Bajau tribe evolved huge spleens so they can dive deeper in the ocean | Hacker News Reader

Bajau tribe evolved huge spleens so they can dive deeper in the ocean

metro.co.uk

42 pointsEurongreyjoy26 comments

Previous discussion, based on better NYT article: https://news.ycombinator.com/item?id=16881818

Original paper in Cell (full text): http://dx.doi.org/10.1016/j.cell.2018.03.054

This is so ridiculous I'll repeat it in this thread.

The "enlarged spleens" they saw (~200 cm^3) are actually closer to half the size of typical spleens according to their own reference for spleen measurement (~500 cm^3). They apparently found another group to compare to with even smaller spleens, then acted like that was "normal" size to get this enlarged spleen for diving narrative. Details here: https://news.ycombinator.com/item?id=16884186

Wow. Could there be any explanation for this or is this as bad as it looks? If so, serious question, how do they get away with things like this? It's at Cambridge, I mean you would have higher expectations? Maybe not?

Scientists are under intense pressure to post amazing results. How do they get away with it? All the other scientists are doing the same things and nobody wants to stop the merry-go-round.

It is common sense to check your control group measurements against the literature and see where they stand. I would also expect to mention the results of that search in the paper.

Looking closer at the paper I see they also had some spleen sizes from a European cohort. They do not seem to tell us what those volumes were, instead only reporting p-values. Can anyone find it?

http://www.humanfunctionalgenomics.org/site/?page_id=82 is what they used

Those don't appear to be spleen sizes, though. It looks like they're just saying that they did a regression on some data linking "SNP"s to thyroid hormone levels. Then, they did a different but similar regression on data from the Bajau. I don't know what the relation of the SNPs are to spleen size but don't see anything noted in that area of the paper. IANA social scientist, but it looks quite goofy. They also note that they could not verify any relationship between spleen and thyroid sizes anyway.

I think they did look at "other" spleen sizes and just chose not to mention it. This really just looks like another case of "reject null hypothesis -> conclude whatever we want".

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)?

    > So how did this evolve over the past 1000 years?

The article says "For more than 1,000 years". That doesn't mean that whatever features these people have have evolved in that time period, but that they ran into the limits of recorded history. Humans have been in that area for around 50,000 years.

It's entirely possible that the current tribe derives from some subset of the population that's been doing this sort of thing for much longer than a millennium.

    > Selection pressure?

Maybe, but one thing you and the other replies haven't touched upon is the possibility of selection bias.

These people aren't in isolated population on some island in the middle of nowhere. They've been living around other humans for their entire existence.

So it's possible that this population today isn't just the result of selection pressure, but selection bias. People who were good at hunting underwater due to their genetic aptitude would have found and joined the tribe, who were happy to let them in as they were good at underwater hunting and could pull their weight. Conversely, those in the tribe who weren't good at it might have left the tribe entirely.

The article didn't mention culture, but I would venture to guess that in a society based on diving, the most skilled divers would be the most sought after mates.

This ability gives you a huge competitive advantage in times of limited resources, so most likely others have died/had limited offspring.

Even something more modest like "had on average 0.01 surviving offspring" could make a big difference over many generations.

See the top comment and see how this DID not happen. In any case, if it DID happen this would not have been "evolution" it would have been adaption; in other words selection for genes that are already there. It would not have been the result of new genes.

Evolution mostly works by selecting on variants in existing genes. The large majority of de novo mutations are either neutral or negative. If traits are selected for or against in the population and change in frequency that absolutely is evolution. Andean Indians have different adaptations to Tibetans to living at high altitude in part because the genes involved have been under selection for different lengths of time. Andeans have poorer adaptations because they have been living at those altitudes for a shorter time than Tibetans. The Tibetan adaptations introgressed from archaic hominids, not H. Sapiens, but the Andeans didn’t have that advantage. The term to google if you want to learn more is selective sweep.

There are many examples of recent selective sweeps in recent human evolution, from lactase persistence in Indo-Europeans to depigmentation in people who live at high latitudes.

>>The ancestor who could dive better had more children? Could feed his family better?

I think so too. Also the deep diver got the most beautiful /youngest /healthiest bride who would in turn bear healthier children. Rinse, repeat, with the offspring who inherited same genes. Over 1000 years of the same, the population changes.

The understanding of evolution in the title of this article is appalling... They didn't evolve large spleens so they could dive.. they dove a lot which resulted in selection bias which resulted in larger spleens...

While it might be confusing for a layperson without a solid grip on evolution, I don't think it's uncommon for people who understand selection bias to nevertheless speak like this. It's just so much quicker to say "they evolved larger beaks so they could crack the new island's bigger nuts" than "on arriving to the new island, the birds with bigger beaks had more success taking advantage of the generally larger nuts and thus were better able to survive and pass on their genes..."

Replace "so" with its synonym "therefore" and the ambiguity is resolved in a more pleasing way.

Fair enough. When I see "so" used in this way I generally see it as meaning "so that", which is also a perfectly valid inference. Perhaps it's an Anlgo/American grammatical difference?

Well it is ambiguous, so that is a headline-writing failure. Especially since this is a common misunderstanding of evolution anyway! In some sense this would be a logical ambiguity even if the writer meant to say that adaptations are goal-driven. Headlines simply shouldn't be written like this. Perhaps we're looking at this the wrong way, however. One gets the sense that most journalists don't really concern themselves with logic and clarity of thought anymore, since their intended audience is similarly unconcerned.

Isn't this how evolution works?

How do wooden goggles work? What did they use for glass? How did they make a seal?

Also from shells https://luangkanlahsejenak.files.wordpress.com/2009/07/lp-in...

I've seen a pair of wooden goggles, long time ago – also in one of the areas with Bajos, in Indonesia. I don't remember the frame having anything but wood and glass – but then again I didn't take a close look to see if the glass had any sealant gum / resin.

LE: this is the closest picture I've found: https://www.dumagueteinfo.com/images/wooden-goggles.jpg you can see glass + some sort of sealant. But no rubber between goggles and face

Transparent oak

Huh, I was thinking it would just be a ledge like a pronounced monobrow, strapped on and sealed to the head with either just pressure or pressure + gum, that would catch exhaled air.

Wouldn't very thin wood implode?

Wow sounds like we could take that thyroid hormone to enlarge our own spleen. I wonder if divers have tried that.

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