Reversal of Aging by Biological Intervention

Same constraint applies to computers. Currently they are much worse if forced to work stand alone for extended periods. They only get past it by having the ability to get back-up copies from other computers.

Cells could be designed to check the accuracy of their copies against others, but they don't do this (well some microbes kind of do). In general biological systems are much more stable and robust than computer hardware.

Nature has definitely not gone as far as it could. Humans are not perfect and evolution still continues. Whether we behaviourly modify the outcome in a fashion that will keep us from moving towards an improved state, we'll just have to wait and see.