The Bajau people have long lived on the waters of Southeast Asia, where they've evolved into sea-dwelling beings with bodies like no other humans on planet Earth.
These 'sea nomads' are the first known humans to have a genetic adaptation to diving. Most people can hold their breath underwater for a few seconds, some for a few minutes. But the Bajau takes free diving to the extreme, staying underwater for as long as 13 minutes at depths of around 200 feet.
The Bajau people live on small boats and have never settled in one location. They continue to sail while catching fish and occasionally go ashore only for selling their catch to buy secondary needs that they cannot make themselves.
They Originate from the Sulu Islands region in the Southern Philippines and because of their nomadic sea life, this tribe eventually spread into the waters of Malaysia, Brunei and Indonesia. Usually, the most appearances of these tribes are in Eastern Indonesia, such as in the waters of Maluku, Raja Ampat, Sulawesi, to the northern part of Kalimantan.
An international team of researchers studied the Bajau and found they had significantly larger spleens than the people of a neighbouring village who primarily farm rather than fish for their food. This was true even for members of the Bajau community that don't dive, suggesting that it is an inherited trait rather than a change in individuals caused by a lifetime of diving.
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.
Other genes that varied among the Bajau more than would be expected in the general population were associated with the way the body responds to diving.
One such gene caused blood to be squeezed out of the limbs and non-essential areas of the body so that the brain, heart and lungs could continue to receive oxygen.
Another prevented high levels of carbon dioxide from building up in the blood.This all suggests that natural selection has helped to shape the Bajau so that they can dive deeper and longer.
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