The Bajau people of Southeast Asia are traditionally nomadic and seafaring, surviving by collecting shellfish from the sea floor. Scientists studying the effect of this lifestyle on their biology found that their spleens are larger than those of related people from the region. Located close to the stomach, the fist-sized spleen removes old cells from the blood and acts as a biological “scuba tank” during long dives. The Bajau dive repeatedly for about eight hours a day, spending about 60% of their time underwater at depths of over 200 feet. Astonishingly, these deep dives are performed only with a wooden mask or goggles and a weight belt. There’s a human dive response that’s triggered by holding your breath and submerging yourself in water. Your heart slows down, you have peripheral vasoconstriction where the blood vessels in your extremities get smaller to preserve the oxygenated blood for your vital organs, and the spleen contracts. The spleen is a reservoir for oxygenated red blood cells, so when it contracts, it gives you an oxygen boost. Studies have shown that the Bajau have spleens that are 50% larger on average. Scientists now believe that they developed the larger spleen to sustain long, frequent dives.
