How long can you hold your breath underwater? Most people probably couldn’t make it for a full minute but there are some who may practice and be able to hold their breath for a minute or two. Those individuals are specifically trained in static apnea so they can hold their breath underwater by taking in pure oxygen before they go under.
Imagine, however, if there was an entire group of people who were genetically adapted to stay underwater for an average of 13 minutes without oxygen. It may come as a surprise, but the Bajau Laut people of Southeast Asia are able to do so. They aren’t trained in modern static apnea but they have discovered how to be both physiologically and genetically ready to stay under the water for extended amounts of time.
When most of us are submerged underwater, something that is known as the diving reflex kicks in. The spleen contracts, the blood vessels get narrower and the heart rate slows because of the lack of oxygen. Your body makes these adjustments to maximize your oxygen reserves until you are on the right side of the surface of the water again. One of the most important factors is the contraction of the spleen because it releases red blood cells and allows your blood to hold more oxygen.
The Bajau people are a nomadic, seafaring fishing clan that spend about 60% of their waking hours deep diving under the ocean. In 2018, the Journal Cell published a study that shows how those people may have a larger spleen, perhaps even 50% larger than most people. It adjusts the diving reflex to allow them to stay underwater longer. Since the larger spleen is producing more red blood cells, it works wonders for diving deep under the water.
You will find the Bajau people near Indonesia, Malaysia and the Philippines living on lepas, which are houseboats. The only time they typically come to town is to trade to get other items or if a storm is approaching. As a group, they have lived at sea for hundreds of years but about two centuries ago, some populations began to come on land, especially on the coast of Malaysia.
They fish in a number of traditional ways, but the most common is to dive for the fish. They use wooden goggles and hand weights to swim as deep as 100 feet into the water to catch fish. They also dive for a type of sea cucumber known as trepang. They use that sea cucumber to make various delicacies and soup.
The research discovered that members of the tribe who don’t dive also have an enlarged spleen. The PDE10A gene is thought to be responsible for the mutation, as it controls T4, which is a thyroid hormone. Since they have more T4 available, they have larger spleens. In studies on mice, higher levels of T4 resulted in larger spleens but lower levels resulted in smaller spleens.
“If there’s something going on at the genetic level, you should have a certain sized spleen. There we saw this hugely significant difference,” said Melissa Ilardo, lead scientist in the research at National Geographic.
It seems as if there are other genetic differences that allow the Bajau to stay under the water for extended amounts of time. For example, when the diving response occurs, their bodies may send blood to the hearts and lungs from the extremities. In addition, they may not have to worry about hypercapnia, an issue that occurs when underwater for extended amounts of time that results in elevated levels of carbon dioxide.
Additional physiological adaptations also seem to be taking place with the Bajau people. Richard Moon, a scientist from the Duke University School of medicine has looked into the reaction of the body to extreme depths and high altitudes. When people dive, the blood fills the vessels in the lungs. If those vessels in the lungs are ruptured, it would only be a matter of minutes before they would die. Moon thinks that constant diving and regular training could strengthen the walls of the lungs to allow them to withstand greater volumes of blood.
“The lung chest wall could become more compliant. There could be some looseness that develops over your training. The diaphragm could become stretched. The abs could become more compliant. We don’t really know if those things occur,” he said to National Geographic. “The spleen is able to contract to some extent, but we don’t know of any direct connection.
That adaptation is commonly seen in Tibetians and the Baju. The Tibetans live at very high altitudes in the Himalayas, so they have adapted in the same way but for living in the mountains rather than under the seas.
Even though the Tibetans and the Bajau live far away from each other, hypoxia may have been a serious problem in past generations. Hypoxia occurs when there isn’t enough oxygen in the tissues to sustain our normal functions. It may be that the Tibetians and Baju suffered from that problem to the extent that genetic mutations occurred to allow them to live in those extreme locations.
Studying those clans may teach us a lot about hypoxia and how to manage it.
For now, segregation and marginalization are making things difficult for the Bajau. They don’t receive equal treatment as others in the areas where they live. Many of them have also migrated because of pressure from industrial fishing. Ilardo worries that scientists may not get to study those adaptations before they are fully dispersed.