Sea Nomads Evolved To Have Bigger Spleens To Stay Underwater

Sea Nomads Evolved To Have Bigger Spleens To Stay Underwater
Image credit: Melissa Ilardo

The Bajau people of Southeast Asia, known as Sea Nomads, spend their whole lives at sea, working eight-hour diving shifts with traditional equipment and short breaks to catch fish and shellfish for their families. In a study published April 19 in the journal Cell, researchers report that the extraordinary diving abilities of the Bajau may be thanks in part to their unusually large spleens. The adaptation, the researchers say, is a rare example of natural selection in modern humans–and one that could provide medically relevant insight into how humans manage acute hypoxia.

“Humans are pretty plastic beings. We can adapt to a number of different extreme environments just through our lifestyle changes or our behavioral changes, so it wasn’t necessarily likely that we would find an actual genetic adaptation to diving,” says first author Melissa Ilardo, a doctoral student at the University of Copenhagen working with co-senior researchers Rasmus Nielsen (@ras_nielsen) of the University of California, Berkeley, and Eske Willerslev of the University of Copenhagen and the University of Cambridge. “The first sign that we were maybe onto something was when we saw that both the Bajau divers and non-divers had larger spleens than the Saluan, a nearby, non-diving population.”

Spleen size is significant because of the organ’s role in the human dive response, which occurs when our faces are submerged in water and we hold our breath. As our heart rate slows and blood vessels in our extremities constrict, the spleen contracts, releasing oxygenated red blood cells and making more oxygen available in the bloodstream. A larger spleen means that more oxygen gets released. Perhaps for this reason, large spleens have also been documented in diving seals.

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