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 great 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 
Arctogaeans, 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 establishment 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 fin 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 
