ch. xii GEOGRAPHICAL DISTRIBUTION OF ORGANISMS 339 
familiar. He would also anticipate that diversities of climate 
would always be associated with a corresponding diversity in 
the forms of life. 
Now these anticipations are to a considerable extent justi¬ 
fied. Remoteness on the earth’s surface is usually an indi¬ 
cation of diversity in the fauna and flora, While strongly 
contrasted climates are always accompanied by a considerable 
contrast in the forms of life. But this correspondence is by 
no means exact or proportionate, and the converse propositions 
are often quite untrue. Countries which are near to each 
other often differ radically in their animal and vegetable pro¬ 
ductions ; while similarity of climate, together until moderate 
geographical proximity, are often accompanied by marked 
diversities in the prevailing forms of life. Again, while many 
groups of animals—genera, families, and sometimes even 
orders—are confined to limited regions, most of the families, 
many genera, and even some species are found in every part 
of the earth. An enumeration of a few of these anomalies will 
better illustrate the nature of the problem we have to solve. 
As examples of extreme diversity, notwithstanding geo¬ 
graphical proximity, we may adduce Madagascar and Africa, 
whose animal and vegetable productions are far less alike than 
are those of Great Britain and Japan at the remotest ex¬ 
tremities of the great northern continent; while an equal, or 
perhaps even a still greater, diversity exists between Australia 
and New Zealand. On the other hand, Northern Africa and 
South Europe, though separated by the Mediterranean Sea, 
have faunas and floras which do not differ from each other 
more than do the various countries of Europe. As a proof 
that similarity of climate and general adaptability have had 
but a small part in determining the forms of life in each 
country, we have the fact of the enormous increase of rabbits 
and pigs in Australia and New Zealand, of horses and cattle 
in South America, and of the common sparrow in North 
America, though in none of these cases are the animals 
natives of the countries in which they thrive so well. 
And lastly, in illustration of the fact that allied forms are 
not always found in adjacent regions, we have the tapirs, 
which are found only on opposite sides of the globe, in 
tropical America and the Malayan Islands; the camels of 
