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have been acquired by independent acts of 1859 1860 1861
have been independently acquired by 1866
were independently acquired through 1869 1872

being effected by 1859 1860 1861 1866
having been effected through 1869 1872

animal in the ordinary state, 1859 1860 1861 1866
ordinary animal, 1869 1872

for their similarity by inheritance from a common
progenitor,
parent,
and
consequently must
must therefore
believe that they have been acquired by independent acts of natural selection. I will not here enter on these several cases, but will confine myself to one special difficulty, which at first appeared to me insuperable, and actually fatal to
the
my
whole theory. I allude to the neuters or sterile females in insect-communities: for these neuters often differ widely in instinct and in structure from both the males and fertile females, and yet, from being sterile, they cannot propagate their kind.
The subject well deserves to be discussed at great length, but I will here take only a single case, that of working or sterile ants. How the workers have been rendered sterile is a difficulty; but not much greater than that of any other striking modification of structure; for it can be shown that some insects and other articulate animals in a state of nature occasionally become sterile; and if such insects had been social, and it had been profitable to the community that a number should have been annually born capable of work, but incapable of procreation, I can see no
especial
very great
difficulty in this being effected by natural selection. But I must pass over this preliminary difficulty. The great difficulty lies in the working ants differing widely from both the males and the fertile females in structure, as in the shape of the
thorax,
thorax
and in being destitute of wings and sometimes of eyes, and in instinct. As far as instinct alone is concerned, the
wonderful
prodigious
difference in this respect between the workers and the perfect females, would have been
far
far
better exemplified by the hive-bee. If a working ant or other neuter insect had been an animal in the ordinary state, I should have unhesitatingly assumed that all its characters had been slowly acquired through natural selection; namely, by
an
an
individuals
individual