[gerdesj]

That's very different. Birds have a full lung load of air stored in sacs and bones and that fills the lungs as the stale air is expelled.

  Mammal: Inhale -> burn -> exhale
  Bird:   Inhale -> burn 
                 -> inhale -> exhale 

I think I've over simplified the bird method but basically they inhale and exhale at the same time as required. They literally have double ended lungs, you push air in at one end and exhale CO2 at the other end. We mammals use the same route in and out of our lungs and the whole thing is driven by our diaphragm which pumps the bottom of our pleural cavity.

The bird mechanism is obviously efficient for oxygenation but it must have a cost that our body plan discarded or at least failed to even consider many millennia ago.

[kmarc]

(Am I the only one who have read this as a Haskell function declaration, and the signature just didn't make any sense?)

[SkittyDog]

> ... it must have a cost that our body plan discarded ...

Our body plan didn't discard this mechanism, any more than it discarded wings or beans. We never had any of those features in our ancestry, because mammals aren't descended from birds. Our most recent common ancestor is much, much earlier than bird ancestors began evolving any mechanisms related to flight or high-altitude breathing.

[robbiep]

> but it must have a cost that our body plan discarded or at least failed to even consider many millennia ago.

You only climb mount improbable, you don’t go down it

[rightbyte]

I guess the main drawback of such a solution is coughing up stuff? Probably harder to make air go the other way?