The warm soft folds of the intestines are teeming with thousands of species of bacteria. Collectively known as the gut microbiome, these microbes help break down food, synthesize vitamins, regulate weight and resist infection. If they're so key to health, what factors shape an individual's gut microbial makeup?

Previous studies have pointed to the food we eat, the drugs we take, genetics, even our house dust. Now, a new study in baboons suggests that relationships may play a role, too.

The researchers studied social interactions, eating habits and bacteria in the feces of 48 wild baboons from two groups living near Mount Kilimanjaro in Kenya. Their findings appear in the March 16 issue of the journal eLife.

"Poop contains a goldmine of data," said Duke University biologist Jenny Tung, who co-authored the study. "Ninety-eight percent of the DNA in poop doesn't come from the animal itself or the foods they eat -- it's bacterial."

Using powerful sequencing machines to tease out each microbe's unique genetic signature, the researchers identified the names and relative amounts of nearly 1,000 bacterial species thriving in the baboons' bowels.

The cast of characters includes relatively high levels of Firmicutes, Proteobacteria, Actinobacteria and Bacteroidetes -- all of which are also commonly found in human guts.

Baboons from the same troop had more similar gut microbes than baboons from different troops.

The results are consistent with previous studies in humans showing that people who live together harbor similar gut germs. The connection has largely been attributed to couples and housemates eating many of the same foods in the same relative proportions, but Tung and co-author Elizabeth Archie of the University of Notre Dame and colleagues wondered if additional factors might be at play.