Researchers have discovered the first evidence that
people can genetically adapt to deep diving, as shown by the unusually large
spleens in indigenous people of Indonesia known as the "Sea Nomads,"
a study said Thursday.
The spear-fishing Bajau people regularly free-dive to
depths of up to 230 feet (70 meters), with only weights and a wooden mask.
They spend up to 60 percent of their work day diving for
fish, spearing octopus and gathering crustaceans -- an amount of time rivaled
only by sea otters -- and can stay underwater up to 13 minutes at a time, said
the report in the journal Cell.
Intrigued by this unusual ability, American researcher
Melissa Ilardo, then a post doctoral candidate at the Centre for GeoGenetics at
the University of Copenhagen, wondered if they had genetically adapted somehow
to be able to spend more time underwater than other people.
She spent several months in Jaya Bakti, Indonesia, with
the help of a translator, getting to know the Bajau and another nearby group
that did not dive, the Saluan.
"I spent my whole first visit to Jaya Bakti
introducing myself, the project, and the underlying science," she told
AFP.
"I wanted to be sure that they understood exactly
what I was asking of them so they could help to direct the project to reflect
their interests. They were very curious and excited about the research."
Before her second visit, she learned some Indonesian in
order to be able to communicate directly with the Bajau.
- Scans and gene tests -
She took genetic samples and did ultrasound scans, which
showed that Bajau had spleens about 50 percent larger than the Saluan.
Spleens are important in diving -- and are also enlarged
in some seals -- because they release more oxygen into the blood when the body
is under stress, or a person is holding their breath underwater.
Spleens were larger in the Balau people whether they were
regular divers or not, and further analysis of their DNA revealed why.
Comparing the genomes of the Bajau to two different
populations, the Saluan and the Han Chinese, scientists found 25 sites that
differed significantly.
Among them was one site on a gene known as PDE10A, which
was determined to be linked to the Bajau's larger spleen size.
In mice, "PDE10A is known for regulating a thyroid
hormone that controls spleen size, lending support for the idea that the Bajau
might have evolved the spleen size necessary to sustain their long and frequent
dives,' said the study.
More research is needed to understand how thyroid hormone
affects human spleen size.
The findings could boost research in medicine by helping
researchers understand how the body reacts to a loss of oxygen in various
contexts, from diving to high-latitude climbing to surgery and lung disease.
"This really tells us how valuable and important
indigenous populations are around the world that are living extreme
lifestyles," said co-author Eske Willerslev, a professor at the University
of Copenhagen.
Willerslev admitted he initially urged Ilardo not to
pursue the research for her PhD thesis, believing it was too risky and that she
may find nothing.
"She said she wanted to do it anyway and that paid
off. Melissa was right and our concerns were wrong."
Ilardo said she was aware of the risks but "believed
so strongly in this project," that she had to push on.
"The Bajau and other Sea Nomads are simply
extraordinary and I wanted to be able to prove that to the world," said
Ilardo, now a US National Institutes of Health postdoctoral scholar at the
department of Molecular Medicine at the University of Utah.
Melissa Llardo/AFP / Melissa Llardo
