A new study about gastrointestinal microbes is shedding light on years-long diets of humans, and it explains how they have evolved from primates.

The Study

Scientists from the Center for Infection and Immunity at Columbia University's Mailman School of Public Health examined the feces of 87 wild western lowland gorillas from the Republic of Congo over three years. The samples, which were from the Sangha region, were collected by the Wildlife Conservation Society.

The findings were published in the journal Nature Communications on May 3.

By sequencing the genetic material of the fecal matter, researchers concluded that the gorillas' gastrointestinal microbes greatly fluctuated based on the seasons.

Most of the year, the gorillas consume leaves and bark, which are often rich in fiber. However, during the dry season, the gorillas eat more fruits because of their availability.

When the gorillas ate fruit, different microbes appeared in their guts, and the microbes nibbled on a protective layer of mucus in the digestive system. After the dry season was over, the gorillas no longer ate fruit, and these microbes were gone.

"We observed dramatic changes in the gorilla and chimpanzee microbiomes depending on seasons and what they are eating," said author Brent L. Williams, Ph.D., assistant professor of Epidemiology at CII.

During most of the year, the gorillas have microbes that assist with the digestion of leaves and bark. When the dry season started and the gorillas consumed fruit, those microbes vanished and they were replaced by bacteria that attacked the mucus layer.

What Does It Mean For Humans?

Gastrointestinal microbes play an important role in the digestive systems of humans by helping break down some foods and providing some vitamins.

The study says a lot about how humans have evolved from their primate ancestors. Unlike other primates, the microbiomes for humans are different because most food sources are available all year.

With no seasonal diet changes, the mucus-eating microbes and other harmful bacteria can stay in the digestive systems of humans during the entire year. As a result of the year-round diets, some humans might consistently lack fiber. This could mean that microbes are feeding on the mucus layer all year, hence, humans are more vulnerable to getting deadly diseases such as colon cancer.

"The fact that our microbiomes are so different from our nearest living evolutionary relatives says something about how much we've changed our diets, consuming more protein and animal fat at the expense of fiber," said Williams.