New York: The microbes living in people's guts play a very important role in keeping us healthy, but the ones existing in our body today are a lot less diverse than the ones present within the humans' closest relatives, the African apes, says a research.
What is more, the evolutionary trend of declining gut bacteria appears to be speeding up in modern societies, the findings showed.
People in non-industrialised societies have gut microbiomes that are 60 percent different from those of chimpanzees.
Meanwhile, those living in the US have gut microbiomes that are 70 percent different from those of chimps.
"It took millions of years, since humans and chimpanzees split from a common ancestor, to become 60 percent different in these colonies living in our digestive systems," said study co-author Howard Ochman, professor of integrative biology at the University of Texas, Austin in the US.
"On the other hand, in apparently only a hundred years - and possibly a lot fewer - people in the United States lost a great deal of diversity in the bacteria living in their gut," Ochman added.
The study is based on an analysis of how humans and three lineages of apes diverged from a common ancestor.
One possible explanation for humans evolving to have less diversity in their gut microbiomes is that they shifted to a diet with more meat and fewer plants.
Plants require complex communities of microbes to break them down, which is not true for meat.
The researchers analysed the genetic makeup of bacteria in faecal samples from humans, chimpanzees, bonobos and gorillas to draw their conclusions.
The study appeared in the journal Proceedings of the National Academy of Sciences.