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We prove that the quotient map from Aut(Fn) to Out(Fn) induces an isomorphism
on homology in dimension i for n at least 2i + 4. This corrects an earlier proof by the
first author and significantly improves the stability range. In the course of
the proof, we also prove homology stability for a sequence of groups which
are natural analogs of mapping class groups of surfaces with punctures. In
particular, this leads to a slight improvement on the known stability range for
Aut(Fn), showing that its ith homology is independent of n for n at least
2i + 2.
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