Modern city dwellers have lost about half their gut microbes
Deep in the human gut, myriad "good" bacteria and other microbes help us digest our food, as well as keep us healthy by affecting our immune, metabolic, and nervous systems. Some of these humble microbial assistants have been in our guts since before humans became human-certain gut microbes are found in almost all primates, suggesting they first colonized a common ancestor.
https://www.science.org/content/article/modern-city-dwellers-have-lost-about-half-their-gut-microbes
