South Korea’s women of the sea – an evolutionary phenomenon

They don’t mind cold water, wind or high waves. Haenyeo, or women of the sea, from Korea’s Jeju Island, have surprisingly adapted to diving as deep as 20 meters for food. How is this possible? Scientists have confirmed apparent adaptive changes in their DNA.

Haenyeo’s long-standing tradition

Jeju is South Korea’s largest island, located nearly 83 kilometers south of the mainland. It is inhabited by 678,000 citizens, has its own language and unique traditions related to the sea. As early as a thousand years ago, local residents began to toil to extract from the depths sea cucumbers, seaweed, oysters, octopus and, above all, abalone, a snail considered a unique delicacy.

Initially, the difficult fishing was handled exclusively by men – and for good reason. The sea currents can be very strong, the water temperature is low, and the abalone are so firmly planted on the stone bottom that it takes quite a bit of force to pull them off. Sharp lava rocks, poisonous jellyfish and occasionally even sharks are also a threat.

Despite these challenges, Jeju women began accompanying men in their fishing as early as the 17th century, and in the following century they completely dominated the profession. Thus was born the tradition of Haenyeo, or women of the sea, inscribed on UNESCO’s Representative List of Intangible Cultural Heritage of Humanity in 2016.

Korean women of the sea

Haenyeo go out to sea regardless of the weather. Today they use neoprene wetsuits, but as recently as 50 years ago they were diving in thin cotton suits. An indispensable part of their equipment is also a tewak, a drift buoy at work to which a fishing net is attached.

Women of the sea do not use oxygen cylinders. They usually work for about an hour, regularly holding their breath for 1-2 minutes and diving several meters into the sea. This strain of lowering body temperature and slowing heart rate while raising blood pressure would cause most adults to faint. However, the Haenyeo return to work after a break, often spending several hours a day underwater. The extent and amount of fishing is determined within the local community, a great example of sustainable hunting practices.

Learning this unusual craft traditionally begins at age 11, and lessons are offered by two specialized schools on Jeju Island. Girls dive first near the shore, gradually getting used to greater depths and holding their breath longer. It takes three years to master the technique, and five to become an expert.

For centuries, diving has continued even into the final weeks of pregnancy, although it significantly increases the risk of complications, such as life-threatening pre-eclampsia for mother and baby. Today, most Haenyeo are over 60 years old, and new adepts are beginning to be scarce, raising questions about the future of women of the sea. The UNESCO recognition is one of the measures to maintain the unique tradition from Jeju Island.

DNA altered by the sea

Scientists studying the seafaring women found a surprising tolerance to cold and an increase in blood carbon dioxide levels, typical of diving. The cause was initially suspected to be an enlarged spleen observed in traditional divers from the Philippines, Indonesia and Malaysia. This is because the spleen is tasked with filtering and storing blood, and shrinks extensively in the apneic state to help transport oxygen in the body. The larger the spleen, the more pronounced this effect is.

Seafaring women from Jeju, however, appear to benefit from other adaptations. To get to the bottom of them, a US-Korean research team analyzed the genome of 30 Haenyeo, 30 non-diving women from Jeju and 30 Seoul residents. It turned out that the key to explaining the mystery is a specific gene variant that determines permanently reduced diastolic pressure (by 10 mmHg compared to the general population). Variations were also discovered in genes responsible for the number of red blood cells and sensitivity to cold and pain.

According to Melissa Ilardo, the lead investigator of the study in question, the results of which were published May 2, 2025 in the journal Cell Report, the adaptation of a gene associated with blood pressure reduction is clear evidence of a physiological attempt to protect Haenyeo and their unborn children from the disastrous effects of prolonged breath-holding. The altered DNA has been passed down from generation to generation and is also detected today in non-diving female residents of Jeju Island.

An extraordinary workout for body and mind

Gene modification, most likely related to diving during pregnancy, only partially explains Haenyeo’s unusual physiological adaptations. According to the scientists, the women of the sea also benefit from skills passed down between generations and long years of experience in the cool sea water. Their organisms have surprisingly adapted to conditions that are not natural to humans.

Unfortunately, back in the 1960s there were about 20,000 women of the sea in Korea – today there are only about 2,500 left. Despite support from the South Korean government and increased media attention in recent years (including a 2024 documentary film directed by Sue Kim called The Last of the Sea Women ), there are not many willing divers among today’s Jeju residents. Today’s Haenyeo generation may therefore be the last.

MAIN PHOTO: Brian Miller/Flickr