And, a related question, why can they bark but not speak? The answer has to do with one of the things that makes us both human and also significantly more vulnerable, right up there with brains so big they make birth potentially fatal. (Hardly a triumph of effective design.) You see, the human larynx, though in many ways very similar to that of other mammals, has a few key differences. It’s much further down in the neck and it’s pulled the tongue down with it. As a result, we have the unique and rather stupid ability to choke to death on our own food. Of course, an anatomical handicap of that magnitude must have been compensated for by something else, otherwise we wouldn’t be here. And the pay-off in this case was pretty awesome: speech.
But what does all this have to do with dogs? Well, dogs do have a larynx that looks very like humans’. In fact, they make sound in very similar ways: by forcing air through abducted vocal folds. But dogs have a very short vocal folds and they’re scrunched up right above the root of the tongue. This has two main effects:
- There’s a very limited number of possible tongue positions available to dogs during phonation. This means that dogs aren’t able to modulate air with the same degree of fine control that we humans are. (Which is why Scooby-Doo sounds like he really needs some elocution lessons.) We do have this control, and that’s what gives us the capacity to make so many different speech sounds.
- Dogs have their soft palate touching their epiglottis when they’re at rest. The soft palate is the spongy bit of tissue at the back of your mouth that separates your nasal and oral cavities. The epiglottis is a little piece of tongue-shaped or leaf-shaped cartilage in your throat that flips down to neatly cover your esophagus when you swallow. If they touch, then you’ve got a complete separation between your food-tube and your air-tube and choking becomes a non-issue†.
Some humans have that same whole palate-epiglottis-kissing things going on: very young babies. You can see what I’m talking about here. That and how proportionally huge the tongue is is probably why babies can acquire sign quite a bit before they can start speaking; their vocal instruments just aren’t fully developed yet. The upside of this is that babies also don’t have to worry about choking to death.
But once the larynx drops, breathing and swallowing require a bit more coordination. For one thing, while you’re swallowing breathing is suppressed in the brain-stem, so that even if you’re unconscious you don’t try to breathe in your own saliva. We also have a very specific pattern of breath while we’re eating. Try paying attention next time you sit down to a meal: while you’re eating or drinking you tend to stick to a pattern of exhale — swallow — exhale. That way you avoid incoming air trying to carry little bits of food or water into your lungs. (Aspiration pneumonia ain’t no joke.)
So your dog doesn’t choke for the same reason it can’t strike up a conversation with you: its larynx is too high. Who knows? Maybe in a few hundred years, and with a bit of clever genetic engineering, dogs will be talking, and choking, along with us.
† That doesn’t mean that something large or oddly-shaped can’t get stuck in esophagus, though.