The surprising trait of the deep-diving 'sea nomads' of southeast Asia
New study suggests the Bajau people evolved to hold their breath underwater for long periods
Quick: hold your breath.
By the time you're done reading this, your body will probably be crying out for oxygen.
Unless, that is, you're one of the Bajau people — a "sea-nomadic" people who inhabit the coasts and islands in and around Malaysia, the Philippines, and Indonesia.
As expert deep-sea divers, the Bajau are famous for their ability to hold their breath for sustained periods of time, and for requiring little rest in between submersions. But researchers never understood why.
But according to a new study published in the journal Cell, the Bajau have actually evolved separately from other humans, and this ability is baked into their genes.
Melissa Ilardo is the lead author of the study, and was working out of the University of Copenhagen at the time of the research. She spoke with As it Happens host Carol Off. Here is part of their conversation.
Miss Ilardo, just how good are the Bajau people at holding their breath?
They're really exceptional — not just in terms of the length of time they can dive, but it's also the breaks between their dives are extremely short, even compared with other groups of traditional divers.
And what do they use that skill for?
Everything they need, they're getting from the sea. So the sea is their source of food. It's also the source of things like jewellery. It's just a huge part of their lives.
How much time then do they spend underwater?
They'll be working for about eight hours a day. And of that, they'll spend about 60 percent underwater — which is actually similar to the sea otter.
And what were the theories as to their ability to hold their breath?
It was thought that this was purely a matter of practice — something that could be trained in any individual. And a lot of this thinking came from the fact that the world-record holders in free diving and breath holding aren't Bajau people. So it seemed that if you could train European individuals to dive this well, then there must be nothing special about the Bajau people.
- QUIRKS & QUARKS: Deep-diving 'sea nomads' have evolved an internal scuba tank
- DAY 6: What it's like to free-dive 124 m below the ocean
What did you see about how they dive, how deep they go?
It's a very natural form of diving. Because they're not diving competitively, they're diving functionally — they're just following whatever it is they're looking for that day. The one time I was diving with some Bajau divers, they noticed something about 30 to 50 feet deeper than where we were, and just dropped down immediately to that depth to go after the particular shellfish they were interested in. It's not meant to see how long they can hold their breath.
Rather than diving headfirst, they just drop feet-first. So they have this really incredible buoyancy control.- Melissa Ilardo
Were you holding your breath or wearing equipment?
No, I was holding my breath. One of them joked with me, "Oh, let's see who can hold their breath for longer." And it's like, "I don't think that's a fair competition."
One thing that I found really remarkable was that rather than diving headfirst — like I might dive — they just drop feet-first. So they have this really incredible buoyancy control. And I think that is coming from the sheer amount of time they're spending in the water.
I've never seen anything like it before.
And so your assumption was there was something different about their physiology. What did you think might be the case?
I started looking into the physiology of diving, and came across this "human dive response." It's something that's triggered by the combination of holding your breath, as well as submerging yourself in water. You can trigger it just by submerging your face in cold water.
And what happens is that first your heart rate slows down. Then you have peripheral vasoconstriction — the blood vessels in your extremities are getting smaller. And this preserves that oxygenated blood for your organs that need it the most while diving: your heart, your brain, your lungs.
And then the third component is contraction of the spleen. The spleen stores oxygenated red blood cells. And so as you're diving, it contracts, and pushes these red blood cells into your system. And this gives you an oxygen boost that allows you to dive for longer.
Think of it as a biological scuba tank — their tank is a little bit larger than ours. So that allows them to stay underwater for longer.- Melissa Ilardo
What did you find out about the Bajau people and their spleens, especially?
We found that the Bajau have these disproportionately large spleens — 50 per cent larger than a population living very close by to them, and fairly genetically-similar. And this is true both of Bajau divers and Bajau non-divers.
This is probably giving [them] some kind of advantage in diving. Because they have this larger spleen — if you think of it as a biological scuba tank, their tank is a little bit larger than ours. So that allows them to stay underwater for longer.
And the fact that we see this in both the divers and non-divers, tells us that it's probably happening at the genetic level.
And so you believe they evolved this way over time?
Yeah, we do. We identified a gene statistically associated with this spleen-size phenotype. And so we believe that natural selection has acted on this gene to give the Bajau larger spleens.
Was it a chicken-and-the-egg thing? Do you think they turned to diving because the Bajau people had the larger spleen, or they were diving and it developed over time?
It's hard to say.
But I would favour the explanation that as certain environmental changes were happening, and there was this shift to a marine-based lifestyle, that they began diving and natural selection acted on this particular trait.
Written by Julian Uzielli and Kevin Ball. Interview produced by Julian Uzielli. Q&A edited for length and clarity.