The Bajau people living in Indonesia have unusually large spleens suited for underwater fishing activities.
On the island of Borneo, surrounded by vast skies and seas, not far from the town of Semporna (located in the state of Sabah, Malaysia), a tribe that seems “lost” still exists in their own unique way.
The Bajau people are renowned as exceptional divers with extraordinary breath-holding abilities, allowing them to dive without the need for scuba gear, earning them the nickname “sea nomads.” They have sustained their livelihoods through fishing and harvesting marine products for centuries. These “sea people” can dive to the ocean floor to hunt for fish and octopuses using only handmade spears.
According to legend, the Bajau people originated from a Malaysian princess named Johor who was swept away in a flood. The king, heartbroken, ordered a group of people to venture offshore to search for her, and they could only return once they found the princess. The search failed, and the group was unable to return to land, leading to the formation of the nomadic sea tribe Bajau.
Most Bajau people are Sunni Muslims, and they largely believe in the spiritual world of the seas. Villagers view the ocean as their common home.
The Bajau tribe lives separately from modern civilization, about an hour’s boat ride away, in makeshift huts built near coral areas. Depending on the tide, the water level at the base of their homes can reach several meters high.
The Bajau tribe in Indonesia possesses an unusually evolved large spleen that aids them in free diving to depths of up to 70 meters. This is the first time scientists have discovered genetic changes in humans that adapt to underwater diving activities.
Bajau people can dive very deep. (Photo: James Morgan).
The Bajau tribe, also known as “sea nomads,” have been living on boats and fishing by free diving in the southern waters of Asia for over 1,000 years. They currently reside in Indonesia and are famous for their breath-holding abilities. Tribe members can dive very deep without any supporting equipment aside from a set of weights and goggles.
The spleen plays a crucial role in helping the body respond when diving. Heart rate decreases, blood is directed to essential organs, and the spleen contracts to push oxygen-rich red blood cells into circulation. The shrinkage of the spleen can increase the oxygen levels in the body by 9%. A larger spleen contains more oxygen-rich red blood cells, thereby extending breath-holding time.
Recent studies indicate that the spleen of the Bajau people is 50% larger than that of the Saluan people who primarily live on land. “There isn’t much information about the spleen in terms of physiology and genetics, but deep-diving seals like the Weddell seal possess extremely large spleens. I think if natural selection leads seals to have larger spleens, then humans could likewise,” said scientist Melissa Ilardo from Cambridge University.
A Bajau diving trip to catch fish. (Photo: James Morgan).
Ilardo spent several months in Jaya Bakti, Indonesia, collecting gene samples and ultrasound imaging of the Bajau and Saluan people. Results showed that the spleen of the Bajau people is permanently larger and not just temporarily due to diving.
DNA analysis revealed that the Bajau carry the PDE10A gene that the Saluan do not have. This gene is believed to influence spleen size by regulating thyroid hormone levels. “In mice, thyroid hormone and spleen size are related. If a gene alteration results in mice lacking the thyroid hormone T4, their spleen size significantly decreases, whereas supplementing T4 has the opposite effect,” Ilardo explained.
In 2014, another research team published evidence showing genetic adaptations that allow Tibetans to thrive at high altitudes.
In this case, the gene variant is thought to have originated from an ancient group known as the Denisovans, who are believed to be “siblings” of Neanderthals. This gene variant was passed to modern humans through ancient interbreeding (a process known as “gene flow”) and subsequently became more prevalent in the Tibetan highlands due to favorable conditions.
Ilardo commented: “Currently, it is still unclear how long the Bajau have been leading such a unique lifestyle, or exactly when the adaptation phenomenon occurred that provided us with genetic data.”
However, the genetic data obtained indicates that the Bajau diverged from the Saluan group, who do not dive deeply, about 15,000 years ago. According to Ilardo, the Bajau have had more time to adapt to life at sea.
The Bajau people dive with long spears to catch seafood.
Professor Rasmus Nielsen remarked: “This is a remarkable case of how humans adapt to their surroundings, but this phenomenon may also attract significant interest from the medical community.” According to the professor, compared to the adaptation to high altitudes in Tibetans, the Bajau might provide relatively more helpful insights for medicine. Rasmus Nielsen concluded: “Through studying the Bajau, we can discover some genes that help predict individual differences in responses to low blood oxygen levels.”
For thousands of years, the Bajau people have dived with long spears to catch seafood. From a young age, Bajau children help their parents fish, starting as early as eight years old. Due to their nomadic lifestyle at sea, the Bajau do not enjoy the benefits of birth certificates, social insurance, and welfare.
