Eta

Here is where the 'idea' of a commensal becomes fuzzy, and it's why people like me get all excitable and philosophically rigorous when we get to show off why we think Plato's theory of Forms is a pile of paapecack (or tutti as the kids in Bombay would say).

Our best guess (as I'm sure you know), is that mitochondria were part of the process of developing eukaryotes - cells with well-defined nuclei, as opposed to the prokaryotic cells of the bacteria and archaea. So mitochondria were originally bacteria, perhaps initially parasitic upon larger prokaryotic cells. In time, though, mitochondria became 'commensals' within cells. In further time (only about a billion years), mitochondria have become an integral part of the eukaryote package.

Or have they?

As you point out, they have their own DNA. They do not engage in sexual reproduction. They have their own genetic diseases. They have their own lineages, distinct from 'our' own. So are they parasites? Commensals (which would in general be taken to include symbiotes)? Parts of ourselves? Stick that in your cave of shadows and tell us, Mr Plato.

cheer

the sunshine "nominalism rocks" warrior