Humans are only walking digestive tracts. From an evolutionary perspective, all other organs originated from a primitive gut and have only one purpose: to serve it.
(credits to /u/susieq0044@sh.itjust.works who phrased it so well in this post, even though i had the thought already years ago)
The microbiome changes daily based on the day’s diet, so we’re all quite unique from this perspective. It’s also more than just bacteria as there’s also fungi, archae, and even some bacteriophages (viruses that infect specific bacteria) present!