Washington: A new study has found that microbes residing within the guts of our ancestors helped them thrive and evolve into more stable and resilient populations.

The human race survived because our ancestors were robust enough to handle environmental changes and the natural disasters they encountered, it added.

To look at the microbiome’s effects on people as they age, researchers created a mathematical model to simulate an ancient hunter-gatherer population.

During the study, Martin Blaser, microbiologist at New York University’s Langone Medical Center, noticed that the stomach bacteria Helicobacter pylori could live symbiotically in people’s guts for decades, without causing them any harm.

But it could also cause stomach ulcers and stomach cancer – a risk that grows with age.

“I began thinking that a real symbiont is an organism that keeps you alive when you are young and kills you when you are old. That is not particularly good for you, but it’s good for the species,” Blaser was quoted as saying in a LiveScience report.

Their calculation suggests that bacteria may have evolved to target the older people in the population.

“It is possible that these bacteria helped reduce the number of elderly people in a population, thereby allowing the children to get a greater share of food and resources,” the authors wrote.

The bacteria allow the extraordinarily long childhood that humans experience in comparison with other animals, they suggested in a paper that appeared in the journal mBio.