the lineage of this intelligence goes back in an unbroken line to their first common ancestor billions of years ago,
Nonsense. If cell walls ever had the ability to replicate themselves, totally autonomously, without the rest of the cell -- they've very certainly lost that ability. That loss of self-sufficient replication is quite a big "break" in the line.
Your argument might apply to ribosomes, however. The nucleus needs the ribosome for replication every bit as much as the ribosome needs the nucleus. And the ribosomal DNA is one of the very, very rare things that has hardly changed at all in the history of life -- humans and yeast have 75%-identical ribosomal DNA. Yeast!