Why is showering bad for our skin bacteria? (evolutionary questions)

After reading Alanna Collen’s 2015 book 10% Human: how your body’s microbes hold the key to health and happiness, I have become interested in, among other topics featured in the book, the work of the AOBiome company. Collen mentions this company in the context of aspects of our modern lifestyle which may be detrimental to the beneficial microbes that live on and in us. In this particular case, it is the practice of showering every day with body soap and deodorant that may be disproportionately displacing certain types of bacteria that process ammonia and help control the bacteria responsible for giving us body odor. AOBiome proposes that by replenishing these ammonia-oxidizing bacteria (AOBs) on our skin, we can reduce or eliminate the need for deodorants and showers. We can also replenish them through contact with soil or untreated (an unpolluted) water, according to Collen. I have read up on AOBiome a bit, and their scientific logic seems sound and is backed up by pilot studies they have done (see end for links). However, I have some questions about the evolutionary biology side of things: Continue reading

How fast is evolution?

This question came up during a class I took during my masters studies at the ETH Zurich. What is the maximum speed of evolution? On what factors does it depend? We discussed the idea that selection curbs the speed of evolution, acting as a brake by removing some phenotypes from the population and preventing evolution from continuing down those trajectories.

In that case, evolution without brakes means evolution in the absence of selection. All individuals reproduce in a statistically equal way, and individuals carrying mutations that in the real world would be lethal have just as many offspring as anyone else.

If we think of evolution in terms of travel through sequence space, then we can ask what affects the speed of that travel. Imagine that we start with a single reproducing genotype GREEN of length K in an environment that imposes no restrictions on population size or anything else.

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