The Bajau Laut people have spent a millennium traversing the ocean near Indonesia on houseboats, living as sea foraging hunter-gatherers. They’re often called Sea Nomads or Sea Gypsies. Everything they eat, well most of it anyway, comes from what they harvest from the ocean. They spend more than half their waking hours underwater and are maybe the world’s greatest natural divers. With nothing more than simple wooden goggles and a bit of weight, the Bajaus can freedive to depths greater than 200 feet.

A recent article in the journal Cell explains their secret: they’ve evolved massive spleens.

When you see a big scary set about to steamroll you and you take a big breath, cross your fingers, and dive under the first wave, your spleen, of all things, kicks into action by releasing a bunch of oxygen-saturated red blood cells into your bloodstream. This prolongs how long you can spend underwater. Seals do this too. It’s a mammal thing.

The spleen, more important for surfing than you ever possibly imagined, huh?

Researchers, studying why the Bajau are so good at breath holding, now think it’s at least partially due to their having developed much larger spleens than the general population. Bigger spleens means more oxygen-rich blood, which means really good natural freediving abilities.

To figure this out, these scientists headed to an Indonesian peninsula, picked a Bajau village and a nearby village of people who don’t spend all day underwater called the Saluans, and used ultrasound machines to figure out the average spleen size among groups from both villages. The result: Bajaus, even those who don’t actually freedive, had way bigger spleens than the Saluans. Sure seems like the Bajaus are evolving larger spleens.

“Overall, our results suggest that the Bajau have undergone unique adaptations associated with spleen size and the diving response, adding new examples to the list of remarkable genetic adaptations humans have experienced in recent evolutionary history. ”

So next time you’re underwater for too long, and you start freaking out a little, blame your small, non-Bajau-sized spleen.

Photo top: Jodeery