Our machines might someday be independent of us,
But they evolved due to our conscious intervention; they could not have arisen independently through selection, and they cannot evolve independently of us, at least, not yet. As an aside, if humanity vanishes and our machine or software descendants start contemplating their own origins, will they have intelligent design/natural selection debates like we do?

We do rely on our intestinal flora, but we had nothing to do with it. We evolved together. We took advantage of each other's metabolisms and we both changed where we found it mutually advantageous, all through natural selection.

But these are all pretty predictable developments. I believe Nick was referring to life forms based on totally different principles, like plasmas, wave forms, sub-atomic particle interactions, and other exotic substrates. I guess you could call them "SDAIborgs".

Such critters may well exist, but we have yet to find them, we haven't even found sufficiently complex structures of this type to even suggest they might be possible.