Why do humans have only one windpipe?

I didn’t sleep much the other night. At about 2 in the morning, my wife woke up choking and gasping horribly – apparently she had swallowed wrong in her sleep. It was nothing serious and after a minute of coughing she cleared her lungs. But the shock of being woken up by this, not knowing if she was breathing her last, etc, kept me pretty much awake the rest of the night…

Anyway, during this long period of worry and insomnia, I got to wondering: why is the human respiratory system set up so we can choke to death? Although we have two lungs (why two? So if one collapses etc, the other can still do its job). But then why do we have only one windpipe (trachea) leading to both? If that gets blocked, we are finished. Why don’t we have two tracheae???

I am sure there is a great answer to this, but it isn’t obvious to me…

The problem that causes humans to swallow wrong and chocke is not number of windpipes, but location of windpipe and food pipe - they cross each other, and if the flap closes wrong, people choke.

The “reason” for this: none. Evolution doesn’t have a reason to do things, or an aim it tries to reach. The explanation is simply that the choking hazard is not big enough a disadvantage to successful survival and reproduction to get selected away. When pipes were rearranged during the development to speech (where a part of the breathing apparatus dropped), the advantage of speech was big enough to overcome the other problems. Evolution works by selection of the best adapted under the circumstances, not the best engineering solution designed. While it’s possible that other mutations/development would have reduced the choking hazards, it wasn’t urgently necessary, and further altering the windpipe might have resulted first in a compromised speech function, which would be selected against.

I guess the reason is that the area of two circles whose diameter is the same as one larger circle is substantialy smaller than the area of the larger circle.

Yes, I guess the fact that Evolution has seen to leave us with a single trachea means that it was not selected against. But intuitively it just seems that in the early days lots of people must have choked to death. I mean they were eating really tough meat and also didn’t have any public awareness campaigns or anything. I wonder if Oog’s mom ever told him he must take small bites and to chew his food 30 times…

You only need to live long enough to procreate. People may have choked a lot (though I doubt that that was the main killer), but they were having babies in their teens so…

The problem goes back way beyond Oog, and originates from the fact that in the first air-breathing vertebrates the organ that would eventually become the lungs developed as an outpocketing of the digestive system. This relationship, going beck more than 350 million years, is so entrenched in early vertebrate development that it has evidently been very diffcult to modify the basic arrangement. Instead a valve - the epiglottis - has developed between the respiratory and digestive systems, and this works well enough in most circumstances.

One exception to this is whales. Most whales have an arrangement in which the digestive and respiratory systems are completely separate. Whales can breathe only through their nostrils (blowholes), not through their mouths. Since many whales feed deep under water, where there are very high pressures, such an arrangement is indispensible to prevent water from being forced from the mouth into the lungs throug the epiglottis.

The connection between the respiratory and digestive systems in vertebrates is a prime example of “unintelligent design,” and a good illustration of how evolution works by cobbling together a solution that is workable rather than one that is optimal.

From what I’ve read in recent articles of Scientific American (among other pop-science magazines), the running theory of why humans alone among all mammals have the crossed windpipe/foodpipe thing has to do with the physical changes necessary for us to produce the sounds of human language (an elongated pharynx, for example).

Clearly the evolutionary advantage of producing a wider range of vocal sounds exceeded the disadvantage of possibly choking to death.

You have this wrong, somehow. Almost all air-breathing vertbrates have crossed windpipes/foodpipes (with the exception of whales, as I noted).

What you’re thinking of is the fact that humans can’t eat and breath at the same time, as can most other mammals. In fact, human babies can do this, but shortly after birth the larynx descends to its adult postion. Some biologists postulate that this is an evolutionary compromise that facilitates the ability to produce a variety of sounds for language.

Snakes also have an intersting arrangement so they han breath while thier entire head is around thier food.

(Thgier was a recent Nature special on snakes. I didn’t catch the whole thing, so I wont describe the mechinism)


Snakes have an extensible epiglottis. While they are swallowing prey, they can exend it out of the side of the mouth around the prey to breathe.

It seems to me that is an illustration of the weakness of Intelligent Design. Since a design exists that virtually precludes choking to death, why would an Intelligent Designer use a different design for the object of his affection? The biologists’ postulate relies on the idea that evolution works with what is available and adapts it to another use. An Intelligent Designer shouldn’t have to do that in order to produce speech.

Yes, I know that God moves in mysterious ways that are beyond any possibility of our understanding. Also the the Designer of Intelligent Design is not necessarily the God of the Bible. Sure.

As a bit of a hijack, as I understand it, if you are coughing, you are not really in any danger of choking to death. That is, if you are coughing, you are breathing, and to choke to death your windpipe has to be completely blocked which means you wouldn’t be able to cough.
Is this correct?

Yep, like dozens of other unintelligently deisgned features of our anatomy. If there was a designer, we got his 3rd rate assistant instead.

I saw it last night. Very good show!

According to a former co-worker of mine who volunteered at the Dolphin Research Center in south Florida, this also applies to dolphins.

He also noted that when a dolphin “talked” at a human, the action of moving their mouths while making chirps and whistles with their blowholes/mellon was a learned behavior - i.e., the humans show their teeth and flap their tongues when they talk, so I’ll do it when I talk to them.

This is contrary what some claiming to be evolutionists promote.
They suggest or outright claim the organisms are or have self determination. ? ? ?

I’ll be pedantic just because this a GQ thread: Dolphins are whales.

Nonsense. Then they are not actually evolutionists.

Please provide some cite for this claim.

What we call dolphins and whales are really overlapping groups of aquatic mammals. For scinetific purposes, there really isn’t any such thing as a whale. A better term would be cetacean, which includes all the animals we refer to as dolphins, whales and porpoises. For instance, you probably know that a Killer Whale (Orca) is more closely related to Flipper than to Moby Dick.

Right. We always have to remember that somewhere out there the individual who graduated at the bottom of the engineering class of the worst engineering school in the world is designing things. :slight_smile: