If you want to be a successful freediver, work out your spleen.
Here’s a fun science experiment you might have done in grade school. Get a bucket full of ice water that’s big enough to fit your head. Now dunk your face in and see how long you can stay. Most people can’t remain under for longer than a minute—and for the average human, it’s pretty dangerous to try. But during that minute, your body goes through some pretty nifty changes. To conserve oxygen, your heart rate slows (what’s called bradycardia), the veins in your extremities constrict, enabling you to distribute the oxygenated blood to your vital organs like your heart and lungs, and your spleen, which stores oxygenated red blood cells, contracts, releasing those cells into your bloodstream.
All of this is to allow you to survive during this brief period sans-oxygen. Now, scale that up. Imagine freediving several hundred feet down into the cold ocean. Extreme, yes, but that’s how a group of human sea nomads—the Bajau people—have survived for thousands of years.
Since the spleen stores those red blood cells, a larger spleen should mean a greater capacity to hold your breath. Plus, the researchers already knew that contraction of the spleen was a key component of the mammalian diving reflex (like when you dunk your head in a bucket of cold ice water). So, the scientists surmised that the Bajau might have evolved to have super large spleens over time.
In studying the adaptations that people make to live in certain areas or engage in certain activities that aren’t suited for the average human, scientists have identified several similarly ingenious mechanisms. In 2014, researchers studied people living in particularly low-oxygen environments in the high altitudes of Tibet. They found that those populations all share a gene mutation that prevents the body from having too many red blood cells circulating in the bloodstream. Over time, high levels of red blood cells can cause health problems. However, the body rightfully responds to being at high altitudes by doing two things: Increasing the amount of hemoglobin in the blood and the number of red blood cells, since they are the ones that contain oxygen. Being able to suppress that means that you thrive in those conditions without the potential negative health effects.
So can the Bajau help us become more super human? Maybe. In an accompanying news release, Eske Willerslev, a senior author of the paper, noted that human populations that live in extreme environments can tell us a great deal about genetic and physiological adaptations to tough conditions. And these populations are rarely studied. But when they are, they can lead to treatments that help all humans. A better understanding of how the Tibetans live in low oxygen could help us understand how to treat patients in critical care units with low levels of oxygen in their blood.
The researchers involved plan to better study the connections between spleen size and diving ability as well as its connection to our production of certain thyroid hormones, with the hope of uncovering novel mechanisms at play.