3 ms·

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 b

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.

frotaur 7mo ago
Nitpick, but the volume increases cubically (it scales with volume), not exponentially.
- observationist 7mo ago
  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 7mo ago
    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 7mo ago
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 7mo ago
  > 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 7mo ago
    That just means the walls of the heart would need to grow thicker. Are they at the limit already?
    - Qem 7mo ago
      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.
      - fluoridation 7mo ago
        >chamber volume/workload by x^3. So workload outruns available power. What do you mean by workload? Are you referring to the oxygen cost per stroke, or what?
        Qem 7mo ago
        Power demand. Volume pumped each cycle * (systolic pressure - diastolic pressure) / time.
manwe150 7mo ago
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)
- observationist 7mo ago
  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 7mo ago
    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?
    - observationist 7mo ago
      Because the cost to things that allow the whale to survive is greater than the benefit of being larger, on the whole. If they get bigger, they die and are survived by slightly smaller versions, and over a long period of time, you get a range of slightly bigger and slightly larger whales, centered around whatever average size best fits the niche for that particular time span. It's usually a whole suite of interrelated reasons that are affecting any given feature - size would include hearts, nervous system performance, food intake, protection from predation, and so on, with dozens of factors playing a part.
manquer 7mo ago
> 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 7mo ago
  > 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 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 https://en.wikipedia.org/w/index.php?title=Reflex These tend to be actions that need fast feedback loops.
Evidlo 7mo ago
> 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.

frotaur 7mo ago

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

observationist 7mo ago
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 7mo ago
  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 7mo ago

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 7mo ago
> 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 7mo ago
  That just means the walls of the heart would need to grow thicker. Are they at the limit already?
  - Qem 7mo ago
    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.
    - fluoridation 7mo ago
      >chamber volume/workload by x^3. So workload outruns available power. What do you mean by workload? Are you referring to the oxygen cost per stroke, or what?
      - Qem 7mo ago
        Power demand. Volume pumped each cycle * (systolic pressure - diastolic pressure) / time.

manwe150 7mo ago

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)

observationist 7mo ago
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 7mo ago
  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?
  - observationist 7mo ago
    Because the cost to things that allow the whale to survive is greater than the benefit of being larger, on the whole. If they get bigger, they die and are survived by slightly smaller versions, and over a long period of time, you get a range of slightly bigger and slightly larger whales, centered around whatever average size best fits the niche for that particular time span. It's usually a whole suite of interrelated reasons that are affecting any given feature - size would include hearts, nervous system performance, food intake, protection from predation, and so on, with dozens of factors playing a part.

manquer 7mo ago

> 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 7mo ago
> 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 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 https://en.wikipedia.org/w/index.php?title=Reflex These tend to be actions that need fast feedback loops.

Evidlo 7mo ago

> 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.