Gut microorganisms live organisms have decreased in number during the last 2,000 years. That is one of the preliminary results from studying fossilized human feces extracted from rock shelters using a genomic approach. Since the atmosphere in this may be a ton, researchers assume it could be effective for microbes to grow and change. There are more antibiotic-resistant bacteria in the modern gut microbiota. The findings may be helpful to us in understanding the implications.

Reference

Mass Extinction in The Human Gut Revealed by Fossil Remains of 2,000-Year-Old Feces. https://www.sciencealert.com/2-000-year-old-feces-fossils-reveal-mass-extinction-in-the-human-gut