These 60 gut microbes have evolved alongside humans since we first left Africa

When homo sapiens made their way out of Africa, they were carrying tiny little friends with them.

A new study has shown those same friends – gut bacteria – have been evolving, or “codiversifying,” alongside us for the last couple of hundred thousand years.

As well as allowing us to understand more about ourselves, it’s hoped the new research will also give us more information on how to treat microbiome-based diseases or create new therapies.

The study – published in Science – looked at the differences and similarities between our closest bacterial friends in 1225 humans living around the world. The team found 59 bacterial species, and one archaeon, that have evolved in parallel with humans. (An archaeon are a domain of single-celled organism, originally thought to be bacteria, but are now known to be more similar to eukaryotes – multi-cellular organisms like us.)

The human gut microbiome contains hundreds of species of bacteria, and many of the most prominent species are found in people worldwide, says Andrew Moeller, an evolutionary biologist at Cornell University in an accompanying paper. “Gut bacterial communities are not haphazard collections of bacteria but reflections of the distinct ancestries of human populations.”

Read more: Gut bacteria linked to undernutrition recovery

However, within microbial species, some strains can show remarkable genetic diversity between specific human populations. Whether or not this diversity arose through a shared evolutionary history between humans and their microbes hasn’t yet been fully understood.

Max Planck Institute for Biology microbiologist Taichi Suzuki and his team evaluated 1225 people living in Gabon, Vietnam, and Germany and discovered 60 microbial strains that, between and within countries, have evolutionary histories that indicates codiversification.

The team also found that the species displaying the strongest codiversification appear to have also independently evolved traits such as oxygen and temperature intolerance and reduced genomes, which means they really are stuck with us – also known as host dependency.

“The list of human health conditions linked to the microbiome ranges from malnutrition to allergies and cardiovascular disease,” the team write in their new paper.

“An awareness of differences in gut microbial strains between populations has already led to the notion that probiotics for treating malnutrition should be locally sourced.

“The microbiome is a therapeutic target for personalized medicine, and our results underscore the importance of a population specific approach to microbiome-based therapies.”  

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