• There is a wide variety in the populations of bacteria found in the human gut microbiome around the world.
  • Researchers believe the microbiome's ability to adapt helped early humans to survive and spread around the globe by allowing them to digest the new foods they encountered as they travelled.
  • Our ancestors could even have used these microbes to ferment food.

Our feet may be made for walking but it’s our gut bacteria that enabled us to spread so far around the globe, according to a new study. Research carried out by a team of scientists at North Carolina State University in the US suggests our microbiome could be the crucial factor that allowed us to adapt and survive in new locations.

The hypotheses suggested by this study still need to be tested by paleoanthropologists, ecologists and medical researchers but Dr Rob Dunn, the biologist who led the team, hopes it will shift the emphasis of future research.

“We’re hoping the findings will change some questions and that other researchers will study the consequences of changes in the human microbiome,” says Dr Dunn. “Hopefully the next decade will see more focus on microbes in our past and less on sharp rocks.”

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By using data from previously published studies of gut bacteria found in humans and other primates, the team found that there are big differences in the function and composition of a person's microbiome depending on their location, their diet and their lifestyle.

The team thinks that when our ancestors arrived in new places and encountered new foods, their gut bacteria’s ability to adapt is what allowed them to detoxify and digest them.

But the team also believes that our ancestors learnt to process food by employing the bacteria from on and in their bodies to initiate the fermentation process. Similar methods are still in use today: bacteria in saliva are used to produce alcoholic drinks in Latin America and skin bacteria are involved in the production of some soft cheeses and sourdough breads.

By using their bacteria to ferment certain meats, tubers and roots our ancestors were able to enrich their vitamin content and preserve them to provide a lasting source of nutrition in a particular location.

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“We outsourced our body microbes into our foods,” says Dr Dunn. “That could well be the most important tool we ever invented. But it’s a hard tool to see in the past and so we don’t talk about it much. Stone artefacts preserve but fish or beer fermented in a hole in the ground doesn’t.”

Tim Spector, Professor of Genetic Epidemiology at King’s College London and author of The Diet Myth, echoes the sentiment. “The hypothesis that microbes helped our ancestors adapt to new environments is compelling, though hard to prove. Our gut microbes are the most unique and modifiable part of our bodies and will rapidly react to new foods and environment.


"We share only around 25 per cent of our microbes with each other compared to over 99 per cent of our genes, so it makes sense that we relied on them for the rapid adaptations needed as we expanded.”

Reader Q&A: What happens in my body when I get food poisoning?

Most of us are all too familiar with the unpleasant symptoms of food poisoning, from vomiting to diarrhoea and debilitating stomach cramps. Although viruses play a role, bacteria are common offenders, with Salmonella and Campylobacter topping the poisoning charts.

Some bacteria wreak havoc by multiplying in the body before delivering their toxins, which spark an immune reaction in the gut. Others, such as Staphylococcus aureus, poison us by contaminating food with toxins.

  1. Bacteria enter Some bacteria or enterotoxins (intestinal toxins) can survive harsh stomach conditions, making their way to the gut. There, the misery begins, sometimes up to 72 hours after eating the offending meal.
  2. Bacteria multiply Undetected by the body’s immune system, the bacteria quietly multiply, producing toxins. These invade and penetrate the gut lining, setting off a strong immune response.
  3. Immune response Immune cells release signalling proteins called pro-inflammatory cytokines, which set in motion a series of steps causing gut inflammation and swelling, leading to discomfort.
  4. Flooded intestines The intestinal wall is designed to absorb nutrients and water from food. Bacterial toxins can cause pores to open in the wall, allowing water and other molecules to flood in.
  5. Diarrhoea and dehydration The excess fluid and electrolytes in the gut lead to watery diarrhoea, which has a beneficial role of flushing out the bacteria and their toxins. It can, however, cause dehydration.
  6. Vomiting Some bacteria don’t cause vomiting, but Staphylococcus aureus enterotoxins do. Research suggests that they may stimulate the vagus nerve which transmits a signal to the brain’s vomiting centre.
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Before going freelance, Rob spent almost four years on staff at BBC Science Focus magazine subediting news, features and reviews. He's now a freelance journalist and has written about everything from electric cars to decomposing bodies… although space and speed are what fascinate him most.