Checks on Increase 



the increase of a species and of the comparative 

 powerlessness of the attacks of raptorial creatures. 



The failure of the sandgrouse to establish a 

 footing in England is, we believe, due to the fact 

 that it is constitutionally unfitted to withstand our 

 damp climate. 



The camel is an animal that revels in dry 

 habitats, hence the difficulty of keeping camels 

 in damp Bengal, although they seem to thrive 

 well enough in the drier parts of India. 



"When a species," writes Darwin (p. 86), 

 " owing to highly favourable circumstances, in- 

 creases inordinately in numbers in a small tract, 

 epidemics at least, this seems generally to occur 

 with our game animals often ensue ; and here 

 we have a limiting check independent of the 

 struggle for life. But even some of these so- 

 called epidemics appear to be due to parasitic 

 worms, which have from some cause, possibly 

 in part through facility of diffusion amongst 

 the crowded animals, been disproportionately 

 favoured : and here comes in a sort of struggle 

 between the parasite and its prey." 



Thus inadequately does Darwin deal with that 

 bar to the increase of organisms, which is only 

 second in importance to the effect of climate. 

 The check occasioned by disease and parasites 

 is one to which naturalists have as yet paid but 

 little attention. The result is a very general 

 misunderstanding of the true nature of the 



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