Yeah. Indeed in the organism human cells are outnumbered in ratio of something like x10 by non-human microbiota - bacteria, archea, fungi, viruses ... 90%+ of our DNA is 'silent' consisting of ancient viruses most of which predate humanity with hundreds of millions of years and found the best survival stategy - to inscribe into the host's very code and to not be exposed to the risks to insert, copy etc. which may be subject of errors and immune reactions. May be , Dana, you'll find useful the concepts of https://en.wikipedia.org/wiki/Merkwelt & https://en.wikipedia.org/wiki/Umwelt