By “we” I suppose I mean all vertebrates? Are there any exceptions?
It seems to me like having your digestive tract be separate from your breathing tract could be a beneficial mutation. Why do we have a single tract with valves to switch between “stomach mode” and “breathing mode”? Are there any advantages to it?
In: Biology
We don’t have a single tract, the trachea (which handles getting air to the lungs) is separate from the esophagus (which gets food to the stomach). The only place that these tubes overlap is in the mouth. Vertebrates evolved a separate nasal cavity to handle breathing which is very handy because, for one thing, animals like some reptiles which have no separation between the nasal cavity and the mouth have to hold their breath when they are eating. And for another, the nasal cavity is designed a lot more for breathing than for eating. But we don’t really know why these features evolved “overlapping” as it were. There are definitely some advantages of having it though, like being able to make loud sounds with your mouth, or being able to pant or otherwise breathe heavily through your mouth, which probably explains why it wasn’t phased out in favour of a completely separate nasal tract
Well, obvious exceptions are whales (and possibly dolphins, not sure about those though)–they breathe entirely through the blowhole on top of their head, so they can’t actually breathe through their mouth. This is obviously an adaptation imposed by them being aquatic animals. I suppose it’s difficult to see how regular land mammals would get a similar adaptation, though–where would the breathing hole go?
The lungs seem to have developed from pockets in the esophagus that allowed fish to gulp down some air increasing their access to oxygen. So the connection of the larynx and upper esophagus is just an evolutionary vestige – this feature was/is convenient enough that there was no evolutionary pressure to fully separate the pathways of air and food intake, the epiglottis closing the larynx to prevent water or food from getting into the trachea works just fine.
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