Ancient human gut microbes changed fast in modern societies

Scientists report that the trillions of microbes living in human guts stayed stable for tens of thousands of years before changing quickly in industrialized nations.

Microbial Loss

Researchers studied people in Africa and South America and found more than 600 species of bacteria that were once common in the gut. These bacteria are now rare or missing entirely from most modern societies today. Justin Sonnenburg, a microbiome scientist at Stanford University and study author, stated that this changing microbiome may have helped increase disorders in the industrialized world ranging from allergies to dementia. He noted that the average Californian has around 270 bacterial species, while the average Hadza hunter-gatherer in Tanzania has around 730.

Historical Shift

Early apelike ancestors had a microbiome suited to raw plants and meat. This composition shifted hundreds of thousands of years ago when humans started cooking with fire, and changed again about 10,000 years ago when farmers began domesticating crops. In recent decades, a more substantive shift occurred as billions of people began eating food rich in sugar and refined grains. Modern medicine, such as antibiotics, also destroyed beneficial microbes in the gut.

Comparing Groups

Scientists compared the Hadza group with the Tsimane, a group living in remote Amazon villages in Bolivia who farm, hunt, and forage. The Tsimane descend from people who left Africa 50,000 years ago and crossed to the Americas about 15,000 years ago, while the Hadza's ancestry stays restricted entirely to Africa. Researchers found 848 species shared by both groups that were rare or absent in industrialized countries, and analyzed 636 species that were especially abundant. Michael Gurven, an anthropologist at the University of California, Santa Barbara, and a study author, suggested the ancestral microbiome might help explain why the Tsimane appear protected from heart disease and other chronic conditions. However, Marie-Claire Arrieta, a microbiome scientist at the University of Alberta not involved in the research, cautioned that people should not try to culture a hunter-gatherer microbiome due to infectious potential.

Context

The human gut microbiome plays a vital role in human digestion, immunity, and overall health. Scientists study ancient and remote populations to understand how modern diets and lifestyles have altered our internal biology compared to our ancestors.