949 
INSTINCT. 
Chap. VII. 
their parents^ has originated. We can see how useful 
their production may have been to a social community 
of insects, on the same principle that the division of 
labour is useful to civilised man. As ants work by in¬ 
herited instincts and by inherited organs or tools, and 
not by acquired knowledge and manufactured instru¬ 
ments, a perfect division of labour could be effected 
with them only by the workers being sterile; for had 
they been fertile, they would have intercrossed, and 
their instincts and structure would have become blended. 
And nature has, as I believe, effected this admirable 
division of labour in the communities of ants, by the 
means of natural selection. But I am bound to con¬ 
fess, that, with all my faith in this principle, I should 
never have anticipated that natural selection could 
have been efficient in so high a degree, had not the 
case of these neuter insects convinced me of the fact. 
I have, therefore, discussed this case, at some little but 
wholly insufficient length, in order to show the power 
of natural selection, and likewise because this is by far 
the most serious special difficulty, which my theory has 
encountered. The case, also, is very interesting, as it 
proves that with animals, as with plants, any amount of 
modification in structure can be effected by the accu¬ 
mulation of numerous, slight, and as we must call them 
accidental, variations, which are in any manner profit¬ 
able, without exercise or habit having come into play. 
For no amount of exercise, or habit, or volition, in the 
utterly sterile members of a community could possibly 
affect the structure or instincts of the fertile members, 
which alone leave descendants. I am surprised that 
no one has advanced this demonstrative case of neuter 
insects, against the well-known doctrine of Lamarck. 
Summary,—I have endeavoured briefly in this chapter 
