Saturday, February 18, 2006


[evomech] Mutation and adaptation: the directed mutation controversy in evolutionary perspective

[Lenski & Sniegowski, Annual Review of Systematics, Nov '95]


A central tenet of evolutionary theory is that mutation is random with
respect to its adaptive consequences for individual organisms; that is,
the production of variation precedes and does not cause adaptation.
Several recent experimental reports have challenged this tenet by
suggesting that bacteria (and yeast) ''may have mechanisms for choosing
which mutations will occur'' (6, p. 142). The phenomenon of nonrandom
mutation claimed in these experiments was initially called ''directed
mutation'' but has undergone several name changes during its brief and
controversial history. The directed mutation hypothesis has not fared
well; many examples of apparently directed mutation have been rejected
in favor of more conventional explanations, and several reviews
questioning the validity of directed mutation have appeared (53, 54,
59-61, 79, 80). Nonetheless, directed mutation has recently been
reincarnated under the confusing label ''adaptive mutation'' (5, 23, 24,
27, 35, 74). Here we discuss the many experimental and conceptual
problems with directed/adaptive mutation, and we argue that the most
plausible molecular models proposed to explain ''adaptive mutation'' are
entirely consistent with the modern Darwinian concept of adaptation by
natural selection on randomly occurring variation. In the concluding
section of the paper, we discuss the importance of an informed
evolutionary approach in the study of the potential adaptive
significance of mutational phenomena. Knowledge of the molecular bases
of mutation is increasing rapidly, but rigorous evolutionary
understanding lags behind. We note that ascribing adaptive significance
to mutational phenomena (for example, ''adaptive mutation'') is beset
with some of the same difficulties as ascribing adaptive significance to
features of whole organisms (29). We consider some examples of
mutational phenomena along with possible adaptive and nonadaptive

Full text at:,%20ARES,%20Sniegowski%20&%20Lenski.pdf

John Latter

*Model of an Internal Evolutionary Mechanism* [Evolution]:

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