Date: 2017-05-10 03:58 am (UTC)
From: (Anonymous)
Many years ago my graduate class went to a talk by a speaker who had done an experiment with unexpected results. It involved making E. coli cells which needed two separate mutations in order to use an alternative food source, then starving the coli of everything but that food source and waiting for a strain to evolve that could eat it.

You could measure the frequency of the two separate mutations, and calculate their product, and conclude that you weren't going to get anything. But he did, every time he ran the experiment.

He proposed an explanation that involved the cell "trying out" potential mutations by making mutant RNA molecules, then systematically back-copying into DNA the ones that worked.

Current thinking is that these findings were due to mutator loci--loci at which mutations can raise the mutation rate, throwing off your math. But if instead it had turned out to be systematic mutation to favorable states, it would have radically changed our view of how evolution works.

As I recall, the talk got a "radical claims require radical evidence" response from my classmates and I, but not outright rejection; we agreed that if true it was terrifically important.
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