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As a SciShow viewer, you can keep building your STEM skills with a 30-day free trial and 20% off an annual premium subscription at Brilliant.org/SciShow. It’s happened to all of us.

You’re in the middle of a conversation, and for some reason, you take a weird breath and suddenly, you’re having a coughing fit. Why is it so easy for us to end up hacking up a lung, just because of our own saliva? Like, that feels like the kind of flaw that evolution should have gotten rid of by now.

As it turns out, those coughing fits are part of a trade-off that happened over the course of millions of years. And what we got in return for some awkward moments was a critical thing that makes us, well, us. [♪ intro music] Every time you go to swallow something, it kicks off a complex series of movements in your mouth and throat. When something gets pushed to the back of the mouth with the tongue, it enters the pharynx, which is the part of the throat directly behind the mouth.

That’s where the swallow reflex begins, which causes several small but important motions to occur. First, the soft palate shifts to prevent the thing being swallowed from going up into the nasal cavity. The reflex also causes the tongue to block the item being swallowed from going back into the mouth.

And the space between the vocal cords, called the glottis, also closes. Finally, the larynx, or voicebox moves up and forward, and a flap of cartilage called epiglottis closes the entryway into the larynx, which protects objects from going into the trachea, or the windpipe. Once these actions are complete, whatever you just swallowed can go down your esophagus and continue along the digestive tract.

All in all, a pretty fancy dance for your dinner to do! The timing of these motions has to line up for you to swallow without choking. Since this reflex requires the epiglottis to cover up the airway temporarily, your breathing has to pause for just a couple of seconds to protect the windpipe while you swallow.

But if you breathe in anyway, or say, start to laugh while you’re mid-swallow, you can end up choking something that should have gone down the esophagus. The same thing can happen if you swallow too fast or while laying down, or if you have muscle weakness in the larynx, which can happen with disease, injury, or age. So we know why choking happens in us.

But why haven’t we evolved out of it by now? As it turns out, all those awkward moments are an evolutionary trade-off that enables us to do something pretty crucial. It’s that thing that I’ve been doing for the last several minutes - talk.

And the anatomy of our mouths and throats is distinctly specialized to allow us to produce complex sounds and thus, spoken language. And we can see those differences by comparing our throats’ anatomy to other, less chatty mammals, including our closest living relatives, chimpanzees. We can start face-first.

Humans have much flatter faces than chimps do, which affects the proportions of everything else down the line. Our flat faces also came with changes to the mandible, or jawbone, giving our tongues more space to move around. Our tongues are also rounder than chimpanzee’s tongues, and we can do more precise movements with them than our ape cousins can.

Tongue position is crucial for forming a variety of sounds, particularly consonants, so our rounded and wiggly ones are pretty vital as far as speaking goes. And the base of our tongues sit slightly lower in the throat, due to the position of the hyoid bone, which serves as an attachment point for the tongue muscles. This descent increases the distance between the soft palate and the epiglottis, which is the primary place where things get stuck and make us choke.

Chimps also have a small organ called a laryngeal air sac that attaches to the hyoid bone, which also shifts their hyoid bones up a bit, and the base of the tongue muscles with it. These air sacs help chimps generate loud, fast, and high-pitched calls to one another, like this, [Chimpanzee Vocalization] But those sacs also mean the chimp’s vocal cords can’t make as many of the complicated moves that ours can. Which means that even if they had the brain-power to do so, they couldn’t develop verval language since they can’t physically make enough sounds to do so.

So when you put all the changes together you end up with a human mouth and throat capable of making a lot of complex noises, which is step one to producing speech. It’s just also a lot more capable of goofing up and sending things down the wrong way, like our own spit. So essentially, the advantages of talking were so important for our survival that it’s worth the risk that we’ll look really awkward in front of our friends.

Feels pretty worth it, but I might change my tune next time it happens to me. This SciShow video is supported by Brilliant: the interactive online learning platform with thousands of lessons to choose from in math, science, and computer science. You know, the stuff that explains everything I just talked about in this video.

Swallowing, talking, and choking all come down to throat geometry. So to learn more about the geometry of complex 3D spaces, like your throat, you can check out the Brilliant course on 3D Geometry. It’s more than just a weird cylinder.

And this course can help you understand all of the ways to understand that shape, with lessons on faces, edges, cross-sections, and more. Brilliant does a lot of work to gamify your learning and make it more engaging. So in this course, you’re dropped into a cube-world and you need to find the shortest path to your destination.

Without a Magic School Bus, this is the most intimate understanding you’ll get of the 3D geometry all around you that you can apply to your own body. You can learn more at Brilliant.org/SciShow. That search will start you off with a free 30 day trial and 20% off an annual premium Brilliant subscription.

Thanks for watching and thanks to Brilliant for supporting this video!