Ruin Explorer
Legend
The issue is the DNA is evolved, not designed.Its actually an interesting question if that kind of longevity is even possible. Sake of argument lets say your a super advanced race that uses nanites or something to repair and maintain everything, perfect over time. Well those nanites themselves have to be repaired and replicate....and with every replication comes the risk of an imperfection.
Our DNA is amazing at replicating accurately at high speed, but mistakes still happen. And even if a nanites system has a replication ability that is even more accurate....unless its 100% some measure of error will be introduced over time, and eventually the system will shift in some direction away from its exact function.
Is it actually possible to replicate things so perfectly that no error is ever introduced?
Nanites, presumably, would be designed.
So you could have much stronger and more reliable error-correction, which doesn't evolve, because it just doesn't matter that much so long as a creature doesn't get terrible errors before it reproduces.
If you somehow had the tech to build nanites that could build and maintain structures and themselves, then frankly the error-correction would be absolute child's play compared to that first step. That's not to say something bizarre couldn't happen, but so long as the nanites were programmed to eliminate nanites which were not reproduced correctly (and/or to self-eliminate) you'd be looking at something insanely more reliable than DNA. Potentially there's no clear limit on how long that could operate for. Maybe there are processes we don't know about but if so they're unknown unknowns rather than even known unknowns.
Everything has a cost though, note. Making error correction a priority for nanites could probably keep them operating for 100k or 2m or w/e years, but would probably making the require more energy/processing power and reproduce more slowly (this is true down to a cellular level with living things too - basically nothing is free - even when a bacterium evolves drug resistance to an antibiotic, for example, that has a cost, to the efficiency of that bacterium, that limits it in certain ways).