Rebuttal: adaptive point mutation (Rosenberg and Hastings).

The Rosenberg-Hastings paper (4) defends a model much like that of Foster (1) and argues that the observed mutagenesis contradicts predictions of the amplification model. On the contrary, amplification indirectly causes weak mutagenesis and allows that mutagenesis to have a detectable effect on lac reversion. However, this mutagenesis is a minor side effect that is neither sufficient nor necessary to explain reversion. Mutagenesis has distracted attention from the main message of this system—a target number increase during growth under selection.