< The all-female free divers of Jeju Island have a 'superpower' in their genes

JUANA SUMMERS, HOST:

The haenyeo are a group of South Korean women, mostly elderly, who dive in frigid ocean waters almost every day to fish. A new study reveals the adaptations that make that superpower possible. NPR science reporter Ari Daniel has more.

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ARI DANIEL, BYLINE: In this video, a motorboat chugs along near Jeju, an island some 50, 60 miles off the coast of South Korea. Before the vessel even comes to a stop, an older woman in a wet suit, fins and mask steps into the water.

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DANIEL: Two others follow her.

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DANIEL: These women belong to a long line of female free divers on Jeju Island called the haenyeo, who rely on nothing more than holding their breath to stay underwater for as long as two or three minutes at a time. They swim off, each with a net bag in tow, to collect seafood to eat and sell.

MELISSA ILARDO: Things like abalone, sea urchins, you know, harvest seaweed sometimes.

DANIEL: Melissa Ilardo is an evolutionary geneticist at the University of Utah. She recorded that video of the haenyeo, who routinely dive in waters that she says are 50 degrees at best.

ILARDO: One of the first times I was there, it was snowing. They said, as long as there's not a risk that they're going to be blown away to sea, then they still go out in the water, no matter how cold it is.

DANIEL: The women start diving as girls and continue well into old age across all of life's milestones. Diana Aguilar Gomez is a population geneticist currently at UCLA.

DIANA AGUILAR GOMEZ: They dive throughout their whole pregnancy. They say they just dive until basically before they give birth.

ILARDO: And then they were back in the water three days later.

AGUILAR GOMEZ: Yeah, it's amazing.

DANIEL: The question that Melissa Ilardo had was how the haenyeo are capable of enduring such an extreme lifestyle.

ILARDO: How evolution might have shaped the haenyeo to be better divers, to dive more safely, to dive for longer.

DANIEL: So she decided to compare the haenyeo to other elderly women on the island who aren't divers but have a similar genetic background, and to still others off-island who aren't related - about 30 in each group. But here's the thing...

ILARDO: You can't take 70-year-old women who have never been diving and, you know, throw them in the open ocean.

DANIEL: Fortunately, there's a workaround - a simulated dive.

ILARDO: You hold your breath and put your face in a bowl full of cold water, and your body responds as if you're diving.

DANIEL: The haenyeo found it a little silly, but their response was clear. Their heart rates fell by about 50% more than their nondiving peers.

ILARDO: We had one diver whose heart rate dropped over 40 beats per minute in 15 seconds.

DANIEL: Ilardo says the haenyeo response is due to a lifetime of training - classic physiological adaptation. Next, the researchers took saliva samples to look for genetic differences. Everyone from Jeju, both the haenyeo and the nondivers, had basically the same genes.

ILARDO: What this suggests is that everybody in Jeju has an equally likely chance of being a descendant of a diver.

DANIEL: Two genes stood out. The first was one that seems to be related to cold tolerance.

ILARDO: Maybe that protects them from hypothermia.

DANIEL: The second gene was associated with blood pressure, says Diana Aguilar Gomez, likely connected to blood vessel structure and function.

AGUILAR GOMEZ: Diving increases your blood pressure, and, particularly through pregnancy, that can be very dangerous. It can increase your risk for preeclampsia.

DANIEL: And other potentially life-threatening complications.

AGUILAR GOMEZ: Even if you didn't die, like, probably women that were protected against this would be more likely to have more children.

DANIEL: And more likely to pass their genes along. Melissa Ilardo thinks the low stroke mortality on Jeju Island could be related to this second protective gene.

ILARDO: Wouldn't it be amazing if, by studying divers in Korea, we can translate these findings to develop a therapeutic that protects people from stroke around the world?

DANIEL: The results are published in the journal Cell Reports. Stephen Cheung studies extreme physiology at Brock University in Canada. He wasn't involved in the research, which he finds fascinating.

STEPHEN CHEUNG: By pushing the body to its limits, we get a better sense of where those limits are but also just what the human body is capable of.

DANIEL: Melissa Ilardo says we have much to learn from the haenyeo and what makes them, in her words, extraordinary. Ari Daniel, NPR News.

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