Humans always end up with clogged arteries, right? That’s not what the lives of the Tsimane in the Amazon basin tell us

If the last 5 million years of human evolution is compressed into a single calendar year, we’re hunter-gatherers from 1 January until 11:40 pm on 31 December.
– Ben Trumble, Arizona State University

I’m on a Zoom call with 20 faces, a biweekly meeting of an improbable collaboration of international scientists. They call themselves the Horus/Tsimane Group because they study the hearts and brains of both Egyptian mummies and the living Bolivian foragers and small-scale farmers known as the Tsimane.

The Horus Group, named after the Egyptian god of healing, is an international team of cardiologists, archaeologists and radiologists who have studied more than 200 mummies in Egypt, Peru, the Aleutian Islands and Italy with computer tomography (CT) scans and genetic analyses. They wanted to see if atherosclerosis, one of the leading causes of death in the world, is a disease of modernity, our high stress, cholesterol-laden lifestyle, or if it had been there all along. Are we dealing with a mere century of clogged arteries – or can we find the same pathology in the arteries of mummies that are 5,000 years old?

Turns out, many mummies died with heart disease. The Horus Group found that, on CT scans, almost 38 per cent of the mummies had the primary pathological evidence of atherosclerosis, deposits of calcium lining their aortas, and other major arteries.

To be mummified, you had to be rich, powerful, a priest, a relative of the pharaoh; the Egyptian elite were not foragers like the Tsimane. They lived a relatively lavish, sedentary lifestyle and, according to hieroglyphic papyri, ate a lot of meat and suffered from cardiac symptoms. In 2013, the results of the Horus study were published in the preeminent medical journal The Lancet and major cardiovascular journals.

In 2022, I was invited to join an extraordinary Zoom meeting by the anthropologist Hillard (Hilly) Kaplan, co-director of the Tsimane Health and Life History Project, and my friend of many years. I’m a physician, and in 2002, I had joined Kaplan and a small group of young anthropologists and Bolivian physicians in a project that would ultimately conduct one of the most logistically complex and comprehensive health assessments of any group of people in the world, a rare model of cooperative scientific effort across multiple disciplines and cultures.

Horus Group scientists who had found heart disease in mummies would join with the Tsimane Project and analyse CT scans of the hearts of the Tsimane, an Indigenous tribe of about 17,000 people living in the lowland Bolivian jungle. They would find almost no heart disease. What’s more, continuing research with the Tsimane shows rates of dementia among the lowest ever observed, and they have only minimal cognitive impairment with ageing.

Now, on the Zoom, I met Caleb (‘Tuck’) Finch, professor of gerontology at the University of Southern California. Finch has been studying the neurobiology of ageing, the evolution of the human life course and the causes of Alzheimer’s disease for most of his career. He had long known about the Horus Group and their mummy slides; he’d met Kaplan and knew about his findings on the Tsimane foragers too.

In 2014, at a gerontological sciences meeting, Finch had arranged to meet Kaplan and the cardiologist Greg Thomas, lead investigator of the Horus Group (whom I also met on the Zoom call). Thomas and Kaplan were giving back-to-back papers: Thomas was arguing that the mummy evidence suggested atherosclerosis was a fundamental feature of the biology of human ageing. Kaplan was contending that the Tsimane study showed little apparent evidence of heart disease.

Thomas was initially sceptical about talking to an anthropologist about heart disease, or its supposed lack. But: ‘I got the two together,’ Finch later told me, on a phone call, ‘and after two minutes they said: “We’ve gotta work together.”’ Their resulting study is a groundbreaking 2017 article in The Lancet, which says: ‘Despite a high infectious inflammatory burden, the Tsimane, a forager-horticulturalist population of the Bolivian Amazon with few coronary artery disease risk factors, have the lowest reported levels of coronary artery disease of any population recorded to date.’ In short, it appeared possible that coronary artery disease emerged, on a population-wide scale, from lifestyle, not our genes.

All these professional relationships and our intersecting work go way back. Kaplan and I have been friends for almost 40 years. In 1987, we were the first anthropologist and physician allowed to enter the interior cultural zone of Manú National Park in the Peruvian Amazon, a UNESCO Biosphere Reserve and World Heritage Site. Manú is almost 4.2 million acres of incredible biodiversity, extending from the rain-forested Andes to the Amazon basin in southeastern Peru. The people, fauna and flora living in the biosphere are ‘protected’ by UN covenant, and we were there to study the Machiguenga, a tribe with very limited previous contact.

We were a team of four: Kaplan, Michael Alvard, then an anthropology grad student, and my then wife Mary Daitz, an experienced nurse. Just getting there was an adventure in a 1952 Chevy truck piled high with gear, rambling over the Andes and down a muddy single-track road through the rainforest to the Madre de Dios, a tributary of the Amazon.

We hired a guide and Machiguenga translator who knew the river and its people.

On the bank of the Madre de Dios, we watched a felled log become a dugout canoe, powered by a small outboard motor, a peci-peci, which is what it sounds like. We peci-pecied upstream, from the Madre de Dios to the Manú, and then past red clay cliffs festooned with macaws and past giant river otters floating on their backs. We frequently got in the water with the piranhas to edge our canoe through log jams. We camped on the pristine oxbow beaches of the Manú, first chasing away 8- and 10-foot black caimans, and dreading having to go out to pee at night.

What were their family units like? Who did what, and how much time did they spend doing it?

The people living in the Manú biosphere had no idea what a doctor did, nor an anthropologist. I was conflicted – excited about the opportunity to help but concerned about whether we’d be doing more harm than good, about whether there would be any follow-up care. The Peruvian Ministry of Health was responsible for managing healthcare in its vast Amazon basin, but very few physicians ventured over the Andes. Would these people ever be vaccinated? If we found folks who had a communicable disease, like TB, what would we do? If we diagnosed diabetes, heart disease or malaria, what next, after we left?

Kaplan and Alvard’s work would centre on examining the life course of the Machiguenga. Kaplan had already lived, hunted and foraged with the Aché people of eastern Paraguay. Before getting his PhD in anthropology at the University of Utah, he’d earned a degree in communication from the University of Pennsylvania and a masters in anthropology from Columbia. He picked up languages easily, spoke excellent Spanish, and knew some basic phrases of Machiguenga, the language of the people we were heading to meet in the village of Tayakome, on the upper reaches of the Manú.

Kaplan wanted to learn what their family units were like. Who did what, and how much time did they spend doing it? How many children did women have on average? What was their nutritional status, their height and weight? Where and what did they hunt and fish, and did they share food and drink? What were the roles of grandparents?

Meanwhile, as a family doctor, I was seeing patients, and teaching residents and medical students at the University of New Mexico School of Medicine. I’d worked in a clinic for migrant farmworkers in California and helped organise rural clinics in northern New Mexico. I spoke reasonable Spanish, and had some experience treating typhoid, malaria and TB in Mexico.

On our fourth day on the Manú, we spotted Tayakome, the largest of the Machiguenga villages, sited high on a clay cliff. We were welcomed by a group of Machiguenga villagers. Word of our arrival had somehow travelled faster on the river than we’d done.

Tayakome is a village of extended family groups living in jungle clearings, in expertly constructed reed houses with thatched palm roofs and raised sleeping and eating platforms, providing good protection in the rainy season and some degree of safety from snakes and jaguars. Each family compound was separated by hundreds of yards but connected by trails.

We slept in our own little compound, in tents peered in at all hours by children and adults who shyly came to meet us. The Machiguenga are handsome people, adults and kids dressed in their traditional kushmas, simple gowns of rough, ivory-coloured, hand-spun jungle cotton.

The Machiguenga were gracious and kind, offering to share their plentiful fish and game with us; peccary (wild pig), smoked Amazon catfish big enough for several families to feast on, turtle eggs, wild bananas, chilies, and the omnipresent manioc and masato, a thick, milky beer, made from the manioc root, the tuberous cassava, the chief carbohydrate of Amazonia. We watched women make it, from digging up the long, potato-coloured root in their gardens, to peeling, chopping, masticating and spitting the communal mash into a large gourd, their saliva starting the fermentation process. We were offered masato on our arrival, and I drank it several times afterwards, until I was pretty sure that one of the women spitting in the bowl had tuberculosis. I later suspected two other people in the same family group might have TB, but I had no way of confirming my diagnosis.

We gave out wood paddles for stool samples, pantomiming the collection process to our chagrin and their amusement

I did physical exams on about 300 people living in Tayakome and Diamante, another village on the Manú, and was seeing a remarkably healthy group of people, infants to elders, generally fit, active and well-nourished. They were hunters, fishermen, farmers and foragers, had been forever, and they were good at it.

I never heard a heart murmur or recorded an elevated blood pressure. There were no obvious clinical cases of diabetes or chronic heart disease, but I did see several cases of leishmaniasis, an invasive skin infection caused by sandflea bites. Everyone was constantly attacked by murmurations of mosquitoes, and we treated lots of infected mosquito bites, including our own. Dental problems, including badly worn teeth in young women, perhaps from chewing manioc, were common. Older folks complained of arthritic hips, knees and low back pain, and observing their activity I understood why. They were grateful for aspirin and acetaminophen (Tylenol/paracetamol).

I’d lived and worked in rural Mexico where intestinal parasites were a problem, as they were here but I had no medication to treat them. We distributed vials and small wood paddles for collecting stool samples, pantomiming the collection process to our chagrin and their amusement. The samples arrived, day after day, deposited in a box by our tent by different family groups. A month later, on our return, I smuggled home 200 stool samples in the bottom of a duffle bag.

How could we best provide rudimentary medical care for geographically and culturally isolated people? Would they even want it? How would a community decide one way or the other? Who were the community leaders and potential influencers? Who were the traditional healers? What would be the role of the Peruvian Ministry of Health?

Although the Machiguenga had been in limited contact for some time, I had expected – considering the devastating disease history of contact on native peoples – that basic immunisations would be a primary concern, but no one had been vaccinated. Could we, as outsiders, suggest basic public health concepts like vaccines and latrines to keep their water supply safe? Working in Manú was public health at the limits, certainly a dilemma for the Peruvian government, and a worrying one for me. These were just some of the issues we talked about on the river and around our fire at night, swatting mosquitoes.

When I opened my duffle bag-full of stool samples for the microbiologist at the New Mexico State Scientific Laboratory, she was in parasite paradise. Almost all the samples contained five to seven different intestinal parasites, or helminths, such as tape worms, hook worms and whip worms. Was that the norm for other forager/horticulturist people? And what about heart disease, hypertension and diabetes? I’d expected to find some evidence of these common diseases but didn’t. Was there something about the Machiguenga lifestyle that somehow protected them from the chronic scourges of modernity?

Spending time with Kaplan, I found myself thinking about his big concept: that the evolution of the human life course could best be studied among the last people who still lived as our ancestors had.

To pursue the answer, Kaplan studied fertility patterns among the nomadic peoples who mix foraging with small-scale farming that he and other anthropologists had lived with, and developed complex mathematical models of parental investment. He looked at peoples’ regional biodiversity and the availability of nutritionally high-quality food. His research, along with many collaborators, has become seminal in the study of these societies.

It has also helped distinguish humans from other primates. Among our most unique characteristics, he counts our long life span, about 70 years for forager/horticulturalists; our long childhood dependence on parental support; and the familial contribution of grandparents and elders. The returns on parental and grandparent investment in children means increased familial productivity later in life, more hunters and farmers, a higher fertility rate, and an evolutionary self-sustaining society. And of course, all of us are dependent on access to nutritionally rich food, the energy that drives the whole process.

For the most part, they are living without market economies, healthcare or schools

There’s another important element in the evolution of our life course – disease. We now know that in addition to heart disease, Egyptian mummies had intestinal parasites, malaria, leishmaniasis, TB and smallpox – for starters.

In 2002, neither Kaplan nor I knew anything about the health of mummies but, to test his life course theory, a much larger forager population was needed. Kaplan asked me if I wanted to go to the Bolivian Amazon to visit the Tsimane, a group much like the Machiguenga, and a little easier to reach. I took a leave of absence from my practice and teaching.

There are about 17,000 Tsimane living in 80 scattered, lowland jungle communities east of the Andes, a vast territory along the Rio Maniqui and its tributaries. The majority of Tsimane and their neighbours, the Moseten, are foragers, hunters and fishermen, and for the most part they are living without market economies, healthcare or schools, although some of the Moseten and people living in villages closer to San Borja, a frontier town of around 17,000, were more acculturated. We’d be trying to assess their overall health status.

One of Kaplan’s former doctoral students, Michael Gurven, was then assistant professor of anthropology at the University of California, Santa Barbara, and had spent three months securing permission from the Tsimane Tribal Council for us to pursue the life course study. Most importantly, in return, we would do health assessments, and provide some limited primary medical care for the Tsimane. With funding from the National Science Foundation, Kaplan and Gurven assembled a team of Bolivian and US anthropology grad students and three young Bolivian physicians, all recent medical school graduates.

The anthropologists would be asking many of the same societal questions they had asked of other groups, like the Machiguenga in Manú: what makes a good hunter or fisherman or farmer or weaver? How do people spend their days? What is the social structure of the community? What, and how much, do they eat? How many children do they have? All the collected data would augment the life course study. The physicians would do their best at taking histories, translated from Tsimane to Spanish, listening to hearts and lungs, and treating basic problems as best we could with a combination of US and Bolivian medicines. All of us, living together with these people, would be trying to learn how their health and their life course interacted.

From our base in the frontier jungle town of San Borja, it was about 60 miles to the village of Cuvirene, but it took us seven hours in a vintage Ford truck, our team and our equipment piled in back. We picked up Tsimane people along the way: a hunter with a bow and long arrows, a peccary slung over his shoulders; women, old beyond their teenage years, with babies at the breast; in total, about 30 people crammed into our truck.

The village of Cuvirene in Bolivia was like Tayakome in Peru, with the same palm-thatched, elevated dwellings, but a bit more upscale with pots and plastic. Kids were stalking chickens with bows and arrows, and people could have been distant cousins, except they were wearing old soccer shirts instead of kushmas. There was a road to Cuvirene, but the main thoroughfare for the far-flung villages of the Tsimane is the nearby river, the Rio Maniqui, where canoes of families floated by to the same tune of the peci-peci.

In the morning, only women and children were around; the men had gone hunting. Alfredo Zelada, a Tsimane man, translated this information for us. He was a promotor de salud, a community health worker trained with other Spanish-speaking Tsimane in a one-month course in San Borja.

We heard reports of multiple intestinal parasites, but not heart murmurs, high blood pressure or diabetes

His first job was smoothing our way with the very frightened women and children who had never seen a group as white or gear laden as ourselves and, when the hunters returned, he quashed the rumour that we’d come to rape their women.

Later, Zelada spoke to the assembled community of perhaps 50 people. He explained why we’d come, and over the next week we were able to do health histories and physical exams on 160 people, practically the entire populations of Cuvirene and the neighbouring village of Aperecito. Zelada shuttled back and forth, translating for the anthropologists in the morning, and the four doctors taking histories in the afternoon. Kaplan told me Tsimane is a tough language to learn. It starts somewhere on the back palate and then whines out the nose, with a little reverse spin.

Very few Tsimane had been immunised. Like the Machiguenga in Peru, we saw chronic cases of dermatitis from infected insect bites, eye and ear infections in children and adults, and the widespread need for dental care. In the village of Aperecito, there were cases of pneumonia, and a man who we thought might have TB. We heard reports of multiple intestinal parasites, but we didn’t hear heart murmurs, record high blood pressure, or suspect anyone had diabetes.

A patient I saw, reportedly a great hunter, could no longer hunt because of a huge inguinal hernia dropping his scrotum halfway to his knees. Loops of herniated bowel gurgled in my stethoscope. I asked him if he would consider going to San Borja for an operation. He said yes, although Zelada and I wondered if he knew what we were talking about; but when we left Cuvirene, we brought him to San Borja, and the next day his hernia was repaired. The surgeon told me it was the biggest he’d ever seen.

We accomplished more than we expected. We viewed this as a shakedown trip, a chance for the team members to get to know one another, to work out kinks, and we’d talked about important next steps as the project continued. The plan was that Gurven and the anthropology graduate students and doctors would spend the next year living and working in about 12 different Tsimane communities. Immunisations, public health teaching, and training more Tsimane health workers were all top priorities, along with trying to do some basic lab studies, and all those expectations were in competition with limited grant funding.

Several months later, Kaplan went back to Cuvirene to check on the fledgling project. On his way back to San Borja, in the middle of the night on the same mud-slick jungle logging road, he was told that a Tsimane man had been shot and was dying. They were able to find the man at a campsite, alive, but with a bullet hole in the middle of his chest and a broken leg. Kaplan transported him to the hospital in San Borja, where the man was denied care because he had no money, but, even if he’d had money, the hospital had no functioning X-ray machine, so Kaplan paid for the man and a translator to be flown to Trinidad, a Bolivian city of around 130,000, which had one. Luckily, the bullet had lodged in his shoulder. He was treated and returned to his village.

The Tsimane weren’t getting any treatment or medical care because of poverty and racism, Kaplan told me: ‘They weren’t even getting to go to the hospital.’ So he called a meeting with the mayor of San Borja, the president of the Tsimane Council and the director of the hospital, and said: ‘Can we work together?’ Kaplan offered to give the hospital $1,000 for medicines, and the group signed a convenio, an initial agreement to provide some help for the Tsimane.

‘Wow! They’re looking like American and Canadian athletes’

The research groups’ name became the Tsimane Health and Life History Project, and today, 23 years later, Gurven is its co-director with Kaplan. Over the past two decades, the two of them have assembled a team of anthropologists, cardiologists, geneticists, neurologists, geriatricians, radiologists and graduate students to work on one of the most logistically complex but comprehensive health assessments of any group of people in the world.

With the support of the Tsimane Tribal Council, and with healthcare as a primary focus, Gurven, his graduate students and the Bolivian doctors gradually expanded their work among the far-flung Tsimane communities. Histories and physical exams were complemented by demographic interviews, and simple tests measuring overall fitness and nutritional health.

‘From the earliest data: normal heart exams, low blood pressures, which didn’t increase with age, low resting pulses, exercise step-tests, very little obesity. And from doing interviews,’ Gurven said on a Zoom call, ‘I was able to tell that people weren’t dropping dead from heart attacks, and I thought: wow! They’re looking like American and Canadian athletes.’

In 2006, Kaplan was able to hire a Bolivian biochemist to do standard tests like blood glucose screening for diabetes and cholesterol levels. The glucose levels were essentially normal, and the total cholesterol and LDL levels were low. Combine that data with a nutritious, junk-free jungle diet, an activity-demanding lifestyle, and, Kaplan said: ‘At that point, what we were trying to sell in grant proposals was good heart health.’

With funding from the US National Institute on Aging at the National Institutes of Health (NIH), they finally came up with an agreement with the Tsimane Council. In return for doing life history science in all the communities, they would help with healthcare and hospital costs, and, by 2010, roving medical teams were seeing people in about 50 villages.

Abinash Achrekar, a cardiologist and professor of medicine at the University of New Mexico, recalls Kaplan reaching out to his cardiology division. ‘He had a fairly simple but unusual request,’ Achrekar said. ‘Would cardiology faculty read a few hundred EKGs of the Tsimane people of Bolivia? I was intrigued by the request.’

‘We’ve only seen one heart attack in this population since we’ve been working with them in the last 12 years’

The EKGs in people aged over 45 were all normal, so they decided to do echocardiograms, soundwave images of the heart’s chambers and blood flow. Soon, Edhitt Cortez Linares, one of the young Bolivian physicians who had stayed on with the team, was trained as an echocardiographer and using portable machines right there in the jungle to do that work.

Kaplan realised he needed to get more clinical expertise to better evaluate the cardiovascular data and laboratory tests, like cholesterol. ‘That’s when we hooked up with Ben Trumble, a biological anthropologist at Arizona State, and Tuck Finch, and that’s when we really started working, writing papers on no blood pressure increase with ageing, and lipid profiles,’ he said. And that’s when, in 2014, Finch introduced Kaplan to Thomas of the Horus Group and their mummies.

Thomas’s team had already concluded that ‘atherosclerosis was ubiquitous, was part of human genetics.’ But the news from Bolivia was that the Tsimane didn’t have it, so the conclusion must be wrong.

By 2014, Thomas and his team had arrived in the Amazon to do some scans themselves.

Easier said than done. You could do an echocardiogram in the jungle, but instead Kaplan, Gurven and another physician, Daniel Eid Rodriguez, figured out the transportation logistics of bringing 700 Tsimane, 40 years and older, on a two-day trip to Trinidad, which had a CT machine. And bringing teams of radiologists and cardiologists to Trinidad to read the CT scans, looking for the tell-tale calcium deposits in hearts and coronary arteries.

‘There was just no calcium in people 60 years or older, and minimal calcium in people 70 and over. It was just dramatic!’ Thomas said.

In the 2017 Lancet paper, the Horus/Tsimane group looked at the CTs, lipid levels and inflammatory markers of the Tsimane, and compared them with data from almost 7,000 American participants in the Multi-Ethnic Study of Atherosclerosis (MESA), the longest-running study of cardiovascular disease in the US. The Tsimane hearts were clear winners, ‘like marathoners’, Thomas said. ‘We’ve only seen one heart attack in this population since we’ve been working with them in the last 12 years.’

I asked Thomas about the impact that the Tsimane findings had on his own patients. He said: ‘When we found heart disease in mummies, I told them they shouldn’t feel guilty about getting heart disease or having a heart attack, it’s part of human nature. That’s what I preached for a long time.’ And now, I asked? ‘Prevention works,’ he told me. ‘The amount of exercise the Tsimane do, which amounts to 17,000 steps a day for men and 16,000 for women (about 7-8 miles), and their diet which has 5 per cent saturated fat versus a Western diet of 15 per cent, and they do that by eating a lot of fish and wild animals. And you can’t be going down the street with a bow and arrows, but you can improve your diet and exercise for a lot of the day.’

I met Margaret Gatz on the Horus/Tsimane Zoom call, and again after she just returned from a visit to the Tsimane and the Moseten where she was observing assessments for dementia. Gatz, professor of psychology, gerontology and preventive medicine at the University of Southern California, and a widely published expert on depression and dementia in the elderly, was recruited by Finch to join the research group.

‘There’s very little dementia, and that would be consistent with not much heart disease,’ she told me. In fact, her study of more than 600 Tsimane and Moseten, conducted in 2022, found that their prevalence of dementia, particularly Alzheimer’s disease, is among the lowest in the world, and that’s consistent with their low coronary calcium levels and lipids, their activity levels and their healthy diet.

The researchers did find mild cognitive impairment consistent with other populations, however, and started seeing calcifications in the arteries of the brain. ‘We have this interesting contradiction between the heart, where we’re seeing virtually no calcification, and the brain, where it’s very prevalent and associated with neurological impairment,’ Kaplan said.

So, one of the next studies will be trying to figure that out, and Trumble will be working to that end. Over the next year, his main task will be helping to direct a staged, carefully coordinated convoy of more than 1,000 Tsimane and Moseten from their villages on another two-day trip to Trinidad, where a rotating team of neurologists, cardiologists and radiologists will examine them, and analyse CT scans of their brains, hearts and abdomens. On the way back, in San Borja, they’ll see a dentist for the first time, the results of their imaging will be available, explained and, for significant conditions, follow-up care arranged.

Could parasitic ‘inflammation’ in the Tsimane gut microbiome provide a cardio-protective role?

Care like treating the parasites – deja vu my duffle bag – that cause abdominal pain, diarrhoea, weight loss and anaemia, and are a tremendous burden of disease in poor countries. Two-thirds of Tsimane have them. In the Horus/Tsimane Group’s 2017 Lancet paper, although there was little evidence of coronary calcium and atherosclerosis, the Tsimane helminths (tape worms, whip worms, hook worms and others) were the primary cause of high levels of inflammation in lab tests.

And inflammation is the ‘Big Bang’ theory equivalent in cardiology. It is the pathological genesis of cardiovascular disease, priming the environment for cholesterol-laden plaque to block arteries. Inflammation was the Horus Group’s thinking when they found that mummies had parasites and other infections that could potentially lead to heart disease.

But could parasitic ‘inflammation’ in the Tsimane gut microbiome, along with their diet, abundant activity and good genes, somehow provide a cardio-protective role?

‘We’ve co-evolved with parasites for millions of years. They’re “old friends”,’ Trumble said. ‘Old friends’ is another name for the ‘hygiene hypothesis’ that suggests early childhood exposure to bacteria and parasites seems to protect against allergies, asthma and inflammatory diseases. ‘So, helminths burrow into your intestines and eat lipids out of your bloodstream before you get a chance to absorb them and, when we remove them, it causes shifts in immune function, like cytokines.’

Cytokines are proteins that moderate our immune responses. During COVID-19, ‘cytokine storms’ kicked immune systems into high gear, and the resulting systemic inflammation caused many deaths worldwide. But Trumble and his colleagues, and yet unpublished studies, suggest that the Tsimane, with their high parasite loads, already have a higher background of cytokines and a more active innate immune system. The idea is that they have an initial immune response that helps them get a jump on the virus. Although many Tsimane and Moseten got sick from COVID, there was only one reported death.

We’re witnessing the fast-forward evolution of a people’s health and life history, in real time

When we first met the Tsimane in 2002, I watched a hunter make an arrow, a six-foot reed shaft with a red-brown feather trimmed and tied with expert precision. Nowadays, Tsimane men must walk a week to hunt or fish for their families, because commercial logging, fishing, hunting and climate change have forever altered their landscape and lifestyle. A people who never depended on a market economy are now poor. New roads have brought cellphones, cigarettes, alcohol, STDs and racism.

‘I can say that the change is already huge,’ Rodriguez, the Bolivian physician, told me. ‘Now we are looking at a prevalence of hypertension close to 20 per cent and, when we started, it was below 5 per cent. At the beginning, we didn’t have cases of diabetes, and now we have many. It’s the same with obesity. They can no longer rely on their traditional food resources so, inevitably, they will end up in a modern lifestyle.’

In Massachusetts, the Framingham Heart Study (FHS) has been evaluating the health of our modern lifestyle over its 77 years of research and three generations of participants. The FHS first identified the risk factors for heart disease: hypertension, high cholesterol, obesity, smoking and physical inactivity, and, most importantly, how to prevent or treat these conditions. FHS research is now focused on stroke, dementias, genetics, and – holy shit! – the gut, our intestinal biome.

Perhaps one day we’ll see the two studies graphically merged; a blended portrait of our family tree, the evolution of the human life course and our diseases, from foragers to mummies to modern Massachusettsans.

History tells us that the Tsimane, and their neighbours the Moseten, are people in an inevitable transition, and what we’re witnessing is the fast-forward evolution of a people’s health and life history, but in real time. What does that mean for the Tsimane?

Maguin Gutierrez Cayuba is the president of the Gran Consejo Tsimane, the tribal chairman representing the Tsimane among Bolivian and South American Indigenous groups. On the phone, he explained in Spanish that he was hired by the project in 2002 to help the anthropologists with hunting and fishing research for their nutritional studies. He said that, over the years, the skills he’d learned, the communities and families he’d met, the grandparents he’d talked to, were the factors that influenced him to run for president. ‘Thanks to the project,’ he said, ‘I’ve been able to understand the key needs that my people, my community have, and gain their loyalty. The project needs to continue, and there are many young people from the Indigenous sector who are already being trained. I’ve always said that we are going to work in coordination for the good of all the communities.’

When I asked whether the Tsimane understood the outcomes of the health research, he told me: ‘Many people are surprised that this research is important. The concern is that the people who live near the city are often going to get sick, and the brothers who live deeper in the jungle are not. The brothers who live near the city are already suffering from diabetes.’

Trumble is optimistic that community education and early intervention can keep the Tsimane healthy. ‘The crown jewel of the Tsimane project is first understanding cardiovascular ageing and brain ageing, so we can see how many people are converting from being healthy to being unhealthy,’ he said. ‘Or are there some protective things that keep them from converting, and what are they? Then we can target these as interventions. I think it could be some combination of diet, physical activity and the immune environment.’

Limited Indigenous access to healthcare increases worse outcomes and reduces life expectancy by 20 years

The project is on its fourth year of a five-year NIH funding cycle, with hopes that the importance of the emerging research will prolong support. I asked Kaplan to sum up the project’s significance. ‘I’m a real believer in the discovery process,’ he said, ‘that we may actually have something important to offer. So I kind of see the importance of the project from a scientific point of view on two timeframes. One is what we can immediately contribute to the understanding of heart disease and arterial disease and brain diseases. And then, also, what can we leave for future researchers. These data will provide insights into fundamental human biology that you wouldn’t get from looking only at people in places like the United States and Europe.’

The World Health Organization is developing a Global Action Plan for the health of the world’s Indigenous peoples, around 6 per cent of the world’s population, whose limited access to healthcare substantially increases worse outcomes and reduces life expectancy by about 20 years.

Bolivia is near the bottom in Western Hemisphere health outcomes, but it’s one of very few countries to endorse universal healthcare coverage. The government’s goal is to provide free care for 50 per cent of underserved Bolivians. Perhaps, because of the Health and Life History Project, the Tsimane are more fortunate than many other Indigenous communities because they are generally healthy, and they are getting primary care and referral services, for now. Kaplan sees the project as a bridge to whatever comes next.

Wendell Berry, the poet and philosopher, wrote that ‘the community – in the fullest sense: a place and all its creatures, is the smallest unit of health, and to speak of the health of an isolated individual is a contradiction in terms.’ In a global sense, the Tsimane represent Berry’s smallest unit of health, and it’s our good fortune that they continue to allow us a mirror into our evolutionary past, and a model for our future wellbeing.