A tribe of Indonesian “fish people” have evolved extra large spleens that enable them to free dive to incredible depths.
The genetic change discovered in the Bajau tribe is the first known example of a human adaptation to deep diving.
For more than 1,000 years, the Bajau — known as “Sea Nomads” — have wandered the seas of southern Asia in houseboats, catching fish by free diving with spears.
Now settled around the islands of Indonesia, they are famous for their extraordinary breath-holding ability.
Members of the tribe can dive up to 230-feet aided by nothing more than a set of weights and a pair of wooden goggles.
The spleen plays a key role in the “human dive response” that puts the body in survival mode when it is submerged in cold water for even brief amounts of time.
As the dive response kicks in, heart rate slows, blood is directed to the vital organs and the spleen contracts to inject oxygenated red blood cells into the circulation.
Spleen contraction can boost oxygen levels in the body by nine percent.
The new study found that the spleens of the Bajau people are 50 percent larger than those of their land-dwelling neighbors, the Saluan.
Scientist Melissa Ilardo, from Cambridge University, investigated the nomadic tribes folk.
She said: “There’s not a lot of information out there about human spleens in terms of physiology and genetics, but we know that deep-diving seals, like the Weddell seal, have disproportionately large spleens.
“I thought that if selection acted on the seals to give them larger spleens, it could potentially do the same in humans.”
Ilardo spent several months in Jaya Bakti, Indonesia, taking genetic samples and conducting ultrasound scans of people from the Bajau and Saluan tribes.
The evidence showed that Bajau spleens were permanently enlarged and did not get bigger simply as a response to diving.
Because the Bajau do not dive competitively, it is uncertain precisely how long they can remain underwater. One of the tribe members told Ilardo that he once dove for 13 minutes.
The study, published in the journal Cell, may help scientists to understand acute hypoxia, a condition in which body tissues experience a rapid loss of oxygen and is a leading cause of complications in emergency care.
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