Comment by flopsamjetsam
12 hours ago
"Analysis of the data suggests that a blue whale’s heart is already working at its limit, which may explain why blue whales have never evolved to be bigger."
Incredible to think of the volume of all the blood it's pumping around.
I don't understand how that would limit evolution. Bigger bodies can evolve together with bigger hearts, as already witnessed with the very whales being researched.
The volume of blood that needs to be pumped increases e̶x̶p̶o̶n̶e̶n̶t̶i̶a̶l̶l̶y̶ cubically with size, meaning the cells have to do more work, or there have to be more of them. The size of the heart has to match the volume of blood being pumped - if they evolved to be larger, the heart might have to be so big that it creates pathology in other areas, or has to pump so hard it damages tissue, or creates forces so great that veins or arteries collapse or burst.
It's probably not as dramatic an issue as that. It could also be sensory - past a certain size, in order to be sensitive enough to detect damage and deal with normal conditions, it would have to be irritated all the time, or numb to potential hazards.
There are all sorts of second and third order consequences limiting how various vital systems can interplay, so more than likely, it's a combination of a whole bunch of things that subtly limit the overall size to where it's at, and any further increase degrades its abilities to survive.
They're just so huge. Their brains are 4 times larger than a human's brain, but we share a whole lot of structure, from the cellular level to the macro, with two lobes, some shared sulcal features (same folding pattern) which indicates that we likely share enough connectomic structure for the ways in which our brains operate to produce similar conscious experiences. Someday, in the distant future, we should be able to use BCI to feel exactly what it's like to be a blue whale (and vice versa.)
Their brains have similar cortical structure, but even though the brains are about 7 times larger, their cortical surface area is only 2-3 times that of a human. It really puts into context how bizarrely massive our brains are for our relatively tiny size.
For contrast, titanosaur hearts would have been around 500 lbs and up to 6 feet in diameter, and their brains were about the size of a big walnut. These land animals were up to 40m long and 100 tons.
Anyway - physics of tissue and frailties of being made of meat are what keep the whales from getting much bigger.
> size of the heart
Size of one heart has restrictions that are determined by diminishing return of physics. That doesn't mean engineering a larger system is impossible or even that very difficult. Same as any other pump system. i.e. there is no reason not to have 2 or 10 hearts.
We do this to move any fluid like water or concrete up to steep terrain or maintain pressure in everything from sewage to oil or gas pipes over long enough distribution systems.
Romanticizing in popular culture not withstanding, heart is just a pump[2] and today can be replaced by (albeit for short duration) entirely by a machine or replaced in a transplant.
We are not talking about say the brain or the central nervous systems[1]. That would be like going to multi-master from single node - lot more fundamental complex rebuild and rethink of the core architecture.
[1]We are not even remotely close to fully understanding let alone attempting to replace.
[2 Amazingly well designed, very efficient, something today we probably could not (yet) build synthetically with similar reliability and durability but it is still a pump nonetheless.
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But also internal space is increasing cubically—so any reason it couldn’t have mutated to have 2 hearts servicing each side of the body?
You could also claim our bodies have massive surface area, molecularly speaking. We just are factory-configured to not sense things that are too small to matter to ourselves as a whole (like small bugs and below)
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Nitpick, but the volume increases cubically (it scales with volume), not exponentially.
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I don't understand how the square-cube law is relevant here. The volume of blood indeed scales cubically with the length, but so does the volume of the heart. Where is the quadratic part of the equation that limits the maximum size of a whale? Why would it not work to take a whale and arbitrarily scale it in photoshop?
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> don't understand how that would limit evolution
Cardiac tissue is a surface. Blood is a volume. I think they’re saying blue whale hearts are near the largest current biology can evolve. Which is interesting because it suggests if we could e.g. engineer whales with carbon-fiber hearts or whatever, they’d evolve to grow even bigger.
Blackheart the whale, lurking the oceans, ever devouring and growing. I think you've got a good Lovecraft/Pirates of the Carribean/Black Mirror mashup premise here.
Cardiac tissue is also a volume. It can be thicker or thinner as the animal requires.
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> Bigger bodies can evolve together with bigger hearts, as already witnessed with the very whales being researched.
Hm? Aren't blue whales the biggest animals to ever have lived that we know of?
Or if not bigger hearts, what about multiple hearts?
Just evolve better blood!
/s
At the risk of being annoying, I'm pretty sure they have evolved to be bigger quite a lot, until they reached their maximum viable size.