You’d need a lot more DNA, and more redundancy in your DNA and more cellular machinery in all your cells to check for mutations and remove them. As a result of more time spent checking, you cells would do less dividing and you’d be less fit for your niche. Something would eat you and your species would die out.
Well, nothing would change. Both in the short term, and the long term, nothing would change (except most cancers would stop being a thing). Long term, this would hault evolution almost entirely. Mutations drive evolution forward, and without new mutations there will never be any new species or new genetic adaptations.
In the very long term, we’d be nothing but simple RNA-like chemicals copying each other in a warm chemical soup.
In the short term, everything would stop evolving at the instant that copying/reproduction became perfect. Pick a point, observe most of the higher animals become extinct as we regress to simple RNA-like chemicals copying each other in a warm chemical soup because nothing can adapt to changing conditions.
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