The village of Sampela in Indonesia. Video by Muan Sibero/Shutterstock.

To attain these world records, competition freedivers learn specific techniques to extend dives by increasing oxygen stores, decreasing their oxygen consumption, and tolerating lower levels of oxygen in the brain. They also learn a process called lung packing: divers use their tongues as a pump to press down small volumes of extra air while above water, adding three liters of air beyond what the lungs typically hold. But many competitive freedivers also have physiological adaptations-a spleen up to twice the average size, or, sometimes they have an extra functional spleen. When oxygen levels in the bloodstream are low, the spleen releases red blood cells, which store oxygen. A larger spleen in competitive freedivers can increase dive times by as much as 30 seconds. But is having a large or additional spleen an extreme individual adaptation or a human evolutionary adaptation to a watery environment?
Rather than viewing this diving ability as an extreme feat, Schagatay sees it as a basic human capacity that we could all unlock if only we explored it for ourselves, within the safety of an organized dive club. In her research, Schagatay noticed that people who train safely often discover that freediving is easy. “It is amazing just how fast some people, without any previous experience, learn the art of deep and long distance diving or breath-holding for several minutes,” she wrote in a 2014 paper. The Bajau divers may be operating closer to the threshold of what the human body can do than the average person.
At our guest house, Schagatay and Abrahamsson set up a makeshift lab and methodically test research volunteers, trying to tease apart the ultimate question: are the Bajau exceptional because of practice or genetic predisposition? The researchers won’t give away details-their conclusions will be published later in a scientific journal-but there are indications of both.
The Bajau’s spleens caused quite a buzz a few months before Schagatay and Abrahamsson’s latest visit to Sampela. Melissa Ilardo, who is now a postdoctoral scholar at the University of Utah in Salt Lake City, published a study in the journal Cell showing that the Bajau of Jaya Bakti near the Indonesian island of Sulawesi had larger spleens than people in a neighboring village on the mainland. Even the Bajau who didn’t dive regularly had bigger spleens, on average, than members of the nearby farming community.
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