Assistant Professor Lauren Ancel Myers.
Courtesy of School of Biological Sciences, University of Texas at Austin.
Bet hedging can be defined as a form of between-individual, non-genetic variation whereby organisms produce diverse offspring as a means of coping with environmental change (Ancel Myers and Bull, 2002, p. 552). The diversity of phenotypes ensures that at least some of the organisms's progeny will survive in an uncertain environment where conditions vary. Hypermutation, by contrast, is a form of "between-individual, genetic variation" in which "the rapid production of variants enables survival in rapidly fluctuating conditions" (Ancel Myers and Bull, 2002, pp. 553-554). There are several mechanisms: a bacterium with a deficiency in the enzymes needed to repair its DNA can give rise to a strain of hyper-mutating bacteria, while other strains may result from randomly jumping transposable elements that disrupt genes. Bacteria may also exhibit higher mutation rates at particular locations, or hotspots, either as a result of random transitions between different ways of expressing a particular gene (phase shifting), or due to mutations at certain repeat sequences called microsatellites, which reduce the fidelity of the replication process.
However, bet hedging and hypermutation are even less promising candidates for intelligent behaviour by bacteria than the regulation of the lac operon. Ancel Myers and Bull explain why:
From the foregoing description, it should be clear that these adaptive forms of bacterial behaviour cannot be interpreted in mentalistic terms. First, they are not even amenable to the intentional stance: the environment is not measured, so no information about it is stored. The application of this stance requires, at the very least, a specification of the organism's information and goals. (See Conclusion I.1 above.)
Second, because the particular mutations that are triggered by environmental stimuli are un-directed (i.e. random) and usually inappropriate for their environment, they cannot be described as an intelligent response to changing circumstances.
Third, these forms of behaviour are not self-initiated: they are triggered by external environmental stimuli. It would be a misuse of language to describe these kinds of behaviour as manifestations of "agency" or "decision-making" on the part of bacteria.
Finally, the behavioural versatility displayed does not occur in an individual bacterium, but in a lineage of related bacteria. Even if we were to regard this adaptive behaviour as intelligent, then we would have to impute intelligence to an extended super-organism rather than to an individual bacterium. However, we have already argued (Conclusion B.3) that an evolutionary lineage cannot be meaningfully described as having mental states.
In short, while bet-hedging, hypermutation and localized elevated mutation rates certainly illustrate the impressive versatility of bacteria, the adaptibility they manifest is not the kind required for the possession of mental states.
... whereas some forms of phenotypic plasticity involve appropriate phenotypic responses to environmental cues, bet hedging and hypermutation produced a range of variants without measuring the environment, only some of which will be appropriate for the current conditions. The SOS response of bacteria is a form of hypermutation that is both 'direct' and 'random' simultaneously. Certain environmental stimuli, including heat shock, radiation and chemical stress, cause the rate of spontaneous mutation to increase. The resulting variation arises in direct response to environmental stresses, yet the nature of that variation is often random, and often not appropriate for the environment (2002, p. 554, italics mine).