110 
DARWINISM 
CHAl*. 
by rivals, or is in process of extinction by enemies, to save 
itself by adopting new habits or by occupying vacant places 
in nature. This is the immediate and obvious effect of all 
the numerous examples of divergence of character which we 
have pointed out. But there is another and less obvious 
result, which is, that the greater the diversity in the organisms 
inhabiting a country or district the greater will be the total 
amount of life that can be supported there. Hence the 
continued action of the struggle for existence will tend to 
bring about more and more diversity in each area, which may 
be shown to be the case by several kinds of evidence. As an 
example, a piece of turf, three feet by four in size, was found 
by Mr. Darwin to contain twenty species of plants, and these 
twenty species belonged to eighteen genera and to eight 
orders, showing how greatly they differed from each other. 
Farmers find that a greater quantity of hay is obtained from 
ground sown with a variety of genera of grasses, clover, 
etc., than from similar land sown with one or two species 
only; and the same principle applies to rotation of crops, 
plants differing very widely from each other giving the 
best results. So, in small and uniform islands, and in 
small ponds of fresh water, the plants and insects, though 
few in number, are found to be wonderfully varied in 
character. 
The same principle is seen in the naturalisation of plants 
and animals by man’s agency in distant lands, for the species 
that thrive best and establish themselves permanently are 
not only very varied among themselves but differ greatly from 
the native inhabitants. Thus, in the Northern United States 
there are, according to Dr. Asa Gray, 260 naturalised flower¬ 
ing plants which belong to no less than 162 genera; and of 
these, 100 genera are not natives of the United States. So, in 
Australia, the rabbit, though totally unlike any native animal, 
has increased so much that it probably outnumbers in in¬ 
dividuals all the native mammals of the country; and in 
New Zealand the rabbit and the pig have equally multiplied. 
Darwin remarks that this “advantage of diversification of 
structure in the inhabitants of the same region is, in fact, the 
same as that of the physiological division of labour in the 
organs of the same body. No physiologist doubts that a 
