During the last decade microbial geneticists have become intriguedwith an extremely unorthodox phenomenon, i.e. the capacity ofcertain mutations to occur more often when the resulting phenotypeis more advantageous for the cell. The increased mutational ratesand different mutation profiles, relative to those observed in bacteriagrown under non-selective conditions, have been observed afterprolonged incubation on nutritionally depleted solid surfaces. Suchmutational events have been described as adaptive, directed,Cairnsian, or selection-induced. The phenomenon is strongly remi-niscent of the Lamarckian view of evolution, and consequently, it isin sharp contrast to the basic tenet of neo-Darwinism that mutationsare random events unrelated to any immediate utility. Quite under-standingly, the original paper "The Origin of Mutants" by Cairnset al.' was followed by a flurry of comments, but also soon byreports confirming the original findings in other systems.
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