Large spleen helps “Sea Nomads” to deep-dive

Large spleen helps “Sea Nomads” to deep-dive
Photo: Photo: Torben Venning

A recent study testified that ability of Bajau minority group to spend much time underwater is caused by enlarged spleen.

Representatives of Bajau minority group live in Malaysia, Indonesia, and Philippines. For more than thousand consecutive years their way of life is very closely linked to the ocean – they spend up to 60% of their labor hours under water hunting for fish and collecting sea cucumbers and corals. For this very reason and because of their nomadic lifestyle they are called “Sea Nomads”.

It is well known that when a person or some other mammal is underwater, the special mechanisms of his body are activated. Thus, his heart rate slows down, spleen contracts, which injects a supply of oxygenated red blood cells into the circulatory system.

Melissa Ilardo, researcher at the University of Copenhagen, decided to explore whether Bajau have some peculiarities of these mechanisms and if so, then what is the genetic origin of such peculiarities. To do this, 59 Bajau and 34 representatives of other ethnic communities, who reside near Bajau and deal with agriculture, were recruited to have their spleen examined. It turned out that median size of a Bajau person’s spleen was 50% bigger.

Moreover, researchers sequenced the genes of both groups of people and found that 25 genes of Bajau differ both from the similar genes of their neighbors and of Han Chinese that were previously studied. One of these genes PDE10A affects the thyroid gland activity that, in turn, affects the spleen size. Other genes may also have relation to Bajau’s adaptation to a prolonged stay underwater.

Researchers point to the fact that genetic differences of “Sea Nomads” exemplify the natural selection among people that most likely took place within a short period of time.