[Symmetry]

Rewrites in how living cells work at a fundamental level is really hard. It took a billion years to go from prokaryotic cells to eukaryotic ones and that was a pretty simple change - just move the energy extracting membrane inside to get out of the squre/cube culs-de-sac bacteria were stuck in. But at the same time it's the sort of thing that would be obvious to an intelligent designer. I'm not sure that microscopic diamondoid self-replicators are possible but I wouldn't rule out the idea that similar improvements are easy pickings in synthetic biology and that's a pretty scary thought.