For most of human history, our guts were exposed only to the wild foods available in our environment. Beginning some 1.8 million years ago, during the time of Homo erectus,humans were a nomadic, hunter-gatherer species whose diet consisted of fish and meat, along with seasonal seeds, nuts, roots, vegetables and berries. It wasn’t until around 10,000 years ago that we transitioned to farming, radically altering our diets, cooking techniques and way of life.
To examine whether this change in lifestyle affected gut microbiome compositions, the researchers collected stool samples from 56 individuals across the four Himalayan populations and from 10 individuals in a control group of North Americans of European descent. These samples were collected over the span of two months. The researchers also gathered information on individuals’ demographics, dietary practices, health status, medications, use of tobacco and alcohol, and several other environmental variables to determine the degree to which the lifestyle variances across the four Himalayan populations correlated to differences in their gut microbiomes.
An analysis of the samples’ contents revealed four distinct types of gut microbiome. Even more exciting, these distinctions paralleled the populations’ transition from hunter-gatherers to farmers. The researchers found that subdivisions of bacteria, including Ruminobacter and Treponemathat are abundant in foraging groups like the Chepang, decrease as populations depart from the hunter-gatherer lifestyle. In fully industrialized populations, such as those in North America, these bacteria are rare or completely absent. Conversely, other bacteria strains, such as Actinobacteria and Verrucomicrobia,are rare or nonexistent in hunter-gatherers but appear as farming and industrialization take hold.
With the Raute and the Raji having transitioned to farming within the past 30 to 40 years, these results also suggest that pronounced changes in human gut microbiomes can occur within decades of a population’s departure from a hunter-gatherer lifestyle.
A 2017 study in Science led by Justin Sonnenburg, PhD, associate professor of microbiology and immunology at Stanford, also showed significant gut microbiome changes in a hunter-gatherer society called the Hadza. Specifically, the researchers found that the Hadza’s gut bacteria was linked to their seasonally varying diet. Together with the current study, these findings “really speak to the power of diet in driving change to the microbiota,” said Sonnenburg, senior author of the new paper.
Our microbial identity
With the gut microbiome so easily influenced, Sonnenburg wonders what this means for our definition of human biology.
“We have always thought of humans as human DNA and the collection of humans cells that we walk around with,” he said. “But now we know that we have this microbial identity, and that microbial portion of our biology is malleable. It can change over really short time periods.”