On the Korean island of Jeju, an extraordinary group of women push the limits of human endurance. Known as the Haenyeo, or “women of the sea,” these all-female divers plunge into icy waters year-round without oxygen tanks—even while pregnant.
A new study published in the journal Cell Reports reveals that the Haenyeo’s legendary resilience stems from both intense lifelong training and genetic adaptations that help them survive the brutal conditions beneath the waves.
“We think that natural selection created a protective effect for women who dive while they’re pregnant, and that this effect derives from differences in how blood vessels respond to changes in blood pressure,” study author Melissa Ilardo, a geneticist at the University of Utah, told the Debrief. “Therefore, we think that the implications of this could be profound—this might be something we could use to develop treatments for high blood pressure-related conditions, including those that affect pregnancy outcomes, or even conditions like stroke. Imagine if evolution gave us the answer to protecting everyone from stroke?”
A Diver Defying Cold
Scientists have long marveled at the Haenyeo’s ability to dive to impressive depths and hold their breath for minutes at a time, often into their 70s and beyond.
Curious to understand how they achieved such feats, researchers compared the heart rates, blood pressure, and genetic makeup of 30 Haenyeo divers to non-divers from Jeju and women from mainland Korea, all around the same average age of 65.
The results were stunning. While everyone experienced a slowed heart rate during a “simulated dive,” where participants submerged their faces in bowls of cold water, the Haenyeo’s heart rates dropped dramatically more.
“Because the Haenyeo have been diving for a very long time, their heart rate has been trained to drop more,” explained Ilardo. “This was something we could actually visually see — we had one diver whose heart rate dropped by over 40 beats per minute in less than 15 seconds.”
Beyond training, genetics also played a crucial role. DNA analysis revealed that Jeju residents, whether divers or not, were genetically distinct from mainland Koreans, suggesting a shared ancestral background on the island. Yet, two critical genetic variants were far more common among Jeju residents, possibly giving the Haenyeo an edge: one gene associated with cold tolerance and another linked to lower diastolic blood pressure, which may protect women who dive while pregnant.
A Legacy of Strength and Grace
For Ilardo, the project was deeply personal. “Since working with the Bajau in my PhD, I have been passionate about working with groups of people who have deep, meaningful connections with the sea,” she said. “After learning more about the Haenyeo, I was enthralled. Not only are they divers, but they’re all women. It was such an exciting possibility to get to connect with this group.”
She didn’t expect to be so impacted by the divers’ spirit and character during her research.
“What surprised me most was this incredible balance they manage between being sweet, feminine ‘halmeoni’ (a Korean word for grandmother that is used endearingly), but also some of the strongest and most capable divers I’ve ever seen,” she added. “I saw divers in their late 70s jump off a boat for a day of diving before the boat stopped moving. I could go on for days about how impressive they are!”
Gaining the Haenyeo’s trust was no small task. Ilardo credits Joo Young Lee, her collaborator at Seoul National University, for forging a bond with the community over more than a decade. Thanks to that relationship, the divers were open to participating in the study, though they had some good-natured skepticism.
“The one aspect of the study they were not impressed with was the simulated dives — after a lifetime of diving in the open ocean they found it a bit ridiculous to call sticking your face in a bowl of water ‘diving’,” Ilardo added. “But they were still interested and curious, and found the results interesting when we went back to share what we found.”
A Diver’s Guide to Human Evolution
The study reveals how the Haenyeo have adapted to their environment, opening up exciting possibilities for modern medicine. By better understanding the Haenyeo’s natural resistance to cold and blood pressure adaptations, researchers hope to uncover clues that could lead to new treatments for hypertension, pregnancy-related cardiovascular issues, and even stroke.
“Similarly, understanding the nature of the Haenyeo’s well-established cold tolerance could have implications for human performance or medical issues around circulation,” Ilardo said. “We don’t know what we don’t know, and this kind of basic science could be transformative for advancing medical fields beyond what we even realize with the data we have.”
The work is far from over. Ilardo hopes to continue collaborating with the Haenyeo and studying other traditional diving populations worldwide.
“There is a lot more work that we can do to better understand how exactly this adaptation is affecting diving and what influence it has on the population of Jeju more broadly,” she says. “I will continue to work with the Haenyeo for as long as they’re happy to keep working with me!”
Kenna Hughes-Castleberry is a freelance science journalist and staff writer at The Debrief. Follow and connect with her on BlueSky or contact her via email at kenna@thedebrief.org