A new study has found the bacteria in our gut has existed for more than 15 million years dating back to our primate former selves.

The team of researchers based at the University of California at Berkeley and led by Andrew Moeller analyzed different bacteria in the faeces of both humans and our closest primate cousins, the bonobo as well as chimpanzees and gorillas. Once they had identified the DNA structure of three different bacterial families found in the faeces, the team were able to trace back to their origin.

They found that the common bacteria found in chimps branched off around 5.3 million years ago, where the same bacteria found in gorillas and humans branched off much earlier – around 15.6 million years ago. It seems at these points, the bacteria evolved to better serve our modern-day primates and for us as humans.

“We are showing that some human gut bacteria are the direct descendants of gut bacteria that lived within our common ancestors, with apes. It shows there has been an unbroken line of inheritance or transfer from one generation to another for millions of years, since the dawn of African apes,” said Moeller in a statement.

The results came as a surprise because up until now scientists believed most of our gut bacteria evolved from our environment – from what we eat and drink, where we live to what medicines we ingest.

The study also brings up a possible way to identify early human migration as Moeller stated that gut bacteria present in the American participants were slightly different to that in Malawi.

“If our gut bacteria have been tracing our human lineage for millions of years, it could be used to reconstruct the path of human migration. Different populations likely have different strains of the gut bacteria.”

Details of the study were published in the journal Science.