Colony event records.

Image: Simulation of colonies seeded from single lesion mutant cells and exposed to different levels of lesion stress. The cellular events in the colony are monitored till detectable colony size or colony extinction are reached. Graph adapted from Lennart Hilbert, 2013, Phys. Biol. 10:026001 doi:10.1088/1478-3975/10/2/026001

Over the past 30 and some years, an increasingly convincing set of studies was executed, which show that Stress-Induced Hypermutation (SIH) occurs across various organisms. SIH refers to the phenomenon that, in response to a an environmental challenge or stress, the mutation rate is dynamically adapted on the individual organism level – not by differences in genetic constitution, but as a “proactive” strategy to adapt more quickly overcome evolutionary challenges. This thinking is somewhat at odds with the established dogma that variance (the existence of organisms with different genetic constitution) and selection (the differential capability of the different genetic constitutions to become more prevalent in future generations) are two parts of evolutionary adaptation that are strictly independent. After all, organisms that increase their mutation rate because they “know” that now is the right moment – that sounds too much like some divine engineer had a hand in there.

While Evolved Evolvability is a great explanation that solves the above paradox, I wrote this article in Physical Biology to entertain the idea that SIH occurs as a plain physical necessity, a physical property of life, without a need to specifically develop. To round things off, four thought experiments which (I hope) can be executed relatively easy in the more and more common robotic microbiological laboratories.

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