432 Life and Immortality. 
beasts of prey, for even the tiger in India, bold and 
venturesome as he is known to be, rarely dares to attack 
a young elephant protected by its mother. Climate, also, 
plays an important part in determining the average num- 
ber of a species, and periodical seasons of extreme cold 
or drought are seemingly the most effective checks of all. 
The action of climate appears at first sight to be altogether 
independent of the Struggle for Existence ; but in so far as it 
chiefly acts in the reduction of food, it brings on the most 
severe struggle between the individuals, whether of the 
same or different species, which subsist on the same kind of 
fare. Even when climatc, extreme cold for example, acts 
directly, it will be the least vigorous animals, or those which 
have been the poorest fed through the advancing winter, that 
will suffer the greatest. This will be most readily seen from 
what we shall now relate. When we travel from south to 
north, or from a damp region to a dry, we invariably sce 
some species getting rarer and rarer by degrees, and finally 
disappearing. Change of climate being conspicuous, we are 
inclined to ascribe the entire effect to its direct action, but 
this is a false interpretation of the phenomenon, for we fail to 
remember that each species, even where it most prevails, is 
constantly suffering enormous destruction at some period of 
its existence, from enemies or competitors for the same sta- 
tion and food; and if these enemies or competitors be the 
least favored by any slight change of climate, they will neces- 
sarily increase in numbers, while the other species, each area 
being already stocked with inhabitants, will correspondingly 
decrease. And when we travel southward and see a species 
decreasing in numbers, we may feel reasonably sure that the 
cause lies quite as much in other species being favored as in 
this being hurt. So it is when we travel northward, though 
in a less degree. When we go northward, or when we 
ascend a mountain, we far oftener meet with stunted forms, 
due to the directly injurious action of climate, than we do 
when we go southward or descend a mountain. When, 
