Bacteria can evolve over a much slower period of time. It's entirely possible that the Khaara are an invading species who left when they found the planet unsuitable, and the remaining strand became what they are now.
That said, it's also entirely possible that the Khaara were originally a native species.
no subject
That said, it's also entirely possible that the Khaara were originally a native species.
We simply don't know enough.