
Bodies Remodeled for a Life at Sea - sohkamyung
https://www.nytimes.com/2018/04/19/science/bajau-evolution-ocean-diving.html
======
curun1r
No, plunging 200 ft underwater isn't a physiological marvel. Learning to hold
your breath for up to 8 minutes is not some mysterious ability, it just takes
training. And anyone who can hold their breath for that long can go down to
60m. Just taking 3 levels of AIDA training will take you down to 40m and
another year or two of training will get you to 60-70m depth, which is where
these supposed "marvels" from the article dive to.

The medical community has been repeatedly made to look foolish whenever
they've speculated on what is and isn't possible for freedivers. These people
are no doubt excellent freedivers from the many years of practice they have
with it, but nothing in the article suggests they're capable of anything that
us normal human cannot do.

FWIW, my PB is 55m (~180 ft), and with a bit more regular training, I feel
confident I can go another 15m or so.

~~~
sohkamyung
I believe this part of the article addresses that concern:

 _Diving itself might somehow enlarge the spleen. There are plenty of examples
of experience changing the body, from calloused feet to bulging biceps._

 _Only some Bajau are full-time divers. Others, such as teachers and
shopkeepers, have never dived. But they, too, had large spleens, Dr. Ilardo
found. It was likely the Bajau are born that way, thanks to their genes._

~~~
curun1r
I know they did. If they had just stuck to the part about genetic tests,
that'd be fine. It's the flowery language about how they're adapted to depths
that would kill normal human beings that I was objecting to. They should have
said that generations of divers have made these people have larger spleens
which makes them marginally better at deep diving. But that's less dramatic
and, presumably, gets fewer clicks.

~~~
nonbel
It looks worse than that. In figure 1 of the paper[1] they only make a
comparison between Bajau and Saluan populations. They show the "enlarged
spleens" have volume of ~200 cm^3.

However, if you look at humans overall, apparently even these "enlarged
spleens" are much smaller than the average spleen:

>"The mean splenic dimensions were ... 333.6 ± 116.1 cm2 in volume."
[https://www.ajronline.org/doi/abs/10.2214/ajr.184.1.01840045](https://www.ajronline.org/doi/abs/10.2214/ajr.184.1.01840045)

[1]
[http://www.cell.com/cell/fulltext/S0092-8674%2818%2930386-6](http://www.cell.com/cell/fulltext/S0092-8674%2818%2930386-6)

EDIT:

They write:

>"We made ultrasound measurements in two planes such that we were able to
calculate spleen volumes according to the methodology outlined in Yetter et
al. (2003)"[1]

So lets look at Yetter 2003 for their spleen volumes, in table 2 it shows they
are >500 cm^3 on average:
[https://www.ajronline.org/doi/abs/10.2214/ajr.181.6.1811615](https://www.ajronline.org/doi/abs/10.2214/ajr.181.6.1811615)

So it looks like these "super spleen divers" actually have relatively small
spleens...

~~~
defen
The patients in the Yetter paper were all being evaluated for liver disease,
so their measurements might not be what you want to use as normal.

~~~
nonbel
Thanks, looking closer at the Yetter paper:

>"Normal cadaveric splenic volumes reported by Loftus et al. [8] are 26–250
cm3 with a mean volume of 110 cm3 and an SD of 70 cm3. Henderson et al. [19]
reported a normal splenic volume of 219 cm3 as calculated from axial CT
acquisitions."

So an average of 219 cm^3 according to axial CT is still larger than what is
seen here. I'm not sure about the cadaver spleens, do they shrink? The Loftus
paper only reports maximum length vs actual volume so we can't see that direct
correlation.

Some other papers report 184 cm^3
([https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4549594/](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4549594/))
and 214.6 cm^3
([https://www.ncbi.nlm.nih.gov/pubmed/9038125](https://www.ncbi.nlm.nih.gov/pubmed/9038125))

------
mrfusion
My ears hurt when I dive even five feet. Is this dangerous for your ears? Do
you need to relieve that pressure as you dive deeper?

Do you need to worry about Benz as you come up?

~~~
maaaats
Yes, if it hurts it's dangerous. But you can equalize the pressure to avoid
it. Many methods, see
[https://en.wikipedia.org/wiki/Ear_clearing](https://en.wikipedia.org/wiki/Ear_clearing)
A tip is to equalize very often on the way down, even before you feel it. When
you feel it, your tubes are shut closed from the pressure so it's too late.
Valsave is the easiest to learn (pinch your nose and blow)

No, no bends. Unless you have been diving scuba earlier the same day. As you
don't breathe deep down, only bring air from the surface in your longs, it
won't happen.

What you should be worried about is shallow water blackout when ascending. So
never hyperventilate, never push your limits, and never dive alone. Limits to
breath holding should be pushed on land instead.

~~~
curun1r
> No, no bends. Unless you have been diving scuba earlier the same day. As you
> don't breathe deep down, only bring air from the surface in your longs, it
> won't happen.

Freedivers can have nitrogen absorption issues if they make too many dives in
too short a period. A good freediving computer will alert you when you're
approaching your limits. What makes it less of an issue than for scuba divers
is less the not breathing at depth part and more the spending less time at
depth part. Even a scuba diver would have fewer nitrogen absorption issues if
they only spent a few minutes at depth. You're also missing the nitrogen
narcosis danger, and freedivers have more narcosis issues than recreational
divers because of the greater depths.

Everything in your last paragraph is sage advice, though you can push your
breath hold limits at the surface or in a pool as long as you have a trained
partner who knows how to handle a blackout. Static holds need to be trained
wet before deep diving and dynamic holds can be safely trained horizontally to
take pressure changes out of the equation.

------
novalis78
So how did this evolve over the past 1000 years? Selection pressure? The
ancestor who could dive better had more children? Could feed his family
better? Was it just one person with mutation that started it? Or, did the
frequent exposure to deep diving triggered something in one generation that
influenced the genes of their children (along the lines of Epigenetic magic)?

~~~
loblollyboy
In article they speculate that maybe this happened because deep diving can
kill you

------
Symmetry
I started reading that thinking that that's a much more complex adaptation
than I'd expect to see differentiating different groups of humans, given how
recent a population bottleneck our species went through. But apparently it's
just a single gene mutation that can increase spleen size? Genes are weird,
man.

------
amriksohata
I'd like to see data on how they came to the conclusion they evolved or was it
just that people who were good at swimming naturally colluded to live near the
sea and enjoy that area more?

~~~
sohkamyung
The study referred to in the article can be found at [1]

[1]
[http://www.cell.com/cell/fulltext/S0092-8674(18)30386-6](http://www.cell.com/cell/fulltext/S0092-8674\(18\)30386-6)

------
mrfusion
Do they have metabolic differences too because of the different thyroid
hormone levels?

------
dogma1138
I wonder if this provides any further support to the aquatic ape/water side
evolutionary hypothesis.

[https://en.m.wikipedia.org/wiki/Aquatic_ape_hypothesis](https://en.m.wikipedia.org/wiki/Aquatic_ape_hypothesis)

~~~
Symmetry
If all humans had larger spleens than other primates that would provide
evidence for that. I have no idea whether that's true.

------
youpassbutter
Humans adapt to their environments? What's next? The tibetans and sherpas have
adaptations to high altitude? The inuit have adaptations for the cold? Norse
have adaptations for low levels of sunlight?

Is this really "news"?

