Indonesian Divers Have Evolved Large Spleens To Stay Underwater Longer

Posted: Apr 22 2018, 11:07am CDT | by , Updated: Apr 22 2018, 1:33pm CDT, in News | Latest Science News

 
Indonesian Divers have Evolved Large Spleens to Stay Underwater Longer
Credit: Melissa Ilardo

This is the first time a genetic adaptation to diving has been identified in humans

Bajau people from Indonesia possess remarkable diving abilities. They can dive to a depth of 230 feet and stay underwater as long as 13 minutes, which is far beyond an average human’s capacity. It turns out that these indigenous people have bigger spleens which enable them to hold their breath much longer than usual. This is the first time a genetic adaptation to diving has been identified in humans.

The spleen is an organ that is located under the ribcage. It plays an important role in enabling humans to stay underwater for prolonged periods but the relationship between spleen size and endurance for free dive in the ocean has never been examined before. The spleen stores oxygen-rich red blood cells and releases them into the bloodstream for performing basic body functions during long dives. When researchers took genetic samples and conducted ultrasound scans on the spleens from the Bajau people and their non-diving neighboring group, they found that the former group actually has enlarged spleens. The results showed that the Bajau have a spleen size 50% larger than the other group that can help explain their extreme diving prowess.

"We can't really make experiments in humans, where we expose people to new conditions and have controlled genetic experiments in the same way we can do in fruit flies and mice. But nature has made experiments for us that tell us how humans react and adapt genetically to a whole new set of physiological conditions so that we can explore and learn much more about the interaction between genetics and physiology." Rasmus Nielsen, a professor of integrative biology at the University of California at Berkeley said in a statement.

Bajau, also known as sea nomads, live around the islands of Indonesia. They spend much of their day underwater using spears and other traditional equipment to collect fish and shellfish and they have been doing this for more than 1000 years. Bajau people have possibly evolved larger spleens as a result of their extreme lifestyle and these physical and genetic changes have enabled them to dive longer and deeper.

"We believe that in the Bajau they have an adaptation that increases Thyroid hormone levels and therefore increases their spleen size," said lead researcher Melissa Ilardo from the University of Copenhagen. "It's been shown in mice that thyroid hormones and spleen size are connected. If you genetically alter mice to have an absence of the thyroid hormone T4, their spleen size is drastically reduced, but this effect is actually reversible with an injection of T4."

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