[flopsamjetsam]

"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.

[tmoravec]

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.

[observationist]

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.

[manquer]

> 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.

[Someone]

> We are not talking about say the brain or the central nervous systems. That would be like going to multi-master from single node - lot more fundamental complex rebuild and rethink of the core architecture.

The central nervous system already is “multi-core”, with tiny logic handling such things as the patellar reflex. https://en.wikipedia.org/wiki/Patellar_reflex#Mechanism: “This produces a signal which travels back to the spinal cord and synapses (without interneurons) at the level of L3 or L4 in the spinal cord, completely independent of higher centres”

Other examples at https://en.wikipedia.org/w/index.php?title=Reflex

These tend to be actions that need fast feedback loops.

[manwe150]

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)

[krisoft]

> any reason it couldn’t have mutated to have 2 hearts servicing each side of the body

There are probably no hard reasons. It is most likely that the path of incremental changes leading to that solution is either unlikely, or does not convey an advantage to propagation of genes.

[observationist]

Klingon whales, now?

There are measurements suited to purpose, then there are "technically you could do that" measurements, and it's the former we'd want to use when measuring what sorts of power and pressure and material properties of the vascular system and cardiac tissue of a whale. Enormous amounts of blood are being pumped around, and I'd have to imagine you're in the million miles of arteries and veins and capillaries ballpark, so there's a lot of pressure holding that mass back.

That'd be a fun model to figure out for a weekend project - what sorts of forces are we talking about - how efficient is it compared to say, a hummingbird, or a human, or an earthworm heart?

[zakki]

But when things evolve they don't think if they will have enough heart capacity to pump the blood. They just evolve and by chance they got it right.

So why whale didn't get the chance to be bigger yet?

[adrian_b]

Some animals have multiple hearts, for instance cephalopods, like octopuses & squids, have 3 hearts.

However, for vertebrates it would be difficult to evolve to have extra hearts, because they have relatively rigid bodies.

A heart needs a space in which to expand, so it is not enough for the muscles in the wall of a blood vessel to increase in size and become capable of periodic contractions. You also need for all the space around it to evolve in providing an extra cavity inside which the new heart will be able to move without interaction with the surrounding organs, like the pericardium provides for the heart. In vertebrates, it was possible to evolve the pericardium because it has not evolved from nothing. It has evolved from a cavity (the so-called coelom) that existed in the ancestors of vertebrates long before having a skeleton and long before having a dorsal chord and even before having a blood vascular system. The modification of the coelom into a pericardium was a simple change, while the creation of a new internal cavity would be a very complex change. Moreover, also the nervous system requires changes, to be able to control the new heart.

So such changes are very unlikely in an animal like a vertebrate, because any intermediate stages would result in an animal that is disadvantaged in comparison with its competitors, only the final stage, with a functional second heart would be an improvement.

In general the evolution of animals does not happen at a constant rate. When an animal reaches a well optimized structure, it can keep that structure unchanged for hundreds of millions of years, because any deviation would result in a less competitive animal, which would be eliminated without descendants. For instance, there are a few species of sharks that have changed very little since Triassic, more than 200 million years ago.

Great changes in the structure of an animal happen only when there is no competition, which allows the intermediate worse forms to survive and produce descendants. Such lack of competition happens when a natural catastrophe kills most competitors or when an animal succeeds by chance to arrive in a new place, where nothing like it lived before, e.g. when passing accidentally to a different island or continent.

[inopinatus]

A binary vascular system? Do you want regenerating whales in the time vortex?

[frotaur]

Nitpick, but the volume increases cubically (it scales with volume), not exponentially.

[observationist]

Thank you, I'll correct that. I was thinking inverse square law, then instead of asking an AI like a good nerd, I just winged it.

[setsewerd]

Some might say you're a purist in that regard

Side note, would positing an argument online without doing an AI fact check first be considered rawdogging your answer?

It seems fitting.

[fluoridation]

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?

[Qem]

> Where is the quadratic part of the equation that limits the maximum size of a whale?

Muscle power output increases with cross section area, ~L^2, not with volume. The heart have no separate power unit. It relies on the same muscle walls that comprise its chambers to power itself.

[fluoridation]

That just means the walls of the heart would need to grow thicker. Are they at the limit already?

[Qem]

Wall thickness increasing by x increases cross section/power by x^2, but also increases chamber volume/workload by x^3. So workload outruns available power. It's because of this people abusing steroids get heart failure eventually.

[Evidlo]

> we should be able to use BCI to feel exactly what it's like to be a blue whale (and vice versa.)

One day we will gift these whales the experience of Italian brainrot and Skibidi toilet.

[JumpCrisscross]

> 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.

[observationist]

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.

[fluoridation]

Cardiac tissue is also a volume. It can be thicker or thinner as the animal requires.

[adrian_b]

Yes, but the force of a muscle does not increase with volume, but only with its section.

So a bigger heart would need to have thicker walls in comparison with its internal volume, which would increase disproportionately the volume of the heart walls, so for bigger and bigger hearts the useful internal volume that is filled with blood would be a smaller and smaller fraction of the total heart volume.

The lower efficiency of a bigger heart would require a higher contraction frequency to compensate, but the bigger a heart is the smaller is its maximum contraction frequency, due to the small speed of the propagation of an excitation through muscle cells and nervous cells.

[fluoridation]

>The lower efficiency of a bigger heart would require a higher contraction frequency to compensate

If that's the case, then how come rats have a higher heart rate than humans, who have a higher heart rate than whales? Do whales have hearts with thinner walls than humans, while rats have big lumps of muscle with teeny tiny chambers?

[JumpCrisscross]

> the force of a muscle does not increase with volume

It does. But it must still impart that force through a surface to a volume. And at a certain point, you hit the mechanical limits of that surface’s ability to hold itself together.

[boxed]

Or just a lot of smaller hearts.

[Sharlin]

As usual when it comes to scaling of mechanical things including organisms, it’s a matter of the square–cube law.

https://en.wikipedia.org/wiki/Square%E2%80%93cube_law

[kadoban]

> 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?

[adrian_b]

Yes. There are many extinct animals that had sizes comparable with sperm whales, including some dinosaurs, but none of them had sizes comparable with blue whales.

The reason for this is simple, few animals have developed a method of feeding like that of the baleen whales, by filtrating huge amounts of sea water, which can provide enough food for such a huge body.

Other animals that have developed similar feeding methods, like 4 groups of species of sharks or rays, including the whale shark, have also become much bigger than their relatives.

[robotnikman]

Or if not bigger hearts, what about multiple hearts?

[meroes]

Just evolve better blood!

/s

[BurningFrog]

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.