For example bacteria that evolve resistance can often lose them fairly quickly if they are not needed as they are not without cost.
Interesting though :)
If you inject L-gulonolactone oxidase into your liver, you will produce vitamin C. Evolution didn't decide to save energy. It decided that if the users don't notice the bug before the warranty period expires, it isn't worth working the issue.
Evolution exhausts the lowest energy possibilities first, before moving on to higher energy configurations. The surviving lower energy configurations are then in effect used as legos to create higher energy, more expensive configurations. If any of those building blocks are "deprecated", perhaps this effects things up the line, leading to the probability that cheaper, more basic constructions will survive longer because they have fewer steps in a given dependency chain.
Maybe this is obvious to people that understand evolution well, but I hadn't considered it that way before.
In this way, upon reaching some equilibrium where there are base features that reliably survive, evolution "decides" to try more complicated things. My abstraction could be totally off though, so feel free to tell me so if that's the case.
Copying long chains of barely-used DNA is relatively cheap for higher-order multicellular organisms with intergenerational intervals spanning 25 years instead of 12 hours.
Bacteria are better poised to re-evolve the capability when necessary, but if your species only expects ten thousand generations between solar or geomagnetic events, keeping that anti-radiation gene around for 250 kiloyears makes more sense. Of course, during that time, it may get damaged by mutation and not be repaired by sexual reproduction, but you only need one male with a functional antiradiation gene and enough females to not die before reproducing, and you can repopulate the species within 10 generations of a radiation crisis, instead of spending 100k generations reinventing radiation resistance.
If there is no selective pressure, this gene is free to build up mutations and diverge away.
