Korea's Haenyeo Divers: How Genetic Evolution Gave Them Superpowers

A community of women from a South Korean island who engage in extensive free-diving might have undergone genetic changes. The research suggests possibilities for future medical breakthroughs.

Here’s what you should understand

An isolated island near Korea’s coastline houses a uniquely adapted human community. Known as “haenyeo” or “women of the sea,” these individuals possess genetic traits enabling extended diving sessions compared to others. It appears that the residents of this island carry specific genes which safeguard against fluctuations in blood pressure that could impact pregnancy.

A maritime cultural practice passed down through many generations might have endowed the inhabitants of a remote South Korean island with distinct genetic advantages—lower blood pressure and adaptations to cold temperatures—that could potentially aid scientists in crafting novel medical therapies in years to come.

The Haenyeo — literally "sea women" — divers live on Jeju Island, 53 miles (85 km) south of the South Korean mainland.

Starting from their teenage years, they undergo training for deep diving with the purpose of collecting sustenance from the ocean floor.

A research group spanning across the Atlantic has discovered that the Haenyeo’s centuries-old cultural tradition has assisted them in developing adaptations that allow them to dive for extended periods compared to other people.

However, they have similarly developed genetic traits that result in reduced blood pressure and improved tolerance to cold water.

If the research team’s conclusions hold true, then the Haenyeo would be among just two documented groups of humans who have, essentially, adapted biologically for diving.

The Haenyeo difference

Genomic analysis revealed that the Haenyeo have evolved at least three distinct characteristics.

The initial one is a non-genetic adaptation known as bradycardia, which refers to a slower than normal heart rate of less than 60 beats per minute.

This occurrence may be triggered by certain medical conditions but can also arise from cardiovascular exercises. During profound dives, bradycardia appears as well, which is part of an evolutionary adaptation known as the mammalian dive reflex.

"As soon as someone goes underwater, the act of holding their breath along with being submerged activates the mammalian dive reflex," explained Melissa Ann Ilardo, an expert in human biological adaptations at the University of Utah in the United States, who was leading the study.

"A component of that, is that your heart rate slows down."

This aids the mammal — specifically humans — in conserving oxygen, thereby providing more time before another breath becomes necessary.

Ilardo stated that "when compared to individuals sharing similar genetics, the trained divers exhibited a higher heart rate response."

This adaptation does not have a genetic foundation, and the researchers believe that anyone could acquire the same capability with extensive lifelong practice.

Other adaptations might be linked to successive stages of genetic evolution.

Deep down, the ocean's pressure narrows blood vessels, which restricts oxygen supply to the brain, lungs, and heart.

"Your body essentially communicates 'There isn’t much oxygen available, so we should preserve it for the organs that require it most,' " clarified Ilardo, noting additionally that blood pressure increases during profound dives to guarantee sufficient oxygen reaches vital organs.

Elevated blood pressure generally doesn’t pose a significant problem for most divers. However, the Haenyeo engage in deep-sea activities even during pregnancy—a time when hypertension can be risky.

Typically examined in women who suffer from sleep apnea, breath-holding has been linked to various pregnancy complications. According to Ilardo, for expectant mothers with sleep apnea, it seems like they inadvertently "take a dive" during their sleep.

However, it seems that the Haenyeo counteract this effect due to specific genetic changes. Ilardo's team contrasted the genome sequences of residents from Jeju Island with those from non-Jeju populations.

The research revealed that the people of Jeju Island descend from genetically unique groups. Additionally, it identified two evolutionary adaptations within this population: one mutation enhances their ability to tolerate cold temperatures, while another contributes to lower diastolic blood pressure.

Ilardo mentioned that evolution seemed to safeguard these pregnant women during dives. Their diastolic blood pressure didn’t rise as significantly compared to individuals with a differing genetic makeup, irrespective of their level of training.

Natural selection on a remote island

Charles Darwin, the British naturalist, was the first to observe evolutionary adaptations in unique environments among the finches of the Galapagos Islands.

Darwin noted the birds spread across these islands had different beak shapes and sizes. It suggested the various populations had evolved specific adaptations over time to help them feed on food sources specific to their island.

In a similar vein, the Jeju people show how humans can also evolve genetic adaptations, in this case as a response to long-standing marine-based cultural practices.

"Ilardo stated that at one time, diving was the primary economic driver for Jeju Island. They believe that in the past, virtually every person living on Jeju was involved in diving activities," he explained.

A a similar project that Ilardo was involved in discovered that the Bajau people of Southeast Asia have evolved larger spleens to store more oxygenated blood, enabling them to remain submerged without breathing for extended durations.

Previous studies have examined various cultures located in regions such as Tibet, Ethiopia, and the Andes, where populations have developed distinct genetic adaptations allowing them to thrive at elevated heights. For instance, the Quechua people from Peru and individuals in Tibet carry differing variations of a specific gene; however, these changes appear to grant an enhanced ability to tolerate low-oxygen environments characteristic of higher elevations.

Ilardo hopes to expand this research to other diving cultures around the world and potentially compare these with people living at high altitudes. This could also lead to new medical therapies.

"Jeju has one of the lowest rates of stroke mortality in all of Korea, so it's interesting to think about the gene that's been evolving, influences the actual physiology of the blood vessels.

"Maybe that [gene mutation] has a protective effect that could be used, in theory, to develop therapeutics to treat stroke in people all over the world."

Sources

Functional EPAS1 / HIF2A missense variant is associated with hematocrit in Andean highlanders Adaptations in Genetics and Training Among Jeju Island's Haenyeo Divers, South Korea

Edited by Zulfikar Abbany

Author: Matthew Ward Agius

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