Carl Zimmer in The New York Times:
In Tanzania, not far from the Serengeti, live the Hadza, a community of about 1,300 people. For such a small group, they attract a lot of scientific attention. Many of the Hadza live solely on the animals they kill, along with honey, berries and a few other wild foods. For the first 95 percent of our species’ history, there was no other way to live. So the Hadza have been closely scrutinized for clues about the hunter-gatherer way of life: how they find their food, how much energy they use — even how much sleep they get. On Thursday, scientists described another way in which the Hadza are exceptional. Their gut microbiome — the bacteria that live in their intestines — swings through a predictable annual cycle. Some bacterial species disappear entirely and then return, in a rhythm that likely reflects regular changes in the Hadza diet. Many gut bacteria that wax and wane drastically are rare in people living in industrialized societies. “We don’t have a good grasp of what these seasonally varying microbes even do,” said Justin Sonnenburg, a microbiologist at Stanford University and lead author of the new study. Each of us carries about 30 trillion bacteria, belonging to thousands of species. Dr. Sonnenburg hopes that by comparing the microbiomes of hunter-gatherers with those of people in different societies, scientists will be able to learn how diets influence their composition. As more societies switch to a Western diet, their microbiomes may change, altering their health. “We have to think of ourselves as these composite organisms, with microbial and human parts,” Dr. Sonnenburg said.
Until recently, microbiologists have mainly studied the microbiomes of people who eat a Western diet. Now they are casting a wider net. In 2013, Stephanie Schnorr, then a graduate student at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, began the first study of the Hadza microbiome. At a meeting with community leaders, she and her colleagues explained their plan: to collect stool samples and study the microbes in a lab. “One of the camp’s senior men said, ‘Well, we give it to the ground, so why not just give it to her?’” recalled Dr. Schnorr, now a postdoctoral researcher at the University of Oklahoma. Dr. Schnorr eventually extracted DNA from microbes inside 27 Hadza and compared them with samples gathered from people in Bologna, Italy. In 2014, she and her colleagues reported some striking differences. The Hadza hosted a much greater diversity of gut microbial species than did the Italians, the researchers found, and there were some fundamental differences in species they carried. Some that were common in the Hadza were rare or missing from the Italians.