So contend Salverda and de Visser in Current Biology,
Given that there is genetic variation in evolvability, how can it evolve? This is not straightforward, as natural selection benefits organisms with high fitness and not those with increased evolutionary potential. In order to evolve by natural selection, variants with increased evolvability must be associated with direct or indirect fitness benefits. Direct positive effects on offspring fitness are unlikely, at least for short-term evolvability, because genotypes that produce relatively many beneficial mutations tend to be those with relatively low fitness . Variants with increased evolvability thus rely on longer-term benefits arising from the association with rare beneficial mutations, which they produce at an increased rate. Such second-order selection due to hitchhiking with beneficial mutations (Figure 1) is also the mechanism by which mutators, i.e. mutants with an increased mutation rate, reach high frequency in microbial populations .In the new study, Woods et al. report a detailed demonstration of second-order selection of evolvability in a large population of the bacterium Escherichia coli.
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What is particularly beautiful about the study by Woods et al. is that it illustrates in detail how the selection of clones with increased evolvability depends crucially on the interplay between fitness landscape and population dynamics. Given the complex fitness landscape observed, the size and mutation rate of the evolving population set the limits for second-order selection of clones with increased evolvability. Had the population been smaller, the spoT mutation that rescued the EW clone might not have occurred before the clone went extinct, turning the clone into an ‘eventual loser’ instead of the topic of a research project. As the authors mention, a minimal requirement for second-order selection of evolvability is the simultaneous presence of multiple contending clones carrying different beneficial mutations. Beyond that, population size and mutation rate determine how far evolution can look into the future, that is, how many new beneficial mutations are allowed to accumulate before the EW clone fixes. These results support previous claims that there is ample opportunity for higher-order selection of evolvability in microbial populations, since often multiple beneficial mutations accumulate before they fix .
But see other Lenski studies here.
Thoughts? Hearing this, some have been reminded of Werner Heisenberg’s comments on intentionality:
… in the history of the light bulb, the Nernst lamp was replaced by the incandescent lamp almost as soon as it had appeared. The process of biological selection must be envisaged in much the same way. Mutations occur by pure chance, just as quantum theory would expect them to do, and selection eliminates most of these “natural experiments.” Only a few forms, which have proved themselves under the given circumstances, remain.
While thinking about this comparison, it occurred to me that the process of technological advance differs from Darwinian theory in one crucial respect, namely, just where Darwinian theory introduces chance. Human inventions are the result never of accident but of man’s intention and thought. I tried to see what would happen if the comparison were taken more seriously than the speaker would have wished, and if something like intention were associated with Darwinian mutation. But can one really speak of intentions apart from man? At most, we are prepared to grant a dog jumping onto the kitchen table “intends” to eat up the sausage. But has a bacteriophage approaching a bacterium the intention of entering it and of multiplying inside? And even if we are still prepared to say yes, can we also say that genes change their structure with the intention of adapting to their environment? If we did, we would obviously be misusing the word “intention.” But perhaps we could choose a more careful formulation. We could ask whether the aim to be reached, the possibility to be realized, may not influence the course of event. If we do that, we are almost back with quantum theory. For the wave function represents a possibility and not an actual event. In other words, the kind of accident which plays so important a role in Darwinian theory may be something very much subtler than we think, and this precisely because it agrees with the laws of quantum mechanics.
– Werner Heisenberg, Physics and Beyond , Harper & Row 1971, pages 242-243.