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 pupe, 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 not 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 
