The Making of Species 



struggle for existence, in other words, of the 

 modus operandi of natural selection. 



The tsetse-fly in Africa is a far more important 

 check on the increase of some animals than the 

 lions and other beasts of prey. There are in 

 that continent large tracts of country, known as 

 tsetse-fly belts, in which neither horse, nor ox, 

 nor dog can exist. If races of these animals 

 were to arise which could withstand the bite of 

 the tsetse-fly, these species might increase more 

 rapidly than the rabbit in Australia has done, 

 nor would it matter if the creatures in question 

 were bright crimson, or any other conspicuous 

 colour. 



Take the case of the lion in Africa. The chief 

 bar to the increase in numbers of this species 

 appears to be the teething troubles to which the 

 whelps are liable. Now suppose that a mutation 

 were to occur in the lion. Suppose that several 

 members of a litter were all bright blue, and that 

 these suffered from no teething troubles. They 

 would probably all grow up, and although at 

 some disadvantage as hunters on account of their 

 conspicuous colouring, they would nevertheless 

 probably increase at the expense of the normally 

 coloured lions, because of the immunity of their 

 offspring from death from teething troubles. 

 Zoologists would then be at a loss to explain 

 their bright colouring. We should have all manner 

 of ingenious suggestions raised, namely, that in the 



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