STRUGGLE FOR EXISTENCE 69 



check or some few being generally the most potent, 

 but all concur in determining the average number or 

 even the existence of the species. In some cases it 

 can be shown that widely-different checks act on the 

 same species in different districts. When we look at 

 the plants and bushes clothing an entangled bank, we 

 are tempted to attribute their proportional numbers and 

 kinds to what we call chance. But how false a view 

 is this ! Every one has heard that when an American 

 forest is cut down, a very different vegetation springs 

 up ; but it has been observed that ancient Indian ruins 

 in the Southern United States, which must formerly 

 have been cleared of trees, now display the same 

 beautiful diversity and proportion of kinds as in the 

 surrounding virgin forests. WTiat a struggle between 

 the several kinds of trees must here have gone on 

 during long centuries, each annually scattering it* 

 seeds by the thousand ; what war between insect and 

 insect — between insects, snails, and other animals with 

 birds and beasts of prey — all striving to increase, and 

 all feeding on each other or on the trees or their seeds 

 and seedlings, or on the other plants which first clothed 

 the ground and thus checked the growth of the trees ! 

 Throw up a handful of feathers, and all must fall to 

 the ground according to definite laws ; but how simple 

 is this problem compared to the action and reaction 

 of the innumerable plants and animals which have 

 determined, in the course of centuries, the propor- 

 tional numbers and kinds of trees now growing on the 

 old Indian ruins ! 



The dependency of one organic being on another, as 

 of a parasite on its prey, lies generally between beings 

 remote in the scale of nature. This is often the case 

 with those which may strictly be said to struggle with 

 each other for existence, as in the case of locusts and 

 grass-feeding quadrupeds. But the struggle almost 

 invariably will be most severe between the individuals 

 of the same species, for they frequent the same districts, 

 require the same food, and are exposed to the same 

 dangers. In the case of varieties of the same species, 



