We know that the DNA copying mechanism that replicates DNA during cellular division is not 100% accurate and the resultant errors are the source of variation in the members of a population.
At the same time, we are also aware of the benefits of variation - how it is useful in ensuring the survival of a species over time and leading to evolution.
I would however like to know if 100% accurate DNA replication is possible (even if hypothetically) - because in my opinion, organisms can surely survive (atleast individually) without variation or evolution.
If it is so, is it possible that organisms with 100% accurate DNA replication did exist, but eventually their populations died out (due to natural selection) and we were left only with organisms that showed variation?
Putting in simpler terms, it is possible that evolution itself is the cause of variation that now causes further evolution?
Answer
You're asking if cells arose with 100% replication accuracy and if lower accuracy was selected for under a feedback loop. Maybe there was a sweet spot for DNA replication accuracy in terms of efficiency, but it's highly unlikely that our ancestor cells had 100% fidelity in DNA replication because if we look at yeast for example, there are many genes dedicated to different types of post-replication repair including mismatch repair, base excision repair, and translesion synthesis. All of these can lead to mutations if they aren't working properly and some (translesion synthesis) inherently generate mutations. It doesn't seem consistent for a cell to develop all of these sophisticated post-replication repair systems to protect itself from DNA damage and then to give some more leeway to DNA replication because it was just too accurate.
Also there are papers like this that talk about how E. coli have increase mutation rates under stress. But if your hypothesis was true, then E. coli would ideally have 100% replication fidelity under normal conditions and lower it when stressed, or they would just have a higher baseline mutation frequency all the time. But, neither of these is observed. What makes the most sense when all this information is put together is that cells try to have as high DNA replication fidelity as possible under ideal conditions.
As per your other question, maybe it's possible to have a 100% accurate DNA polymerase NEB engineers high fidelity polymerases for lab use maybe someday it can reach 0 errors. But there are other sources of mutations like the spontaneous deamination of cytosine that can generate mutations during replication, but that depends on the chemical properties of cytosine so it's not really fixable unless you use different nucleobases.
Reference:
Mutation as a Stress Response and the Regulation of Evolvability. (2012)
By: Rodrigo S. Galhardo, P. J. Hastings, and Susan M. Rosenberg
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