I wonder if neclei were "invented" by viruses as those safe rooms. There are already theories that DNA was first invented by viruses to protect against cleaving by RNAases, and the presence of UDNA viruses suggests it. It would also explain how DNA had immediate selective advantage over RNA.
In the book The Vital Question the author argues that nuclei were invented to protect against the original mithocondrial DNA:
> Introns are the result of "a barrage of genetic parasites" that early eukaryotes faced from their own endosymbionts; nuclei evolved as a defence against this, allowing spliceosomes to remove introns from transcribed messenger RNA before ribosomes can translate them into proteins.
