Gut bacteria may have played bigger role in human evolution that previously thought: Study

Bacteria living in the guts of our ancestors may have been more important for human evolution than previously thought, according to a study which suggests that the adaptive nature of the microbes may have helped the ancient people survive in new geographic areas. The study, published in the journal Frontiers in Ecology and Evolution, assessed data from previously published studies to compare the community of different species of bacteria (microbiome) living in the guts of humans, apes, and other non-human primates.

According to the researchers, including Rob Dunn from the North Carolina State University in the US, there is substantial variation in composition and function of the human microbiome which correlates with geography and lifestyle. Based on the study, they suggested that the human gut microbiome adapted quickly to new environmental conditions.

"In this paper, we begin to consider what the microbiomes of our ancestors might have been like and how they might have changed," Dunn said. "Such changes aren't always bad and yet medicine, diet, and much else makes more sense in light of a better understanding of the microbes that were part of the daily lives of our ancestors," he added.

When human ancestors walked into new geographic areas, they confronted new diet choices and diseases, and used a variety of different tools to obtain and process food, the scientists said. The adaptive microbiome our ancestors had, may have made it possible to digest or detoxify the foods they were eating in a local region, and increased their ability to endure new diseases, the study noted.

Microbial adaptation, the researchers believe, may have facilitated human success in a range of environments, allowing us to spread around the world. The social sharing of microbes between the ancestral humans might have led to local microbial adaptations, they said.

However, the scientists added that our ancestors did not just share their microbiome amongst each other but may have also outsourced them into their food. Citing an example, they said, with the invention of artificial fermentation methods, similar to those used to make cheese, the early humans may have "extended" their guts outside of their bodies by co-opting body microbes to allow digestion to begin externally.

This may have allowed humans to store food and stay in one place for a longer time, facilitating the persistence of larger groups living together, the study said. When these groups consumed the food items together, the microbes re-inoculated the consumers and the group's microbiota became more similar to each other than to individuals from other groups, it noted.

"We outsourced our body microbes into our foods. That could well be the most important tool we ever invented. But it is a hard tool to see in the past and so we don't talk about it much," Dunn said. "Stone artifacts preserve but fish or beer fermented in a hole in the ground doesn't," he added.

The scientists said the conclusions drawn from the research still need to be tested by paleoanthropologists, medical researchers, ecologists, and other professionals. "We are hoping the findings will change some questions and that other researchers will study the consequences of changes in the human microbiome," Dunn said.

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