> ... 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.
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.