The Bajau adaptation for life at sea
In the course of history, human beings have populated the most uncomfortable places on earth, adapting the environment to themselves and themselves to the environment. It occcured, sometimes, that the dwellers of extreme lands have established a deep and long-lasting relationship with their home, that does not limit to mere survival but twist together the two, resulting in a unique culture and way of living.
The Bajau people, for more than a thousand years, have been traveling the Southeast Asian ocean living on houseboats and basing their whole existence on what they got from the sea. Nowadays, there are many communties scattered close to the coasts of Malaysia, Indonesia and Philippines but they still carry on an entirely marine-dependent life.
(image by Matthieu Paley, National Geographic)
The Indonesian government, in an attempt to shift the traditional marittime nomadic way of life into settled comunities, provided home on the land. However, the Bajau left them to build a stilt village in the sea one kilometer away from the shore. So tight the bond between sea and its dwellers, that the two could not be divided; this is also reflected by the syncretic belief, ritual observances and taboos they follow, which regulate the interaction with the sea.
Although many of the Sea Nomads live in houseboats, some are still spending their whole life at sea, coming to the land just for breef periods of barter.
(Image by James Morgan)
Bajau people indeed are hunter and gatherer, live on what they find and on what they get in exchange of it. In order to conduct such a life, they spend 60% of their daily working time underwater free diving (about eight hour a day), sparefishing with only a set of weights and wooden gogglese. They developed techninques and abilities that make it possible for them to go deeper than 70 meters and stay submerged holding their breath for an incredibly long time.
When Melissa Ilardo first heard that Bajau people could dive up to 13 minutes, she wondered if centuries of that life could have led to a pyshical adaptation that made those people more fitted for the sea. Here started her research.
The first step of the study involved the measurement of the size of Bajau people’s spleen. Indeed, the human body reacts with the so-called “diving reflex” whenever underwater. This phenomenon is a series of physiological responses which result in channeling the blood to the vital organs, such as brain and heart, and most importantly in contracting the spleen, which works as a scuba tanks and injects blood in the oxygenated circulation, in order to avoid hypoxia.
(Image by James Morgan)
After the measurment, Dr. Ilardo traveled to a nearby settlement of farmers to study their spleen as well. The comparison of the two results were univocal; the spleens of the Bajau on average were 50% larger than those of the inland dwellers. This proved a real and total adaptation to the environment. Anyway, the research was aimed at finding an hint of evolution and natural selection that in the end was not ensured by that result.
But what startled Dr Ilardo the most was that the size of the spleen was bigger than the average Bajau measured, also in those people who did not ever dive. This underlined that the peculiar ability was not just result of adaptation: it seemed that Bajau people were born physically shaped for that life.
(Image by James Morgan)
This brought to a further step in the research. Dr. Ilardo took mouth swabs from the Bajau to analyze the DNA and look at the genetic variations and then compared it to those of the people from some countries around the area, such as China.
The outcome of this latter analysis showed genetic variants that were present in the Bajau DNA and not in those of the other specimens. In particular, one variant of a gene called PDE10A influenced the size of the spleen: people with this mutant gene had that organ much bigger than the average, and therefore could hold their breath and dive for much longer than common people. Natural selection played the role of choosing and shaping the Sea Nomads: only those who had the adequate features would have lived and reproduced. It is likely that the people without this genetical variation would have died trying to carry on this way of living.
As Dr. Ilardo underlined: “I would think, as morbid as it is, that if they didn’t have this, it [natural selection] would kill them”.
Besides the scientific relevance of this study, it also tells us a story of evolution. An harsh environment has been modeling and selecting through centuries its peculiar and unique dweller, now genetically adapted to dive and indissolubly linked with its “land”.
Featured image by Matthieu Paley, National Geographic