For now, though, let’s just note that some sort of structural constraint must have acted equally on both of the two great domains of prokaryotes, the bacteria and archaea, forcing both groups to remain simple in their morphology throughout an incomprehensible 4 billion years. Only eukaryotes explored the realm of complexity, and they did so via an explosive monophyletic radiation that implies a release from whatever these structural constraints might have been. That appears to have happened just once – all eukaryotes are related.
