Evolution in the absence of selective pressures

biochem_geek,That's exactly the conclusion I came to. I figured if there is no selection, ie. everything is supplied, then a loss of complexity would result via random drift. There's no selective pressure to maintain any system beyond that required for replication. A bit like humans losing the ability to synthesise vitamin C when it is freely available anyway. No loci will be under selective constraint apart from the machinery that allows replication. Essentially you would be left with a minimal molecule that only has to replicate.Your (good) analogy with intracellular symbionts must break down at some point. The organism has to keep its host alive, thus introducing some sort of selective pressure to maintain it's "part of the bargain". Remove that, & via genetic drift you could get as simple as a self-catalysing, self-replicating molecule that fills up the entire universe .Mark

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There are 10 kinds of people in this world; those that understand binary, & those that don't

A current Nature paper describes removal of selective pressure in the lab, and the genetic results after a few hundred generations: From the 'New & Views' article on the paper: In other words, the authors removed selective pressure by removing competitors, as opposed to the scenario proposed in the opening post, which provided an 'ideal environment' to prevent selective pressure.The primary result described in the above paper is a ten-fold increase in accumulated mutations when compared to other worms raised conventionally in the presence of other worms. The conclusion is not that the mutation rate increased in the selection-free worms, but rather that in the absence of selective pressure, mutations were not selected against, and so accumulated in the genome - resulting in low fitness.A simple yet elegant experiment - it gets around the impossibility of providing an ideal environment, although at the cost of examination of population structure.