The deepest dive recorded by the free-diving Bajau Laut people of Southeast Asia was to an impressive 79 metres, and the longest time spent underwater by them was just over three minutes. Although the Bajau do not dive to these depths or for this length of time during their day-to-day fishing, they spend up to 60% of their working life underwater.
New research published in the journal Cell shows that they have some physical and genetic adaptations to help them make these amazing dives. It seems that, although we tend to see ourselves as at the pinnacle of the natural world, evolution still has a grip on some groups of people. It is changing them to better suit their environment and their unusual lifestyle.
The Bajau Laut have traditionally lived a nomadic life on houseboats, exploiting the rich resources of the coral reefs and mangrove forests of the region. During the 20th century, some populations of Bajau settled on the shore but continued living a subsistence lifestyle (working just to survive) based on their traditional methods of fishing. Since the only diving equipment available is a pair of wooden goggles and some hand weights, their success depends on their ability to dive deep and hold their breath for a long time.
The size of the spleen is important because it is a reservoir in which red blood cells are stored. During a dive, the spleen contracts and pushes these extra red cells into the circulating blood, increasing its capacity to carry oxygen. This response has also been found in diving mammals such as seals.
DNA analysis revealed another change that turned out to be one of the most frequent gene variations in the Bajau population. This was in a gene that helps to control levels of a hormone called T4, which is produced by the thyroid gland. This hormone causes increases in metabolic rate (the amount of energy the body can use in a given time period), which can help to combat low oxygen levels, but is also associated with larger spleen size in mice.