By immersing yourself in water and holding your breath, the body automatically activates what is known as immersion reflex. The heart rate slows, the blood vessels constrict and the spleen also contracts; Such reactions help save energy when oxygen levels are low.

Normally you hold your breath for a few seconds, in other cases it may take several minutes. But a group of people known as the Bajau take freediving to the extreme: they can dive to a depth of 60 meters for 13 minutes. These people are part of the nomadic population that lives in the waters of the Philippines, Malaysia and Indonesia, where they dive to fish or look for natural elements that can be used in crafts.

A 2018 study published in the journal cell provides the first evidence of a DNA mutation that has a larger spleen, giving the Bajau a genetic advantage in deep diving.

The spleen

Of all the organs in the human body, the spleen may not be the most necessary; life is possible without it. However, this organ contributes to maintaining an immune system and recycling red blood cells.

Previous research has shown that the spleens of seals, marine mammals that spend a large part of their lives underwater, are disproportionately large. The author of the study Melissa Llardofrom the Center for Geogenetics at the University of Copenhagen, Denmark, wanted to see if the same was true for people who dive.

“I wanted to get to know the community first, not just show up with scientific instruments and disappear,” he says of his first trips to Indonesia. “On the second visit I brought a portable ultrasound machine and equipment to collect saliva. “We went to different houses and took pictures of their spleens.”

He also obtained data from a group of related people called Saluan, who live on the main island of Indonesia. After comparing the two samples in Copenhagen, his team found that the average size of a Bajau spleen was 50 percent larger than the same organ in a Saluan individual.

“If something happens at the genetic level, there has to be a spleen of a certain size. Here we see this huge difference,” he says. Llardo theorizes that natural selection over time might have helped the Bajau, who have lived in the region for thousands of years, develop this genetic advantage.

Under pressure

According to Richard Moon of the Duke University School of Medicine in the United States, other adaptations may be involved. Moon studies the response of the human body to high altitude and extreme depth.

When a person goes deeper into the water, the increased pressure causes the blood vessels in the lungs to fill with more blood. In extreme cases, the blood vessels can rupture, which can result in death. In addition to genetically inherited adaptations, regular training could help prevent this effect.

According to Moon, the lung chest wall could adapt. The diaphragm can extend. The abdominal muscles could be adjusted. (JO)