The Bajau, sometimes known as the "Sea Nomads," are a coastal people who've lived in close connection with the ocean across Southeast Asia for close to a thousand years. Many live in stilted houses built directly over the water, spending much of their day diving, fishing, and foraging beneath the surface using traditional free-diving techniques.
An unexpected biological discovery
Researchers studying the Bajau found they have significantly larger spleens than neighbouring populations who don't dive regularly, around 50% larger on average. While the spleen isn't typically associated with diving, it plays a key role in oxygen storage. When the body is submerged and oxygen becomes scarce, the spleen contracts and releases oxygen-rich red blood cells into circulation, effectively giving divers extra reserves to draw on.
Melissa Ilardo, the study's lead author from the University of Copenhagen, described the effect as working like a biological scuba tank.
A demanding daily routine
Bajau divers reportedly spend up to eight hours a day in the water, often diving to depths beyond 70 metres using traditional wooden goggles and weighted belts. At any given point, they can spend around 60% of their time underwater, with individual dives ranging from around 30 seconds up to several minutes.
This lifestyle relies on the human dive response, a set of physiological reactions that slow the heart rate, restrict blood flow to the limbs, and trigger the spleen to release stored oxygen. Over generations, researchers believe the Bajau have evolved to enhance this natural response beyond what's typically seen in other populations.
A genetic basis for the adaptation
The research went further than physiology alone, identifying a genetic link behind the trait. The team found that a gene called PDE10A, known to influence spleen size, was significantly more common among the Bajau than in comparison populations. Co-author Professor Rasmus Nielsen from UC Berkeley said the gene stood out clearly once researchers compared genetic variants across groups.
The finding echoes similar adaptations seen in other populations under extreme environmental pressure, such as Tibetans living at high altitude, whose own genetic adaptations are believed to trace back to ancient interbreeding with Neanderthals.
An uncertain future
Despite this remarkable adaptation, the Bajau's traditional way of life is increasingly under threat. Tribal elders have raised concerns about pollution, particularly plastic waste, alongside broader pressures from modernisation and climate change, leaving the long-term future of their ocean-based culture uncertain.
