Some of the bacteria in our guts was passed down from a time before we were even human, it has been discovered.

Bacteria in our gut helps to guide the early development of our intestines and train our immune systems to fight pathogens.

Scientists had thought that most of our gut bacteria came from our surroundings - like what we eat, where we live, and the medicines we take.

Now a new study suggests they may have been passed down over millions of years, suggesting evolution plays a larger role in people's intestinal-microbe makeup than previously thought.

Their research suggests that microbes in our ancestors' intestines split into new evolutionary lineages in parallel with splits in the ape family tree.


The research was carried out by an international team of scientists, led by Howard Ochman, professor of integrative biology at The University of Texas at Austin.

Image: The researchers dug through faecal samples of apes and monkeys

Prof Ochman said: "It's surprising that our gut microbes, which we could get from many sources in the environment, have actually been co-evolving inside us for such a long time."

To understand the evolutionary relationships between gut bacteria in different ape species, the researchers dug through faecal samples of apes and monkeys, as well as humans from Connecticut.

They found genetic evidence that the bacteria split into distinct strains around the same times as their hosts were splitting into distinct species.

One bacterial split happened about 15.6 million years ago as the gorilla lineage split from the other hominids.

The other bacterial split happened around 5.3 million years ago as the human lineage separated from the lineage which led to chimps and bonobos.

Postdoctoral researcher Andrew Moeller said: "We've known for a long time that humans and our closest relatives, the great apes, harbour these bacteria in our guts.

"The biggest question we wanted to answer is, where did these bacteria come from?

"Did we get them from our environment or from our evolutionary history?

"And how long have they persisted in host lineages?"