A new study has presented evidence of both genetic adaptation and physiological changes among the Haenyeo, a unique group of women in South Korea’s Jeju Island known for diving up to 10 m underwater and up to seven hours a day to collect shellfish.
“In a society where established traditions have historically shaped gender roles, the Jeju-Haenyeo culture has emerged as an exceptional phenomenon,” the UNESCO said after including the community in its ‘Intangible Cultural Heritage’ list in 2016.
The genetic variant identified in the study may reduce pregnancy-associated hypertension risks, according to the researchers. The findings were published in the journal Cell Reports.
The researchers explored whether long-term diving practice and natural selection have shaped distinct traits in this community, particularly with respect to bradycardia (the slowing of heart rate), blood pressure regulation, and genetic variants associated with cold tolerance and pregnancy-related cardiovascular stress.
The researchers studied 91 women divided into three groups: 30 Haenyeo divers from Jeju, 30 non-diving Jeju ‘controls’, and 31 non-diving Seoul ‘controls’. The physiological data collected included spleen volume (using ultrasound), haematological parameters like hemoglobin and hematocrit levels, and cardiovascular responses during a simulated dive (immersing one’s face in cold water while holding breath).
Haenyeo divers were found to be more bradycardic during simulated dives than both control groups, which the researchers said suggested a robust diving reflex likely due to training. This said, the individuals’ spleen sizes were not significantly different between Haenyeo and non-Haenyeo Jeju women — even though both groups had larger spleens than the participants from Seoul. This, the researchers argued, reflected regional factors rather than genetic adaptation.
The Haenyeo and Jeju controls also had higher diastolic blood pressure than the Seoul participants across the baseline, dive, and recovery periods. The difference persisted even after the researchers adjusted for confounding variables, indicating a potential adaptive feature that enhanced the force that pumped blood to the brain during dives. The systolic pressure remained unchanged, however.
With whole-genome sequencing of 84 individuals from the cohort, the researchers confirmed that Jeju Island residents — both Haenyeo and non-Haenyeo — are genetically distinct from mainland Koreans. They estimated the populations began to diverge around 5,000-7,000 years ago.
Finally, the team used the tools of population genetics to identify several gene variants strongly associated with diastolic blood pressure during diving. One in particular, called rs66930627, was significantly more common in Jeju residents and was linked to lower diastolic pressure, a trait they may have evolved to reduce the risk of hypertension during pregnancy.
The team also found that this variant correlated with changes in the expression levels of some other genes with known roles in immune modulation and hypertension. According to the researchers, this association supported their hypothesis that natural selection among the Haenyeo may have targeted the rs66930627 variant to reduce the risk of preeclampsia in diving pregnant women.
“The Haenyeo are amazing, and their incredible ability is written in their genes,” University of Utah geneticist and study coauthor Melissa Ilardo said in a release. “The fact that women are diving through their pregnancy, which is a really tough thing to do, has actually influenced an entire island’s people.”
Published – May 06, 2025 09:08 am IST