Mutated tribe are the first known humans to genetically adapt to being underwater

There's a reason why we can't hold our breath for too long underwater.

Typically, as you swim deeper into the ocean an increase in water pressure causes the lung's blood vessels to fill with access blood, causing a rupture and, in some cases, death.

It's your spleen that helps you recycle red blood cells but there's only so much it can do when you're that deep into the water.

The Bajau tribe of Indonesia, however, are not your average divers and their genetic makeup could potentially be the reason why some of its members are able to 'swim to the bottom of the ocean'.

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The Bajau people live in houseboats and spend a lot of their time in the ocean.

So it comes as no surprise that they are great at fishing, diving and swimming.

Some of the tribe say they can dive up to 230 feet using just a set of weights and a pair of wooden goggles.

For context, most divers rarely dive deeper than 130 feet.

Melissa A. Ilardo, from Cambridge University, says the nomadic people can 'dive repeatedly for eight hours a day, spending about 60 percent of their time underwater'.

After studying the tribe, she discovered that they have a genetic advantage when swimming underwater, in part, because of their extra large spleens.

Some of their divers claim to have been under the sea for as long as 13 minutes, all while 'reaching the bottom of the ocean'.

Members of the tribe can stay underwater for as long as 13 minutes. (YouTube/BBC)

Ilardo told the BBC: "There's not a lot of information out there about human spleens in terms of physiology and genetics, but we know that deep diving seals, like the Weddell seal, have disproportionately large spleens.

"We believe that in the Bajau they have an adaptation that increases thyroid hormone levels and therefore increases their spleen size.

"It’s been shown in mice that thyroid hormones and spleen size are connected. If you genetically alter mice to have an absence of the thyroid hormone T4, their spleen size is drastically reduced, but this effect is actually reversible with an injection of T4."

The research team also discovered a gene called PDE10A, which, in mice, is linked to spleen size.

The Bajau tribe of Indonesia are not your average divers. (YouTube/BBC)

Ilardo thinks that natural selection over time would have helped the Bajau divers develop the gene.

Richard Moon, from the Duke University School of Medicine, also noted that other internal organs might be helping the tribe swim underwater.

“The lung chest wall could become more compliant. There could be some looseness that develops over your training. The diaphram could become stretched. The abs could become more compliant. We don't really know if those things occur,” he told National Geographic.

“The spleen is able to contract to some extent, but we don't know of any direct connection between thyroid and spleen. It may well be.”

Meanwhile, Cynthia Beall, an anthropologist from Case Western Reserve University, said she wants more measurable biological evidence before being convinced that a genetic trait is helping the divers last so long in the sea.