43 2 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 climate, 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 see 

 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, 



