The diving reflex consists of automatic responses that occur when the face of an air-breathing mammal is submerged into water, including splenic contractions, blood vessels constriction, and slower heart rate.  The body attempts to maximize its oxygen reserves until you can breathe in oxygen again.

The average healthy person not trained in static apnea can hold their breath for a maximum of two minutes underwater, after breathing in pure oxygen.

However, there is a tribe, an ethnicity genetically adapted to survive underwater without oxygen for at least 13 minutes on an average, without being trained in modern static apnea.

The Bajau Laut people have been discovered to have evolved physiologically and genetically, and the new features that have basically turned them to human seals. These seafaring, nomadic fishermen spend almost 60 percent of their life deep-diving underwater.

They live in long houseboats called lepas, in the waters of Indonesia, Malaysia, and the Philippines, and have lived there for centuries. Yet, about two centuries ago, some of them started settling on the shores, especially in Malaysia.

They fish for their food and only come to the town to trade for other items or to seek shelter from storms. Diving is their most common traditional fishing method, and they use wooden goggles and hand weights and swim 30 meters (100 feet) into the water to catch fish and a particular sea cucumber species known as trepang.

Their unique abilities intrigued  American researcher Melissa Ilardo, then a postdoctoral candidate at the Centre for GeoGenetics at the University of Copenhagen, and she suspected that they had genetically adapted somehow to be able to spend more time underwater than other people.

Therefore, she spent several months in Jaya Bakti, Indonesia, with the help of a translator, in an attempt to meet the tribe and investigate them.

On the second visit, she had a portable ultrasound machine and spit collection kits. She went around to different homes and took images of the spleens of people.

She also took data from a related group of people who live on the Indonesian mainland, called Saluan. When she got back in Copenhagen, she compared the two samples and discovered that the median size of a Bajau person’s spleen was 50 percent bigger than the same organ in a Saluan individual.

She later explained that in case something is going on at the genetic level, you should have a certain sized spleen. At this point, they noticed a significant difference.

This 2018 study published in the Journal Cell found that they may have evolved to have larger spleens, estimably 50 percent bigger than that of an average person, which helps them maintain the diving reflex for much longer while underwater.

The larger spleen serves as a more sufficient red blood cell reservoir that can carry more oxygen to the blood and improves the efficiency for utilizing the oxygen they breathe in.

Researchers have found that members that do not dive have enlarged spleens too, so they suspect that a particular gene known as PDE10A might be responsible for this mutation.

This gene controls a thyroid hormone known as T4 which increases metabolic rates and fights low oxygen levels in times of distress.

Additionally, scientists have found other diving-specialized genes as well, one of which would cause blood to rush from the limbs and other non-essential parts to the heart and lungs as soon as the diving response kicks in.

Another gene prevents the occurrence of hypercapnia from extended periods spent underwater, which results from raised levels of carbon dioxide in the blood.

Moreover, Richard Moon, a scientist from the Duke University School of medicine, maintains that regular training and constant diving strengthen the walls of the lungs and make them more adapted to withstand high volumes of blood, so they do not get ruptured.

Researchers also claim that the Tibetans and the Bajau may have suffered extensively from hypoxia in older generations, a condition characterized by a lack of oxygen in the tissues to sustain bodily functions. Severe hypoxia might have caused the gene mutation to enable them to cope with it.

Rasmus Nielsen added that this is a wonderful example of how humans can adapt to their local environments, but there may be some medical interest, as there has been a lot of interest in understanding hypoxia adaptations.

Yet, by the time scientists are ready to research these adaptations, thousands of Bajau people might migrate from the seas, or even fully disperse, due to increased industrial fishing, as marginalization, and segregation make their life exceptionally difficult in their native dwellings.

Sources:
www.straitstimes.com
www.bbc.com