Low-temperature electron micrograph of a cluster of E. coli bacteria. Each individual bacterium is oblong shaped. Photo by Eric Erbe, wikipedia

Beneficial mutations are often seen as the engine of evolution (Mutations: evolution’s engine becomes evolution’s end!). However, beneficial mutations by themselves don’t solve the problem (see Beetle Bloopers). Mutations not only have to be beneficial, but they have to add biological information, i.e. specified complexity. However, practically all beneficial mutations observed have beenlosses of specified complexity (The evolution train’s a-comin’), with only a few disputable examples of mutations increasing information ever found (e.g. bacteria that digest nylon, citrate orxylitol).

Epistasis: how do mutations interact?

However, mutations need to be more than beneficial and information-increasing to produce new coordinated structures and systems, as microbes-to-man evolution requires. Mutations don’t act alone; the effect of a mutation on an organism’s phenotype depends on other genes, and mutations in those genes, in the genome. This is called epistasis; it is an important consideration for evolution because how mutations interact will determine if they could possibly build new structures in a stepwise manner.

For microbes-to-man evolution to occur, mutations need to be not just (specified) information-increasing and beneficial, they also need to work together. This also has to be the main dominant trend in adaptive evolution so that the mutations can together produce new biological structures and systems. This phenomenon is called synergistic epistasis (SE), where the combined effect of mutations is greater together than the sum of their individual effects. This is obviously a good situation for beneficial mutations, but very bad for harmful mutations. In harmful mutations, SE can result in synthetic lethality1, where the combined effects of several harmful mutations are compounded by each other’s presence, resulting in such a bad effect that it kills the organism.2 So evolution needs SE to be commononly in beneficial mutations; it works against evolution when it occurs in harmful mutations….

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