Darwin's Artificial and Natural Selection 141 



Can we possibly be expected to believe that it has been to 

 the advantage of this species to give up its original regular 

 method of incubating its own eggs, and acquire such a 

 haphazard, new method ? Does not the explanation prove 

 too much, rather than give support to Darwin's hypothesis ? 

 Is it not better to conclude, that despite the disadvantages 

 entailed by a change in the original instincts, the species 

 is still able to remain in existence ? 



Darwin points out, in the case of the slave-making ants, 

 that the slave-making instinct may have arisen in the first 

 instance by ants carrying pupae, that they have captured, 

 into their own nests. Later this habit might become fixed, 

 and, finally, after passing through several stages of develop- 

 ment, the ants might become absolutely dependent on their 

 slaves. It is also supposed that those colonies in which this 

 instinct was better developed would survive in competition 

 with other colonies of the same species on account of the 

 supposed advantage of owning slaves. In this way natural 

 selection steps in and perfects the process. 



It is far from proven, or even made probable, that a species 

 of ant that becomes gradually dependent on its slaves is 

 more likely to survive than other colonies that are not 

 so dependent. All we can be certain of is that with slaves 

 they have still been able to maintain their own. Moreover, 

 we must not forget that it is no.t enough to show that a 

 particular habit might be useful to a species, but it should 

 also be shown that it is of sufficient importance, at every 

 stage of its evolution, to give a decisive advantage in the 

 " struggle for existence." For unless a life and death 

 struggle takes place between the different colonies, natural 

 selection is powerless to bring about its supposed results. 

 And who will be bold enough to affirm that the presence of 

 slaves in a nest will give victory to that colony in competi- 

 tion with its neighbors ? Has the history of mankind taught 

 us that the slave-making countries have exterminated the 



