Brought to you by Cosmos Magazine and The Echo
Humans have adapted to extreme conditions to live in nearly every environment on Earth. The Haenyeo, a group of all-female divers from the Korean island of Jeju, dive without breathing equipment in frigid waters year-round.
New analysis has uncovered the behavioural and genetic changes that help these women survive the intense physiological stresses of free diving, even while pregnant.
‘Every day, they head out and get in the water, and that’s where they work all day,’ says Dr Melissa Ilardo, a geneticist and assistant professor of biomedical informatics at the University of Utah in the US.
‘I saw women over 80 diving off a boat before it even stopped moving.’
Haenyeo translates to ‘women of the sea.’ They dive up to 10m below the surface to harvest seaweed, abalone, sea urchins and other food for their communities. Though each dive only lasts for about 30 seconds at a time, the women spend 4-5 hours in the water each day.
Haenyeo begin training at around age 10 and continue for their entire lives, including during pregnancy. But the practice is waning, with most divers are now in their 60s and 70s.
‘Their incredible ability is written in their genes,’ says Ilardo.
Ilardo’s team compared the genomes of 30 Haenyeo divers to 30 non-Haenyeo people from Jeju and 31 people from mainland Korea.
They revealed that all Jeju residents, including the divers, were genetically distinct from individuals from mainland Korea. The island of Jeju is about 80km off the Korean peninsula and is relatively isolated.
‘We can essentially think of everyone from Jeju as either ‘diving Haenyeo’ or ‘non-diving Haenyeo,’ because their genetics are the same,’ says Ilardo.
The inhabitants of Jeju were found to carry a gene variant which has previously been associated with cold water tolerance and may make the divers less vulnerable to hypothermia.
Breath-hold diving limits the body’s oxygen supply and raises blood pressure. But Ilardo and her team found that the Haenyeo and other inhabitants of Jeju are more than 4 times more likely than mainland Koreans to have a genetic change associated with lower diastolic blood pressure while diving.
‘This association may reflect natural selection to mitigate the complications of diastolic hypertension experienced by female divers while diving through pregnancy,’ says Ilardo.
They speculate that the genetic change may help the Haenyeo avoid blood pressure conditions during pregnancy, such as preeclampsia which can be fatal.
‘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,’ says Ilardo.
The researchers hope that their discovery of a genetic difference linked to blood pressure will ultimately advance care for health conditions, like stroke, that are related to high blood pressure.
‘We’re really excited to learn more about how these genetic changes may be affecting the health of the broader population of Jeju,’ says Ilardo.
Intriguingly, Jeju Island has one of the lowest rates of stroke mortality in Korea, raising the possibility that the genetic change could help protect against stroke, she adds.
‘If we can more deeply characterise how those changes affect physiology, it could inspire the development of therapeutics to treat different conditions, such as hypertensive disorders of pregnancy and stroke,’ says Ilardo.
The research appears in the journal Cell Reports.
For four decades The Echo has printed the stories some people loved, some people hated, and some pretended not to read. If you want us to keep telling the truth, the real truth, not the sugar-coated version. We’ll need your support to keep the presses rolling. 
