In the 1990s, scientist Ivan Casas traveled to the Peruvian Andes in search of human microbes. Casas was head of research for a Swedish probiotics company called BioGaia. He believed that mammals, including people, passed beneficial microbes to their young via breast milk. But he’d been unable to isolate one species he thought should be there (Lactobacillus reuteri) in breast milk from women in the US or urban areas elsewhere in the world.

So he headed to the poor, indigenous communities of the Peruvian Andes, where he thought people lived a more natural life. And when he analyzed a sample collected there, sure enough, he found a unique reuteri strain.

Dr. Casas has since died. But L. reuteri proctectis, a descendant of the microbe originally isolated from a Peruvian woman’s breast milk, lives on, sold as a probiotic supplement and included in some Nestlé infant formulas. Its origin story—a microbe isolated from the breast milk of a woman living far away from the corrupting influence of modernity—is touted as part of its appeal.

In many ways, Casas’s ideas were ahead of their time. Thirty years later, as research on the human microbiome has taken off, many microbiologists now make a similar argument. People in the developed world may have lost certain heirloom-like, mutualistic microbes, they say (including, it turns out, L. reuteri, which does indeed seem to be disappearing from westernized populations). Our health may be suffering as a consequence of these losses, contributing to the rise in recent decades of asthma, autoimmune diseases, obesity, diabetes, and more.

If we can restore the bugs that have disappeared, some argue, perhaps we can reverse the trend, treat, and even prevent these disorders. We in the developed world could “rewild” our bodies, goes the theory, with microbes derived from, say, Amerindian hunter-gatherers. Arguably, anyone who imbibes BioGaia’s L. reuteri protectis is already doing a version of that.

We’re still a long way away from actually repopulating our bodies with “primeval” flora. Scientists are just beginning to catalog microbes from non-westernized groups and they still have no idea which are beneficial, which are harmful, or if such a transfer is even possible, let alone desirable.

Nevertheless, the microbiome field is making rapid progress in figuring out how to extract good bacteria from people and using them to treat various conditions. The shining success so far—the fecal transplant, which is over 90% effective in vanquishing colitis, caused by the gut pathogen Clostridium difficile—is essentially a crude form of microbial ecosystem restoration, in other words, the transplant of a healthy person’s microbiome to a diseased person.

Companies like Seres Therapeutics and Vedanta Biosciences are working to develop more refined products—US government-approved therapies to treat obesity and inflammatory diseases, using microbes harvested from other healthy people in the developed world.

Ultimately, though, the only way to recover certain essential bugs lost to us in the developed world may be to acquire them from people who, like Dr. Casas’s Peruvian woman, still have them. And so, microbiologists are hurrying to study the microbes of peoples living more “traditional” lifestyles, including Amerindians in the Amazon, east African hunter-gatherers and Papuans, before their microbiomes modernize—before they urbanize, get flush toilets, take copious antibiotics, transition to a refined-food diet, and do all the other things thought to distort and deplete the human microbiota.

At this point, scientists are careful to characterize the research as purely descriptive. They’re only trying to understand what’s there, they say, and what it does. Yet the mere possibility of one day rewilding our bodies with microbes harvested from other people raises a fraught question: Who owns these microbes, and how should we compensate them for their use? Say that a microbial mix originally isolated from a Yanomami tribesman becomes a bestseller fix for asthma. Should the donor, or his tribe, receive a share of the profits? For that matter, did that Peruvian woman receive compensation? (Bo Möllstam, BioGaia’s technical director, says that the company is careful to comply with research ethics requirements of the countries it works in, and it did so in that case.)

One line of thinking holds that because microbes are widespread and naturally occurring, they don’t belong to anyone. You can patent treatments and methods, or genetically modified organisms, but you can’t patent free-living organisms, even if those organisms are living on your body. Sure, donors can be compensated for time and effort—on average, the stool banking non-profit OpenBiome pays its donors up to $4,320 a year—but ultimately, it’s scientific know-how that transforms human feces into medicine.

“The donors didn’t come up with the knowledge that allowed us to create an ecosystem,” says Emma Allen-Vercoe, a microbiologist at the University of Guelph in Canada. As it is, there’s already too much red tape slowing research, she says. The field doesn’t need more.

Here’s the wrinkle, though: Ivan Casas went to the Peruvian Andes precisely because he thought those populations had something Americans didn’t. Ditto with the scientists now studying peoples in the Amazon or East Africa. They suspect the microbiomes of these populations are unique and unlike our own—a suspicion that has so far proven correct. Amerindians in the Amazon harbor up 50% more microbial species than North Americans. They possess microbes we simply don’t.

Maria Gloria Dominguez-Bello, a microbiologist at New York University who studies remote Amerindian groups, feels strongly that, legal reasoning aside, there’s a moral obligation to share the benefits of research with subjects. Compensation can raise other sticky issues, though. For instance, how do you pay an Amerindian hunter-gatherer who has no use for money? You might give them medicine and goods—they particularly like digital cameras, Dominguez-Bello says—or open a health clinic, but then you begin changing their way of life.

“We spoil the very place we come to study,” she says.

BioGaia’s Möllstam acknowledges these concerns as “something that needs to be dealt with in a serious way.” “We need to realize that we need to share whatever comes out of [research]”, he says. But modern gene sequencing technology may also make the issue moot. These days, when scientists understand how a healthful bacterium works, they can study its genome and find other microbes that behave the same way—something that was impossible in the past. BioGaia, which has a catalog of thousands of L. reuteri strains, wouldn’t go to Peru today searching for lactobacilli, he says, because it wouldn’t need to.

“When you know what you’re looking for,” he says, “you can pick microbes up almost anywhere.”