into manhood. 



In short there are no general regions, not even for each class 

 separately, unless this class be one which is confined to a com- 

 paratively short geological period. Most of the gi-eat classes have 

 far too long a history and have evolved many successive main groups. 

 Let us take the mammals. Marsupials live now in Australia and in 

 both Americas, because they already existed in Mesozoic times ; 

 Ungulata existed at one time or other all over the world except in 

 Australia, because they are post-Cretaceous ; Insectivores, although 

 as old as any Placentalia, are cosmopolitan excepting South America 

 and Australia ; Stags and Bears, as examples of comparatively recent 

 Ai'ctogaeans, are found everywhere with the exception of Ethiopia 

 and Australia. Each of these groups teaches a valuable historical 

 lesson, but when these are combined into the establislunent of a few 

 mammalian "realms," they mean nothing but statistical majorities. 

 If there is one at all, Australia is such a realm backed against the 

 rest of the world, but as certainly it is not a mammalian creative 

 centre ! 



Well then, if the idea of generally applicable regions is a mare's 

 nest, as was the search for the Holy Grail, what is the object of the 

 study of geographical distribution? It is nothing less than the 

 history of the evolution of life in space and time in the widest sense. 

 The attempt to account for the present distribution of any group of 

 organisms involves the aid of every branch of science. It bids fair to 

 become a history of the world. It started in a mild, statistical way, 

 restricting itself to the present fauna and flora and to the present 

 configuration of land and water. Next came Oceanography concerned 

 with the depths of the seas, their currents and temperatures; then 

 inquiries into climatic changes, culminating in irreconcilable astro- 

 nomical hypotheses as to glacial epochs ; theories about changes of 

 the level of the seas, mainly from the point of view of the physicist 

 and astronomer. Then came more and more to the front the import- 

 ance of the geological record, hand in hand with the palaeontological 

 data and the search for the natural affinities, the genetic system of 

 the organisms. Now and then it almost seems as if the biologists 

 had done their share by supplying the problems and that the 

 physicists and geologists would settle them, but in reality it is not 

 so. The biologists not only set the problems, they alone can check 



