12. Millstein’s definition of “directed mutation” – that I reformulate in the negative in order to define the notion of “evolutionary chance mutation” – is reminiscent of Lenski and Mittler’s definition of “directed mutation” (Lenski and Mittler 1993, 188). They claim that a directed mutation is a mutation that “occurs at a higher rate specifically when (and even because) it is advantageous to the organism, whereas comparable increases in rate do not occur (i) in the same environment for similar mutations that are not advantageous, and (ii) for the same mutation in similar environments where it is not advantageous.” Conditions (i) and (ii) suggested by Lenski and Mittler respectively correspond to the conditions (2) and (1) I have suggested above.

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