How Asia’s Super Divers Evolved for a Life At Sea
Scientists are starting to uncover the genetic basis of the Bajau people’s incredible breath-holding abilities.
Sometimes known as “sea nomads,” the Bajau have lived at sea for more than 1,000 years, on small houseboats that float in the waters off Indonesia, Malaysia, and the Philippines. Traditionally, they came ashore only to trade for supplies or to shelter from storms. They collect their food by free diving to depths of more than 230 feet. They have no wet suits or flippers, and use only wooden goggles and spearguns of their own making. Sometimes, they rupture their own eardrums at an early age to make diving easier.
Not all of them dive; some avoid it entirely. But those who do take the skill to an extreme. Each day, they’ll spend more than five hours underwater, capturing between two and 18 pounds of fish and octopuses. The average dive lasts for just half a minute, but the Bajau can hold their breath for far longer. In the clip below, from the BBC documentary Human Planet, a man named Sulbin stays underwater for almost three minutes. “I focus my mind on breathing,” he told the BBC. “I only dive once I’m totally relaxed.”
The spleen acts as a warehouse for oxygen-carrying red blood cells. When mammals hold their breath, the spleen contracts, expelling those cells and boosting oxygen levels by up to 10 percent. For that reason, the best competition free divers tend to have the largest spleens, as do the deepest-diving seals. It’s even possible to train your spleen: Erika Schagatay, from Mid Sweden University, found that after climbing Mount Everest, mountaineers empty more of their spleens while holding their breath than they could before.
But Bajau spleens aren’t big just because of training. Ilardo and her team, led by Eske Willerslev and Rasmus Nielsen at the University of Copenhagen, found that even Bajau villagers who never dive still have disproportionately large spleens. “When we saw that, we thought, okay, something’s going on and it’s likely genetic,” Ilardo says.
Using blood samples collected from the same 59 Bajau villagers, she and her team compared their DNA to that of 34 Saluan individuals and 60 Han Chinese. They 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—at least, in rodents. This might explain why the Bajau have such large spleens, and thus, such extraordinary breath-holding skills. “This shows, for the first time, that there may be a genetic background to the spleen response in humans,” says Schagatay, who was not involved in the study.
PDE10A is only part of the story. Ilardo’s team also found signs of adaptation in other genes, which they now plan to study further. One of these, BDKRB2, is the only gene that’s been previously linked to diving in humans. It affects the constriction of blood vessels in the extremities, and so controls how much oxygen reaches the core organs like the brain, heart, and lungs.
But it’s also important for geneticists to give back to the communities they study. Ilardo is fully committed to this; she’s already planning a return trip to Jaya Bakti to tell Bayubu and the other Bajau about her results. “I think it’s wrong to take the samples and disappear forever,” she says. “I hope they get something out of it. And I want to spread a positive message about this population.”
Ilardo says that the Bajau, like many nomadic groups around the world, face a lot of stigma from surrounding populations. One official from an Indonesian university warned her that they weren’t trustworthy. Another told her to stay away from their “love potions.” “There’s a lot of mysticism around them,” she says. “They live physically on the fringe of society, which causes them to be seen with suspicion. But they were just the most welcoming people I’ve ever met. Kepala Desa Hasan, the chief of the village, took me into his home. I have a Bajau mom and dad who adopted me.”
Their traditional lifestyles are also disappearing. Several government programs have forced many of these nomads to come ashore, and their floating homes have become harder to maintain. “They used to make their houseboats from trees with light wood, but that tree is now endangered for reasons that have nothing to do with them,” says Ilardo. “They have to use trees with heavier wood, which means motors, which means gas, which is expensive. They’re slowly becoming connected to the land, but some of them still build houses on stilts to maintain a connection to the sea.”
BY ED YONG.
Source – theatlantic.com