2
$\begingroup$

As the title suggests, can mammal evolve unidirectional breathing? Not the same as in birds but still qualifies as a unidirectional breathing.

(I was trying to make a future mammalian species surviving in future Pangaea and the lower oxygen could incentives them to evolve it)

Improve this question
$\endgroup$
1
  • $\begingroup$ For future reference, our goal here on Worldbuilding per the help center is to help you develop an imaginary world. We've debated forever whether or not "can my fantasy creature exist in the real world?" questions are on-topic and, generally, they're not. In other words, what we want to answer are questions like, "how can I rationalize my fantastic creature?" (We're actually quite good at that.) As for evolution, generally, given enough time, anything is possible - so the only answer you can have to this is "yes" because nobody can prove the answer wrong before the sun burns out. $\endgroup$
    – JBH
    Commented Jul 17 at 19:31

2 Answers 2

Reset to default
2
$\begingroup$

It is possible, but very unlikely.

Consider that the way the respiratory system works it's deeply related to the anatomy and to the general body plan of the organism, which is related to the anatomy of the original ancestor behind all the species in the class.

Changing that would require a drastic change in the anatomy, let's call it a U turn than a slight deviation, achieved as superposition of several small changes, each bringing some fitness advantage to its bearer.

Improve this answer
$\endgroup$
3
  • $\begingroup$ Seconded. We're possibly talking tens of millions of years - but the OP might consult a paleontologist for further details on an estimate. $\endgroup$
    – Escaped dental patient.
    Commented Jul 17 at 12:50
  • $\begingroup$ @Escapeddentalpatient.: Birds inherited the basic design of their respiratory system from their theropod dinosaur ancestors; the iconic T. rex had the same kind of respiratory system. $\endgroup$
    – AlexP
    Commented Jul 17 at 13:18
  • $\begingroup$ Say, it is possible (even if it's unlikely) what are the steps of changes in their inner anatomy that would allow them to adopt such breathing? (Also thx, this is my first time here) $\endgroup$
    – Ŧor Desaċ
    Commented Jul 17 at 13:51
2
$\begingroup$

There is nothing in the mammalian body plan which forbids the evolution of a unidirectional respiratory system. It is perfectly possible to imagine a mammal with such a respiratory system. But why on Earth would it evolve?

The normal expected evolutionary response to lower oxygen levels would be larger and more efficient lungs, not the complicated mechanism birds developed to compensate for their small rigid lungs.

Thing is, mammals are not worse than birds at extracting oxygen from air. Yes, birds use their complicated mechanism for unidirectional breathing, but on the other hand mammals have much larger lungs, with much larger gas exchange surface.

For a detailed comparison between the respiratory systems of bats and of birds, see J. N. Maina's "What it takes to fly: the structural and functional respiratory refinements in birds and bats", in The Journal of Experimental Biology 203, 3045–3064 (2000). Money quote:

Bats improved a fundamentally mammalian lung to procure the large amounts of oxygen needed for flight. The lung/air sac system of birds is not therefore a prescriptive morphology for flight: the essence of its design can be found in the evolution of the reptilian lung, the immediate progenitor stock from which birds arose. The attainment of flight is a classic paradigm of the remarkable adaptability inherent in organismal and organic biology for countering selective pressures by initiating elegant morphologies and physiologies.

Birds are theropod dinosaurs, more specifically maniraptoran coelurosaurs. They have inherited the basic design of their respiratory system from their dinosaurian ancestors. This design evolved in order to compensate for having a rigid rib cage; birds cannot inflate their lungs, so that by necessity the part of the respiratory system which inflates to inhale and deflates to exhale has to be placed beyond the lungs. On the other hand, we mammals have can inflate and deflate our lungs, and we have plenty of room in our chests for big lungs, so that we do not need the avian mechanism of respiration.

Improve this answer
$\endgroup$
2
  • $\begingroup$ avian respiration is about twice as efficent as the mammalian system, mammals would gain a huge benefit from switiching. But once you already have a derivied breathing mechanims switching requires decreasing the efficency first which is highly unlikely to evolve. this efficency is why birds can handle altitude changes far better than mammals. inflating and deflating the lungs make them far less efficent becasue you need more connective tissue and low capilary density AND you have a large portion of "dead air" during a breath. $\endgroup$
    – John
    Commented Jul 18 at 14:12
  • $\begingroup$ Birds also don't need to waste space on a negative pressure cavity around the lung and diaphram like mammals. lack of this space is also why a a puncture to a birds lung or air sacs don't stop them from workling like a mamals does. More on a comparision between the breathing mechanisms. erj.ersjournals.com/content/29/1/11 $\endgroup$
    – John
    Commented Jul 18 at 14:24

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .