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I'm working on a planet that has very similar conditions to earth. Now, I had the idea of animals having four (or even more) lungs. Would that be possible (I imagine there must be a possibility to inhale large masses of air to sustain all lungs?) and if yes, what would the benefits and other effects be? (Maybe a larger body?)

Thanks :)

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  • $\begingroup$ Mammals have two lungs, but they are divided into five independent lobes with borders anyway (three in the right side and two in the left lung) and each lung has its own bronchi. I assume you mean doubled lung capacity, and not merely four lungs? $\endgroup$ – YviDe Dec 11 '15 at 17:35
  • $\begingroup$ yes, that's what I meant! $\endgroup$ – Romenna Dec 14 '15 at 21:45
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It's quite possible, and some animals already have them.

Some arachnids have what are known as book lungs - small respiratory cavities that actually are not lungs, but different respiratory organs. They formed separately (in terms of evolution), but have taken the place of lungs in these arachnids.

Some organisms with book lungs have them in two pairs, while others have anywhere from one pair to four pairs. The reason for this many is simple: The book lungs are small. That said, arachnids are (in general) quite small, but some of them are still too big to be sustained by only one pair (or one book lung).


What exactly can extra lungs do in creatures that already get enough oxygen with just one pair? Well, you will have to solve the issue of body structure. Extra lungs take up a substantial amount of space, and animals won't necessarily evolve to be bigger, because they might not benefit much from the extra pair.

Let's assume, though, that a creature does have four lungs. What are the effects? You essentially have a creature with a larger lung volume, assuming that the lungs retain their same size - in other words, assuming that you're adding a pair of lungs to a creature which already has one pair. This means it can

  • Survive at higher elevations.
  • Grow larger/taller.
  • Have different voices (see Iwarsson (2001)).
  • Be more resistant to effects from diseases like emphysema, that attack the lungs.

Also, lungs do lots of other things besides helping creatures breathe, including

  • Regulate blood pressure.
  • Balance blood pH.
  • Attack blood clots.
  • Protect the heart (or hearts, if you're being creative!).
  • Act as backup storage for blood in cases of severe bleeding.

All of these capabilities (and more) would be increased with an extra pair of lungs.

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    $\begingroup$ "severe breathing" → "severe bleeding"? $\endgroup$ – Vectornaut Dec 9 '15 at 5:18
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    $\begingroup$ @Vectornaut I dunno about you, but I'd rather have severe breathing than severe bleeding. $\endgroup$ – Nic Hartley Dec 9 '15 at 12:20
  • $\begingroup$ @Vectornaut Yep, you're right. Thanks. $\endgroup$ – HDE 226868 Dec 9 '15 at 16:28
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    $\begingroup$ Having more lungs doesn't necessary equal more lung capacity. If I have two gallon bottles, they have more volume than four quart bottles. Lungs come in different sizes; purely for increase in volume, there is no reason to have more [pairs of] lungs. More pairs would add some redundancy, but also additional vulnerability. $\endgroup$ – Seeds Dec 9 '15 at 23:35
  • $\begingroup$ @Seeds True, although I was assuming adding a second pair of lungs in addition to an already existing pair. You're right, though, in that that's not necessarily the case. I'll clarify that. $\endgroup$ – HDE 226868 Dec 9 '15 at 23:37
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Four lungs wouldn't be radically different to two lungs twice the size. Their design matters far more. (multiple lungs with no shared airways might make pneumonia less of a threat to life)

If you want an organism that can support a metabolism burning calories at a much higher rate than a mammal then we have them. Birds! Avian lung design is very different. They have a number of bladders to move air through their lungs along a path such that freshly ingested air does not get to mix with exhaled stale air. This is a big part of how they can fly. The other big part is a better version of haemoglobin in their blood. Google if you want the full and rather complex anatomical detail.

Birds can fly at altitudes where humans have trouble surviving let alone being active.

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Many animals have extremely different lungs than we do. Look up how birds breathe for example. It actually takes two full inhale/exhale cycles for air to move all the way through their respiratory system. On the first breath in air moves into their first "air sacs" at the back, then they breathe out and it moves into their lungs, then in and it moves into their second set of air sacs at their front, and finally out where it exits their body.

Mammal lungs are actually very inefficient and the heightened efficiency of bird or pterosaur (flying dinosaurs) lungs are one of the reasons you might have heard things like "an albatrosses can fly for years at a time without ever stopping". If you can properly oxygenate your muscles you wouldn't ever tire out during long periods of aerobic exercise (flying,running,etc.). Air sacs systems being more efficient are also one of the reasons that GIANT dinosaurs as big as blue whales were able to even power their muscles enough to fight gravity and one pterosaur that was as tall as a giraffe was literally able to fly.

So yeah, I think it would be really cool to put some stuff like that into a story.

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