The Haenyeo divers of Jeju Island, South Korea, stand as a remarkable example of human adaptation to extreme environmental conditions, combining both genetic inheritance and lifelong training to perform breath-hold diving in frigid waters. These all-female divers, who have been practicing their craft for generations, possess extraordinary physiological capabilities that allow them to dive repeatedly without modern breathing apparatus, even during pregnancy. A recent study published in the journal Cell Reports uncovers the complex interplay between genetics and training that underpins the Haenyeo’s enduring abilities, offering new insights into human physiological adaptation and evolutionary biology.
For centuries, Haenyeo, literally "women of the sea," have harvested seafood from the depths around Jeju Island, diving to depths that challenge most untrained individuals. This traditional practice involves synchronized social groups, with divers beginning their training around the age of ten and continuing into advanced age. Their expertise is not merely cultural but deeply physiological; they endure cold, exert physical effort underwater, and maintain control over their cardiovascular and respiratory systems under duress. Understanding whether these capacities arise primarily from genetic adaptations, environmental pressures, or extensive training was the central question motivating the latest research.
The investigative team, led by geneticist Melissa Ilardo from the University of Utah, undertook a comprehensive experimental study to differentiate inherited traits from acquired skills among the Haenyeo. The study involved 30 Haenyeo divers, 30 non-diving residents from Jeju, and 31 individuals from mainland Korea, all matched for age with an average of 65 years. Participants underwent physiological testing during simulated dives, which involved breath-holding and facial immersion in cold water, recreating the diving reflex in controlled laboratory conditions while monitoring heart rate and blood pressure responses.
Results from these experiments revealed that Haenyeo divers exhibited a significantly greater reduction in heart rate—an average decrease of 18.8 beats per minute—compared to the non-diving Jeju residents, who saw a 12.6 bpm drop. This pronounced bradycardia is a classic component of the diving reflex, a physiological response that conserves oxygen by slowing the heart and redirecting blood flow to vital organs. Importantly, because the genetic background of Jeju residents was homogeneous regardless of diving status, the enhanced bradycardia observed in Haenyeo likely results from extensive training and repeated exposure to diving rather than inherited traits.
Genomic analysis further deepened understanding by comparing the genetic makeup of the groups. Jeju Islanders, including both divers and non-divers, were genetically distinct from individuals of mainland Korea, indicating a shared ancestral gene pool specific to Jeju. Within this population, however, researchers identified two notable gene variants present predominantly among the Haenyeo. One variant is linked to increased tolerance to cold environments, providing a genetic mechanism for resistance to hypothermia in the icy waters where these divers operate. The other variant correlates with reduced diastolic blood pressure, a discovery with intriguing implications given the cardiovascular stresses imposed by diving and pregnancy.
The presence of the gene variant associated with lowered diastolic blood pressure in 33% of Jeju participants compared to only 7% of mainland Koreans suggests natural selection may be at work to offset hypertensive risks in female divers. This is especially compelling because Haenyeo women routinely dive during pregnancy, when vascular health is critical. The parallels drawn to the Bajau people—a well-known traditional diving group from Southeast Asia—underscore a potential evolutionary trend where reproductive factors drive genetic adaptations related to diving lifestyles.
Physiologically, the diving reflex observed in Haenyeo is a sophisticated survival adaptation. Bradycardia reduces oxygen consumption, while peripheral vasoconstriction prioritizes blood flow to vital organs such as the brain and heart. The Haenyeo’s ability to amplify this reflex more than other Jeju residents likely contributes to prolonged underwater endurance and mitigates the risks associated with repetitive aquatic foraging. This integration of environmental, genetic, and learned components creates a compelling blueprint for understanding human plasticity and adaptation.
This study not only illuminates the physiology and genetics of the Haenyeo but also opens new avenues for biomedical research. Insights into cold tolerance and cardiovascular regulation could inform the development of novel therapies targeting hypertensive disorders and ischemic conditions related to oxygen deprivation. The researchers highlight the value of studying traditional populations like the Haenyeo as natural experiments in human biology, where evolutionary forces and cultural practices intersect in unique ways.
By combining genomic tools with detailed physiological assays, the research team successfully teased apart the contributions of training versus genetic background in shaping the divers’ abilities. The training-induced enhancement of the diving reflex, manifested in the more pronounced bradycardia of Haenyeo, represents a striking example of physiological plasticity. Meanwhile, the genetic variants associated with blood pressure regulation and cold adaptation illustrate how natural selection can facilitate long-term adjustments in isolated populations subjected to extreme environmental challenges.
Ultimately, the story of the Haenyeo challenges our understanding of human limits. Women diving to great depths without breathing gear, even while pregnant, defy conventional expectations of human physiology. Their story is a testament to the power of adaptation at both the genetic and behavioral level, intertwining biology and culture in a way rarely documented outside anthropology and evolutionary genomics.
The research also holds broader implications for understanding how human populations evolve in response to environmental pressures. The combination of physiological training effects and genetic evolution seen in the Haenyeo may be mirrored in other specialized groups worldwide, adapting to unique ecological niches. Exploring these adaptations provides a window into the dynamic relationship between environment, culture, and genetics in shaping human physiology.
Future investigations will look to expand on these findings by examining how these genetic variants influence health outcomes within the broader Jeju population. Researchers speculate that uncovering the molecular pathways involved may inspire therapeutic innovations, especially in treating hypertensive complications in pregnancy or stroke. As such, the Haenyeo represent not only a cultural icon but also a valuable biological resource for modern medicine and evolutionary science.
In summary, the Haenyeo of Jeju embody a remarkable integration of genetic evolution and lifelong training, enabling extraordinary breath-hold diving performance in extreme environments. Their enhanced diving reflex results from years of repeated practice, while key genetic adaptations provide physiological resilience to cold and cardiovascular stress. This dual-model of adaptation offers a powerful framework for understanding human evolution in the context of traditional subsistence lifestyles and opens new horizons for medical research.
Subject of Research: People
Article Title: Genetic and Training Adaptations in the Haenyeo Divers of Jeju, Korea
News Publication Date: 2-May-2025
Web References: http://dx.doi.org/10.1016/j.celrep.2025.115577
References: Aguilar-Gómez et al., “Genetic and training adaptations in the Haenyeo divers of Jeju, Korea.” Cell Reports
Image Credits: Melissa Ilardo
Keywords: Human physiology, Genome diversity, Adaptive evolution, Pregnancy, Social research, Hypertension, Natural populations, Seawater, Respiration, Genetic variation, Heart rate, Genomic analysis
