Many centuries ago, so the legend goes, a beautiful princess was kidnapped and taken out on to the Pacific. Her father ordered his people to search for her but she was never found. Ashamed to return, they stayed at sea, building houses on stilts and diving for food. They became the Bajau, Indonesia’s sea nomads.
Even today, the Bajau rarely touch land, subsisting in the ocean thanks to their astonishing freediving abilities.
Now we know that that princess must have been kidnapped a very long time ago, because a study has shown that the Bajau have had time to evolve to become world leaders in holding their breath.
A genetic analysis has found that they have developed specific traits that let them store more oxygenated blood, helping them to dive further for longer.
The analysis was conducted by Melissa Ilardo, a scientist who learnt about them while working on coral genetics in Thailand.
“I heard about these people called sea nomads,” she said. “I heard about their extraordinary abilities and extreme lifestyle.”
It is common for them to stay underwater for four or five minutes at a time while hunting, and go as deep as 70m. To Dr Ilardo, this meant one thing: there would be a strong incentive to evolve.
“Freediving is extremely dangerous. Even highly trained freedivers will sometimes die. It is really easy to lose consciousness and drown. There is a very strong selection pressure.”
There was one organ in particular that she thought might be affected by this. Not the lungs, but the spleen. “There’s a human dive response, triggered by a combination of holding your breath and submerging yourself in water. The heart rate slows down. Blood vessels in the extremities get smaller. The last thing is this contraction of the spleen.”
The spleen is a store of oxygenated red blood cells. When it contracts it releases them into the blood supply. In seals, we know that the species that dive the longest have the biggest spleens. Was the same true in humans?
Dr Ilardo travelled to the Bajau to find out. For a paper in the journal Cell, she showed that their spleens were 50 per cent larger than those of people in a neighbouring land-based village. This was true even in those Bajau who did not dive — implying that it was not because their bodies had adapted over the course of their lives.
As further evidence, when she looked at their genomes she found that a particular gene variant appeared far more often in the Bajau.
But what did the Bajau make of it? Were they pleased to learn the secret of their lifestyle? Dr Ilardo said they were extremely interested, if a little puzzled initially. “I just showed up at the house of the chief of the village, this bizarre, foreign girl with an ultrasound machine asking about spleens,” she said. “They’re explorers, so I think they’re inherently curious and want to know more about the world, including their own biology.” The Times
