The Bajau, often known as “sea nomads,” have spent over 1,000 years at sea, living on miniature houseboats that float in the waterways of Indonesia, Malaysia, and the Philippines. They used to only come ashore to trade for food or to seek refuge from storms. Free diving to depths of over 230 feet is how they acquire their food, without wetsuits or flippers, relying only on homemade wooden goggles and spearguns. They live off the things they catch inside. Sometimes, at an early age they even rupture their own eardrums to make diving easier.
According to a new study, scientists have discovered a genetic abnormality that allows them to dive far better than everyday people. It seems like they have developed exceptionally large spleens – 50 percent bigger than those of the Saluan, a neighboring group who barely interact with the sea. This permits them to utilize oxygen more effectively, allowing them to stay underwater for longer periods of time. The Bajau tribe’s genetic mutation is regarded to be the first example of humans changing their bodies to make them more adapted to deep diving.
When the body is submerged in cold water for even brief periods of time, the spleen plays a critical part in the “human dive response,” which puts the body into survival mode. The heart rate lowers, blood is diverted to the vital organs, and the spleen contracts to inject oxygenated red blood cells into the circulation when the diving response kicks in. The constriction of the spleen can increase oxygen levels in the body by 9%.
Scientists looked for genes with variants that are more common in the Bajau than in the other populations—a sign of natural selection at work. And they found several contenders. One gene, known as PDE10A, stood out. It does many things, but it’s especially active in the thyroid gland, and controls the release of hormones. The version of PDE10A that’s common in the Bajau is associated with higher levels of thyroid hormones, and those hormones, in turn, make spleens grow bigger.
Another candidate, FAM178B, influences the levels of carbon dioxide in the blood—which is also an important factor to control when holding one’s breath. The version of FAM178B that’s common in the Bajau seems to have come from the Denisovans, a group of ancient hominids who lived in Asia. It’s clear that when modern humans entered Asia, they entangled with Denisovans and inherited some of their DNA. One Denisovan gene provides modern Tibetans with a crucial adaptation that allows them to survive at high altitudes. It’s possible that another gives the Bajau an advantage underwater.
These discoveries might have important medical implications. Several disorders, including strokes and heart attacks, starve the body of oxygen, so the genetic tricks that help the Bajau thrive underwater might inspire new ways of protecting patients on dry land.
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