Can you point to a study that suggests this? I have no opinion one way or another but making statements like this without any backing is misinformation.
Once that's true it does seem there's a lot of host and microbiome interactions we've only begun to explore, but it shouldn't be surprising that co-evolution of the microbiome and host begins to take over as soon as you have one. One great example is short-chain-fatty-acid (SCFA) producing bacteria in the human gut. [1] These seem to be essential, and if there was a general takeaway to improve health, it would be to eat your roughage so they can do their job.
This is also why high alpha-diversity (community richness in particular) is such a dead-ringer for healthy vs diseased states. And frustratingly, is often exactly where the story ends for a lot of observational studies.
Also, in case you are curious, artificially sterile mice (gnotobiotic mice) tend to act differently than other mice, which is pretty odd to be honest, and why the gut-brain axis is a plausible mechanism to research further. [2]
[1]: https://pmc.ncbi.nlm.nih.gov/articles/PMC10180739/ [2]: https://www.sciencedirect.com/science/article/pii/S088915912...
https://pmc.ncbi.nlm.nih.gov/articles/PMC6503789/
tl;dr > The oral microbiome usually exists in the form of a biofilm. It plays a crucial role in maintaining oral homeostasis, protecting the oral cavity, and preventing disease development.
That NIH article also refers to some fields that are experiencing wide recent advances: the gut/brain axis, and communication from the skin microbiota that stimulates the first immune responses to pathogenic organisms.
This link describes some aspects of the skin microbiome:
https://www.news-medical.net/news/20250402/How-your-skine280...
I up-voted your post. I don't think there should be a penalty for asking for a reference. Although, I'm not always in the mood to dig up _good_ links on subjects that I've read enough to form an opinion.